GEOGRAPHIC
VARIATION
CALIFORNIA
AND
EVOLUTION
IN
THE
GULL (LARU$ CALIFORNICU$)
JOSEPHR. JEHL, JR.
Sea World Research Institute/ Hubbs Marine Research Center, 1700 South ShoresRoad,
SanDiego,California92109USA
ABSTRACT.--The
CaliforniaGull (Laruscalifornicus),
currentlyregardedasa monotypicspecies,
is separableinto a small, dark-mantledrace (L. c. californicus)
that breedsprimarily in the
Great Basin of the United States,and a larger, paler race (L. c. albertaensis)
from the Great
Plains of the north-central U.S. and south-centralCanada.The breeding rangesof thesetwo
races,previously disjunct,have expanded recently, and a zone of secondarycontactseems
to be forming eastof the RockyMountainsin the northern United States.Received
13November
1986,accepted23 January1987.
THE California Gull (Laruscalifornicus)
has a
discontinuousbreeding range in the western
United Statesand Canada,extendingfrom Great
Slave Lake, N.W.T. (62øN) south to San Fran-
ciscoBayand Mono Lake, California (38øN)and
east to the Dakotas (A.O.U. 1983, pers. obs.).
Except for a brief study by Zink and Winkler
(1983), who found only minor size and genetic
differencesbetween gulls from Mono Lake and
Great Salt Lake, Utah, there has been no effort
distinctassemblages.
I then used stepwisediscriminant function analysis(BMDP7M; Dixon 1983) to determine which variablescontributedto the separation
of groups,using locality as the grouping variable.
RESULTS
Although California Gulls are well represented in museum collections, material from the
breeding grounds is scanty. Even so, considerable geographic variation in size is obvious
(Appendix). A preliminary comparisonof the
only two large samples,from Alberta and Mono
METHODS
Lake, showed that Alberta birds were signifiMuseumspecimensusedin thisanalysiswere taken cantlylarger in culmen,wing, tarsus,and mass
in the breedingrangebetween1 April and 15August. (t-test, P < 0.05); they also had a paler mantle.
Becausesomegullsare still migrating to inland breedSimple inspectionof the data showed that the
ing stationsin April, and becauseadults begin to size differences did not conform to a simple
move coastwardby the lastdaysof July,samplesfrom latitudinal gradient, as might be expectedfrom
western parts of the range may have included mi- Bergmann'srule; someof the largestbirds were
to investigate geographic variation in this
species,which is pronounced.
grants. I took standardmeasurementson length of
the exposedculmen,flattenedwing and tarsus,depth
of the bill at the gonys, and body mass.The large
sample from Mono Lake is based mainly on birds
found freshlydeadon nestingislets;a representative
from North Dakota (48øN) and some of the
smallestfrom Utah (41øN) (Fig. 1). Principal
componentsanalysis showed that 58% of the
variation
in females
and 61% in males was ex-
plained by a single factor and that within each
sex two assemblagescould be recognized(Fig.
2). These assemblages
correspondedbroadly to
could not be determined accuratelywere excluded physiographic provinces in western North
series was preserved as museum specimens. Some
California Gulls begin to show extensivewear of the
primaries by March. Specimenswhose wing length
from the analysis.Additional size and massdata were
extracted from the literature. I also noted the patterning of the primariesand the color of the mantle.
Although variation in the latter was evident, I could
America.
data by sex and used principal componentsanalysis
(BMDP4M; Dixon 1983) to test for patterns of variation. The analysisshowedthat the gulls fell into two
Nevada, Utah, and California), as well as those
Gulls
from
the northern
Great Plains
of the north-central United States,the prairie
provinces of Canada, and the Northwest Territories were large and clustered with the Alnot measureit consistentlybecauseof the generally
berta sample.Thosefrom the Great Basinof the
soiled condition of most specimens.
For analysisof size variation I separatedmensural western United States (Washington, Oregon,
421
from nearby regions in Colorado, Wyoming,
and Idaho, were small like those from Mono
The Auk 104:421-428. July 1987
422
JOSEPH
R. JEHL,
JR.
[Auk,Vol. 104
Lake. Although samples from many regions
were very small, the available data did not reveal any indication of clinal variation.
',
"r
I
I
'
External
differences
between
the Great Basin
and Great Plains forms are greater than those
characterizingmost currently recognizedraces
of North
American
birds.
I describe
them
as
subspeciesbecausemorphologicaland historical (seebelow) data indicate they have had separateevolutionaryhistories.The type specimen
of the species(Amer. Mus. Nat. Hist. No. 46070)
was taken near Stockton, California,
and is an
adult (cf. Greenway 1978) female of the Great
Basin population, which becomesL. c. californicus.Its measurementsare: exposed culmen,
43.7 mm; depth of bill at gonys,15.8mm; tarsus,
55.4 mm; wing, 380 mm. For the larger form I
proposethe name:
Larus caliœornicus
albertaensis
ssp. nov.
Holotype.--University of Michigan Museum
of Zoology No. 224,653,adult male, from Frog
Lake, Alberta, 53ø55'N, 110ø15'W;collected by
Philip H. R. Stephey, 9 July 1985.
Diagnosis.--Distinguishedfrom L. c. californicusby greater size, particularly in bill dimensions and body mass(Table 1, Fig. 3). Mantle
paler gray, lessbluish than in L. c. californicus,
approachingor matching the palenessof L. argentatus(Fig. 4). Measurementsof holotype:exposedculmen, 52.5 mm; depth of bill at gonys,
18.7 ram; tarsus,62.6 ram; wing, 424 ram; mass,
809 g. Using stepwise discriminant function
analysisfor the entire sample,I coulddetermine
the racial identification
for 87.9% of the females
of a bird of known
sex
of L. c. albertaensis and
95.3%of the femalesof L. c. californicus,
and for
87.0% of the males of L. c. albertaensis and 92;4%
I
of the males of L. c. californicus
(Fig. 5) by the
following formulas, where a score >0 is albertaensis
and a score<0 is californicus:
for females,
0.36 culmen (mm) + 0.31 bill depth (mm) +
0.06 wing (mm) - 45.60; for males,0.25 culmen
Fig. 1. Mean dimensions of (A) wing length, (B)
culmen length, and (C) tarsuslength of California
Gulls. For each state or province, data for males are
listed abovethosefor females.The samplefor Wyoming was basedon unsexedindividuals. Sample sizes
are in parentheses.
July1987]
Evolution
in theCalifornia
Gull
423
20-
10MALES
1;•3
2333123333
3
11• 3533123333
3
3
z
34333533
o
n-
20-
10FEMALES
0
312
--3
--2
--1
0
23
I
3
2
3
PC-1
Fig. 2. Plot of first principal componentof male and female California Gulls. Numbers refer to localities:
! = Northwest Territories, 2 = Saskatchewan,3 = Alberta, 4 = Montana, 5 = North Dakota, 6 = Washington,
7 = Oregon, 8 = Idaho, 9 = Mono Lake, California, 10 = other California, 11 = Nevada, 12 = Utah, and 13 =
Colorado.
(ram) + 0.15 tarsus(ram) + 0.05 wing (ram) -40.21.
Range.--Nests on lakes, often of slight to
moderate alkalinity or salinity, in North (and
South?) Dakota, Manitoba, Saskatchewan, Al-
berta, and the Northwest Territories (Fig. 6).
Southern and western limits unknown,
as the
range of the speciesis changing rapidly. Presumably winters through the range of the
species,mainly alongthe Pacificcoastfrom British Columbiato BajaCalifornia.
Variation.--Larus
c.albertaensis
averages5-12%
largerthan L. c.californicus
in linear dimensions
and 27%greaterin body mass.All of thesedifferences are highly significant (t-test, P <
0.0001). Indeed, females of albertaensisexceed
male californicus
in mean culmen length and
mass.In addition, albertaensis
hasa paler mantle,
and the gray areason the inner vane of the
primaries average larger and paler, although
the latter differencesare minor. The pattern of
white markings("mirrors")on the primariesof
adults is variable (see Dwight 1925: figs. 115,
117, 119, 120), though not geographically.I
found no differencesin color or pattern in the
downy and juvenile plumagesof 10 gulls from
Mono
Lake and
10 from
Beaverhill
Lake
that
were hatchedand reared in captivity. Among
wild-taken birds, juvenile and subadultplumages were too variable for analysis.Juveniles
from Mono Lake, for example,range from pale
tan to dark brown in their general coloration,
which may be modified dramatically by exposure to alkaline water and intense sunlight.
Studies of allozyme variability revealed no
diagnosticgeneticdifferencesbetweenthe two
populations(Karl et al. 1987).
Specimens
examined.--Thetype seriesof 9 males
424
JOSEPH
R.JEHL,
JR.
[Auk, Vol. I04
TABLE
1. Sizedifferences
betweenracesof CaliforniaGulls(Larus
californicus).
a
Wing (mm)
Race
albertaensis
•
californicus
•
Culmen (mm)
Sex
No.
Mean
Range
SD
No.
Mean
M
48
412.2
385-431
9.6
49
53.0
F
38
391.3
369-408
9.7
38
M
146
393.7
365-415
9.6
145
F
202
372.3
341-390
8.2
165
42.6
Range
SD
47.3-57.4
2.1
47.8
41.2-52.0
2.4
47.3
40.5-59.2
2.5
38.0-48.4
1.8
Pooleddata from Appendix.
Northwest Territories, Saskatchewan,Alberta, and North Dakota.
Washington,Oregon, Idaho, California, Utah, Nevada, and Colorado.
and 3 femalesfrom Frog Lake and Beaverhill lation (albertaensis) became isolated in the
Lake, Alberta,is housedin the Universityof northernlakeson outwashplainsnear the marMichigan Museum of Zoology (2 skins), the gins of the glaciers.Until recentlyalbertaensis
Provincial Museum of Alberta (2 skins),and the
SanDiegoMuseumof Natural History(4 skins,
4 skeletons).Other specimensexaminedare in
the museumsacknowledgedbelow.Tissuesamplesof both forms,includingthe type of L. c.
albertaensis,
havebeendepositedin the Museum
of Zoology,LouisianaStateUniversity.
Etyraology.--Named for Alberta, Canada,
provinceof the type locality.
bredmainlyat lakesnearthe edgeof theboreal
forest(seeFig. 6). The other population(californicus)became isolated around lakes in the
steppe-desert of the western United States,
where the speciesis currently most abundant
(Conover 1983).
In the pleniglacialperiod (ca. 12,500-15,000
yr B.P.) the refugium for the cold-desertflora
characteristic of the modern Great Basin, and
presumablyfor L. c. californicus,
was in a small
DISCUSSION
areaof the presentMohaveDesert(Wells 1983).
As the climate ameliorated in the Holocene,
Evolution
andsubspeciation
in theCalifornia
Gull: steppe-desert conditions shifted north into the
ahypothesis.--Rapid
speciation
amonglargegulls
Great Basin, where extensive lakes of varied
in the Northern Hemisphere is presumed to
have resulted from the splitting of ancestral
populationsby eventsin the Pleistocene(Mayr
1963, Smith 1964). I postulatethat when the
hydrologyprovidedbreedinghabitatfor gulls
(Hubbs and Miller 1948, Hubbs et al. 1974). I
inferthattheabsence
of suitablenestinghabitat
in the High Plainshelpedisolatethe GreatPlains
CaliforniaGull stockwas divided, one popu- andGreatBasingulls,whichasrecentlyas1915
were700km apart(Cooke1915;Fig.6). Shortly
thereaftera majorrangeexpansion
began,abet-
Fig. 3. Extremesof geographicand sexualvaria-
tion in bill dimensions
in CaliforniaGulls.Top:L. c.
albertaensis,
male, Frog Lake, Alberta (UMMZ No.
226,654).Bottom:L. c. californicus,
female,Mono Lake,
California (SDNHM No. 44123).
Fig. 4. Variation in body sizeand mantle colorin
CaliforniaGulls.Top: L. c. albertaensis.
Bottom:L. c.
californicus.
Specimens
asin Fig. 3.
July 1987]
TABLE 1.
425
Evolutionin the CaliforniaGull
Extended.
Depth (mm)
No.
Mean
48
17.7
Tarsus(mm)
Range
SD
No.
Mean
15.6-19.2
0.7
48
63.1
Mass(g)
Range
SD
56.8-72.0
3.3
No. Mean
32
841
Range
SD
653-1,045
103.3
36
15.8
14.8-17.0
0.6
36
57.7
52.8-65.1
2.4
19
710
568-903
91.2
142
157
16.6
14.9
13.7-18.8
13.1-16.3
0.9
0.6
132
153
59.0
54.8
47.7-65.0
43.8-60.5
2.3
2.6
64
84
657
556
490-885
432-695
85.3
53.4
ted by the creationof nestinghabitat.By 1932
the Great Basinbirdshad bred in Washington
(Deckerand Bowles1932),and somehad spread
acrossthe Rockies,forming coloniesin Wyoming and Colorado(Baileyand Niedrach1965),
a processthat continuestoday (Findholt 1986,
C. Chasepets. comm.).The regularity of nonbreederssummeringin New Mexico suggests
that colonizationmay be imminent (J.P. Hubbard pets. comm.); at least 5 of 6 specimens
taken there in the summerof 1981representL.
southwest.The small samplefrom Montana (4
males only), for example, includes two birds
that clumpwith the GreatBasinbirds,one with
the Great Plains birds, and one that is inter-
mediate (Fig. 2).
The ancestryof the CaliforniaGull is uncertain. Most authors have considered
it a member
of the Herring Gull complex(Stegmann1934,
c. californicus.
Data for the Great Plainsbirds are
scanty,but the recentestablishment
of a colony
in SouthDakota(Harris 1982)suggests
that their
range, too, is expanding.
Between 1930 and 1980 the U.S. population
increasedfrom 101,000gulls in 15 coloniesto
276,000 in 80 colonies, and the hiatus that ex-
istedin the High Plainsbeganto fill (Conover
1983).The increasedabundanceand rangeexpansion apparently resulted in a zone of secondary contacteastof the Continental Divide,
with birds in that region being derived from
breeding areas to the northeast and from the
I1 Ilfi
--3.0
20
10
O0
10
2O
30
8
Fig. 6. Breedingrange of California Gull, based
on Conover(1983),Findholt (1986),Godfrey(1966),
Harris(1982),C. Chase,III (pers.comm.),andoriginal
observations.
The main range of L. c. californicus
is
-'.
-t
-'.
'.
:
2'.o 3:0 4'.o do do
hatched;outlyingcoloniesare indicatedby opencircles.Therangeof L. c.albertaensis
is stippled;a colony
Fig. 5. Resultsof discriminantfunctionanalysis. in SouthDakota('k) is presumedof be of this race.
Stippledareasreferto samplesfrom the rangeascribed Forpreciselocationof U.S.coloniesseeConover(1983).
to L. c. albertaensis,
openareasto rangeof L. c. califor- Coloniesknown to Cooke(1915)are indicatedby
nicus.
crosses.
426
JOSEPH
R. JEHL,
JR.
Fisher and Lockley 1954, A.O.U. 1983), and
among extant forms it is reminiscent of Thayer's
Gull (L. thayeri)in its small size, dark iris, relatively dark mantle, juvenile and subadult
plumages,east-westmigration route, and west
coast wintering range. Schnell (1970, pers.
comm.), on the other hand, using only speci-
[Auk, Vol. 104
ACKNOWLEDGMENTS
I examined
collections
in the Museum
of Vertebrate
Zoology,University of California, Berkeley;California Academyof Sciences;University of California,
LosAngeles;LosAngelesCountyMuseumof Natural
History; U.S. National Museum of Natural History,
Field Museumof Natural History;and SanDiegoMumens that I would classifyas L. c. californicus, seumof Natural History. Information on other col-
found that the speciesclusteredmore closely
with the smallerRing-billed (L. delawarensis)
and
Mew (L. canus)gulls than with the Herring Gull.
While I suspecta reanalysisthat includedlarge
specimensfrom the Great Plains might lead to
a different result, I doubt any conclusionswill
be fully satisfactoryuntil the possiblerelationship of L. californicus
to two small Pleistocene
species,L. oregonus
and L. robustus,
is considered.
Those speciesare known only from inland lo-
lectionswasprovided by C. M. White (BrighamYoung
University,University of Utah), R. M. Mengel (University of KansasMuseumof Zoology),K. C. Parkes
(CarnegieMuseumof Natural History), R. W. Starer
(The Universityof Michigan Museumof Zoology),L.
Cancadeand P. Stepney (Provincial Museum of Alberta),M. Gillman (CaliforniaAcademyof Sciences),
G. Schnell(University of Oklahoma),M. R. Browning
(U.S. National Museum of Natural History), C. Chase,
III (Denver Museum of Natural History), T. Miller
(British Columbia Provincial Museum), and L. Oring
calities in the Great Basin (Howard 1946, Jef-
(University of North Dakota). G. McCaskie, P. Step-
ferson 1985), the area now inhabited by L. c.
californicus.
Samplingprocedures.--Thepaucity of preserved material from many parts of the gulls'
range is deplorablebut easily remedied. Collecting east of the Continental Divide, especially, is needed to documentcurrent morphological variation more precisely and to
ney, S. Findholt, and C. Chasehelped in many ways.
determine
whether
the
differences
described
Special thanks are due S. I. Bond for continual assistance in all phasesof this and complementary research.Computerprogramswere run at the SanDiego
State University Computer Center. The manuscript
was improved by the commentsof T. R. Howell, S.
A. Karl, R. W. Starer, R. W. Zink, G. D. Schnell, A.
H. Brush, D. M. Power, M. Conover, and B. L. Monroe,
Jr. This researchwas supportedby grantsfrom the
Los Angeles Department of Water and Power.
above will be swamped or reinforced as the
speciescontinues its increaseand range expansion.
Considerable sampling bias in currently
availablematerial is manifestedby the sexratios
of specimensused in this study, which vary
among localities (see Appendix); indeed, femaleswere unrepresentedin somesamples.The
high incidence of males (109 males vs. 69 females) from localities other than Mono Lake
LITERATURE CITED
AMERICAN ORNITHOLOGISTS' UNION.
1983.
Check-list
of North American birds, 6th ed. Washington,
D.C., Amer. Ornithol.
Union.
BAILEY,g. M., & R. J. NIEDRACH. 1965. Birds of Colorado. Denver,
Colorado,
Denver
Museum
of
Natural History.
BEHLE,W. H.
1958. The bird life of Great Salt Lake.
probably stemsfrom their greater aggressiveSalt Lake City, Univ. Utah Press.
nessand likelihood to approachwithin shotgun BURGER,
J. 1983. Determining sex ratios from colrange (Butler and Janes-Butler 1982, Burger
lected specimens.Condor 85: 503.
1983).Bycontrast,the high incidenceof females BUTLER,
g. G., & S. JANES-BUTLER.
1982. Territoriality
in the Mono Lake (72 males vs. 124 females)
and behavioral correlatesof reproductive success
of the Great Black-backed Gulls. Auk 99: 59-66.
sample, derived largely from birds dying of
M.R. 1983. Recentchangesin Ring-billed
trauma or predation in the colony, reflectsthe CONOVER,
and California gull populations in the western
females' greater risk of mortality early in the
United States. Wilson Bull. 95: 362-383.
nesting season(Jehl and Chase1987, Jehl MS).
--,
& G. L. HUNT, JR. 1984. Female-female pairThesecontradictoryratiosillustrate further the
ing and sexratiosin gulls: an historicalperspecinherent risks in drawing inferencesabout sotive. Wilson Bull. 96: 619-625.
cial structure from the sex ratios of preserved COOKE,W. W. 1915. Distribution and migration of
specimens,when bias in collection or preserNorth American gulls and their allies. U.S. Dept.
vation is not, or cannot be, known (Burger 1983;
cf. Conover and Hunt 1984).
Agr. Bull. 292.
DECKER,F. R., & J. H. BOWLES.1932. Two new breed-
July1987]
Evolution
in theCalifornia
Gull
427
ing recordsfor the stateof Washington.Murrelet
Desert, California. Contrib. Sci., Los Angeles
13: 53.
County Mus. No. 362.
DIXON, W. J. (Ed.). 1983. BMDP statistical software.
Los Angeles, Univ. California Press.
DWIGHT,J. 1925. The gulls (Laridae) of the world:
their plumage,moults,variations,relationships
and distribution.
Bull. Amer.
Mus. Nat. Hist. 52:
63-408.
FINDHOLT, S. 1986.
Status and distribution
of Cali-
fornia Gull nestingcoloniesin Wyoming. Great
Basin Natur.
46: 128-133.
FISHER,J., & R. M. LOCKLEY. 1954. Sea-birds. An in-
JEHL,J. R., JR., & C. CHASE,III.
1987. Foraging pat-
terns and prey selectionby avian predators:a
comparativestudy in two coloniesof California
Gulls.
Stud. Avian
Biol. 10.
KARL,S. A., R. M. ZINK, & J. R. JEHL,JR. 1987. A1-
lozymeanalysisof the CaliforniaGull (Laruscalifornicus).
Auk 104:in press.
MAYR,E. 1963. Animal speciesand evolution. Cambridge, Massachusetts,Belknap Press, Harvard
Univ.
troductionto the natural historyof the sea-birds SCHNELL,
G. D. 1970. A phenetic study of the subof the North Atlantic. Boston,Houghton Mifflin
order Lari (Aves) II. Phenograms,discussionand
Co.
GODFREY,W. E. 1966. The birds of Canada. Ottawa,
Queen's Printer.
GREENWAY,
J. 1978. Type specimensof birds in the
AmericanMuseumof NaturalHistory.Bull.Amer.
conclusions.Syst. Zool. 19: 264-302.
SMITH,J. E., & K. L. DIEM. 1972. Growth and devel-
opment of young California Gulls (Laruscalifornicus).Condor 74: 462-470.
SMITH,N. G. 1964. Evolution of some arctic gulls
Mus. Nat. Hist. 161: 1-305.
(Larus):an experimentalstudyof isolatingmechHARRIS, B. 1982. First nest record for California Gulls
anisms.Ornithol. Monogr. No. 4.
in South Dakota. South Dakota Bird Notes 34: 42.
STEGMANN,
g. 1934. Ueber die Formen der grossen
HOWARD, H. 1946. A review of the Pleistocene birds
Mowen ("subgenusLarus")und ihre gegenseifrom FossilLake, Oregon. Carnegie Inst. Washtigen Beziehungen.J. Ornithol. 82: 340-380.
ington Publ. 551: 141-195.
VERMEER,
K. 1970. Breeding biology of California
HUBBS,C. L., & R. R. MILLER. 1948. The zoological
and Ring-billed gulls: a study of ecologicaladevidence: correlation between fish distribution
aptation to the inland habitat. Can. Wildl. Serv.
and hydrographichistoryin the desertbasinsof
Rept. Ser. No. 12.
western United States.Pp. 17-166 in The Great WELLS,P.V. 1983. Paleobiogeographyof montane
Basin,with emphasison Glacial and Postglacial
islands in the Great Basin since the last glaciotimes. Bull. Univ. Utah 38 (Biol. Ser. 10).
pluvial. Ecol.Monogr. 53: 341-382.
, --,
& L. C. HvB•s. 1974. Hydrographic ZINK, R. g., & D. W. WINKLER. 1983. Genetic and
historyandrelict fishesof the north-centralGreat
morphologicalsimilarity of two California Gull
Basin. Mem. California Acad. Sci. 7: 1-259.
populationswith different life history traits.BloJEFFERSON,
G. T. 1985. Review of the Late Pleistochem. Syst.Ecol. 11: 397-403.
cene avifauna from Lake Manix, central Mojave
428
JOSEPH
R. JEHL,
JR.
[Auk,Vol. 104