TAXONOMIC
STATUS OF THE CALIFORNIA
GNATCATCHERS
OF NORTHWESTERN
BAJA CALIFORNIA,
MEXICO
ERIC MELLINK, Centro de Investigaci6nCientificay Educaci6nSuperiorde
Ensenada,B.C., Apdo. Postal2732, Ensenada,Baja Californiaor P.O. Box
434844, SanDiego,California92143
AMADEO M. REA, San Diego Natural History Museum,P.O. Box 1390, San
Diego,California92112
The CaliforniaGnatcatcher(Polioptilacalifornica)wasfirstdescribed
as
a new speciesby Brewster(1881) from specimens
collectedat Riverside,
California.Later,Grinnell(1926) mergedit with Polioptila melanura,asa
subspecies.
Phillips(1980) andRea (1983) considered
it a differentspecies,
and Atwood (1988), in a taxonomicrevisionof the black-tailedgnatcatcher
complex,demonstrated
thatthe two formsare sympatricin BajaCalifornia
on the east side of the central peninsula(29ø-31ø N), have distinctly
differentvocalizations,and mate non-randomly.Therefore, he concluded
that they weredifferentspecies.The CaliforniaGnatcatcher
rangesfrom
the southerntip of the peninsulanorth to about 31 ø N. From there
northwardit is restrictedto the Pacificcoastalarea as far as Los Angeles
and Riverside,California.
The CaliforniaGnatcatcheris a polytypicspecies,that is, geographic
variationin it has been expressedby the naming of subspecies.
The
northernmostsubspecies,
nominatecalifornicaastraditionallyunderstood
(AmericanOrnithologists'
Union 1957, Wilbur1987), rangesfrom 30ø N
in BajaCaliforniato southernCalifornia(SanDiego,Orange,LosAngeles,
and Riversidecounties).In examiningthe few fresh-plumaged
(fall-winter)
specimens
fromnorthwestern
BajaCalifornia,however,we foundthatthey
did not seemto be nominatecalifornica,althoughthey alsodifferedfrom
thoseof the centralpeninsula.
We didnot knowwhetherthesedifferences,
througha north-southdistanceof 360 km, werepart of a gradualtransition
or a steppedcline.Many othersedentarybirdsvarygeographically
within
thisarea. Thereforewe undertooka more intensivestudyof the California
Gnatcatcher's
variationin northernBaja Californiawith newlycollected
specimens.
TAXONOMIC
HISTORY
The firstadditionalsubspecies
of the CaliforniaGnatcatcherto be named
wasP. c. margaritaeRidgway,1888, described
from IslaMargarita,Baja
CaliforniaSur (24o25' N). It was considered
by Grinnell(1926, 1928) to
rangenorthto 29ø30' N. In 1926, Grinnellsegregated
thepopulation
from
the Cape region,Baja CaliforniaSur, as P. c. abbreviata.Van Rossem
(1931) considered
abbreviataindistinguishable
from margaritae,but describedP. c. nelsonifrom Bahiade San Francisquito,
on the coastof the
Sea of Cortez, 28 ø 26' N. This subspecies
was saidto be intermediatein
colorand sizeas well as rangebetweencalifornicaand margaritae.The
subspecific
name nelsoniwas preoccupied
by P. nelsoni(= P. caerulea
50
WesternBirds25:50-62, 1994
CALIFORNIA
GNATCATCHER
TAXONOMY
nelsoni) Ridgway,1903, and van Rossemhimselfrenamedthe subspecies
as Pc. pontills.
This was the taxonomyacceptedin the fifth editionof the American
Ornithologists'
Union'schecklist
(1957), whichgavethe distribution
of this
intermediateform as from Bahia de San Bartolom•, 27040 ' N, on the west
coast,SanIgnacio,27ø17'N, in the interior,andBahiadeSanFrancisquito,
28026' N, on the Gulfof California,southat leastto San Bruno,lat 2709' N.
Atwood(1988), in hisanalysis
of the distributional
limitsof the members
of the black-tailed
gnatcatcher
complex,commentedbrieflyon the variability foundin the peninsula.He concludedthat only two formsshouldbe
admitted,P.c. californica and P.c. margaritae. He reported an abrupt
transitionin many characteristics
at about25 ø N but only a slightclinal
variationto the north. However,in spiteof its broadtitle, Atwood's(1988)
monographprimarilyaddresses
the issueof specieslimits(seesummary,p.
67), which it doesadmirably.The problemof geographicvariationwithin
the rangeof the segregated
speciesP. californicais onlyincidentally,
and
not meaningfully,addressed.In a later work, Atwood (1991) recognized
three subspecies:
nominatecalifornica,occurringfrom the northernlimit
of the speciesto about30 ø N, margaritaebetweenapproximately24 øand
30 ø N, and abbreviatasouthof 24 ø N.
Phillips (1991:25-26) also addressedthe taxonomy of Polioptila
californica. He too consideredthe nominatesubspecies
P.c. californ ica to
rangesouthto 30 ø N. He tentativelyrecognizedP.c. pontills in the central
peninsula,and P.c. margaritaefrom about 27 ø N southward,synonymizingP. c. abbreviatawith a query.He couldnot agreewith Atwood's(1988)
abrupttransitionat 25 ø N. Under "remarks"on the nominate(northernmost)race, Phillipsstated,"Geographicvariationwithinthesedark [northern] populationsis indicated;needI repeatendlessly,
'Thereare few clean,
fresh-plumagedspecimens'?Sorry." At least two subspecifictaxa are
representedsouthof 30 ø N. Thereforewe will usethe name pontills as
traditionallyunderstood(A.O.U. 1957, Phillips1991).
METHODS
The fieldwork for thisstudywasconducted
in the northwestern
part of
the stateof Baja California,Mexico,betweenthe internationalborderand
El Rosario.The vegetationis composedof Mediterraneancommunities:
coastalsageand maritime succulentscrub,near the coast,and chaparral,
farther inland.
We collected40 specimensfrom 19 localitiesbetween 16 Januaryand
27 Februaryand againin December1991. Some springvisitswere made
to determineif there was a replacementof the individuals
that had been
removed. The gnatcatcherswere collectedwith .mist nets. At first we
attemptedto attract the birdswith a tape recording.Later we usedthe
recordingto find the birds,then herdedthem into the net. Capturedbirds
were sacrificed or released. We removed for measurement one outer rectrix
from mostmalesthat were released.Thisalsoenabledusto recognizethem
subsequently
in the field. The collectedbirdswere preparedas studyskins
51
CALIFORNIA
GNATCATCHER
TAXONOMY
by Philip Unitt (San Diego Natural History Museum),without chemical
preservatives.
Thesespecimens
werecomparedwithspecimens
of the two neighboring
subspecies,
P. c. califomica and P. c. pontills, from the followingcollections:AmericanMuseumof NaturalHistory,New York(AMNH), California
Academyof Sciences,San Francisco(CAS), CarnegieMuseumof Natural
History, Pittsburgh,Denver Museum of Natural History, Los Angeles
CountyMuseumof NaturalHistory(LACM),Museumof VetebrateZoology,
Universityof California,Berkeley(MVZ), San Diego NaturalHistoryMuseum(SDNHM), Universityof California,LosAngeles(UCLA), and Western Foundation
for VertebrateZoology,Camarillo.We compareda totalof
72 femalesand81 malesfromthe rangesof thesetwoformsastraditionally
defined.Additionally,we compared17 malesand 13 femalesof P. c.
rnargaritae.
In analysesof gnatcatchers,
many variableshave been measured(see
Atwood 1988:5-8). Of these, only the followinghave been foundtaxonomicallyrelevant(Atwood1991, Phillips1991, this study):darknessof
both upperpartsand underparts,brown wash (back, flanks, crissum)of
females,amountof white in the tail, and tail length.Bill sizemight be a
significantvariablein the southernquarterof the species'range,but it was
not significant
withinthe area of our study.
The majorityof museumspecimensof the CaliforniaGnatcatcherare
males,sincethey are more responsiveon territoriesand easierto collect
than females.However,geographicvariationin this speciesis greaterin
females,as in many other passerines,for example,thraupines,icterines,
emberizines,and carduelines(Rea 1983:122).
We attemptedto quantifyplumagecolorby meansof a spectrophotometerbutfoundthatthisinstrumentfailedto giveconsistent
readings,evenof
a singlespecimen.The spectrophotometer,
designedto measurethe colors
of fiat and uniform surfaces,seemsill suited for the variable texture of
feathers.Thereforewe made our comparisons
visually,usingonly natural
lightfrom a north-facingwindowor from an east-facing
windowwhen the
sky was overcast.For color comparisonswe used Ridgway's(1912) and
Smithe's (1975) standards.
Unfortunately,many skinsfrom the northernend of the species'range
(LosAngeles,Riverside,San Bernardinocounties)are severelysoiled(see
alsoRea and Weaver1990:92-94). Most of thesewere takenearlyin the
twentiethcenturyand havesoot-stained
plumage.To be surethat we were
comparinggeneticdifferences,not artifactsof industrialization,
we had to
excludeover half of the fall/winter specimensfrom southernCalifornia
from analysis.A listof theseexcludedspecimens
is availablefrom the Birds
and Mammals Department, San Diego Natural History Museum. The
ultimatenorm for evaluationwassevencleanearlyfall specimens
collected
in the early 1980s by Atwoodand Rea (LACM, UCLA, SDNHM). We also
excludedworn specimenstaken from April, occasionally
March, through
August.Insofaras possiblewe segregatedrecentlytaken specimens(12
years or less museum age) from more ancient skins. However, in this
species,foxing(colorchangeassociated
withtimeafterpreparation)isslight
and seems restrictedlargely to the gray underparts,with little or no
52
CALIFORNIA GNATCATCHER TAXONOMY
apparentchangein brownareas(Figure1). In evaluatingthe amountof
whitein the tail, we usedonlythosespecimens
withevidentlyadultrectrices
(crisppatternsandunfrayedtips).
The specimens
collectedfor thisstudywere depositedin the vertebrate
collectionof the Escuelade Bioiogia, UniversidadAut6noma de Baja
California.Later,24 of them were exchangedwith the San DiegoNatural
History Museum.
RESULTS
AND DISCUSION
Within the area studied(the stateof Baja Californiabeginningat 28 ø N
northwardthroughcoastalsouthernCalifornia)there is a steppedclinein
the geographic
variationof Californiagnatcatchers,
withthreeincrements,
representingthree subspeciesor races (Figure 2). All populationshave
reducedwhiteon the tipsof the outerpair of rectrices(maximum4.5 mm)
andall arelargelygraybelow,unlikepopulations
southof, at least,25ø 30'
N, which have extensivewhite in the outer rectrices(4.5 mm or more) and
are largelywhite below.
Polioptila c. califomica
The northermoststep in the cline representsthe nominaterace, P. c.
californicaBrewster.It is characterized
by femaleswith the darkestand
Figure1. Femalesof Polioptila c. californica,showinglack of evidentfoxing.Left,
three old specimens(MVZ, SDNHM, LACM); rightthree recentspecimens(UCLA,
SDNHM).
53
CALIFORNIA
GNATCATCHER
TAXONOMY
warmest(morepinkish)brownbacksand the moststronglybrown-washed
flanksandcrissum.
TheirbackcolorisnearestSepiaof Ridgway(1912) and
similarto color 23, Raw Umber, of Smithe (1975) but diluted.The ventral
brownsare near SnuffBrown of Ridgwayand similarto color 33, Cinnamon-Brown, of Smithe. In both sexesthere is lesswhite on the abdomen
than in the raceto the south.There is a greatertendencyin malesto have
04/•2
54
0
TIJUANA
I
•
ENSENADA
•
.
•
'•
•o/•
.o,,
SAN
QUINTIN
•-:/0
I
118ø
I1• ø
118
ø
1150
114
ø
I1•ø
Figure2. The distribution
of CaliforniaGnatcatchers
in BajaCalifornia,Mexico,and
California,
U.S.A.Opencircles,
P.c. californica;
solidcircles,
P.c. atu•oodisubsp.
nov.;half-filled
circles,
intermediates
between
theabovetwo;triangles,
P.c. pontills.
Numbersindicatenumbers
of males,thenfemales,examined
fromeachlocality.
Somelocalitiesin closeproximityhavebeenlumped.
CALIFORNIA
GNATCATCHER
TAXONOMY
a dilutebrownwashon the back(22 of 25 cleanspecimens)
thanin the next
race.
The followingspecimensdocumentthe known southernlimits of the
nominaterace:alongthe coast,a femaletakenin BajaCalifornia5 miles(8
km) south of monument258, the westermostinternationalboundary
marker(MVZ 52719, 1 January1928). Three femalesandtwo malestaken
in the TijuanaRivervalleyjustnorthof the borderin October1917 are also
good P. c. californica (UCLA 25370, 25371, 25379, 25378, AMNH
758890). Both males have a brown wash on the back. Farther inland,
californica is representedby a female from Dulzura, San Diego Co.
(AMNH 377606, 26 October1891). Thisspecimenis shownin Figure3.
The nextstepin the clineisundescribed.
The populationof northwestern
Baja Californiamay be known as
Polioptila californica atwoodi subsp.nov.
Types.Adultfemale,adultor possiblyimmaturefemale,and adultmale,
SDNHM 48443, 48444, and 48442, respectively.Collected6.5 to 7 km
west of Coloneton the road to San Antonio del Mar, Baja California(31ø
06' N) by Eric Mellink,preparedby PhilipUnitt. Tail lengths48.4, 50.15,
and 52.6 mm, respectively.
Weights5.25, 5.65, and 5.7 grams,respectively.
Description.Similarto P. c. californicain sizeandtail markings,but in
femalesbackpaler and grayer,lessbrown,betweenBrownishOlive and
Olive-Brownof Ridgway,similarto color33, Cinnamon-Brown,
of Smithe
(Figure3); flanksand crissumgrayer,lessbrownish,the colortendingmore
towarddiluteTawny-Oliveof Ridgway,similarto color29, BrownishOlive,
of Smithe(Figure4). In freshplumagedmales,backsusuallycleargray(2 of
11 witha faintbrownishwash)(Figure5). There isa strongtendencyfor the
secondary
edgingsto be whiterin atwoodi,dullerandburlierin californica.
In both sexes,darkergray, both aboveand below,than in P.c. pontilis
(Figures6, 7).
Range. From Rio de las Palmasand Valle de las Palmas(30 km SE of
Tijuana)in the interiorand at leastPuntaBandaalongthe coastsouthto
ArroyoEl Rosario,32 øto 30 øN. The extensionof thisracefarthernorthin
the interiormay be associated
with the dryerclimateof the area (170 mm
rainfallin Valle de las Palmasvs. 270 in Tijuana, Garcia 1973).
Habitat. Nominate P. c. californica inhabitssoft chaparralor coastal
sagescrub(sensuWestman1983) withlittleverticalstratification
exceptfor
scatteredLemonadeberrybushes(Rhus integrifolia) and Laurel Sumacs
(Malosrna!aurina). Oberbauer(1992) estimatedthat southernCalifornia
haslostbetween80 and 90% of its totalcoastalsagescrubto agriculture
and urbanization.
P. c. pontills occursin SonoranDesertvegetationwith
microphyllouslegumes,cacti, the CreosoteBush(Larrea tridentata), and
otherhighlyxerophilousplants.
Betweentheseextremes,atwoodi is restrictedto the coastalsagescrub
andmaritimesucculent
scrubcommunities,
nearlymatchingthedistribution
of Westman's(1983) "coastalsucculentscrub."Approximately107 plant
speciesare endemic to this area (Oberbauer 1992), and at least 12
55
CALIFORNIA
GNATCATCHER
TAXONOMY
Figure
3. Female
California
Gnatcatchers,
dorsal
view.Left,P.c.atwoodi;
right,P.c.
californica.Notethedarkerandmoreextensive
brownof P. c. californica.
Figure4. Female
California
Gnatcatchers,
ventral
view.Left,P.c. atwoodi;
right,P.
c. californica.Notedarkerandmoreextensive
brownwashof flanks,belly,and
crissurnof nominatecalifornica.
56
CALIFORNIA
GNATCATCHER
TAXONOMY
polytypicbird speciesreputedlyhave differentiatedsubspecific
forms here
(A.O.U. 1957).
In northwesternBaja Californiathe coastalsagescrubcommunitiesare
more verticallystratifiedthan in the U.S.. Two speciesin particularcontribute to this: the Parry Buckeye(Aesculusparryi) and the ChaparralAsh
(Fraxinus trifoliata). The CoastalAgave (Agave shawii), also givesthe
habitata characteristic
appearance.Frequently
the two southernCalifornia
dominants of gnatcatcher habitat, the Coast Sagebrush(Artemisia
californica)and Flat-topBuckwheat(Eriogonurnfasciculatum),are only
the fourth or fifth most abundantwoodyspecies,and sometimes,in the
south,they are an insignificantcomponentof the communityor absent.
The abundanceof arboreallichens(especially
on the Cliff Spurge,Euphorbia misera) in the southernhalf of this area indicatesair moisterthan in the
northernhalf or in California.Exceptionsto thisgeneralhabitatcharacterizationare at two marginallocalities,Valle de las Palmasand San Jos• de
Meling,where the habitathad someelementsof hard chaparral.
Althoughin someareasof northwestern
BajaCaliforniagnatcatchers
are
commonand the territoriesseemto be tightlypacked,in other areasof
what appeared to us excellent habitat we were unable to to locate the
species,even by playingtaped recordingson repeatedvisits.Thus it is not
possibleto estimate the numbers of atwoodi on the basis of available
habitat.
Figure5. Male CaliforniaGnatcatchers,
dorsalview.Left,P. c. atwoodi;right,P. c.
californica. Note only slightlyolive-brownwashon back of atwoodi in contrastto
more extensive,browner wash of californica. Recentlycollectedspecimensof
cafifornicaon top andbottom,showinglackof evidentfoxing.
57
CALIFORNIA
GNATCATCHER
TAXONOMY
The distinctivehabitatoccupiedby atwoodi "is rapidlybeingdeveloped
with condominiums,
campgrounds,
and resorthousing,mostlyfor a U.S.
tourist[trade].Landsthat are not beingconvertedto theseusesare being
convertedto agriculturaluses"(Oberbauer1992). Grazing,burning,and
off-roadrecreationalvehiclesare additionalfactorsin habitatdegradationin
this area.
Etymology.We namethissubspecies
in honorof JonathanL. Atwood,
who resolvedthe relationships
betweenthe gnatcatcherspeciesPolioptila
melanura and P. califomica and hascontributedso muchto the conservation of California Gnatcatchers in the U.S.
Polioptila c. pontilis
South of the range of P. c. atwoodi, there is a secondabrupt step in
characters,matchingan equallyabrupthabitattransitionto SonoranDesert
vegetation.This populationis P...c. pontills van Rossem.It is paler gray
above (Figure 6) and whiter below than the two northern races. The
whitenessof the entireunderparts(throat,chest,belly)is especiallynoticeable.The flanksandcrissumof pontillsare lessstronglywashedwithbrown
thanin eitheratwoodior nominatecalifornica(Figure7). Thisbrownwash
is near Saccardo'sBrownof Ridgway(1912).
All specimenswe have seen southwardto the state line (28ø N) are
pontills. Unlike Phillips(1991:26) and Atwood (1991) we find pontilis
readilyseparablefrom P. c. margaritaeRidgway.The latteris paler,even
whiter below, and has extensivewhite in the outer rectrices.However, too
few usefulspecimensexistin collectionsto resolvethe racialtaxonomyof
CaliforniaGnatcatcherssouthof 26 ø N. Adequatesamplesare needed
from the mainlandas well as from islasMargarita,San Jos•, and Espiritu
Santoto determineif more than one raceoccursin the Cape region.
Intergrades
Within the race atwoodi we find no indication of clinal variation: females
from the northernpart of the rangein Vallede lasPalmasare justas pale
and olive brown as those from the river bed soumeast of El Rosario.
The only place where extant specimensdemonstrateintergradation
betweennominatecalifornicaand atwoodi is alongthe coastin extreme
northwesternBaja California. A female (E. Mellink 91-40, 8 December
1991) takenalongthe coastnear Plazade SantaMaria, 43 km southof the
border, has the brown of the back and flanks intermediate between the
warm brown tone of recently taken californica and the olive tone of
atwoodi. It is darker above and below than atwoodi. Another female taken
fromthislocality(SDNHM 48453, 29 February1991) appearsto haverich
brownson the lower flanksand lowerbackbut was undergoingextensive
molt, so the remainderof the specimencouldnot be evaluated.
Thirty-fivekilometersfarthersouth,a female(SDNHM 48439, 16 January 1991) takenon Cerro El Vigia in Ensenadais dark in the grays,above
and below,like the nominaterace,but it is nearerthe darkestexamplesof
atwoodiin olive-brown
tones(forexample,syntypeSDNHM 48443, near
Colonet, and SDNHM 48450, near San Quintin).It may representthe
58
CALIFORNIA
GNATCATCHER
TAXONOMY
southernextentof somenominatecalifornicainfluencealongthe coast.As
noted,the threefemaleswe tookin the interiorat Vallede lasPalmasare
typicalatwoodi,although
the localityis only32 km southof the Dulzura
specimennotedabove.
AtypicalSpecimens
Amongthe 153 specimens
we examined,excludingthe 3 intergrades,
we encounteredan occasionalspecimenthat was not typicalof the local
race (4% of 75 in californica,7.7% of 34 in atwoodi, and 2.3% of 44 in
pontilis).
Range of californica. Two femalesfrom Los Angeles Co. (AMNH
94797, 14 November 1897, Claremont; LACM 12776, 1 December
1895, San Fernando)are both pale, with the browntonesof back and
underpartssimilarto thoseof atwoodi.
Another female, from Riverside(CAS 56647, 29 December 1887) is
exceptionally
pale. It is in lax, freshplumage.The browns,bothaboveand
below,arepalerthanin somepontilis,whichit mostcloselyresembles.
The
head,nape, upperback,and chestare far too pale for atwoodi.In 1980
Phillips annotated this as "(lucida x californica)" (see also Phillips
1991:25); lucidaisthe raceof Polioptilarnelanura occupying
the Sonoran
Deserteast of P. californica.This odd specimenmay be an interspecific
hybrid.However,the tail showsonlyminimalwhite(2.1 ram).P.rn. lucida
usuallyhas 7.5 mm or more of whiteon the innerweb of the outerrectrix
andhasthe entireouterweb white,reachingthe rachis.
Rangeof atwoodi.One femalefromSanJos• [deMeling],31øN, 2500
feet (750 m) (lV[VZ46531, 7 October1925) hasthe brownof the backand
flanksasdarkandpinkishasin nominatecalifornica.We collected
a female
here (SDNHM 48454, 21 February1991), althoughsomewhatworn and
molting,withthe colorsof atwoodi.
Another female, from El Valle de la Trinidad, 2500 feet (750 m) (MVZ
50418, 7 December1926), has rich and dark browns.Eventhe rectrices
arebrownratherthanblackish,perhapsowingto chemicalchange.Atwood
(1988:18) foundboth speciesof gnatcatcherat this locality,where the
Cfissal(Toxostornacrissale)and California(T. redivivurn)thrashersalso
overlap.
Rangeofpontilis. All the brownsof one femalefrom Chapala,29ø21' N
(SDNHM 13749, 16 October 1930) are dark, as in P. c. californica.The
graysand whitesof the underpartscan be matchedby paler,cleanspecimensof the nominaterace,suchasUCLA 37981 (Banning,RiversideCo.)
and lV[VZ9981 (SanFernando,LosAngelesCo.).
The aberrantspecimens
from Chapalaand El Vallede la Trinidadcould
be vagrantsfrom the north.Althoughthe CaliforniaGnatcatcheris consideredsedentary,limitedvagrancymighttakeplace.It seemsmorelikelyto us
that theserepresentvariantsof the localpopulations.
Alternatively,their
unusualcolorscouldbe an artifactof chemicalsusedin preparation:the
atypicalskinsin the north are a centuryold.
59
CALIFORNIA
GNATCATCHER
TAXONOMY
Figure6. FemaleCaliforniaGnatcatchers,
dorsalview.Left,P. c. pontills:fight,P. c.
atwoodi. Note that atwoodi is darkergray,especiallyon crown,with more brown
wash on back.
Figure7. FemaleCaliforniaGnatcatchers,
ventralview.Left,P. c. pontills;fight,P.
c. atwoodi. Note whiterchestof pontills and grayerunderpartsof atwoodi.
60
CALIFORNIA
GNATCATCHER
TAXONOMY
SUMMARY
The CaliforniaGnatcatchers
of northwesternBajaCaliforniarepresenta
previouslyundescribed
subspecies,
hitherto includedunderPolioptila c.
californica,for whichwe proposethe nameP.c. atwoodi.Rangingfrom
aboutEnsenadaand Valle de las Palmassouthto El Rosario,it differsfrom
nominatecalifornicain the paler,grayer(lessbrownish)back,flanks,and
crissum
of females.Malesdifferin onlyrarelyhavingthe faintbrowntinge
to the back frequentin nominatecalifornica. From P.c. pontills, the
subspecies
of centralBaja California,bothsexesof atwoodidifferin their
darkerupperpartsandgray,not whitish,underparts.
ACKNOWLEDGMENTS
The specimenswere collectedunder a permit issuedto Eric Mellink by the
Secretar•ade DesarrolloUrbano y Ecologia.Field work and publicationof color
photographswere supportedby the Chevron Land and DevelopmentCompany
througha grant administeredby the Foundationfor Field Research.We thank
DouglasElyfor beingsoinstrumental
in thissupport.EduardoPalacios,LuciaAlfaro,
PhilipUnitt, and DanielGroutassisted
with fieldwork. DavidJerge,FrazeePaints,
assistedwith spectrophotometric
analysis.Robert Parks providedphotographic
assistance.We thank the curatorsof the eight institutionswho made specimens
availablefor this study.Philip Unitt and KennethParkeskindlysuppliededitorial
commentson thispaper.
LITERATURE
CITED
AmericanOrnithologists'
Union. 1957. Check-listof North AmericanBirds,5th ed.
Am. Ornithol. Union, Baltimore.
Atwood,J. L. 1988. Speciationand geographicvariationin black-tailedgnatcatchers. Ornithol.Monogr.42.
Atwood,J. L. 1991. Subspecies
limitsand geographicpatternsof morphological
variationin CaliforniaGnatcatchers
(Polioptilacallfore ica).Bull.S. Calif.Acad.
Sci. 90:118-133.
Brewster,W. 1881. On the affinitiesof certainPolioptilae, with a descriptionof a
new species.Bull. NuttallOrnithol.Club 6: ! 01-107.
Garcia, E. 1973. Modificaciones
al Sistemade Clasificaci6nClim•tica de K6ppen,
2nd ed. Institutode Geografia,UniversidadNacionalAut6noma de M•xico,
M•xico, D.F.
Grinnell,J. 1926. A criticalinspectionof the gnatcatchers
of the Californias.Proc.
Calif. Acad. Sci. (4th ser.) 15:493-500.
Oberbauer,T. A. 1992. Vegetationof northwesternBaja California.Fremontia
20:3-10.
Phillips,A. R. 1980. •Subespecieo especieolvidada?El caso de Polioptila
californica (Aves: Sylviidae). Resgmenesdel 4to Congreso Nacional de
Zoologia,Ensenada,B.C., p. 100.
Phillips,A. R. 1991. The KnownBirdsof North and MiddleAmerica,part II. A. R.
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61
CALIFORNIA
GNATCATCHER
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Accepted 1 August 1993
California Gnatcatcher
Sketch by Tim Manoils
62