HARVARD UNIVERSITY

Ernst Mayr Library

of the Museum of

Comparative Zoology

DEC

4 2006

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JUL 2 9

TAXONOMY OP

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THE MARSH WREN

m SOUTHERN CALIFORNIA

by

Philip Unitt, Karen Messer, and Marc Thery

No. 31

31 May 1996

Proceedings of the

San Diego Society of Natural History

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ISSN 1059-8707

PROCEEDINGS :^%^

of the ^^( 2 9

San Diego Society of Natural History

1996

Founded 1874

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Number 31 31 May 1996

Taxonomy of the Marsh Wren in Southern California

Philip Unitt

San Diego Natural Hisloiy Museum. P. O. Box 1390. San Diego, California 92 112

Karen Messer

Departmenl of Mathematics. California State University, Fullerton, California 92634

Marc Thery

Centre Nationale de la Recherche Scientifique, URA 1 1 S3. Museum National d'Histoire Naturelle, Lahoratoire d'Ecologie

Generale, 4 Avenue du Petit Chateau. 91800 Brunoy. France

ABSTRACT. — At least three subspecies of the Marsh Wren (Cistnlluinis /xj/i/.t/n.t) occur in southern California C /) plesimlpuhenus is a widespread

migrant and winter visitor and breeds in the Owens Valley south to Owens Lake It is charactenzed by large size, pale tawny rump and scapulars, a nearly

white breast, mostly brown crown, and bold white back streaks It amves m its winter range mainly in mid to late September and departs mainly in April.

A distinction between plesius and puherius seems likely but was not examined in this study. C. p aestiuinmis is resident from the Colorado River and

Imperial Valley northwest locally through the Mojave Desert, and along the coast from Ventura County north through northern California to southwestern

Oregon. It is charactenzed by its medium size, moderately dark rufous rump and scapulars, a crown partly black and partly brown, and narrow to moderate

white back streaks. Its breast ranges from moderately buff (usually in the Colorado Desert; frequently in the Mojave Desert and along the coast) to deep

buff or brown (usually in the Sacramento Delta; frequently in the Mojave Desert and along the coast) A distinction between aesluannm and deserticola

could be maintained if specimens from the type localities only (Sacramento Delta and Imperial Valley, respectively) were considered, but the area of

intergradation is so large (Mojave Desert, coastal central and northern California) that the distinction does not seem broadly useful

The resident population of coastal southern California (Los Angeles to San Diego counties) is differentiated by its small size, largely black crown,

and deep rufous rump and scapulars At least 94% of specimens of this population can be distinguished from all other Marsh Wren subspecies, so we

propose it be known by the new name Cistolhoni.s paluslris ilarkae.

No California Marsh Wren population agrees with that of southwestern Washington, with its largely dark brown crown, broad brown nape collar, and

consistently narrow whitish streaks on a reduced brownish black back patch That subspecies, paludicola. extends south only to northwestern Oregon

INTRODUCTION ranges in v/idth from practically zero to about 9 mm. The patch

on the back ranges from small and brownish black with obscure

The subspecies of the Marsh Wren (Cistothorus palustns) in whitish streaks to large and completely black with white streaks

California were reviewed most recently by Rea (1986). The fonnat as broad as the black between them. The scapulars, rump, under

of that review (Phillips 1986), however, did not allow a species with tail coverts, and background color of the tail range from me-

variation as complex as the Marsh Wren's to be analyzed as thor- dium buffy brown to deep rufous. The underparts range from

oughly as appropriate. Also, specimens collected over the last ten practically white to mostly buff or brown with only small pale

years now allow that variation to be described more accurately than patches on the throat and in the center of the belly. The variation

was previously possible. Here we attempt to describe the Marsh in size is most easily expressed by wing length.

Wren's vanation as it relates to southern California and to apply the

information to understanding of the species' distribution and migra- HISTORICAL BACKGROUND

tion. Our central goal is to place the resident Marsh Wrens of coastal

southern California within the framework of the species' variation. Ridgway (1904) listed two subspecies of the Marsh Wren for

We also attempt to describe the Marsh Wren's southern California California, the smaller, darker paludicola Baird, 1858, from the

distribution in detail, as this is still poorly understood [e.g., the map "Pacific coast district." west of the Cascade Range and Sierra Ne-

in Zeiner et al. (1990) has many inaccuracies]. vada (type locality Shoalwaler [now Willapa] Bay, Pacific County,

In western North America, various populations of the Marsh Washington), and the larger, ^dXtx plesius (Oberholser, 1897) from

Wren differ in color, pattern, and size. The crown ranges from the "Rocky Mountain plateau district," west to northeastern Califor-

entirely brown to black with only a small brown patch in the nia (type locality Fort Wingate, New Mexico, in the winter range),

center of the forehead. The dark crown patch is separated from Gnnnell ( 1903) first recognized />/f.v;n.v as a winter visitor to coastal

the black and white patch on the back by a brown collar, which southern California.

Philip Unitl, Karen Messer, and Marc Thery

Swarth (1917) described aesluannus, type locality Grizzly Is-

land, Solano County, California, as darker still than paludicola but as

large as plesius. He ascribed to aestuarinus a range extending Crom

Suisun Bay through the San Joaquin delta and valley, with scattered

specimens of migrants trom more coastal localities. Cistothorus p.

paliuiicola he believed resident along California's entire coastline,

extending inland in the lowlands of southern California, though he

cited a few inland specimens from northern California as well.

Grinnell and Miller (1944) followed Swarth (1917) closely, desig-

nating coastal specimens of aestuarinus and inland specimens of

paludicola as migrants. They extended the breeding range of

aestuarinus to the Imperial and Colorado River valleys.

Aldrich (1946) subdivided plesius, describing a duller, less

rufescent subspecies pulverius (type locality Sprague, Lincoln

County. Washington). He ascribed lo pulverius a breeding range from

eastern Washington south to northeastern California and northwest-

em Nevada. The fifth edition of the American Ornithologists' Union

(1957) checklist followed Grinnell and Miller (1944) for the dark

lowland forms but did not distinguish pulverius. Phillips et al. ( 1 964)

took an even more conservative approach, reverting to Ridgway

(1904) in recognizing only one dark lowland subspec\ef,, paludicola,

and one pale plateau subspecies, /)/<\v/h.?. Mon.son and Phillips ( 198 1 ),

however, accepted pulverius and equivocated on aestuarinus.

Not until Phillips (19X6) was the species as a whole revised

again. In this work, Rea contnbuted the characterizations of the dark

lowland subspecies of western Marsh Wrens, while Phillips himself

covered the remainder of the species. Phillips recognized both

pulverius and plesuts, while Rea recognized aestuarinus, segregated

the desert population from aestuarinus as deserlicola, and suspected

the coastal California population to represent an undescribed subspe-

cies, "brighter and richer" than paludicola. aestuarinus, or

deserticola.

Figure 1 shows the general breeding distribution of the Marsh

Wren in western North America, the type localities of the named

subspecies addressed m this study, and the sites in coastal southern

California where Marsh Wrens were collected for this study.

METHODS

Specimen Resources

The taxonomic identity of the Marsh Wrens of coa.stal California

cannot have been adequately assessed previously because of a dearth

of specimens known to represent the local breeding populations.

Migrants of pulverius and plesius, especially the latter, are common

in southern California in winter, and their arrival and departure dates

have not been known precisely.

The ideal specimens on which to base a taxonomic study of the

Marsh Wren should be collected as soon as possible after a complete

molt and therefore with the least worn plumage with its maximum

genetically determined information content. The birds' constant

contact with rough, often damp vegetation wears and stains the

plumage more than in many species. Though in the eastern United

States the Marsh Wren has a complete prealtemate (prenuptial) molt

in spring (Kale 1966). such a molt is not common in the West. Of 1 1

February-May specimens from southern California examined dur-

ing this study, all are too worn to have undergone an extensive recent

molt, and of the three whose molt status was described on their label,

all specified "no molt." Likewise two March specimens from south-

western British Columbia [San Diego Natural History Museum

(SDNHM)] are rather worn and not molting. Of eight May-June

specimens from southeastern Oregon, at least four are too worn to

have molted recently. But three February-March specimens from

Solano County, California (Carnegie Museum of Natural History,

Pittsburgh) are molting their throats, and one of these was replacing

its tail (K. C. Parkes pers. comm.). Since a prealtemate molt in

western Marsh Wrens is rare or at least inconsistent, we based our

study on specimens collected shortly after the prebasic molt, in late

summer or fall.

For the resident Marsh Wrens of southem California, therefore,

the ideal specimens are those collected after the completion of molt

but before the amval of migrants. For such a sample, in 1994 Unitt

mist-netted Marsh Wrens at three sites along the coast of San Diego

County where the species was known to breed. Birds still in juvenal

plumage or heavy molt were released, while those whose molt was

nearly or quite completed were collected and prepared as study

skins. The field work began on 23 August and ended on 7 October,

when pale migrants had cleariy arrived and were outnumbering the

dark local birds. In all, 24 specimens from coastal San Diego County

were collected for this study.

Since 1984. for basic data on land birds' distribution and migra-

tion. Roger Higson and Unitt have been collecting in the Imperial

Valley, southeastern California, whose avifauna has not been studied

in detail. Over 12 years, we have accumulated 33 specimens of the

Marsh Wren, on dates from 4 August to 12 February. This sample

includes both representatives of the local population and migrants

from farther north.

In October 1984 and September 1986, Amadeo Rea, Kem

Hainebach, and Unitt visited Grizzly Island and adjacent Joice Island

in the delta of the Sacramento River, collecting 30 Marsh Wrens

around the type locality of aestuarinus ( 12 in October 1984. 18 in

September 1986). On 12 September 1986. we also took two at Gray

Lodge State Wildlife Area. Butte County.

For a sample of nominate paludicola, we borrowed from the

Burke Museum, University of Washington (UW), 20 specimens

collected in Pacific and Grays Harbor counties, Washington, on 20

September 1985, 18 November 1985, and I and 2 October 1986. To

gain a broader sample from southern California, we borrowed 13

specimens from the San Bemardino County Museum (SBCM), 41

from the Los Angeles County Museum of Natural History (LACM).

4 from the Santa Barbara Museum of Natural History (SBMNH), 2

from the Museum of Systematics and Ecology, University of Cali-

fornia, Santa Barbara (UCSB), and 1 from the Museum of Vertebrate

Zoology, University of California, Berkeley (MVZ).

The sample of specimens on which we base our characterizations

of Marsh Wren subspecies were all collected within the past 15

years. We excluded older specimens because comparison of new and

old specimens revealed obvious foxing of specimens collected in the

first half of the century: among the darker individuals, the rump and

scapulars of all the old specimens were more mfous than the recently

collected ones. Because mmp and scapular color appeared to be an

important variable, and we know of no means for correcting for this

shift, widespread among birds, we used only the recent specimens.

Once the framework was established with the recent specimens, we

used a few older specimens to augment our geographical and histori-

cal perspective.

Character Assessment

The features in which the Marsh Wren varies geographically

differ qualitatively, so they had to be assessed in vanous ways. AH

measurements and visual assessments were made by Unitt.

Wing chord was measured to the nearest 0.1 millimeter Body

size, as reflected in wing length, is the only feature in which the sexes

differ. The mean wing chord of males, in the entire sample of

specimens, was 1 .06 that of females. Therefore, so that the sexes

could be combined in the statistical analysis, we multiplied the

measurements of the females by 1 .06 to yield an adjusted result,

which we used in the remainder of the analysis. In support of this

adjustment, Messer ran a two-way analysis of variance on our

"enlarged" sample (see below under Categorization of specimens for

analysis) with wing length as the response and population of origin

and sex as the explanatory variables. Residual plots showed the data

to be approximately normally distributed; the ratio of the smallest

Taxonomy of the Marsh Wren in Southern Cahfornia

Figure 1 . Approximate breeding distnbution ofthe Marsh Wren in western North Ainenca (shading). In many areas within this range, the species occurs

in only scattered localized colonies. •, type localities of subspecies addressed in this study; ▲. sites in coastal southern California where Marsh Wrens were

collected for this study.

(0.72) to the largest (2.12) standard deviation was less than .^, with

most sample sizes between 10 and 15. The two smallest groups had

standard deviations near I. There was no significant interaction

between the sex effect and the population-origin effect (/> > 0.05),

justifying the use of a single adjustment for sex across all groups.

Had we used the estimated main effect for sex from this analysis in

our adjustment, the factor would have been 1 .077. a change of 1 .6%.

We did not feel this would affect our results materially and retained

the original adjustment for simplicity. A multiplicative rather than

additive factor was used to bnng the females' standard deviation

(2.01 in the enlarged sample) clo.ser to the males' standard deviation

(2.30 in the enlarged sample).

The width of the brown nape collar (between the black of the

crown and the black of the back) was measured to the nearest

Philip Unitt, Karen Messer. and Marc Thery

millimeter. In specimens in which the rear of the crown is brown, the

crown is a darker shade than the nape collar, and in these the

measurement was made from this fairly abrupt transition. The width

of the collar is affected to some extent by the amount to which the

neck IS elongated or compressed when the specimen is prepared. A

few specimens were not scored for this variable because they were

poorly made or had lost neck feathers. The great majority of the

California specimens were prepared by Unitt; preparation by a single

technician enhances uniformity. Nape-collar width is a significant

variable only in comparisons of the broad-collared puhidicola from

coastal Washington with other populations. The sample of paliulicola

consisted of specimens with naturally proportioned necks all beauti-

fully made, largely by C. S. Wood.

The vanation in crown pattern was assessed by ranking each

specimen on a scale from 1 to 6, in comparison to six specimens

serving as standards. In category 1 (standard SDNHM 43970) the

crown is essentially entirely brown, with only a few black feathers at

the sides. In category 2 (standard SDNHM 44592) the crown is

mostly brown, with some black along the sides. In category 3

(standard SDNHM 44532) the black extends around the rear of the

crown as well as along the sides. In category 4 (standard SDNHM

48937) the crown is about half brown and half black. In category 5

(standard SDNHM 48932) the crown is mostly black with some

brown extending from the forehead into the center In category 6

(standard SDNHM 48982) the crown is black with only a .small

brown patch on the forehead.

The variation in back pattern we assessed by ranking each speci-

men on a scale from 1 to 4. In category 1 (standard UW 40570) the

back is brownish black with very narrow dull whitish streaks. In

category 2 (standard SDNHM 43379) the back is deeper black with

whiter but still narrow streaks. In category 3 (standard SDNHM

48992) the back is deep black with white streaks broader than in

category 2 but still narrower than the intervening black streaks. In

category 4 (standard SDNHM 42843) the pure white and pure black

streaks are of about equal width.

The variation in the color of the scapulars and rump and of the

underparts we assessed by two methods. First, Unitt ranked the color

of the scapulars and rump on a .scale from 1 to 10. Category 1

(standard SDNHM 43469) corresponds to a medium tawny brown,

close to color 26, Clav Color, of Smithe ( 1975). Categories 2 (stan-

dard SDNHM 43972) and 3 (standard SDNHM 44592) are .some-

what darker, the latter close to Smithe's color 121C, Mikado Brown.

Category 4 (standard SDNHM 48954) is close to color 223, Verona

Brown. Categories 5 (standard SDNHM 47685) and 6 (standard

SDNHM 43456) are darker yet, the latter close to color 121B,

Brussels Brown. Categones 7 (standard SDNHM 48937) and 8

(standard SDNHM 48938) are a deeper cinnamon-rufous, category 8

being close to Smithe's color 23, Raw Umber. Finally categories 9

(standard SDNHM 4898 1 ) and 1 0 (standard SDNHM 489 1 2) are the

darkest rufous, the latter close to color 1 2 1 A, Front's Brown.

Later, Thery and Unitt measured the retlectance spectrum of

the rump of each specimen in percentage of a Spectralon (Ancal,

Inc.) white standard, using an Ocean Optics, Inc., PSIOOO diode-

array portable spectroradiometer upgraded for near-ultraviolet light

(range 300-800 nm), a bifurcated fiber-optic retlectance probe,

and an Ocean Optics LS-1 tungsten-halogen lamp. To avoid

specular reflectance, measurements with the reflectance probe were

done at an angle of 45" against the feather surface, measuring an

oval spot 3 mm wide. One measurement was made at the center of

the rump for each specimen, as long as the reflectance curve

averaging 5 scans was stable. Reflectance spectra were recorded

between 350 and 700 nm with a resolution of 1 nm. The measure-

ment range includes some near-ultraviolet light that is not per-

ceived by humans but is by many birds. From retlectance curves,

Thery then assigned each recorded spectrum a score for hue (domi-

nant wavelength), chroma (purity or saturation of the color), and

total brightness, computed following Endler (1990).

Our procedure with underpart color was parallel to that for rump

and scapular color. The specimens were ranked among six catego-

ries. In category I (standard SDNHM 43972) the breast is practically

white with a light buff tinge only along the sides. In category 2

(standard SDNHM 44592) a faint buff wash extends across the

breast. Specimens in category 3 (standard SDNHM 47685) have a

distinct buff breast band. In category 4 (standard SDNHM 48912)

the breast is darker brownish buff and the throat is tinged brown. In

category 5 (standard SDNHM 48938) the breast is still darker,

medium brownish. Category 6 (standard SDNHM 43386) represents

the Marsh Wrens with the darkest breasts; the entire underparts are

brown with only a triangular patch in the center of the belly being

whitish. In the darker-breasted specimens collected very shortly after

molt, in September, the underparts are more rufous, whereas in those

from the same locality collected just one month later, in October, the

color has dulled to a drab medium brown. Because this change

appears to result from some adventitious process, the specimens

were ranked for underpart color on the basis of paleness or darkness

alone, not hue.

Again, we evaluated the breast color of each specimen with a

spectroradiometer, placing the sensor over the darkest point along

the midline of the breast. The results were converted into values for

hue, brightness, and chroma in the same way as those for the rump.

Data Analysis

Speciromdiomeiry. A graphical assessment of the spectrora-

diomelnc results for breast and rump color suggested that brightness

was the variable with the greatest (and probably only) systematic

variation. Scatterplots of spectroradiometric assessment versus vi-

sual ranking for rumpAscapular bnghtness and for breast brightness

(Figures 2 and 3) reveal in both cases a positive but only moderate

correlation (Pearson correlations of 0.51 and 0.58, respectively).

Some difference might be expected because the spectroradiometer

measured a range of wavelengths broader than that to which the eye

IS sensitive, but there may be other confounding factors as well.

Because the visual assessments consistently gave better results, we

did not use the speclroradiometnc results further in the analysis.

The reason(s) why the spectroradiometer proved less satisfactory

than the eye in these comparisons are unclear. Endler (1990) dis-

cussed several reasons why the human eye's and brain's perception

of colors is not proportional to the electromagnetic characteristics of

the light reflected from an object and reaching the eye. He recom-

mended the use of spectroradiometers to circumvent this problem.

He did not address, however, other problems that may affect the

applicability of spectroradiometers in taxonomic studies of birds,

where often subtle rather than gross contrasts require quantification

and testing. We suspect that such problems more than the nonlinear

response of the human eye and brain accounted for the mediocre

agreement between the spectroradiometric and visual assessments in

our study. Possibly variation arising from the irregulariy multilay-

ered structure of plumage overwhelmed the rather subtle vanation in

color we were trying to record. Though we tried to ensure that the

sensor recorded only the pigmented tips of the feathers, possibly it

was influenced irregularly by some of the dark gray bases of the

feathers, confusing the results. The sensor read a much smaller area

of plumage than that embraced by the visual assessments; possibly

because of differences of scale the two are not always comparable.

The low retlectance of the rump and the dullness of both the rump

and breast colors may exceed the equipment's sensitivity. Though

spectroradiometry of plumage has been used occasionally in taxo-

nomic studies of birds (e.g., John.son 1980, Atwood 1988), to our

knowledge, the reliability and sensitivity of vanous spectroradio-

meters and various techniques for using them have not been com-

pared and tested. Since more precise and replicable quantifications

Taxonomy of the Marsh Wren in Southern CaHfornia

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visual ranking: rump/scapular color

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2 3 4

visual assessment: breast color

Figure 2. Scatterplot of visual rankings of Marsh Wren rump/scapular

color versus bnghtness of mmp as specified by the spectro radiometer The solid

hne is the regression line; the dotted lines enclose the 95% prediction inlerval.

predicting the spectroradionieter reading from the visual ranking The plot

shows a positive but moderate correlation (Pearson correlation of 0 51 )

Figure 3. Scatterplot of visual ranking of Marsh Wren breast color

versus brightness of breast as specified by the spectroradiometer The solid

line is the regression line; the dotted lines enclose the 95% prediction interval,

predicting the spectroradiometer reading froin the visual ranking The plot

shows a positive but moderate correlation (Pearson correlation of 0.58),

of plumage color are obviously desirable, such testing is warranted.

N. K. Johnson (pers. comm.) found that a Bausch & Lomb 505 and a

Minolta CR 300 both detected the inost subtle differences visible to

the eye. Zuk and Decruyenaere (1994) reported that a Li-Cor Ll-

1800 spectroradiometer, used on rooster combs and single feathers

glued to a card, gave better results than visual matching to Munsell

color samples. The visual assessments, however, were "constrained

by the available color standards." Because of the difference in

texture, matching plumage colors to flat color samples is difficult.

Use of specimens themselves as standards circumvents this. One

reason that Endler (1990) urged that color be measured electroni-

cally is that insofar as possible color differences should be evaluated

from the animal's point of view. In studies of sexual selection or

social behavior this is clearly important. But human taxonomists are

responsible for classifications, so in this field human perception

remains relevant. Electronic techniques may ultimately yield better

means of expressing the colors of birds, but we felt the questions

about them were still too great for the more traditional visual method

to be abandoned in this case.

Categorization of specimens for analysis. Messer and Unitt en-

tered the measurements of wing chord and nape-collar width and the

rankings of crown pattern, back pattern, underpart pattern, and ruinp/

scapular color into a computer database. We apportioned the speci-

mens among three categories: a core sample of specimens certain to

represent particular breeding populations, an enlarged sample includ-

ing additional specimens inferred to represent those populations, and

the remaining specimens, whose allocation was ambiguous.

The core sample consisted of 72 specimens we are certain to

represent one of five key populations. For 65 of these, all six

variables could be assessed; seven were defective in one or more

characters so had to be excluded from some analyses. First, the core

sample included 10 specimens of plesiiis/pulveriiis, from the Great

Basin or from sites in Arizona where there are no breeding Marsh

Wrens, under the assumption that only ptesiuslputverius are long-

distance migrants likely to reach central Anzona. Second, the core

sample included all 20 specimens from the Willapa Bay area of

Washington, taken to represent the breeding population around the

type locality oi pahidicota. under the assumption that migration of

plesius/pulverius from east of the Cascades is largely or entirely

southward rather than due west. Jewett et al. (1953) did not report

any migration of the inland subspecies to western Washington,

supporting this assumption. Third, the core category included 19

early September specimens from the type locality of aestiuinnus

(five of these were defective in one or more characters). Fourth, it

included five late August and September specimens from the Impe-

rial and lower Colorado River valleys, including the two cotypes of

deserticola. Two of these five were molting the outer pnmaries so

could not be used in comparisons including wing length. Finally, it

included 1 8 specimens from coastal San Diego County. Seventeen of

these were collected in late August and September, and included all

specimens in this interval save one taken on 23 September, which

from its conspicuously paler color and larger size we inferred to be a

migrant plesius/pulverius. The 18th specimen, collected on 28 Feb-

ruary 1984, had enlarged testes (left 5.5 x 4.5 mm), beyond the size

expected in a winter visitor.

This core sample was assessed by both cluster and discriminant

function analysis (see below).

The enlarged sample consisted of the original core sample of

birds whose population of origin was certain plus additional speci-

mens whose origin could be confidently inferred. Nevertheless, we

have distinguished these additional specimens from the core-sample

specimens in all our comparisons. Twenty-nine additional specimens

from the Colorado Desert we assumed to be either local residents or

migrants from the Great Basin, the other western populations being

sedentary. We allocated these desert specimens by means of a linear

discriminant-function analysis confined to the core plesius/pulverius

sample plus all specimens from the Colorado Desert. We used the

discriminant function based on the core specimens to classify the

remaining specimens into the two categories. A canonical variable

plot (Figure 4) shows a clean separation though no gap between the

two categories and a wide separation between the core samples.

Therefore, we defined an enlarged desert sample of 18 specimens.

The remaining 16 Impenal Valley specimens we grouped with the

core sample of plesius/pulverius to constitute an enlarged plateau

sample of 26 specimens. If any specimens of deserticola were

misplaced with plesius/pulverius they could only degrade any sepa-

rability of the plateau subspecies from any of the darker lowland

subspecies.

We repeated this procedure with the October sample from the

Sacramento delta, again under the assumption that the only migrant

Marsh Wrens likely to reach this area are plesius/pulverius. All 1 2 of

the October specimens clustered tightly with the 14 core September

Philip Unitt. Karen Messer. and Marc Thery

Figure 4 Histogram of the canonical variable resulting from a stepwise

discriminant analysis of the core sample of 10 specimens of Cisunlkniis

paluslrisptesiuslpulverius and all Marsh Wren specimens from the Impenal

and lower Colorado River valleys. The discnminant function was based on

the core specimens, and was used to classify the remaining specimens. Rump/

scapular color, underpart color, wing length, and crown pattern, in decreasing

order of importance, are the infomiative variables C, core specimens of

plesius/pulvenu.i: D, core specimens of deserricoln. A, inferred specimens of

plesiuslpulvenus, B, inferred specimens of deserticoUi.

specimens, and this cluster was well separated from the plesiiisl

pulvenus sample ( Figure 5 ). so we enlarged the core September delta

sample by adding the October sample.

These two steps generated the enlarged ■■.ample of 1 1 3 speci-

mens, constituting the second level of inclusiveness. Nine of these

could not be scored for one or more characters and had to be omitted

in compansons such as the discriminant-function analysis of all

populations simultaneously.

Finally, we applied the discriminant functions derived from both

the core and enlarged samples to the 26 remaining specimens. These

specimens are from sites away from those of our five "parent"

populations (coastline from southern Oregon to Ventura County;

oases of Mojave Desert). This procedure allowed us to suggest a

taxonomic placement for those specimens.

Statistical Procedures

Cluster analysis. With the core sample (excluding defective indi-

viduals) of 65 specimens. Messer ran cluster analyses in MINITAB,

version 10 xtra. using a hierarchical agglomerative algorithm. Dis-

tances were computed by means of Ward's method, which finds

clusters with minimum within-cluster sums of squares (Afifi and

Clark 1984: 393). We present results using unstandardized variables;

results for standardized variables were similar.

Discnminanl Analysis. Messer ran discriminant analyses in

BMDP386, version 1990, program 7M. The default stepwise proce-

dure was used in all cases. Scatterplots of the onginal vanables and

canonical variable plots were produced in MINITAB, the latter using

the output from BMDP.

We applied stepwise discriminant analysis to the initial core

sample, once with the three nondefective Colorado Desert specimens

and once without them, to assess the degree of differentiation among

the five key populations. We followed this by a parallel procedure

with the enlarged sample. In addition, we compared each of the five

populations with each of the others, a total of ten pairwise compari-

sons. These comparisons allowed us to evaluate and rank the charac-

ters distinguishing each of the populations.

Results are presented in terms of correct classification rates,

estimated by means of the jackknife procedure in BMDP. This

procedure adjusts the estimated rate downward in an attempt to

correct for overly optimistic estimates that arise because the same

specimens are used in both the construction of the classification rule

(the discriminant function) and the assessment of how well if per-

forms (the classification rates). In addition, in the pairwise compan-

sons the discriminant function was computed on the basis of the core

sample only and was then applied to both the core sample and the

additional inferred specimens when present. In all comparisons ex-

cept the two between plesnislpulvenus and either deserticola or

aestuannus (which were used in classifying some of those inferred

specimens) the additional specimens may be considered an indepen-

dent lest sample, although not a randomly selected one. Thus the

classification rates of the inferred specimens constitute additional

evidence for or against group separation.

We felt that the distance between groups was best presented graphi-

cally in termsof scatterplots of all the data. In all ca.ses, the f statistic for

a test of equality of group means was significant at /> < 0.005, but

because of the stepwise procedure used in vanable selection, the

nonnomial nature of several of the variables, and the nonrandom nature

of the samples, it is questionable how much inference may be drawn

from this fact. For similar reasons, we decline to present confidence

regions or prediction regions based on an assumption of normality.

For ease of interpretability in the pairwise compansons, we present

graphs intermsof the pair of vanables that we felt were most useful in

making a visual assessment of the group separation. TTiis is usually the

pair of variables with the strongest univariate group mean separations

(as measured by the F-to-enter test statistics at step 0 in the stepwise

vanable-selection procedure). Occasionally, this pair did not produce

the most obvious .separation, and in that case the pair of vanables that,

considered together, was most informative was used (as measured by

the f-to-entertest statistic at step 1 in the vanable-selection procedure).

In the figure legends, these are described as "the pair of variables in

which (the groups] differ mo,st." While these plots are more easily

interpretable than the corresponding canonical-vanable plots, they do

not separate the groups as well (compare Figures 4 and 1 1 ).

In assessing which characters were most informative in the

pairwise compansons, we again chose to present them in order of

univariate mean group separations, as we felt these would be the

easiest to use visually. Note that this means the first two variables

listed may not be the/jairof most informative vanables but rather the

two variables that when considered in isolation best differentiate the

groups. When we say a pair of populations "differs significantly" in a

variable, we mean the group means differ significantly at /? < 0.05.

The variables actually used in the discriminant function are indicated

by italics. These are the variables that, when the others are already in

use, conlnbute additional information.

Figure 5 Histogram of the canonical variable resulting from a stepwise

discnminant analysis of the core sample of 10 specimens of Cislothorus

patustris plesnislpuheniis and all Marsh Wren specimens from the San

Joaquin delta. The discnminant function was based on the core specimens,

and was used to classify the remaining specimens. Underpart color, rump/

scapular color, wing length, back pattern, and crown pattern, in decreasing

order of importance, are the informative variables. C, core specimens of

plesiuslpuherius: D. core specimens oi aesmarimis. A, inferred specimens of

plesnislpulvenus. B, inferred specimens of aesiuanints.

RESULTS

Cluster Analysis

Cluster analysis of the initial core sample of 65 specimens,

covering all five key populations, identified three well-defined groups

(Figure 6). The sample from coastal San Diego County was the most

distinct; the 10 specimens of plesiuslpulvenus formed a second

branch. Among the remainder of the specimens, the coastal Washing-

Taxonomy of the Marsh Wren in Southern Cahfornia

27.11

plesius/pulverius

paludicola aestuarinus

Observations

s. Calif.

Figure 6. Cluster analysis of the core sample of 65 specimens of the Marsh Wren, covenngall five key populations on which further analyses were based

Letters designate exceptional specimens not clustering with the rest of their population as labeled A, aestuarinus: C. coastal southern California; D.

deserticolu: W, paludicola. The height of the horizontal bar separating each cluster is proportional to the distance between clusters, as measured by Ward's

algonthni The first dichotomy separates all but one of the coastal southern California sample from the remaining specimens; the second dichotomy separates

the Great Basin population [plesius/pulverius) from the remaining specimens. The population of southwestern Washington {paludicola) segregates only

partially from the remaining specimens, from the Colorado Desert (deserlicola) and San Joaquin delta (aestuarinus).

ton (paludicola) and Sacramento Delta (aestiianiuis) samples clus-

tered together but did not segregate clearly from each other, some

paludicola forming a subcluster, others falling with aeslitannus. Of

the three Colorado Desert (deserlicola) two fell among the cluster of

aestuarinus. one with the sample from San Diego.

The sharp distinction of the San Diego sample from the remain-

ing specimens suggested that it be evaluated as a separate group in

the discnminant analyses; we then used the results of these analyses,

both of the entire sample and of comparisons to each other popula-

tion individually, to assess the level of and basis for this distinction.

Discriminant Analysis: All Five Populations Simultaneously

Core sample, deserlicola excluded. The core sample consisted of

specimens that we are certain, on the combined basis of their locations

and dates, to represent one of our five key or "parent" populations,

corresponding to either named subspecies or the resident population of

coastal southern California. Because the core sample included only

three complete specimens of deserlicola. possibly insufficient to de-

fine a discrete group, we ran the analysis both with and without these

three specimens. Discnminant analysis of the core sample containing

only the remaining four groups yielded a function capable of catego-

nzing 58 of the 62 specimens into the four groups defined by their

ongins, for an overall correct classification rate of 94%. The San

Diego and Great Basin samples did not overlap with any other; the

only misclassification was belween paludicola and aestuarinus. When

the classification rates were corrected via the jackknife procedure, the

results differed only in that one specimen from the San Diego sample

and an additional specimen of paludicola were misclassified with

aestuarinus (Table 1 ). From 86 to 100% of each group was classified

as its origin suggested; for each of the four groups this figure exceeds

the 75% traditionally regarded as the threshold for formal taxonomic

recognition, suggesting each of the four may constitute a valid subspe-

cies. A plot of the two most informative canonical variables associated

with the discriminant function (Figure 7) best illustrates the segrega-

tion among the populations, reducing to two dimensions most of the

information from the six variables with which we describe variation in

western Marsh Wrens.

Core sample, deserticola included. A repetition of the discrimi-

nant analysis including the three August/September specimens from

Table 1. Jackknife-corrected discriminant-function classification

of the core samples representing Cislothorus pcdustris plesiusi

pulverius, C. p. paludicola. C. p. aestuarinus. and the population of

coastal southern California.

Number of specimens classified as

plesius/

pulverius

palu-

dicola

aestu-

arinus

Coastal

S Calif

Percent

Correct

C p. plesius/

pulverius

C p paludicola

C. p aestuarinus

Coastal S Calif

10

0

0

0

Philip Unitl, Karen Messer, and Marc Thery

3 -

UJ ry

>

(J

•E

o

c

o

-2 -

o o

o o

-5

canonical variable

Figure 7. Scatterplot of the two most informative canonical variables

generated by a stepwise discriminant analysis of the core sample of 62 speci-

mens of the Marsh Wren, covenng four key populations (desertkola excluded).

O. specimens from the Great Basin or inferred to have onginated there [plesiusl

pulvenus). +. specimens from southwestern Washington ljkiludicola).x. speci-

mens from the San Joaquin delta Uiesliuiiiinis), D, specimens from coastal

southern California.

the Colorado Desert did not greatly alter the results among the other

four populations, but the attempt to define a group on the basis of

these three specimens alone was unsuccessful. With the jackknife

procedure, two of the three were classified by the discriminant

function among other groups, while the desert "cluster" attracted one

or two specimens from each of the other groups except plesiusl

pulverius. A plot of the canonical variables implies a tendency of the

Colorado Desert population, despite its marginal position geographi-

cally, to be intermediate among the other four clusters in plumage.

Clearly, a larger sample from the Colorado Desert was necessary for

the taxonomic position of that population to be assessed, and this was

the goal of the following step.

Enlarged sample. We repeated the discriminant analysis, with an

attempt to define five populations, on the core sample augmented as

described above under Categorization of specimens for analysis

(including the 12 October specimens from the San Joaquin delta, all

inferred to represent aestiuinnns. the additional 1 3 and 1 6 specimens

inferred, respectively, from companson of deserticola and plesiusl

pulverius to represent those populations; Figure 4). This analysis of

104 specimens (Figure 8) suggested that all five populations could

be considered subspecies. The poorest distinction was between

aesluannus and deserlicola, but even after jackknife correction the

discriminant function still classified 81% of each of these groups as

expected (Table 2).

Discriminant Analysis: Pairwise Comparisons of Five Populations

Cistolhorus p. plesiuslpulverius vs. paludicola. This pair of popu-

lations differs significantly in all vanables, in order of decreasing

importance, wing length, rump/scapular color, underpart color, back

pattern, nape-collar width, and crown pattern. The discnminant

function revealed a wide separation belween paludicola and the core

sample of plesiuslpulverius. With the enlarged sample of plesiusl

pulverius. the separation was not complete; three specimens fell

within the cluster of paludicola. reducing the rate of correct classifi-

cation in the total sample to 93% after correction for over-

classification via a jackknife procedure. Figure 9, a scatterplot of

plesiuslpulverius versus paludicola in wing length versus rump/

scapular color, reveals these three misclassificd specimens. Possibly,

some of the misclassificd plesiuslpulverius in the enlarged sample,

from the Imperial Valley, were misidentified deserlicola (see above

under Categonzation of specimens). But even if not, the two popula-

tions are differentiated well enough to be continued to be recognized

as subspecies.

Cislothoriis p. plesiuslpulverius vs. aestuarinus. This compari-

son yielded one of the strongest distinctions; the two groups differ

significantly in five of six vanables (all except nape-collar width),

and the discriminant analysis, after jackknife correction, classified

100% of the specimens as expected. Rump/scapular and underpart

color are the two variables most responsible for this separation

(Figure 10).

Cistolhorus p. plesiuslpulverius vs. deserticola. These two groups

differ significantly in four variables I rump/scapular color, under-

part color, wing length, and crown pattern), but in the discriminant

analysis the second two did not add any discriminating power be-

yond the first two. Therefore, in Figure 1 1 we present a scatterplot of

the two groups in just these two variables; this allowed us to include

the two specimens in the core sample of deserticola that were

molting their primaries. In this plot, the groups appear well sepa-

rated, hut, as discussed above under Categorization of specimens

and shown in Figure 4, several fall and winter specimens from the

Impenal Valley bridge the gap. Study of a larger sample of both

subspecies may reveal some overlap not evident with our core

samples. Nevertheless, the strong separation obvious in Figure 11,

and the 1 00% separation achieved by the discnminant function, even

after jackknife correction, implies that any ovedap is not extensive

enough to invalidate the distinction between deserticola and plesiusl

pulverius.

Cistotlwrus p. plesiuslpulverius vs. coastal southern California

Table 2. Jackknife-corrected discriminant-function classification of the en-

larged samples representing Cistolhorus paluslris plesiuslpulverius, C. p.

paludicola, C. p. aestuarinus. C. p. deserlicola. and the population of coastal

southern California.

Taxonomy of Ihc Marsh Wren in Soulhem California

-5 0 5

canonical variable 1

Figure 8- Scatterplol of the two inost informative canonical vanables generated by a stepwise discnminant analysis of the enlarged sample of 104

specimens of the Marsh Wren, consisting of the core sample of 65 specimens augmented with 14 inferred specimens of plesius/pulverius. 12 inferred

specimens of aestiuirinus. and 13 inferred specimens of deseriicoUi. •, core-sample specimens of plesius/pulverius: O. inferred specimens of plesiusi

puhenus: H. specimens from southwestern Washington [puludicola): *, core-sample (September) specimens from the San Joaquin delta (aesluarinus):

+. inferred (October) specimens of aesluctnitus from the San Joaquin delta; M, core-sample specimens from the Colorado Desert (desenicohi). 0. inferred

specimens of deserucola from the Colorado Desert; A. core-sample specimens from coastal southern California.

population. Rump/scapular color, wing length, underparl color, and

crown pattern all contributed significantly toward the strong separa-

tion of these two groups. Figure 1 2 is a scatterplot based on the two

strongest vaiiables, rump/scapular color and wing length. Only two

specimens were misclassified by the discriminant function. Both are

inferred specimens oi plesius/pulverius from the Imperial Valley and

not used in the generation of the discnminant function.

Cistolhorus p. paludicola vs. aestuannus. Five variables contrib-

uted significantly toward the differentiation of the Washington and

San Joaquin Delta samples; in order of decreasing importance,

underparl color, nape-collar width, crown pattern, rump/scapular

color, and back pattern. Figure 13, a scatterplot depicting the first

two of these variables, reveals some overlap. Even with all variables

combined in a discnminant function, however, a 100% separation

could not be achieved. Marginal overlap left three specimens of

paludicola and one of aestuarinus on either side of the line of best

separation decided by the discnminant function. Jackknife correc-

tion of the function suggested that 88% of the combined samples

could be assigned correctly. All of the inferred (October) specimens

of aestuarinus were correctly classified. Though the separation is not

total, it appears adequate to support continued recognition of

aestuarinus as distinct from paludicola.

Cistothorus p. paludicola vs. deserticola. Rump/scapular color.

nape-collar width, and back pattern contributed toward a good

separation between this pair of samples (Figure 14). Only one speci-

men was misclassified by the discriminant function, an inferred

specimen of deserticola that by virtue of its rather narrow white back

streaks (rated 2) and rather pale rump (rated 5), and despite its

narrow nape collar (3 mm, outside the range of paludicola), fell in

the middle of the cluster of paludicola as defined by the canonical

vanable generated by the discriminant function. Following the jack-

knife correction, the discriminant function predicted a 97% separa-

tion of these two populations.

Cistolhorus p. paludicola vs. coastal southern California popula-

tion. This pair of samples segregated 1 00%, differing significantly in

all variables, in order of decreasing difference, rump/scapular color,

crown pattern, wing length, nape-collar wuith, hack pattern, and

underparl color. The plot of rump/scapular color versus back pattern

(Figure 15) shows the clearest separation in two variables. The

canonical variable generated by the discriminant function suggested

10

Philip Unitt, Karen Messer, and Marc Thery

2 3 4 5

rump / scapular color

Figure 9. Scatterplot for Cistolhonis pahislns plesiuslpulvenus and C

p. pahulicokt of the two vanahles in which they differ most, vving length and

rump/scapular color So that the sexes could be considered together in one

statistical process, the wing chords of females were multiplied by 1.06, the

factor by which the average male Marsh Wren exceeds the average female

•, core-sample specimens of plesius/putverius; O, inferred specimens of

plesitis/pulverius.M. specimens from southwestern Washington (piitudicdki).

In this and subsequent figures in which one or both of the axes represents a

variable ranked in discrete categones, some "jitter" has been added to avoid

overstnkes and thereby show all points plotted.

not only complete separation but a gap between the two populations

(Figure 16). It is evident that the name pahuiicola does not apply to

the resident Marsh Wrens of coastal southern California.

Cistothorus p. aesluarimis vs. deserticola. Among the 10 pairs of

"parent" populations, this comparison yielded the weakest separa-

tion. The stepwise variable-selection procedure used only a single

variable, underpart color, in the discriminant function. Back pattern

2 3

underparts

Figure 1 1 . Scatterplot for Cisunlumis paluslris plesiuslpulvenus and C p.

deseriicoki of the two vanables in which they differ most, nimp/scapular color

and underpart color 9, core-sample specimens of plesiuslpulvenus, O, in-

ferred specimens oi plesiuslpulvenus; ■ , core (August/September) specimens

of the breeding population of the Colorado Desert (.desenicola): D, additional

October-February specimens from the Colorado Desert inferred as desenicola

(see Figure 4).

is the next most informative variable; its distribution among so few

categories reduces Us contribution to the generation of the discrimi-

nant function. When the function was modified to include back

pattern, however, it placed 3 of the 30 specimens of aestuannus with

desenicola, 1 (not from the core sample of 5 specimens) of the 18

specimens of desenicola with aestiiarinus (Figure 17). Thus a dis-

tinction can be drawn so that only 4 of 48 specimens in the samples

from at or near the type localities overiap, suggesting a valid distinc-

tion between these two subspecies. Application of the discriminant

functions to specimens from elsewhere in California, however, mud-

o

■o 5

•S 4 -

n.

y 3

"d.

E 2

0 12 3 4 5

underparts

Figure 10. Scatterplot for Cislolhorus palustris plesiuslpulvenus and C

p. aestuarinus of the two vanables in which they differ most, underpart color

and rump/scapular color 9. core-sample specimens of plesiuslpulvenus; O.

inferred specimens of plesiuslpulvenus; H , core-sample (September) speci-

mens from the San Joaquin Delta (aesiuarinus); D, additional (October)

specimens from the San Joaquin Delta (inferred aesiuarinus)

10

9

8

7

6

5

4

3

2 H

1

0

CO O ^ (P

*) o© • o • • •

45 50 55

adjusted wing chord

Figure 12. Scatterplot for Cislolhorus paluslris plesiuslpulverius and

coastal southern California Marsh Wrens of the two vanables in which they

differ most, rump/scapular color and wing length. So that the sexes could be

considered together in one statistical process, the wing chords of females

were multiplied by 1 ()6, the factor by which the average male Marsh Wren

exceeds the average female •, core-sample specimens of plesiuslpulvenus;

O. inferred specimens of plesiuslpulverius; ■ , specimens of the breeding

population of coastal southern California

Taxonomy of ihe Marsh Wren m Southern Cahfornia

11

5 -

c« 4 —

a,

(U

T3

3 -

nape-collar width

Figure 13. Scatterplot for Cisiorhonis paluslns pahidicoUi and C. p.

aesluarinus of the two vanables in which they differ most, underpart color

and nape-collar width. A. specimens from southwestern Washington

(paludicola), •, core-sample (September) speciinens from the San Joaqum

Delta (aestuaimus). O. additional (October) specimens from the San Joaquin

Delta (inferred aesuuinnus).

died this distinction substantially, so it does not seem useful on a

broader scale (see below).

Cislollumis p. aestitarimis vs. coastal southern California popula-

tion. The discriminant function analysis, with jackknife correction,

separated these two groups completely, with a substantial gap between

them. Rump/scapular color, wing length, undetpart color, crown pal-

tern, and back pattern, in decreasing order, all differed significantly.

Figure 18, a plot of rump/scapular color versus underpart color, shows

this separation in just two vanables. Evidently, the name aestitannus

does not apply to the Marsh Wrens of coastal southern California.

Cistothorus p. deserticola vs. coastal southern California popu-

lation. The discriminant analysis, from the direct result and after

2 3

back pattern

Figure \^- Scatterplot for Cislalhorus pulustns paludicola and coastal

southern California Marsh Wrens of the pair of vanables in which they differ

most, rump/scapular color and back pattern A, specimens fi-om southwest-

em Washington (paludicola): •, specimens of the breeding population of

coastal southern California.

cross-validation via jackknifing. classified 38 and 37, respectively.

of 39 specimens as expected on the basis of their origins. The

discriminant-function analysis identified four variables as infor-

mative in making this distinction, in order of decreasing impor-

tance, wing length, rump/scapular color, crown pattern, and un-

derpart color. Between this pair of populations, back pattern and

nape-collar width do not differ significantly. Wing length alone

separates the samples totally (with adjustment for sex, the coastal

sample measures 44.0-50.4 mm, the desert sample 50.7-55.9 mm),

though the approach is so close some overlap should be expected in

large samples. Though the two groups differ substantially in rump/

scapular color (only 2 of 1 8 desert specimens rating darker than 7;

only 2 of 1 8 coastal specimens rating paler than 8, and one of these,

collected in February, was likely faded in comparison to the rest of

the sample, collected in August and September), the computer-

o

o

3

o

C/1

11 -f

10

9

8

7

6

5

4 H

3

2

back pattern

Figure 14. Scatterplot for Cistothorus palusiris paludicola and C p.

deserticola of Ihe pair of variables in which they differ most, nimp/scapular

color and back pattern A. specimens from southwestern Washington

[paludicola). •. core-sample (August/September) specimens of the breeding

population of the Colorado Desert (deserticola), O. additional Oclober-Febm-

ary specimens from the Colorado Desert inferred as deserticola (see Figure 4)

20

10

r3

0 -

-13 -12 -11

-10 -9 -8 -7 -6

canonical variable

Figure 16 Histogram of Ihe canonical vanable resulting from a stepwise

discnminant analysis of Cistothorus paluslns paludicola and coastal south-

ern California Marsh Wrens Rump/scapular color, nape-collar width, and

back pattern are the vanables contnbuting to the separation. Shaded bars,

C p. paludicola; white bars, coastal southern California Marsh Wrens.

12

Philip Unitt, Karen Messer, and Marc Thery

back pattern

Figure 17. Scatterplot for Cixtolhorus paluslris aesluarinics and C. p.

deserlicoki of the only two vanables in which they differ significantly, under-

part color and back pattern A. core (September) specimens from the San

Joaquin Delta (aesluarinus). A . additional (October) specimens from the San

Joaquin Delta (inferred aesniannus); 9. core (August/September) specimens

of the breeding population of the Colorado Desert (deserticdhi), O, additional

October-February specimens from the Colorado Desert inferred as deserticola

(see Figure 4)

generated discriminant function did not use this variable, the infor-

mation it provides being redundant with thai for other variables.

The difference in the crown is the coastal sample's averaging more

extensively black. A slight difference in the underparts arose from

25% of the desert sainple's being rated 2, paler than in any of the

coastal specimens. Figure 19 is a scatterplot of these two groups

showing the separation on the basis of wing length and rump/

scapular color

Two specimens of these groups were misclassified by the dis-

cnminant function. One is SDNHM 42931, the single February

(comparatively worn and faded) coastal specimen, the other SDNHM

46003, an Impenal Valley specimen at the dark extreme for the

species in rump/scapular color (rated 10), a color matched otherwise

10

o

3

Q.

a

o

7 -

6 -

5 -

underparts

Figure 18. Scatterplot for Cistothorus paluslris aestuarimis and coastal

southern California Marsh Wrens of the pair of variables in which they differ

most, rump/scapular color and underpans. •, core (September) specimens

from the San Joaquin Delta Uiesluanmis), O, additional (October) specimens

from the San Joaquin Delta (inferred aesluiinmis), ■, specimens of the

breeding population of coastal southern California

10

9 -

6 -

5 -

47 49 51 53

adjusted wing chord

Figure 19 Scatterplot for Cisunhorus paluslris deserlicoki and coastal

southern California Marsh Wrens of the two vanables in which they differ

most, wing length and rump/scapular color So that the sexes could be

considered together in one statistical process, the wing chords of females

were multiplied by 1 06, the factor by which the average male Marsh Wren

exceeds the average female. ■. core (August/September) specimens of the

breeding population of the Colorado Desert (deseriicola), D, additional

October-February specimens from the Colorado Desert inferred as

desenicola (see Figure 4); •, specimens of the breeding population of coastal

southern California.

only along the southern California coast. In wing length and crown

pattern, however, this specimen is like deserticola and unlike the

coastal sample.

The jackknife-corrected discnminant analysis suggested that only

5% of a sample of these two populations should overlap. Therefore,

the name desenicola does not apply well to the southern coastal

population.

ALLOCATION OF SPECIMENS FROM OTHER SITES

We applied the discriminant functions generated by both the core

and enlarged samples to specimens from elsewhere in the Marsh

Wren's breeding range.

Coos County, Oregon

Of two specimens collected 7. 1 miles north of Coos Bay on 22

October 1982 (SDNHM 42077 and 44078), one was placed by the

discriminant functions (from both the core and enlarged samples)

with deserticola, the other with aesluarinus. That neither was placed

with paludicola suggests that the southern limit of paludicola lies

somewhere along the coast of central Oregon and does not reach

California.

Humboldt County, California

A single immature male (SDNHM 3203), collected at Clam

Beach on 18 October 1967, is older than the specimens on which the

discriminant functions were based but we assessed it anyway, as it was

still in heavy molt so presumably represents the local population. With

a rump/scapular rating of 7 and a crown rating of 4, it is at the pale

extreme for the southern California coastal population, but its short

wings (apparently fully grown in at 48.8 mm) are typical of that group,

to which the discriminant functions assigned it. With the exception of

one specimen from the Imperial Valley, it is the only specimen from

outside coastal southern California placed with that group.

Taxonomy of the Marsh Wren in Southern Cahfornia

13

Coastal Central California

Another somewhat aged specimen (SDNHM 35175), collected

18 September 1958 just northeast of Martinez in Contra Costa

County, has paler underparts (rated 3) than the sample from just 10

miles to the northeast across Suisun Bay at Joice and Grizzly islands

(all rated 4 or 5). Therefore, it matches deserticola better than

aeslitannus, and that is where the discriminant functions placed it.

An old, foxed specimen (SDNHM 24642), collected 4 December

1938 at Santa Cruz, though not evaluated by the discrimrnani func-

tions, appears closest to deserticola as well. The breast is only lightly

tinged buff, while the crown is too brown and the wings loo long

(50.7/51.7 mm, female) for the southern coastal population.

A specimen from the mouth of Los Osos Creek on Morro Bay,

San Luis Obispo County, collected 7 September 1986 (SDNHM

44461), was placed with aestuarinus by the discriminant function

based on the core specimens alone, with deserticola by the function

based on the enlarged sample. Of two specimens (SBMNH) from

Dune Lakes, southwestern San Luis Obispo County (28 September

1962, 12 September 1973). the former was placed by the discnmi-

nant functions with deserticola. the latter with aestuarinus. Of two

specimens from the Santa Ynez River mouth. Santa Barbara County

(UCSB). one (4 January 1992) is clearly a rmgxxAplesiuslpulverius.

while the other (10 January 1992) was placed by the discnminanl

functions with aestuarinus. Though the base for drawing a conclu-

sion is rather meager, evidently the Marsh Wrens of coastal central

California bridge the difference between aestuarinus and deserticola.

Oases of Mojave Desert

We examined specimens from two sites in the Mojave Desert.

Harper Dry Lake, San Bernardino County, and Piute Ponds, Los

Angeles County.

The specimens from the Piute Ponds, within Edwards Air Force

Base in the Antelope Valley, are all in the Los Angeles County

Museum. Five were collected on 27 October 1989. Of these, two are

migrant plesiuslpulverius. while the other three fit with deserticola.

Six were collected in spring, from 26 April to 8 May. Three are

juveniles; two are badly worn adults. One adult, a male with enlarged

testes taken 26 Apnl 1989. is still in a condition good enough to be

assessed. It agrees well with deserticola in all variables.

From Harper Dry Lake, we assessed 17 specimens, all collected

in fall and early winter, the earliest fall specimens being taken on 28

September All were therefore taken at a time when migrants should

be expected, and. not surprisingly, of the 17. 6 were identified by the

discriminant functions as plesiuslpulverius. Two additional speci-

mens (SBCM), identified by the functions as paludicola, were prob-

ably migrants from the Great Basin as well. One had a rump/scapular

score of 2, typical for plesiuslpulverius but not (or paludicola. With

nape-collar widths of 5-6 mm, probably their necks were elongated

in preparation in compan.son to the specimens used in the defining

samples, as they were made by different preparators. The other 9

Harper Dry Lake specimens are too dark on the rump, scapulars, and

underparts for the migratory subspecies, so we infer these represent

the resident population. Of the 9, 5 conform with deserticola. while

1 (SBCM 53683), with a nape-collar width of 5 mm and a back score

of 2, was placed by the functions with paludicola. Again, this

specimen may have had its neck overly stretched; in other variables

it agrees with deserticola. Three specimens, by virtue of their darker

underparts (especially striking in SDNHM 48952) or narrower back

streaks, better fit aestuarinus. Though it is possible that these appar-

ent aestuarinus dispersed southeast from the Central Valley, more

likely they represent normal variation in the resident population. The

dark extreme of underparts crops up in one specimen of deserticola

from the Imperial Valley, and the narrower white back streaks (rated

2) in two specimens. As noted above, the distinclion between

aestuarinus and deserticola is comparatively weak, and despite the

wide separation of the main ranges, the intervening oases may

provide an opportunity for gene flow. Even in these nonmigratory

subspecies, substantial dispersal ability likely favors survival of

birds dependent on widely scattered tiny patches of suitable habitat.

Ventura County, California

Unfortunately, we located only a single recent specimen from

Ventura County, a male taken at the sewage ponds in the Point Mugu

military reservation on 13 December 1986 (SBMNH 5090). This

specimen falls within the range of the southern coastal population in

its fairiy dark rump and scapulars (rated 7) and fairly blackish crown

(rated 4) but disagrees in its long wings (53.4). The discriminant

functions placed it with deserticola.

SUBSPECIES DEFINITIONS

These comparisons suggest that plesiuslpulverius, paludicola,

aestuarinus, and the population of coastal southern California are all

differentiated at a level appropriate for designation as subspecies.

Cistothorus p. deserticola presents a more awkward problem.

Cistothorus p. plesiuslpulverius

Our analyses reaffirm the distinctiveness of the more or less

migratory plateau population from the lowland populations nearer

the Pacific Coast, a difference universally recognized since 1897.

This group is identified by its comparatively long wing (a difference

expected between migratory and sedentary populations), entirely

brown to moderately black crown (Figure 20), narrow brown nape

collar, broadly white-streaked back, comparatively pale tawny rump

and scapulars, and pure white or only slightly buff-tinged breast

(Figure 21). In combination these features sufficed to distinguish

92% of our sample.

Assessing the distinction between plesiits and pulverius was not a

goal of this study, and such an assessment was not possible from the

sample used, which lacked specimens from the breeding range of

plesiids. The few specimens from eastern California were among the

largest and palest of the sample, however, suggesting the Marsh Wrens

breeding along the east side of the Sierra Nevada and Cascade Range

(pulverius) represent the extreme development of this group's charac-

ters and may be distinguishable from the majority of winter visitors in

southern California, in which these characters are on average less

extreme and may be migrants from farther east in the Great Basin/

inlermountain region (plesius). The greater abundance of apparent

plesiiis in winter in southern California, despite its breeding range's

being more remote, may be due to a difference between pulverius and

plesius in the winter climate of the breeding range. From the Pacific

Ocean to the Rocky Mountains, winter temperatures tend to decrease

from west to east, and wintering by Marsh Wrens in the ranges of

pulverius and plesius has been reported as irregular and dependent on

iheseventy of the winter (e.g.. Root 1988; Gilliganet al. 1994).

Cistothorus p. paludicola

The sample from southwestern Washington stood apart from the

others largely on the bases of its entirely brown to only slightly black-

margined crown, broad brown nape collar, and nartowly white streaks

on a reduced weakly black-tinged back patch. TTie rump/scapular

ranking of pahuhcola overlapped extensively with those of aestuarinus

and deserticola on our light-to-dark scale, but the hue of these parts of

the p]umage paludicola tends more toward an earth brown, and away

from rufous, than in the other lowland subspecies, a subtle variation

not captured in our analyses but evident in Figure 20. In wing length

and underpart pattern paludicola occupies a position intermediate with

and overiapping several other populations. The weakest separation of

paludicola was from aestuarinus, but the darker underparts, blacker

14

Philip Unite, Karen Messer. and Marc Thery

clarkae

pahidicola

deserticola

plesius

aestuarinus

pulverius

Figure 20 Upperparts of six populations of the Marsh Wren CisUHlwnis paluslns clarkae. based on SDNHM 48915, holotype from Batiquitos Lagoon,

Carlsbad, San Diego County, Cahfomia, 23 August 1994 C /> desenicola (best included under aesuiariims). based on SDNHM 44278, a topolype from 2

miles north-northwest of Seeley, Impenal County, California, 29 September 198-'>. C p. aesnianniis. based on SDNHM 445.^2, virtual topotype from Joice

Island, Solano County, California, 9 September 1986 C /> paludicola. based on UW 40S65, a topotype from the North River mouth, Willapa Bay, Pacific

County, Washington, 18 November 1985 C /> plesius. based on SDNHM 43971, from Picacho Reservoir, Pinal County. Anzona, 24 October 1985. C. p.

pulverius. based on SDNHM 4.3469, from Owens Lake, 5 miles northeast of Olancha, Inyo County, California, 20 September 1984.

Taxonomy of the Marsh Wren m Soulhcrn Cahlorni;

15

clarkae

paliidicola

deserticola

plesius

aestimrmus

pulverius

Figure 21. Underparts of six populations of the Marsh Wren, based on the same specimens as in Figure 20

16

Philip Unitt, Karen Messer, and Marc Thery

crown, narrower nape collar of the latter still served to allow 91% of

that pair of populations to be distinguished.

Cistothonis p. aestuarimis

The Sacramento Delta sample differed from the other groups

primarily on the basis of its dark underparts; the specimens ranked

darkest (5) on the underparts were from this area almost exclusively.

In wing length, rump/scapular color, crown pattern, nape-collar

width, and back pattern the delta sample was in an intermediate

position, as might be expected from its central position geographi-

cally. The extreme developments of some of the peripheral popula-

tions, however, plesius/pulveriiis in large size and plumage paleness,

paliidicola in its broad nape collar and brown crown, and the popula-

tion of coastal southern California in its small size and dark upper-

parts, left aesluarinus adequately isolated from these. The distinc-

tion from deserlicola. on the basis of darker underparts and narrower

white back streaks alone, was the weakest but could be defined so

that only 4 of 43 specimens from near the type localities in the

combined enlarged samples overiapped with the other.

Cislothonis p. dcsi'iticiila

Despite its peripheral position geographically, the population of the

Colorado Desert is the least distinctive morphologically. In all charac-

ters, it lies in a position intermediate among the other subspecies. It

differs from plesius/pulveriiis in its tendency toward a darker rump and

scapulars, buffier underparts, shorter wings, and blacker crown. It

differs from paludicola in its tendency toward darker rump and scapu-

lars, a narrower nape collar, ;ind bolder white back streaks. It differs

from aestnarmus in its tendency toward paler underparts and narrower

white back streaks. Its differs from the population of coastal southern

California in its longer wings, tendency toward paler rump and scapu-

lars and browner crown, and average slightly paler breast.

If only the type localities oi aesluarinus and deserlicola had to be

considered, the two subspecies could be recognized fairly easily. But

the samples from coastal central California and Harper Dry Lake

show the whole range of these phenotypes. A distinction between the

two implies a biogeographically oddly shaped zone of intergradation

at least as large as the core ranges of the subspecies. Therefore,

recognition of deserlicola as distinct from aesluarinus doei not seem

practical, a result implied also by the group's failure to segregate in

the cluster analysis.

The wide range (even to south-coastal Oregon) of Marsh Wrens

matching the characters of deserlicola suggests that the deserlicola

phenotype could represent the primitive appearance of California's

lowland Marsh Wrens and that the dark underparts of aesluarinus are

an innovation that arose in or near the San Joaquin Delta and has

spread to some degree over most of California but has barely touched

the southeastern corner of the state. Conversely, the aesluarinus type

may have originally been widespread, and, especially before the

damming of the Colorado River and irrigation of the Imperial Valley,

deserlicola was confined largely to the Colorado Delta. Changing

water-management practices have probably increased the range and

population of deserlicola enormously in historic time (Rosenberg et

al. 1991), possibly enabling it to invade northwest and mix with

aesluarinus.

Southern California Coastal Population

The sample from San Diego County was well isolated from the

others on the basis of having the shortest wing, most extensively

black crown, and darkest rump and scapulars. In nape-collar width,

back pattern, and underpart pattern it did not differ greatly from

several other samples, overlapping in those features substantially.

But the sample stands at the extreme for the species in three of the six

characters quantified in this study. Cluster and discriminant analyses

consistently identified it as an independent group. In all discnminant

analyses, both pooled and pairwise, 91% or more of this sample was

classified as expected on the basis of origin, while no more than 6%

of any other sample was classified with the San Diego group, even

when the discriminant functions were cross- validated via jackknif-

ing. Because the level of differentiation of this sample well exceeds

the 75% threshold, and equals or exceeds that of other subspecies

recognized in the Marsh Wren, we propose that it be known as

Cistothorus palustris clarkae subsp. nov.

Holotype. San Diego Natural History Museum number 48915,

collected by Philip Unitt (original number 1357) on 23 August 1994

at the east end of Batiquitos Lagoon, city of Carisbad, San Diego

County, Califomia (35" 06' N, 117" 16' W). Adult female (skull

completely pneumatized; ovary granular, 4 x 1.5 mm; ova minute).

Weight 8.1 grams; slight fat. Length in flesh 123 mm, wingspread

1 56 mm, wing chords 47. 1 mm. Prebasic molt completed except for

a few feathers on chin and face.

Diagnosis. Differs from other western populations of the Marsh

Wren in small size (see Table 3), more extensively black crown (at

least 50% black; usually with only a small brown patch in the center

of the forehead), and darker rufous scapulars, rump, upper tail

coverts, and central rectrices, in fresh plumage all of these close to

Raw Umber or Prout's Brown of Smithe (1975).

The new subspecies differs from deserlicola, as suggested by

jackknife-adjusted discnminant analysis, at a 94% level (at least) by

these three characters, plus a slight tendency to a darker breast. A

single exceptionally dark specimen of deserlicola and a probably

laded February specimen of clarkae were the only two confounding

specimens. In the sample examined wing length alone yielded 100%

separation.

From aesluarinus, clarkae differs at a nearly 100% level by its

usually darker rump and scapulars, shorter wing, paler underparts

and flanks (breast pale buff), and blacker crown. In combination

these characters distinguish 100% of specimens from the type local-

ity. From the broader range of aesluarinus, as we redefine it, includ-

ing all of coastal California south to Ventura County and the Mojave

and Colorado deserts (deserlicola), only 2 of 60 specimens (3%)

were placed by the discriminant functions with clarkae.

From paludicola, with which it has traditionally been linked,

clarkae differs al a 100%> level by its bolder white back streaks on a

blacker background, and narrower brown nape collar (2-7 mm in

clarkae. >5 in only 2 of 23 specimens; 4—9 m paludicola, <5 in only

3 of 20 specimens) in addition to the three other characters.

From the migratory plateau subspecies pulverius and plesius,

which invade its range in fall and winter, clarkae differs even more in

the three main characters than it does from the other lowland popula-

tions, plus it has a more intensively buff breast. From the Marsh

Wrens of northeastern North Amenca Uamgi, iliacus, dissaeplus,

and nominate paluslris), clarkae differs in its barred upper tail

coverts as well as its darker rump and scapulars and buff breast band.

From the Marsh Wrens of the coastal southeastern United States

clarkae differs as follows; from lliryophilus by its largely blackish

crown, from marianae and waynei by its more rufous rump and

scapulars and lack of dusky speckling or barring on the flanks or

breast, and from griseus by its far more rufous rump and scapulars

and more extensive black and white patch on the back. From

lolucensis of central Mexico clarkae differs by its less extensive

black and white back patch and paler, less rusty underparts.

Dislnbulion. Coastal lowland of southern California, from the

Tijuana River immediately north of the Mexican border north to Los

Angeles. Of 25 old October-February Marsh Wrens from Los Ange-

les and Orange counties in the Los Angeles County Museum of

Natural History, 22 appear to be migrants of plesius/pulverius, while

Taxonomy of the Marsh Wren in Southern California

17

Table 3. Wing chords of various subspecies of the

Marsh Wren.

3 agree with clarkae in their extensively black crowns (rated 5 or 6),

dark (now foxed and unscorabie) rump and scapulars, and short

wings (46.2 in the one female; 44.7 and 48.2 in the two males). These

are LACM 12289, from the San Gabriel River on 23 December

1895, LACM 2376, from Nigger Slough on 12 February 1918, and

LACM 17629, from Play a del Rey on 20 December 1931. These

specimens demonstrate that the characters of clarkae are long estab-

lished in this population, not an artifact or innovation of the recent

sample from San Diego County.

The breeding Marsh Wrens of western Riverside County prob-

ably belong with clarkae. though this needs confirmation with recent

specimens. The only specimen we have seen from this area, SBCM

3912, is a migrant plesius collected 12 March 1967. For further

details and historical changes, see below.

One specimen implies short-distance dispersal of clarkae across

unsuitable habitat. This is LACM 1 9635, a male collected by George

Willett on 13 November 1939 on San Clemente Island, where the

Marsh Wren is only a rare nonbreeding visitor (Jorgensen and

Ferguson 1984). The rump is as dark as in the three old specimens of

clarkae from Los Angeles County. The crown seems to have lost a

few feathers so is difficult to judge but looks about half black. At

only 48.0 mm. the wing measurement is typical of clarkae.

Etymology. We name this Marsh Wren in honor of Mary Hollis

Clark, in appreciation of her 33 years of support and service, through

good times and bad, to the San Diego Natural History Museum and

its scientific and educational mission. With the help of Mrs. Clark

and her family, many San Diegans have increased their appreciation

of the uniqueness of their natural environment. With its narrowly

restricted range, Cistolhonis palustns clarkae reveals itself as yet

another element of that uniqueness.

Discussion. Our results confirm Rea's (1986) conjecture that the

coastal southern California Marsh Wrens constitute a subspecies,

though not quite on the basis that he suggested. As noted above, the

pigment coloring the rump and scapulars of Marsh Wrens is subject to

foxing, increasing its redness. Evidently, the greater the concentration

of this pigment, the more grossly the specimen foxes. In the pale

extreme of the species {pulverius) the difference is slight; in the dark

extreme (clarkae) the difference is great, as seen in companson of our

1994 specimens with the three collected in Los Angeles County from

1895 to 1 931. The rump and scapulars of old specimens, in which the

natural darkness of clarkae has been foxed into rustiness. look

"brighter and richer" (Rea 1986) than in the other subspecies.

Swarth (1917) noticed that the Marsh Wrens of coastal southern

California were exceptionally small but did not quantify the differ-

ence. Neither he nor subsequent revisers applied this variable to the

population. The difference in crown pattern has not been reported

previously.

Revelation of an undescribed subspecies of bird in a region as

heavily populated as coastal southern California, which has been

studied by thousands of biologists, may seem incongruous. In the ca.se

of Cistothorus palustris clarkae, however, several factors contributed

toward concealing it for so long. In existing collections, the great

majority of specimens of the Marsh Wren from coastal southern

California were taken in winter, and consist largely of migrants from

the plateau region. Since there is .substiuilial variation among these

migrants, probably interpretable as two subspecies, the additional

variation arising from the few specimens of clarkae was less notice-

able. Some individuals of paludicola and aesluarinus were thought to

make long-distance migrations, reaching coastal southern California,

for which we have seen no evidence. The few breeding-season speci-

mens (e.g., SBCM 36797, Nigger Slough, Los Angeles County, 13

May 19l7)are in poor condition, often with wom crowns, faded rumps

and scapulars, and broken primary tips; they do not preserve well the

defining features of clarkae evident in fresh plumage. The very urban-

ization of the range of clarkae discourages collectors from working in

it; collecting birds at most sites in coastal southern Califomia where

Marsh Wrens breed now requires special authorizations beyond the

standard permit from the Califomia Department of Fish and Game.

DISTRIBUTIONS OF THE SUBSPECIES

OF THE MARSH WREN IN SOUTHERN CALIFORNIA

Cistothorus p. plesiuslpulverius

Marsh Wrens from the Great Basin/intermountain plateau region

winter throughout southern Califomia, invading many areas where the

species does not breed. Though Garrett and Dunn ( 1981 ) reported the

Marsh Wren as absent from the "colder northern deserts" in winter, T

Heindel (pers. comm.) finds it more common in the Owens Valley m

winter than in summer West of the Sierra Nevada, Gnnnell and Miller

(1944) reported plesius north only to Tomales Point and Petaluma.

Mann and Sonoma counties. Gabrielson and Jewett (1940) did not

report it from west of the Cascade Range in Oregon, but in Jewett's

collection (SDNHM) are three specimens, from Taft. Netarts. and

Portland, that conform with the intenor population well in both color

and size. The specimen from Portland (6 October 1928, SDNHM

24646, wings 55.5/56.0 mm) apparently represents the northwestem-

most documented point of these migrants' dispersal.

Understanding of the schedule of arrival and departure of plesiusi

pulverius in southern Califomia needs further refinement. We have

not seen any specimen eariier than one taken for this study in the

Tijuana River valley, San Diego County, on 23 September 1994

(SDNHM 48983). But the migration unquestionably begins some-

what earlier than this; M. Heindel (pers. comm.) finds Marsh Wrens

migrating commonly through the desert oases of eastern Kem County

by 10-20 September; M. A. Patten (pers. comm.) has earliest dates

for migrants in the California deserts of II and 17 September;

Lehman (1994) reported migrants as fairly common in Santa Bar-

bara County by the beginning of September Marsh Wrens have been

reported away from breeding sites as early as 29 August in eastern

Kem County (M. Heindel pers. comm), 14 August in San Diego

County (Unitt 1984), and 23 July in Santa Barbara County (Lehman

1994). We suspect the few early records represent short-distance

dispersal from breeding sites nearby and that migrants from the

plateau region do not reach the coast of southern California until

around the middle of September. But the exact schedule and possible

annual variations of this arrival remain uncertain, requiring testing

via further collecting.

Spring departure takes place largely in April. We have not seen

specimens of plesiuslpulverius from the winter range later than 13

Apnl (1923, salt marsh at Santa Catanna Landing, 29" 30' N, Baja

18

Philip Unilt, Karen Messer. and Marc Thery

•O Santa Barbara

Ventura

O \ Los Angeles

San Bernardino

<i

o ^^^^^

Riverside

i Orange) ^

San Diego

Imperial

Figure 22. Distnbution of the Marsh Wren as a breeding species in southern California, Squares, Cistothorus palustns puherius . circles, C p. uesluannus

(including deserticola): upright tnangles, recent sites for C. p. clarkae: inverted triangles, former sites for C. p. clarkae Filled symbols, specimens examined;

open symbols, other sites where the Marsh Wren is known to have bred or summers regularly (subspecies allocation inferred at the.se sites). These sites are

based on published literature, personal observation, personal cominunication from many field ornithologists, and the egg collections of the Western

Foundation for Vertebrate Zoology, Camanllo, and the San Bernardino County Museum, Redlands

California. SDNHM 8626) and 1 6 April ( 1 920, Furnace Creek Ranch,

Death Valley, Inyo County, MVZ 40664). but Marsh Wrens continue

to be seen in dwindling numbers at nonbrecding sites in southern

California nearly or quite to the end of the month. In the Mojave

Desert of eastern Kern County, sightings as late as 15 May are known

but exceptional (M. Heindel pers. comm). Records later in the spring

(4 June, Galileo Hill, Kern County. M. Heindel pers. comm.; 8 June.

Southeast Farallon Island. Pyle and Henderson 1991) may represent

vagrants of far distant subspecies; specimens are needed to test this.

Grinnell and Miller ( 1944) showed the Marsh Wren as absent as

a breeding species from Inyo County, but summenng birds are

currently widespread and common along the entire Owens River,

south to Owens Lake (T. Heindel pers. comm.) (Figure 22). They

occur also at Little Lake. More specimens are needed to confirm this

population aspulverius, but a specimen from Owens Lake, collected

on 20 September 1984 (SDNHM 43469), we believe represents that

population, even though migrants from farther north might be ex-

pected on that date. It was not fat and was still molting its contour

feathers; it is at the extreme for pitlvenus in paleness of crown,

scapulars, rump, and underparts. being scored at 1 in those variables.

Therefore, we suggest the breeding range of piilvenus extends south

in California to Owens Lake and probably to Little Lake, in south-

western Inyo County.

In eastern Inyo County, the Marsh Wren is known to nest at Furnace

Creek Ranch, Death Valley (T. Heindel, M. A. Patten pers. comm.) and

presumed to along the Amargosa River near Tecopa (regular through

the summer. J. Tarble pers. comm). But the only specimen we have

seen from these sites (Furnace Creek Ranch, 16 April 1920, MVZ

40664). is a late migrant. Though the testes are somewhat enlarged

(about 4 mm long, according to the drawing on the label), the bird was

fat and not in breeding habitat ("rank grass and mesquite at edge of

alfalfa," according to the field notes of the collector. Joseph Gnnnell).

In paleness of rump and scapulars, whiteness of rump, boldness of

white back streaks, and large size (wing chord 54.5 mm), it is clearly

plesiuslpidveniis and matches May specimens oi puherius from south-

eastern Oregon. The occurrence of a typically low-desert npanan

avifauna at Fumace Creek Ranch and Tecopa suggests the Marsh

Wrens nesting there are more likely aesluarinusldeserticola.

Cistothorus p. paludicola

We found no specimens suggesting this subspecies occurs in

California. Since the discriminant analysis did not place even the two

specimens from Coos County, Oregon, with paludicola, we infer it

does not reach California as a breeding species. The southernmost

specimen we have seen is fromTaft, Lincoln Co., Oregon (5 January

1935, SDNHM 24647). Though the possibility remains that

paludicola migrates to some extent to northern Califomia, we doubt

this and suggest Khax. paludicola be deleted from the list of California

birds unless further studies confirm it.

Taxonomy ot Ihc Marsh Wren in Southern Cahfornia

19

Cislollionis p. aestuannus

The pattern of variation in the Marsh Wren in California seems

best described by including all the populations of the north and

central coast. Central Valley, and Mojave and Colorado deserts in

this subspecies.

From northern Monterey County, where Marsh Wrens nest

around Monterey Bay and in the lower Salinas Valley (R. F, Tintle in

Roberson and Tenney 1993), the species is absent along the coast

south to Morro Bay, San Luis Obispo County. Another population

breeds in coastal marshes from Morro Bay to the Santa Yne/. River

mouth (Lehman 1994).

Then another gap intervenes until another isolated population

occupies part of Ventura County. In Ventura County Marsh Wrens

nest near the Santa Clara River at the duck ponds 5 km east of Santa

Paula (Z. Labingcr pers. comm.). More intensive study may reveal

them elsewhere along the Santa Clara River, but the population if

any is not large or continuous (M. A. Holmgren pers. comm.). Marsh

Wrens also breed in diked ponds of the Ventura County Gun Club,

just northwest of Mugu Lagoon (D. DesJardins pers. comm.), and in

at least one location around Mugu Lagoon itself, on the grounds of

the Pacific Missile Test Center (T. W. Keeney pers. comm.).

The single specimen we saw that apparently represents the breed-

ing population of Ventura County has a rump and crown at the pale

extreme for clarkae and a wing longer than in specimens from Los

Angeles to San Diego. It is closer to deseriicoia. Ventura County

may represent an area of intergradation between the two, or the

characters of clarkae may have ansen only from Los Angeles south.

One might expect that the oiiginal range of clarkae resembled that of

the Light-footed Clapper Rail, Ralliis longirostns levipes, or

Belding's Savannah Sparrow, Ammodramus scmdwichensis betdingi,

both of which reached their northern limits at Santa Barbara, but the

Marsh Wren, with its freshwater ecology, may be responding to

different selective forces.

In the Mojave Desert, the Marsh Wren occurs through the sum-

mer at several oases. In eastern Kern County, Matt Heindel (pers.

comm.) has confirmed its nesting at three sites: the South Base

sewage ponds on Edwards Air Force Base, near Cantil (about two

territories only), and at China Lake. Also, Marsh Wrens have sum-

mered and probably have nested at California City; regular clearing

of marsh vegetation hinders the birds from establishing themselves

there. The marshes at all of these sites are supported by artificially

developed water sources, so the Marsh Wren's breeding in eastern

Kern County must represent rather recent colonization.

In the Antelope Valley of northern Los Angeles County, the

Marsh Wren breeds abundantly at one known site, the Piute Ponds 1 0

km north-northeast of Lancaster (specimens of both juveniles and

breeding adults in LACM).

In San Bernardino County, nesting has been confirmed at Saratoga

Springs at the south end of Death Valley (Austin 1970), Mojave

Narrows Regional Park along the Mojave River, (S. J. Myers pers.

comm.). Harper Dry Lake (E. A. Cardiff pers. comm.). and (irregu-

lariy) at Morongo Valley. Nesting is possible at Barstow (sewage

ponds). Twentynine Palms. Afton Canyon. Zzyzx Spring, and Camp

Cady (E. A. Cardiff, S. J. Myers, M. A. Patten pers. comm.)

Breeding Marsh Wrens remain locally common the length of the

Colorado River in California, in the Imperial Valley, and around the

Salton Sea, the area assigned by Rea (1986) to deseriicoia.

Cislolhorus p. clarkae

The range of clarkae is confined to coastal southern California

from Los Angeles south, and even within this region is patchy, owing

to the natural localization of freshwater and brackish marshes in this

arid region and the extensive destruction of wetlands over the past

century. Yet in San Diego County the subspecies is widespread and

has apparently extended its range or at least increased in numbers

over the past 25 years. The southernmost site is the Tijuana River

Valley immediately north of the Mexican border, where Marsh

Wrens colonized borrow pits along Dairy Mart Road, beginning in

1980 as the ponds' marshes matured, and becoming common by the

late 1980s, Breeding Marsh Wrens have never been reported along

the Pacific coast of Baja California (Gnnnell 1928, Wilbur 1987);

Kurt Radamaker (pers. comm.) confirms their absence at the north-

ernmost sites with possibly suitable habitat. Descanso and La Misi6n;

neither has he found them in the inland freshwater marshes near Ojos

Negros.

The next known site to the north is Mission Valley, along the San

Diego River in the city of San Diego. Marsh Wrens are not known to

have nested there before 1978. though the San Bernardino County

Museum has a set of eggs taken at "San Diego" in l953(Unitt 1984).

The vegetation along 2.3 km of the San Diego River was removed in

1988 and 1989, as part of a flood-control .scheme. Marsh vegetation

began regrowing along the rccontoured river banks immediately.

Unitt surveyed the site regularly for birds, as part of monitoring a

revegetation program, and found that Marsh Wrens recolonized the

area in the summer of 1993.

The population along Santa Ysabel Creek from Lake Hodges to

San Pasqual in central San Diego County, first noted in 1978 by

Kenneth L. Weaver, is cleariy a recent colonization, since the area

was a center of activity for early twentieth-century egg collectors

(Unitt 1984). Sharp (1907) specifically denied the Marsh Wren's

occurrence at San Pasqual.

In central and northern San Diego County, from Los

Pefiasquitos Lagoon north. Marsh Wrens are resident in every

coastal wetland supporting stands of bulrushes and cattails. Along

the San Luis Rey river, they extend inland at least to 2.4 miles

northeast of Bonsall (male with enlarged testes on 28 February

1 984. SDNHM 4293 1 ); along the Santa Margarita River, to O'Neill

Lake (20 on 28 June 1995, Unitt pers. obs.). From published

literature and the egg collection at the Western Foundation of

Vertebrate Zoology, Guajome Lake is the only site in San Diego

County where the Marsh Wren was confirmed nesting before 1949;

the "San Luis Rey" of Sharp (1907) may encompass the river's

lower floodplain, including Guajome Lake.

In Orange County, Marsh Wrens are abundant through the breed-

ing season at Upper Newport Bay and the San Joaquin Marsh 3 km to

the northeast in Irvine. Elsewhere in this county, however, they are

far less common and less well known. They are resident at the Bolsa

Chica wetlands in the city of Huntington Beach and at Seal Beach

National Wildlife Refuge, but in what numbers is unclear Farther

inland in Orange County, there are no large marshes suitable for

Marsh Wrens. The one known (small) population is in restored

habitat along the Santa Ana River in Anaheim, which the wrens

colonized in the late 1980s. The species may occupy other sites

ephemerally. as in Huntington Central Park, city of Huntington

Beach (D. R. Willick. R. A. Hamilton pers. comm.)

In coastal Los Angeles County, breeding Marsh Wrens are now

restncted to Alamitos Bay. Long Beach, and Harbor Lake, in the

Harbor City district of Los Angeles (K. L. Garrett pers. comm.)

These sites are the last remnants of marshes extensive before the

development of the Los Angeles and Long Beach harbors. Marsh

Wrens nested widely in the Los Angeles Basin before urbanization,

and this area likely represented the core of the range of C. p. clarkae.

In western Riverside County, Marsh Wrens remain common all

year in Prado Flood Control Basin along the Santa Ana River (J. Pike

pers. comm.) and occur locally along the river between Prado Basin

and the city of Riverside (at least at Hidden Valley Wildlife Area at

the western edge of the city of Riverside. M. A. Patten pers. comm.).

Elsewhere in western Riverside County, Marsh Wrens summer along

Alberhill Creek where it enters Lake Elsinore (M. A. Patten pers.

comm.) and at San Jacinto State Wildlife Area near Lakeview (A.M.

20

Philip Unitt, Karen Messer. and Marc Thery

Craig, R. McKernan pers. comm. ). Other unreported colonies in this

area are possible. Specimens from this area are needed to test

whether this population represents ctarkae. aestuarimisldeserticola,

or intergrades. Though the area is closer to the range of clarkae than

to that of aesliiannus/deserlicola, quite possibly clarkae is confined

to a narrow coastal strip.

With urbanization, C. p. clarkae evidently lost much of its origi-

nal core range in Los Angeles and Orange counties. Yet it appears to

have spread its range southward in San Diego County rather recently,

a seeming contradiction. Environmental change, however, may favor

as well as eliminate the Marsh Wren in some cases. Man-made lakes

are quickly colonized by marsh plants, creating new Marsh Wren

habitat. Urbanization of the coastal lowland increases runoff, which

in turn increases the rate of siltation of coastal lagoons. With the

flushing force of their tidal prism reduced by siltation, and typically

reduced further with several levees serving as roadbeds, the lagoons

frequently have their mouths blocked with sand and cobbles. Fresh

water from the increased runoff replaces the salt water from the tides,

and freshwater marsh vegetation suitable for nesting Marsh Wrens

replaces saltmarsh vegetation that isn't. We suspect these processes

are largely responsible for increasing the population of C. p. clarkae

in San Diego County. Efforts at some lagoons (including the type

locality of C p. clarkae) to reinstitule tidal tlushing may reverse this

trend locally, but the forces driving it will probably continue to

sustain a healthy population of Marsh Wrens unless complete elimi-

nation of coastal wetlands resumes. For an accurate assessment of the

subspecies' abundance, however, a rangewide survey is desirable.

ACKNOWLEDGMENTS

We thank Bert and Margaret Mcintosh, Scott Tremor, and Lucie

W. Clark for their indispensable help in the field, with handling the

mist nets. We thank Robert R. Copper and the San Diego County Parks

Department for special aulhonzation to mist-net at San Elijo Lagoon

and in the Tijuana River valley. Michael A. Patten helped with prelimi-

nary statistical analysis and offered many u.selul suggestions through-

out the study. Ned K. Johnson, Mark A. Holmgren, Paul W. Collins,

Robert McKernan, and Kimball L. Garrett graciously lent specimens

from the University of California, Berkeley, University of California,

Santa Barbara, the Santa Barbara County Museum of Natural History,

the San Bernardino County Mu.seum, and Los Angeles County Mu-

seum of Natural History, respectively. Clark Sumida kindly sent cop-

ies of the egg-collection records from southern California in the

Western Foundation of Vertebrate Zoology, Camarillo. Many people

graciously supplied details on the Marsh Wren's current distnbution in

southern California; for this we th;mk Kurt F. Campbell, Eugene A.

Cardiff, Alan M. Craig, Don DesJardins, Kimball Garrett, Robert A.

Hamilton, Tom and Jo Heindel, Matt Heindel, Mark A. Holmgren,

Thomas W. Keeney, Zev Labinger, Robert McKernan, Michael A.

Patten, Jim Pike, Kurt Radamaker, Jan Tarble, and Douglas R. Willick.

We are enormously grateful to Nicole Perrella for lending us her

artistic talent with the exquisite paintings featured in Figures 20 and

21 . We thank Robert W. Dickerman, Robert A. Hamilton, Kimball L.

Garrett, Mark A. Holmgren, and Kenneth C. Parkes for their construc-

tive reviews. And we especially thank Amadeo M. Rea for providing

the initial direction and opportunity to pursue this study.

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