Ornithological Monographs 42

Ornithological
Monographs
No.42

Speciation
and
Geographic
Variation
in Black-tailed
Gnatcatchers

Jonathan
L. Atwood


SPECIATION

AND

GEOGRAPHIC

IN BLACK-TAILED

VARIATION

GNATCATCHERS


ORNITHOLOGICAL

MONOGRAPHS

This series,publishedby the American Ornithologists'Union, has been established for major papers too long for inclusion in the Union's journal, The Auk.
Publication has been made possiblethrough the generosityof the late Mrs. Carll
Tucker and the Marcia Brady Tucker Foundation, Inc.
Correspondenceconcerningmanuscriptsfor publication in the seriesshouldbe
addressed to the Editor, Dr. David W. Johnston, 5219 Concordia St., Fairfax,
Virginia 22032.

Copies of OrnithologicalMonographs may be ordered from the Assistant to
the Treasurer of the AOU, Frank R. Moore, Department of Biology, University
of Southern Mississippi, Southern Station Box 5018, Hattiesburg, Mississippi
39406. (See price list on back cover.)
Ornithological Monographs, No. 42, viii + 74 pp.
Editor, David W. Johnston

Special Reviewers for this issue, Lloyd F. Kiff, Western Foundation of
VertebrateZoology, 1100 Glendon Ave., Los Angeles,California 90024;
Robert M. Zink, Museum of Zoology, Louisiana State University,
Baton Rouge, Louisiana 70803.

Author, Jonathan L. Atwood, Department of Biology, University of California, Los Angeles, California 90024 and Mahomet Bird Observatory, Box 936, Mahomet, Massachusetts02345.
First received, 12 December 1986; final revision completed, 13 October
1987

Issued March 29, 1988

Price $10.00 prepaid ($8.00 to AOU members).

Library of CongressCatalogueCard Number 88-70367
Printed by the Allen Press,Inc., Lawrence, Kansas 66044

Copyright ¸ by the American Ornithologists'Union, 1988
ISBN: 0-943610-53-2


SPECIATION

AND

GEOGRAPHIC

IN BLACK-TAILED

VARIATION

GNATCATCHERS

BY

JONATHAN

L. ATWOOD

Department of Biology
University of California
Los Angeles, California 90024
and

Manomet Bird Observatory
Box 936

Manomet, Massachusetts 02345

ORNITHOLOGICAL

MONOGRAPHS
PUBLISHED

THE

AMERICAN

BY

ORNITHOLOGISTS'

WASHINGTON,
1988

NO.

D.C.

UNION

42


TABLE
LIST

OF FIGURES

LIST

OF TABLES

LIST

OF APPENDICES

INTRODUCTION

OF CONTENTS

..............................................................................................................................................
vi

......................................................................................................................................................
vii

.....................................................................................................................................
vii

.......................................................................................................................
1

GOALS OF THE STUDY ...................................................................................................................................
1
NOMENCLATURAL HISTORY ............................................................................................................................
1

MATERIALS
AND METHODS
.....................................................................................................................
4
MORPHOLOGICAL ANALYSES .......................................................................................................................
5
BIOMETRIC ANALYSES ....................................................................................................................................
8
VOCAL ANALYSES ............................................................................................................................................
9

RESULTS .............................................................................................................................................................
10
GEOGRAPHIC AND ECOLOGICAL DISTRIBUTION ........................................................................
10

Polioptila californica ..........................................................................................................
10
Polioptila melanura ...........................................................................................................
13
Polioptila nigriceps............................................................................................................
17
AREAS OF SYMPATRY BETWEEN POLIOPTIL•I MELANURA AND P. CAL1-

FORNICA ...................................................................................................................................................................
17

Palm Springs, Riverside Co., California ..........................................................................
18

Valle de Trinidad, Baja California, Mexico ................................................................
18

Bahia San Luls Gonzaga(and vicinity), Baja California,Mexico .... 18
"San Felipe Canyon," San Diego Co., California ...............................................
19

BREEDING BIOLOGY ...........................................................................................................................................
21
VOCAL Dilqq•RENCES AND REPRODUCTIVE ISOLATION ....................................................
22

Comparison of major vocalizations .................................................................................
22
Vocal playback experiments ...............................................................................................
30

MORPHOLOGICAL VARIATION ..................................................................................................................
31

Secondary sexual variation .................................................................................................
31
Relative variability .........................................................................................................
33
Character correlations and redundancy ...........................................................................
38
Univariate character analyses ...........................................................................................
38
Geographicheterogeneityamong characters.................................................
38

Geographic patterns of character variation ....................................................
39
Multivariate analyses ...........................................................................................................
50
Inter- and intraspecific variation ..............................................................................
50
Potential hybrid specimens.......................................................................................
56

DISCUSSION
.....................................................................................................................................................
59
SPECIESLIMITS AND TAXONOMY ............................................................................................................
59
COMMON NAMES .............................................................................................................................................
63
HISTORICAL BIOGEOGRAPHY ....................................................................................................................
63
ACKNOWLEDGMENTS

...............................................................................................................................
66


SUMMARY

........................................................................................................................................................
67

LITERATURE

CITED

....................................................................................................................................
68

LIST

Figurel.
2.

3.
4.
5.

6.

OF FIGURES

Approximate geographicdistributions of Polioptila melanura, P.
californica, and P. nigriceps........................................................................................
2
Groupings of specimensofPolioptila melanura into sample areas
for analysis ........................................................................................................................
6
Groupings of specimensof Polioptda californica and P. nigriceps
into sample areas for analysis .........................................................................................
7
Categoriesused in analysisof variation in tail spot shape ...................
7

Polioptila caHfornica habitat in coastal southern California and
Baja California north of 30øN latitude ...........................................................................
11
Polioptila californica habitat in the Vizcaino desertof central Baja
California

.................................................................................................................................................
12

8.

Polioptila californica habitat in the Cape region of Baja California 12
Polioptda melanura habitat in the Sonoran desert of southeastern
California and northwestern Baja California ..........................................................
14

9.

Polioptila melanura habitat in the Sonoran desert of southern

10.

Polioptila melanurahabitat in the Chihuahuandesertof Durango,

11.

Polioptila melanura habitat in the Chihuahuan desert of Guanajuato, Mexico .....................................................................................................................
16

12.

Polioptila nigricepshabitat in the arid thorn scrubof the Mexican

7.

Arizona and the northwestern
Mexico

14.
15.

16.
17.

18.
19.

20.
21.

23.
24.

western

coast ...................................................................................................................
17

Distribution of Polioptila melanura and P. californica in central
Baja California ...............................................................................................................

20
Habitat in the region of sympatry between Polioptila melanura
and P. californica ...........................................................................................................
21
Vocalization Type I in Polioptila californica,P. nigriceps,P. caerulea, P. plumbea, and P. albiloris ..................................................................................
23
Vocalization Type I in Polioptila melanura .............................................................
24
Vocalization Type II in Polioptila melanura ..........................................................
25
Vocalization Type II in Polioptda californica .......................................................
26
Vocalization Types III and IV in Polioptila melanura and P. californica ............................................................................................................................
28
Vocalization Types V and VI in Polioptila melanura, P. californica
and P. nigriceps .................................................................................................................
29
UPGMA phenogram of morphological characters in Polioptila
melanura

22.

..........................................
15

......................................................................................................................................................
15

mainland's
13.

Mexican mainland

..................................................................................................................................................
39

Geographic variation in P6LEN in males ..................................................................
40
Geographic variation in P6LEN in females .............................................................
41
Geographic variation in MASS in Polioptila melanura and P.
californica .......................................................................................................................
42


25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.

Geographicvariation in TLEN .................................................................................

43
Geographicvariation in R5PCT ...............................................................................
46
Geographicvariation in BRSTB ...............................................................................
47
Geographicvariation in R5SPCT .............................................................................
48
Geographicvariation in R6SSH ................................................................................
49
Principal componentsanalysisfor males ....................................................................
51
Principal componentsanalysisfor females................................................................
52
UPGMA phenogramfor males ...................................................................................
53
UPGMA phenogramfor females ................................................................................
54
Geographicvariation in PC1 scores...........................................................................
56
Geographic variation in PC2 scores.............................................................................
57
Geographicvariation in PC3 scores..........................................................................
58
Canonicaldiscriminant analysisof allopatric and sympatricsamples of Polioptila melanura and P. californica ......................................................
58
38. Phylogeneticrelationshipsand distribution in three taxa of North
American xeric-adaptedbirds .....................................................................................
64
LIST

Table

1.
2.

OF TABLES

Specimensusedin analysesof morphologicaland vocal variations
Abundanceof Polioptila melanura and P. californicain areasof

5

sympatry .................................................................................................................................
21

3.
4.
5.
6.

Speciesrecognitionduring playback tests ....................................................................
31
Secondarysexual dimorphism in linear measurements............................
32
Secondarysexual dimorphism in color analyses.................................................
33
Variability and geographicheterogeneityin morphologicalcharacters of Polioptila melanura ...........................................................................................
34
7. Variability and geographicheterogeneityin morphologicalcharactersof Polioptila californica ........................................................................................
35

8. Variability and geographicheterogeneityin morphologicalcharacters of Polioptila nigriceps .............................................................................................
36
9. Geographic differencesin relative variability ..........................................................
37

10.

Correlation

coefficients between correlations

of variation

and lat-

itude and longitude .........................................................................................................
38
11. Correlation coefficientsbetween MASS and morphological char-

acters ................................................................................................................................................................
42

12.
13.
14.
15.

Geographicpatternsof charactervariation in Polioptila melanura 44
Geographicpatternsof charactervariation in Polioptila californica 45
Factor loadingson PCs 1-3 (all speciescombined) ........................................

50
Factor loadingson PCs 1-3 (by species)......................................................................
55

16.

ANOVA

for PCs 1-3

LIST

I.

...............................................................................................................
55

OF APPENDICES

Localitiesof Specimensusedin Morphologicaland Vocal Analyses 71

vii


INTRODUCTION

The gnatcatchers,genusPolioptila, representa well defined yet poorly studied
taxon of New World birds. Comprised of approximately 10 species(Paynter 1964,
A.O.U. 1983), the genushas generally been classifiednear the gnatwrensMicrobatesand Ramphocaenus(Mayr 1946; Mayr and Amadon 1951; Paynter 1964),
although differencesin external morphology, nests,and eggsindicate that Polioptila might not be closelyrelated to thesegenera(Rand and Traylor 1953; Paynter

1964; Kiff 1977). At higher taxonomic levels the position of Polioptila is even
lesscertain, with most authors consideringthe genusto be a member of the Old
World insect eaters (family Muscicapidae, subfamily Sylviinae; Ridgway 1904;
Mayr and Amadon 1951; A.O.U. 1983). However, the resultsofDNA x DNA
hybridization comparisonssuggestthat the gnatcatchers,alongwith the gnatwrens,
Verdin (Auriparusfiaviceps), true creepers(Certhia, Salpornis), and wrens, are
not closely allied to the sylviine warblers but rather represent a monophyletic
New World clade (Sibley and Ahlquist 1985). These authors (pers. comm.) place
the gnatcatchers,gnatwrens,and Verdin in the subfamily Polioptilinae of the
family Certhiidae, with other subfamiliesof the Certhiidae being the Certhiinae
(true creepers)and the Troglodytinae (wrens).
Regardlessof its relationship to other groups of birds, Polioptila itself is a
distinctive, easily recognizedgenuswith little pheneticdivergenceamong its component species.This morphological uniformity has led to some confusion with
regardto specieslimits within the genus.As an extreme example of the taxonomic
difficultiespresentedby Polioptila, Phillips et al. (1973) noted that museum specimens now consideredto representthree distinct species(P. plumbea, P. albiloris,
and P. nigriceps)had earlier been ascribed to a single subspeciesby Griscom
(1930).
GOALS OF THE STUDY

In this study I considera long-standingquestionconcerningspecieslimits within
the "black-tailed" gnatcatchersthat are presently referred to as Polioptila melanura (A.O.U. 1983). Although this systematicproblem is addressedmainly on
the basisof behavioral and ecologicaldata, I also provide information on morphologicalcharactervariation in three (as defined here) sibling species:P. melanura, P. californica, and P. nigriceps(Fig. 1). This study is intended primarily
as a taxonomic revision; however, the resultsare presentedin the context of other
recent studies of geographic variation in birds and thereby contribute to the
growingbody of literature dealing with the evolutionary significanceof intraspecific variability (Zink and Remsen 1986). Also, I compare the distributional and
cladistic patterns of these three speciesof Polioptila with other genera occurring
in the arid regions of western North America, and use these comparisonsas the
basis for discussingthe possible history and mode of speciation in the "blacktailed" gnatcatchers(Cracraft 1982, 1983).
NOMENCLATURAL

HISTORY

The first formal referenceto a gnatcatcherof the "black-tailed" group was the
descriptionby Baird (1854) of Culicivoraplumbea from Arizona. The absenceof
a black cap in the type specimen,a male in basicplumage,was consideredto be


2

ORNITHOLOGICAL

STATUTE

MONOGRAPHS

NO. 42

MILES

FIO.1. Approximate
geographic
distributions
of Polioptilamelanura,
P. californica,
andP. nigriceps.

characteristicof the species.Subsequently,Lawrence (1855) describedfrom Texas
a specimenof a male gnatcatcherwith a black cap and mostly black outer rectrices,
believing it to be an exampleof the black-cappedCulicivoraatricapilla of Middle
America [= present day White-lored Gnatcatcher, Polioptila albiloris (Ridgway

1904; A.O.U. 1983)]. Lawrence(1857) later recognizedthat his black-tailed gnat-

catcherand atricapilla were actuallydifferentspecies.However, either beingunaware of the existenceof Baird's plurnbea or of the similarity ofplurnbea to his
putative species,Lawrence describedthis black-tailed, black-cappedgnatcatcher
from Texas as a new species,naming it Polioptila rnelanurafollowing Sclater's
(1855) changeof the genericname of Culicivorato Polioptila. During theseearly
years, Polioptila plurnbea (Baird) was referred to by the English names LeadcoloredGnatcatcheror Arizona Gnatcatcher,and Polioptilarnelanura(Lawrence)
as the Black-cappedGnatcatcher (Baird et al. 1875; Coues 1878).
Later, Brewster (1881) reported that the presenceor absenceof a black cap in
these birds, rather than being a valid character separatingP. plurnbea and P.
rnelanura,instead was merely dependenton age, season,and sex. Consequently,
he consideredrnelanurato be synonymouswith the older name plurnbea. However,Penard(1923) recognizedthat Pallasin 1769 had incorrectlyassigned
another
speciesof gnatcatcherfrom Middle and SouthAmerica (the present-dayTropical
Gnatcatcher,Polioptila plurnbea) to the genusTodus. Correct placement of this
species(Todusplurnbea) in the genusPolioptila thus resultedin a nomenclatural
conflictwith Baird'sPolioptilaplurnbeaand, becauseof priority, requiredthat
Polioptilaplurnbea(Baird) be changedto Polioptila rnelanura(Lawrence).During
the early 1900s the previous English names for Polioptila rnelanura had been


GNATCATCHER

SPECIES LIMITS

3

replacedin generalusageby the name PlumbeousGnatcatcher(A.O.U. 1886;
Ridgway 1904; Grinnell 1915; Bailey 1927).
Polioptilacalifornicawasalsooriginallydescribedasa distinctspecies(Brewster

1881), with the first associatedEnglish name being the California Black-capped
Gnatcatcher.During the early 1900s, P. californicawas generallyknown as the
Black-tailed Gnatcatcher (A.O.U. 1886; Ridgway 1904; Willett 1912; Grinnell
1915; Bailey 1927).
The presentlyacceptedview of specieslimits in "black-tailed" gnatcatcherswas
proposedby Grinnell (1926). Despite recognizingthat the two forms could be
easily distinguishedvocally (Grinnell 1904), Grinnell believed that P. melanura
and P. californicawere nonethelessconspecific.The primary basisfor this conclusion was the morphological similarity of populations in the Cape region of
Baja California to populations in the Sonoran desert of southeastern California

and Arizona. Accordingto Grinnell (1926), "even thoughcalifornica[of coastal
southernCalifornia and northern Baja California] is to melanura of southeastern
California and Arizona asa full species,variation geographicallyto the southward,
throughthe [centralBaja California population], to the Cape form, and intergradation thencewith melanura through individual variation, warrants considering
[californica]just the extreme in a continuousseriesof subspecies."The English
names Grinnell gave to theseforms were the PlumbeousBlack-tailed Gnatcatcher
for the nominatesubspecies
(includingpopulationslater describedasP.m. lucida)
and the California Black-tailedGnatcatcherfor P.m. californica(Grinnell 1926).
Theserevisionswere acceptedin the 4th edition of the A.O.U. Check-list(A.O.U.
1931).

Recent field ornithologistsin the United Statesand Mexico have generally
ascribedthe English name Black-tailed Gnatcatcher to all populations of gnatcatcherswith outer rectricesthat are mostly black (Peterson1941; A.O.U. 1957).
Someinvestigatorshave distinguishedthe "coastal"Black-tailedGnatcatcher(P.
m. californica)from populationsof P.m. lucida occurringin the desertsof California (McCaskie and Pugh 1964; Atwood 1980). Rea (1983) and Unitt (1984)
both alluded to the possibility of P. melanura and P. californica being distinct
specieson the basisof their vocal differences,but provided no in depth analysis
of specieslimits. Curiously, the most recent contribution to the nomenclatural
confusion surrounding these birds has come from the A.O.U. Check-list Committee itself, which reversed the more traditional associations of common and

scientificnames by applying the English name Plumbeous Gnatcatcher to Polioptila (melanura) californica and Black-tailed Gnatcatcher to Polioptila melanura (A.O.U. 1985).
Here, I use species names and limits in the "black-tailed" gnatcatchersas
follows:(a) Polioptila californica,composedof the currentlyrecognized(A.O.U.
1957) subspeciesP. melanura californica, P. melanura pontills, and P. melanura
margaritae, and (b) Polioptila melanura, composedof the subspecies
P. melanura
melanura, P. melanura lucida, and P. melanura curtara. Support and discussion
of these conclusionswill be provided in subsequentsections.
The third speciesincludedin this study,the mostly white-tailed Black-capped
Gnatcatcher(Polioptila nigriceps),also has had a rather confusednomenclatural
history becauseof uncertaintiesregardingits relationshipto the White-lored Gnatcatcher(Polioptila albiloris).I follow here the treatment usedby the 6th edition


4

ORNITHOLOGICAL

MONOGRAPHS

NO. 42

(1983) of the A.O.U. Check-list. Further information concerning the taxonomic
history ofP. nigricepsis found in Baird (1864), Brewster (1881, 1889), Ridgway
(1904), van Rossem(1931 b), Brodkorb (1944), Friedmann (1957), Phillips (1962),
Paynter (1964), and Phillips et al. (1973).
MATERIALS

AND

METHODS

Field studiesof P. rnelanura, P. californica, and P. nigricepswere conducted
from 1979-1985. While tape recordingvocalizations throughoutthe rangeof each
speciesand obtaining additional specimensfrom localities that were poorly represented in museum collections, I visited 14 states of Mexico (Baja California,
Baja California (Sur), Chihuahua, Coahuila, Colima, Durango, Guanajuato, Hidalgo, Jalisco,Nayarit, San Luis Potosl, Sinaloa, Sonora,Queretaro), and four of
the United States(Arizona, California, Nevada, New Mexico).
Information regarding available specimensof Polioptila rnelanura (including
populationshere consideredto be Polioptila californica) and Polioptila nigriceps
was requestedfrom major ornithological collectionsin the United States and
Canada. Study skins from the following institutions were then borrowed or examined through visit: American Museum of Natural History; University of Arizona;BaylorUniversity, StreckerMuseum;CaliforniaAcademyof Sciences(CAS);
University of California, Berkeley, Museum of Vertebrate Zoology (MVZ); University of California, Los Angeles,Dickey Collection (DC); California State University, Long Beach;California State University, San Jose;National Museum of
Canada; Carnegie Museum; Cincinnati Museum; Cornell University; Delaware
Museum of Natural History; Denver Museum of Natural History; Field Museum
of Natural History; Harvard University, Museum of Comparative Zoology;University of Florida, Florida State Museum; University of Illinois; Los Angeles
County Museum of Natural History; Louisiana State University, Museum of
Zoology; University of Michigan, Museum of Zoology; Milwaukee Public Mu-

seum;Nevada StateMuseum; OccidentalCollege,Moore Laboratoryof Zoology;
Yale University, Peabody Museum; San Bernardino County Museum of Natural

History; San Diego Natural History Museum; Texas A&M University; Texas
Natural History Collection; United StatesNational Museum of Natural History;
Welder Wildlife Foundation. Analysesof clutch sizesand nestingchronologywere
based on data provided by the following institutions: Western Foundation of
Vertebrate Zoology; California Academy of Sciences;University of California,

Berkeley,Museum of Vertebrate Zoology; University of Florida, Florida State
Museum; Harvard University, Museum of Comparative Zoology; and Yale Uni-

versity,PeabodyMuseum. Newly collectedspecimens,preparedmainly as study
skins but also including some skeletal material, are deposited at the Los Angeles
County Museum of Natural History, the University of California, Los Angeles,
and California State University, Long Beach.
A total of 851 study skins (509 males, 342 females) were used in the analysis
of inter- and intraspecific variation; excessively worn or soiled specimens and
specimens still in juvenal plumage were excluded from analysis. Geographic

groupingsof thesespecimensinto 33 sampleareasare shownin Figures2 and 3,
and the number of individuals representing each locality is summarized in Table
1. Becausethe three speciesare non-migratory, specimenscollected throughout
the year were assumedto representprimarily residentpopulations.


GNATCATCHER

SPECIES LIMITS

5

TABLE

1

SPECIMENS USED IN ANALYSES OF MORPHOLOGICAL AND VOCAL
VARIATIONS
Vocal
record-

Linear

measurements

Area
code

Sp.'

Sample area

Males

Females

Color analysis
Males

Females

ings
Males

RI01
NE02
YU03
SF04
BG05

m
m

m
rn
m

Riverside County, California
Needles(Colorado River), California

33
17

27
10

23
8

15
6

7
22

Yuma, Arizona
San Felipe, Baja California

14
12

14
11

7
8

10
6

31
26

Bahia San Luis Gonzaga,Baja California

8

7

8

5

19

A J06
TU07

m
m

HE08
TI09

OB10
CH11
PR12
SAI3
SLI4
DU15
HUI6
GUI7

m
m
m
m
rn
m
m
m
m
m
n
n
n
n
n

LA23
SD24
ST25
ER26
BG27

PP28
SI29
MA30
LP31
ES32
SJ33

c
c
c
c
c
c
c
c
c
c
c

14
16
8
6
15
7
20
11
8
18
16

6
12
30
11
22
9
55
22
15
17
12
12
17

10
17
9
6
6
7
11
5
6
10
7
3
7
20
5
10

3
42
21
8
7
5
3
11

13
12
8
2
12
6
18
8
7
13
14
4
7
20
8
6
7
47
19
14
14

4
11
8

10
12
5
4
4
3
4
4
2
8
6
1
4
10
4
4
2
39
14
7
7
5
2
6

9

12
6
0
11
5

TEl8
NA19
CU20
AC21
CO22

Ajo, Arizona
Tucson, Arizona
Hermosillo, Sonora
Isla Tibur6n, Sonora
Ciudad Obregon, Sonora
Chihuahua, Chihuahua
PresidioCounty, Texas
Sabinas,Coahuila
Saltillo, Coahuila
Durango, Durango
El Huizache, San Luis Potosi
Guanajuato, Guanajuato
Tecoripa, Sonora
Navojoa, Sonora
Culiacan, Sinaloa
Acaponeta,Nayarit
Colima, Colima
Los AngelesCounty, California

San Diego County, California
San Telmo, Baja California
El Rosario, Baja California
Bahia San Luis Gonzaga, Baja California
Punta Prieta, Baja California
San Ignacio, Baja California (Sur)

Totals
Totals
Totals
TOTALS

BahiaMagdalena,Baja California(Sur)
La Paz, Baja California (Sur)
Isla EspirituSanto, Baja California (Sur)
Isla San Jos6,Baja California (Sur)
(P. melanura)
(P. nigriceps)
(P. californica)
(All species)

0
7
9
17
14
3
1
19
0

2
2
24
12
28
22
26
27
31

14

9

6

5

17

25
3
4
229
84
196
509

22
2

I
166
45
131
342

22
0
0
171
48
145
364

16
0
0
105
24
101
230

38
0
0
198
24
225
447

Speciescodes:m = P. melanura;n = P. nigriceps;
c = P. californica.

MORPHOLOGICAL ANALYSES

Nineteenlinear measurementsof major body elementsand featherlengthswere
taken from study skins to the nearest 0.1 mm using dial calipers. These measurementsincluded:(a) bill length[BLEN]--the distancefrom the tip of the upper
mandible to its unfeatheredbase;(b) bill width [BWID]--the distancefrom one
tomium to the other taken at the positionof the nostril;(c) bill depth [BDEP]-the distancefrom the culmento the lower edgesof the rami taken at the position
of the nostril;(d) tarsuslength--the diagonalof the tarsustaken from the posterior
surfaceof the mid-point of the joint between the tibia and the metatarsusto the
upperedgeof the scutepositionedoppositethe origin of the hind toe; (e) middle


6

ORNITHOLOGICAL

MONOGRAPHS

NO. 42

FIG. 2. Groupings of specimensof Polioptila melanura (indicated by squares)into samplesfor
analysis. See Table 1 for sample sizes, and Appendix I for list of exact localities.

toe length--the distance from the upper edge of the scute opposite the insertion
of the hind toe to the base of the claw on the dorsal surfaceof the toe (because
of difficultiesin consistentlyidentifying the scutesthat limited tarsal and middle
toe measurements,these values, based on the same referencescutein each specimen, were summed for analysisto form the combined characterTARTOE); (f)
lengthsof primaries 3-10 [P3LEN-P 10LEN], calculatedas the differencebetween

total wing length (the chord of the unflattened,folded wing taken from the bend
of the wing to the tip of the longestprimary, P6LEN) and the distance from the
tip of the longestprimary to the tip of the particular primary being measured;(g)
tail length [TLEN] -- the distance from the point between the insertions of the
central pair of rectricesto the tip of the longest rectrix; (h) relative length of
rectrices4-6 [R4PCT, R5PCT, R6PCT] -- the differencebetweentotal tail length
and the distance from the tip of the longest rectrix to the tip of the particular
rectrix being measured divided by total tail length.
Body massof freshly collectedspecimenswas recordedin the field to the nearest
0.1 g using a 10-g Pesola balance, and was converted to the cube-root of body
mass [MASS] for analysis.
Twelve characteristics of coloration were examined.

Those characters for which


GNATCATCHER

SPECIES LIMITS

7

LP31

/
0 ,,o•,,0 ,

: ;orio

'

"'

STATUTE
MILES
UCLA-ZOOL06Y.

[NT- Iq6•-2

/

/

Fla. 3. Groupingsof specimensof Polioptila californica(indicatedby circles)and P. nigriceps
(indicated by triangles).SeeTable 1 for sample sizes,and Appendix I for list of exact localities.

a

b

c

d

FiG. 4. Categoriesusedin analysisof variation in tail spot shape.Vertical bar to the right of each
diagrammedrectrix indicatesthe dimensionusedin measuringthe lengthsof differentlyshapedtail
spots.


8

ORNITHOLOGICAL

MONOGRAPHS

NO. 42

linear measurementswere obtained using dial calipers included: (a) cap length

[CAPLEN] -- distanceon alternate-plumagedmalesfrom the non-featheredbase
of the upper mandible to the posteriormargin of the black cap and (b) relative
lengthof tail spotson rectrices5 and 6 [R5SPCT, R6SPCT] -- distanceproximally
alongthe rachisfrom the feathertip (Fig. 4) divided by total tail length.Character
statesdescribingthe coloration pattern of rectrices5 and 6 were subjectively
evaluatedas follows:(a) tail spotshapeon the inner vane [R5SSH, R6SSH], based
on four categories(Fig. 4); and (b) extent of white on the outer vane [R5WEB,
R6WEB] at a point approximately1/3of the total featherlengthfrom the feather
tip, basedon five categories(1 = 100 percentwhite; 2 = 75 percent;3 = 50 percent;
4 = 25 percent;5 = no white present).Additionally, the extent of white eye-ring
feathering[EYERING] on specimensof alternate-plumagedmaleswas estimated
to the nearest 25 percent (no eye-ring = 0 percent; complete eye-ring = 100
percent).

Colorationsof soft parts, includingfoot pad, tarsus,upper mandible, tip (distal
1/3)of lower mandible,base(proximal2/3)of lower mandible,and iris wererecorded
from freshly collectedspecimensby direct comparisonwith standardizedcolor
swatchesprovided by Smithe (1975).
Variation in breastand back plumage coloration was analyzed usinga Bausch
and Lomb Spectronic505 recordingspectrophotometerequippedwith a visible
reflectanceattachment. Flatness of the 100 percent line was maintained within

limits of 1.0 percent, and flatnessof the 0 percent line within 0.5 percent. The
sampleport was narrowedto a diameter of 11 mm to permit examinationof
limited areasof uniformly coloredplumage;backgroundof the contractedhole
was painted with Krylon Spray Paint, Number 1602, Ultra Flat Black Enamel
producedby Borden, Inc. Specimenswith soiled, excessivelyworn or ruffled
plumagewere excluded.The 10 selectedordinatemethod of Hardy (1936) was
used to calculate tristimulus values (X, Y, Z) from the spectrophotometercurves
of percentage
reflectance
between400 and 700 mt•.Dominant wavelength[BRSTW,
BACKW], brightness[BRSTB, BACKB] and excitationpurity [BRSTP, BACKP]
were then determined from these values accordingto the proceduresoutlined by
Judd (1933).
BIOMETRIC ANALYSES

Statistical routines were performed on the DEC MicroVAX II computer at
Manomet Bird Observatory, using SAS (Version 5.16) proceduresCANDISC,

CLUSTER, CORR, DISCRIM, GLM, MEANS, NPARlWAY, PRINCOMP,
REG, TREE, UNIVARIATE, and VARCLUS. Redundancy among characters
was analyzed through phenogramsdepictingthe resultsof oblique component
analysisof the correlationmatrix of 28 morphologicalcharacters.Means, variances and coefficients of variation for each character were calculated for males

and females of each sample area. Geographic variation within each characterwas

examined using analysisof variance (ANOVA) for both sexesof each species;
patternsof variation were summarizedvisually usingpie diagramsto represent
charactermeansfor eachsamplearea.Pearsonproduct-momentcorrelationcoefficients,basedon samplemeans,were calculatedfor malesof P. melanuraand
P. californicato determine the relationshipbetweenbody size (as expressedby
MASS) and six measurements

of body dimensions(BLEN, BWlD, BDEP, TAR-


GNATCATCHER

SPECIES LIMITS

9

TOE, P6LEN, TLEN); the predictive value of MASS as an indicator of thesesix
characterswas further examined using linear regression.
Multivariate analysis of variance (MANOVA) was used to test whether the
location of centroids representingeach sample area, derived from 22 characters
(BLEN, BWlD, BDEP, TARTOE, P3-10LEN, TLEN, R4-6PCT, R5-6SSH, R56SPCT, R5-6WEB), were significantlydifferentin multivariate space.For specimens in which three or fewer characterswere missing, sample area means (calculated by sex) were substitutedfor the missing values in MANOVA and subsequentmultivariate procedures.Specimensin which measurementsof more than
three characterswere missing were excluded from the multivariate analyses.
Two distinct principal componentsanalyses(PCAs), basedon orthogonal,unrotatedeigenvectorsderived from the covariancematrix of the 22 characterslisted
above, were performed as a method of data reduction. To examine broad patterns
of pheneticsimilarity amongputative speciesgroups,principal component(PC)
scoreswere first obtained for all individuals (by sex);mean PC valuesfor each
sample area were then calculated based on these individual scores.Secondly,
separatePCAs were performed for each species,with sample area means again
being calculatedfor the first three PC ordinationsusingthe scoresobtained for
individual specimens.Mean scoresof PCsl-3 for eachsampleareawere displayed
visually using pie diagrams to depict the geographyof intraspecificcharacter
variation, and the Sum of SquaresSimultaneousTest Procedure(SS-STP) (Gabriel
1964; Gabriel and Sokal 1969) was used as a multiple comparison method to
identify maximally nonsignificantsubsetsof these sample means.
Patternsofphenetic similarity betweensampleareaswere alsodescribedthrough
constructionof phenogramsbased on average linkage (unweighted pair-group
method using arithmetic averages,UPGMA) cluster analysis.UPGMA phenogramswere similarly constructedusingthe resultsof canonicaldiscriminantanalysis (CDA), a method of dimension-reductioncomparableto PCA but which

summarizes between-classvariation based on a priori identification of the groups
(in this case,sample areas)being compared.
CDA was alsousedto compare the phenetic similarity of 20 specimenscollected
in a zone of sympatry(BG05, BG27), where hybrid individuals might most likely
be found, with samplesofP. melanura and P. californicaobtained from adjacent
regionsof allopatric occurrence(YU03, SF04, ER26, PP28). Discriminant function analysis(DFA) was similarly usedto examine these20 specimens.Using a
classification criterion calculated from the pooled covariance matrix of the allopatric referencespecimens,DFA assignseachtestindividual (specimensfrom the
zone of sympatry)to the class(specimensfrom allopatricregions)from which it
has the smallestgeneralizedsquareddistance.These assignmentswere then compared to identifications made prior to the analysis on the basis of non-morphological (vocal) characters.
VOCAL ANALYSES

Approximately 20 h of magnetictape recordingsof calls of Polioptila were
collected,representinga total of 447 individual males(Table 1). Recordingequipment included a SennheiserME88 directional microphone and, at different times
during the study, a Uher 4000 Report IC reel-to-reel recorder and a Sony TC
D5M cassette recorder. Verbal descriptions of the behavioral context of each


10

ORNITHOLOGICAL

MONOGRAPHS

NO. 42

vocalizationwere simultaneously
recorded.To confirmuniformityof recording
speedunder battery powered field conditions, standard calibration tones from a

tuning fork were frequentlyincludedduring recordingsessions.Magnetictapes

recordedduring this studyhave beendepositedin the Library of Natural Sounds,
CornellLaboratoryof Ornithology.Soundspectrograms
werepreparedfrom these
recordingsusinga Kay ElemetricsModel 7029A Sona-Graph(wideband setting;
80-8,000 Hz).

Vocalizationplaybackexperiments,similarto thosedevelopedby Lanyon(1963,
1967), were used to evaluate the possible importance of vocal differences in

Polioptilaas reproductiveisolatingmechanisms.Simultaneousplaybacksof recordingsof two specieswere presentedto malesduring the breedingseasonfrom
tape recorderslocated approximately 7-8 m apart. During the initial five-min
exposureperiod the bird's responseto a crudely mounted, male P. californica
specimenpositioned1 m aboveeachtape recorderwascategorized
as either (a)
no evident responseor (b) positive response,ranging from visual orientation
toward the vocalization source, approach toward the vocalization sourceand/or

countersinging
directedtowardthe vocalizationsource,or actualphysicalcontact
with the specimen.One min of taped silencefollowedthe first five-min exposure,
after which the samesequenceof recordingswas repeatedbut with each species'
vocalizationsbeing switchedto the oppositerecorder.Again, the behavioral responseof the testindividual was categorized.To reducethe possibilityof habituationcausedby repeatedexposures,
eachbird wastestedwith only oneplayback
sequence.

RESULTS
GEOGRAPHIC AND ECOLOGICAL DISTRIBUTION

The general distribution of P. melanura, P. californica and P. nigricepsshows
that all three speciesare primarily allopatric or parapatric, although limited areas

ofsympatry existbetweenP. rnelanuraand P. californicaand betweenP. rnelanura
and P. nigriceps(Fig. 1). The following discussionfirst provides an overview of
each species'distribution. Secondly,ecologicaland behavioral observationsare
describedfrom the areaswhere P. rnelanuraand P. californica coexist.

Polioptilacalifornicais nearly endemicto Baja California, with its rangebarely
extendingnorthward into the United Statesalong the coastof southernCalifornia
west of the Peninsular and Transverse Ranges (Fig. 1). It is common and widespreadthroughoutthe Baja California peninsula,except for (a) the area north of
approximately31øN latitude and eastof the SierraSan PedroMfirtir, (b) the higher

elevationsof the SierraJufirez,SierraSan Pedro Mfirtir, and Sierrade la Giganta
characterized by pine-oak woodland and/or coniferous forest, and (c) certain
islands in the Gulf of California (discussedbelow). North of Baja California the
species'recentdistributionhasapparentlyalwaysbeensomewhatpatchy(Grinnell
and Miller 1944), with this pattern being exaggeratedby the extensive habitat
destruction

in coastal southern

California

that has occurred

since World

War II

(Atwood 1980). Becauseits habitat in California is both restricted and declining,
P. californica has been identified as a "Species of Special Concern" in the state

GNATCATCHER

SPECIES

LIMITS

ß77 •. •7 •.,.9.

I

'

11

.,•

'

• "•

'-•.•.

•..•';

,.,' •..:....

•

•-'

, ,.%

.• • ' •.

.

,.•.: :-•'•r-•,,•..•.:-•.

FIG. 5. Polioptila cal•ornica habitat in coastal•uthem California and •ja

California noah of

30øN latitude. Mexico, Baja California, San Telmo.

(Remsen 1978), and is currentlyconsidereda candidatefor listingasa "Threatened
Species" by the California Department of Fish and Game (J. Gustafson, pers.
comm.).

Polioptila californicais found in a variety of major plant associationsover its
geographicrange. North of latitude 30øN the speciesoccursprimarily in coastal
or inland sage scrub plant communities at elevations less than approximately
1,000 m (Fig. 5). Dominant plant speciesin these habitats include Artemisia
californica,Salvia spp., Eriogonumfasciculatum,Rhus integrifolia,Encelia californica, Opuntia spp., and Haplopappusspp. (Munz and Keck 1959; Wiggins
1980). Most of theseplantsdo not extend southof 30øNlatitude, the approximate
limit of the Mediterranean climatic zone (Wiggins 1980; Cody et al. 1983). South
of 30øN latitude, P. californica is less restricted as to habitat or elevation, and
occurs throughout all of the various subregionsof the Sonoran desert which
dominate the remainder of the Baja peninsula (Figs. 6, 7). Dominant plant species
include, in various localities,Agave spp., Yuccavalida, Idria columnaris,Pachycormusdiscolor,Machaerocereusgummosus,Ambrosia spp.,Atriplex spp.,L ycium

spp., Pachycereuspringlei, Lysiloma candida, Erythea brandegeei,Cyrtocarpa
edulis,Acacia brandegeana, Cercidium microphyllum, Bursera hindsiana, Jatropha cinera, Opuntia spp., and Ferocactusspp. In the open desert of the Magdalena
Plains and Vizcaino Peninsula, P. californica appears to be most abundant in
relatively densely vegetated areas such as occur along washes,alluvial fans or
other drainagesystems.Farther south,in the Cape region,it is abundantin dense
thorn scrub habitats.

Murphy (1983b) identified 24 islandsin the Gulf of California with areas >0.5


12

ORNITHOLOGICAL

MONOGRAPHS

NO. 42

i

,,-:Z '

'......

4•? TM

FIG. 6. Po/iopti/aca/ifornicahabitatin the Vizcaino desertof centralBajaCalifornia. Mexico, Baja
California (Sur), 2 km N San Ignacio.

FIG. 7. Po/ioptdaca/ifornicahabitat in the Cape regionof Baja California. Mexico, Baja California

(Sur), 4 km N of Los Barriles.


GNATCATCHER

SPECIES

LIMITS

13

km 2. Specimen records support the occurrenceof P. californica on only two of
theseislands:Espiritu Santo and San Jos• (Fig. 1). Additionally, specimensof P.
californica were available from Isla Santa Margarita and Isla Magdalena on the
Pacific coast of Baja California. These islands are presently separatedfrom the
peninsularmainland by narrow, shallow-waterchannels,and during recent geologic time were connectedto the adjacent mainland.

Cody (1983) did not discriminatebetweenBlue-grayGnatcatchers(P. caerulea)
and "black-tailed" gnatcatchers(including both P. rnelanura and P. californica
as definedhere) during his brief avifaunal surveysof many of the islandsin the
Gulf of California. Consequently, his summary of gnatcatcher distribution on
these poorly studied islands is of uncertain value. Nonetheless,in the absenceof
better information, his observations are discussedhere.
In addition to Espiritu Santo (includingPartida Sur) and San Jos•, Cody (1983)
stated that "black-tailed" gnatcatcherswere recorded on the following Gulf is-

lands:J•ngeldela Guarda(= P. melanura,
seebelow),SanEsteban
(probably
P.

melanura, see below), Cerralvo, Carmen, Santa Cruz, Monserrate, Coronados,
Danzante, San Francisco,and Santa Catalina. In contrastwith these reports, on
collectingtrips Townsend (1923) and Banks (1963a, b) found only P. caerulea on
Cerralvo, Carmen, Santa Catalina, Monserrate, Coronado, and Danzante; Banks
(1963a) failed to find any gnatcatcherson Santa Cruz or San Francisco. The
discrepanciesin these data clearly indicate the need for additional specimenmaterial from islandsin this region, especiallyin light of the migratory behavior of
P. caeruleaand consequenthigh probability of this speciesoccurringon virtually
all of the Gulf islands.

Polioptila californica doesnot occur on any of the southernCalifornia Channel
Islands (Diamond and Jones 1980), on Islas de Los Coronados, located 13 km
W of Tijuana, Baja California (Jehl 1977), or on Isla Cedros,located 23 km NW

of Punta Eugeniaon the Vizcalno Peninsulaof Baja California (Grinnell 1928).
In the Gulf of California, the specieshas been documented by specimensonly
from Espiritu Santo and San Jos& both consideredby Murphy (1983b) to be
"land-bridge" islands that were recently connectedto the Baja peninsula during
periods of lowered sea levels in the Pleistocene.Murphy (1983b) also described
Carmen, Coronados,San Francisco,and Danzante as land-bridge islands,lending
somecredenceto Cody's (1983) report of "black-tailed" gnatcatchersfrom these
localities. BecauseI do not believe that either P. californica or P. melanura is a
probable overwater colonist,and becauseMonserrate, Santa Catalina, Santa Cruz,
and Cerralvo have not been connectedto the Baja California peninsulain recent
geologictime (Murphy 1983b), I am skeptical of Cody's (1983) listing of "blacktailed" gnatcatchers from these localities.
POLIOPTILA

MELANURA

Polioptila melanura is widely distributedthroughoutthe arid landsof the southwestern United States and Mexico in two major, disjunct areas (Fig. 1). One of
these regions,located west of the Continental Divide, follows the general boundaries of the Sonoran desert; the other, situated east of the Divide, the limits of

the Chihuahuan desert. In northern Baja California, P. melanura is restricted to
the area east of the Sierra Jufirezand Sierra San Pedro Mfirtir; in the north central


14

ORNITHOLOGICAL

MONOGRAPHS

NO. 42

F]O. 8. Po/iopti/a me/anura habitat in [he Sonoran desert of southeastern California and nodhwestern Baja California. •exico, Baja California, 16 km N of San Felipe.

portion of the peninsula,it occursonly in the immediate vicinity of the Gulf coast
south to approximately 29øN latitude.

Ecologically, P. melanura occurs in a variety of major Sonoran desert plant
communities. In the western part of its range (Figs. 8, 9) its typical habitat is
dominated in different localities by plant speciessuch as Larrea tridentata, Franseria dumosa, Prosopsisjuliflora, Cercidium spp., Olneya tesota,Fouquieria spp.,
Carnegiea gigantea, Ferocactus Wislizenii, Encelia farinosa, Lemaireocereus
Thurberi, LophocereusSchottii, Jatropha spp., Lysiloma divaricata, Acacia spp.,
and Bursera spp. (Shreve and Wiggins 1964). In the eastern, Chihuahuan desert
portion of the species' range (Figs. 10, 11), dominant plant species frequently
include Larrea tridentata, Flourensia cernua, Parthenium incanurn, Jatropha dioica, Koeberlina spinspa, Prosopsisspp., Lycium spp., Acacia spp., Lophocereus
spp., Cassiaspp., Celtispallida, Agavespp.,Atriplex spp.,Allenrolfea spp.,Mimosa
spp., and Ephedra spp. (Jaeger 1957; Morafka 1977).
I suspectthat as a result of ecological barriers only limited gene flow presently
occurs between the Sonoran and Chihuahuan desert populations of P. melanura.
The closestpoint of presentcontact between thesetwo major desert regionsoccurs

acrossthe Mogollon Plateau of extreme southeasternArizona and southwestern
New Mexico (Shreve and Wiggins 1964). In this area, describedby Morafka (1977)
as the Cochise Filter Barrier, "conditions are arid but not desert and the vegetation
is a transition between desert and grassland" (Shreve and Wiggins 1964). Such
conditionshave probablyexistedto varying degreessincethe Pliocene(6-4 MYBP),
when the formation of present-day uplands coupled with declining temperatures
caused the previously continuous expanse of desert or pre-desert scrub in this


GNATCATCHER

SPECIES

•.

LIMITS

•',,,

15

G:•:•.
' ..•'•_

•

FIO. 9. Po/iopti/a me/an•ra habitat in th• Sonoran d•s•d ofsouth•
M•xican mainland. Arizona, Pima Co., 3 km SE of Quijotoa.

•g•6g

•

' •

•

•

•-'

•'

':

.•

A•zona and th• no•w•st•

'•'•l" '•I

ß .•

F[o. 10. polioptila melanura habitat in the Chihuahuan dcsc• of Mexico. Mexico, Durango, 8 km
W of San Juan dcl Rio.


16

ORNITHOLOGICAL

MONOGRAPHS

NO. 42

FiG. 11. Polioptila melan,ra habitat in th• Chihuahuan desea of Mexico. Mexico. Guanajuato,
1.5 km WSW of Dolores Hidago.

area to be fragmented(Cooper and Silver 1964; Morafka 1977). Polioptila melanura occurs in very low densities in the patchy and limited areas of suitable
habitat in this region, and I speculatethat at the present time individuals only
rarely disperseacrossthe Continental Divide.
The distribution of P. melanura on islands in the Gulf of California is only
slightly less confusedthan that describedabove for P. californica. Becausethe
range of P. melanura on the peninsular mainland does not extend south of approximately 29øN latitude, presumablyonly thoseislandsreferredto as the "midriff" islands (Lindsay 1983; Murphy 1983b) would be potentially included in the
species'range.Specimensof P. melanuraare known from Tibur6n and Angel de
la Guarda. On the basis of vocal characters,T. L. George (pers. comm.) identified

onlyP. melanuraon Angelde la Guarda;additionally,bothGeorgeand Cody
(1983) reportedthis speciesfrom SanEsteban.WhereasTibur6n isa "land-bridge"
island that probably was connectedto the Sonoran mainland during lowered

Pleistocene
sealevels,bothAngelde la GuardaandSanEsteban
areconsidered
"deep-water" islands that were unaffected in their isolation from the mainland

by fluctuating
sealevels(Murphy1983b).BothAngelde la Guardaand San
Esteban are probably of comparatively recent origin, having been formed when
their continental connections were severed by tectonic events approximately one

million yearsago;Angelde la Guardawasformedfrom peninsularregionsof
Baja California, whereas San Esteban is thought to have broken away from the
Sonoransideof the Gulf(Moore 1973; BischoffandHenyey 1974; Murphy 1983b).
None of the other midriff islandsapparently support "black-tailed" gnatcatchers
(Cody 1983), although more field work in this area is needed.


GNATCATCHER

POLIOPTILA

SPECIES

LIMITS

17

NIGRICEPS

The principal range of Po nigricepsextendsalong the arid coast of the Mexican
mainland

west of the Sierra Madre Occidentill

from central Sonora south to Colima

(Fig. 1)oPhillips et al. (1973) described the first discovery of a breeding pair of
this species in the United States, and subsequent observations have identified
several localities in southeastern Arizona where small numbers of P. nigriceps

have been sporadically observed in recent years (Davis and Russell 1984). North

of approximately28øN latitude the speciesmight not be permanentlyresident(So
M. Russell,pers.comm.). Polioptila nigricepsis unrecordedfrom any of the islands
in the Gulf

of California.

Throughout most of its range P. nigricepsoccurs primarily in vegetation describedas Sinaloan thorn scrubor Sinaloan deciduousforest(Fig. 12), usuallyat
elevations less than 800 m (S. M. Russell, pers. comm.). In central Sinaloa the
dominant plant speciesof this vegetation type include Trichlia trifolia, Zizyphus
amole, Guazuma ulmfolia, Ceiba accuminata, Tabebuia rosea, Morisonia americana, and Caesalpiniaeriostachys(Raitt and Hardy 1979). At the northern limits
of its rangein central Sonora and the United States,P. nigricepsgenerallyoccurs
in riparian associationsdominated by Prosopsisjulifiora, Celtis reticulata, Sambucusmexicana,Seneciospp., Salix sppo,and Acaciagreggii(Phillips et al. 1973).
AREAS OF SYMPATRY

BETWEEN POLIOPTILA MELANURA AND P. CALIFORNICA

Three principal areasofsympatry were documentedbetweenP. californicaand
P. melanura: (a) near Palm Springs, Riverside County, California; (b) in the
vicinity of Valle de Trinidad, Baja California; and (c) along the coastalGulf strip


18

ORNITHOLOGICAL

MONOGRAPHS

NO. 42

of north central Baja California. Becauseobservationsmade in these areas form
one of the principal lines of evidencesupportingseparationof P. californicaand
P. melanura as distinct species,details are provided below concerningtheir distribution, ecology,and behavior in localities where they coexist.
PALM SPRINGS,RIVERSIDECO., CALIFORNIA

The sympatric occurrenceof P. californica and P. melanura in the vicinity of
Palm Springsis supportedby three specimensofP. californicataken in this area
in the early 1900s; past and recent specimensof P. melanura collectedfrom the
Palm Springsarea are abundantly representedin museum collections.The first
example ofP. californica recordedfrom this region, a female collected2 mi E of
Palm Springson 1 January 1904 (MVZ 39293), was thoughtby Grinnell (1904)
to be "doubtlessa stragglerfrom the direction of Banning." Subsequentspecimens
(both labeled "Palm Springs") include a male collected on 19 April 1916 (DC
313A) and a female (labeled "breeding," but without additional notes)taken on
4 April 1918 (CAS 56641).
No recentrecordsofP. californicahave been obtainedin the Palm Springsarea,
nor do I know of any recent observationsof the speciesfrom the western side of
San Gorgonio Pass where it was historically common (Atwood 1980). Some
changeshave occurred in the mesic vegetation of the desertwashesfound in the
Palm Springs-SanGorgonio Passarea since World War II, and it is possiblethat
plant associationsonce permitting occasionalcontactbetweenP. californica and
P. melanura no longer exist. No extensivecontactzone has been documentedin
this region.
VALLE DE TRINIDAD, BAJA CALIFORNIA,MEXICO

Valle de Trinidad was identified as an area of sympatry betweenP. californica
and P. melanura by Grinnell (1928). As at Palm Springs,this locality is near a
relatively low-elevation passwhere habitat suitable for P. californicaextendsup
from the west and makescontactwith limited eastwardextensionsof typical P.

melanurahabitat. Polioptilacalifornicais certainlythe more common of the two
speciesin the vicinity of Valle de Trinidad. I am aware of only one specimen
record of P. melanura from this site (MVZ 50414). However, I tape-recordeda
breeding pair of this speciesin desert wash vegetation 2 km NW of Ejido San
Mafias on 5-6 June 1982 (an area where P. californicawas also recorded),and
know of a reliable sight record of P. melanura made on 19 March 1983 approximately 6.5 mi NW of Valle de Trinidad (R. E. Webster,pers.comm.). Polioptila
californicaandP. melanuraapparentlyhaveonlyminimal contactwith oneanother
in the Valle de Trinidad area. The former speciesoccursprimarily in widespread
sagescrub vegetation dominated by Artemisia, Salvia, and Rhus, whereas the
latter is generallyrestrictedto typical (but limited in extent)Sonorandesertwash
vegetation dominated by Prosopsis.

BAHiA SANLUiS GONZAGA(AND VICINITY), BAJACALIFORNIA,Mexico
The third known area of sympatry between P. californica and P. melanura is
more extensivegeographicallythan thoseat Palm Springsor Valle de Trinidad,
and probably representsthe only region where both forms come in contact regularly. This previouslyundescribedareaextendsnorth alongthe coastalGulf strip