The Recent Breeding of California and Laughing Gulls at the Salton Sea, California

THE RECENT BIF!NG OF CALIFORNIA AND LAUGHING AT THE SALTON SEA, C-FORNIA

KATHY C. MOLINA, Sectionof Vertebrates,Natural History Museum of LosAngeles County,900 ExpositionBlvd., LosAngeles, CA 90007

ABSTRACT: CaliforniaGulls successfully colonized the SaltonSea in 1997 with 22 nestingpairs near Obsidian Butte, extending their breeding range 650 km intoone of the world'shottest environments. Although the colonysite is oftensubjected to seasonalflooding, the numberof nestingpairs has increased to at least40 in 1999. One or two pairsof LaughingGulls continue to nestsporadically although unsuccess- fully;a nestingattempt in 1994 extendedtheir range 50 km north into Riverside County.

The CaliforniaGull (Larus californicus)nests widely in the interior of westernNorth America, southto Mono Lake, and alongthe coastat San FranciscoBay (AOU 1998, Winkler 1996). The breedingrange of the LaughingGull (L. atricilla) in westernNorth America extendsfrom the Salton Sea, California,northeastern Baja California Norte (Molina and Garrettunpubl. data), and IslaMontague in the northernGulf of California (Mellinkand Palacios1992) southalong the Pacificcoast of Mexico(Howell and Webb 1995). Sincethe sporadicreports of up to 5 to 10 nestingpairs until the late 1950s (Smalland Pyle 1952, Remsen 1978), the Laughing Gull has not bred at the Salton Sea, thoughit has remaineda common postbreedingvisitor in summer(Garrett and Dunn 1981). Here I describea newly establishednesting colony of CaliforniaGulls at the Salton Sea and documentits breeding phenology, success, and growthfrom 1997 to 1999. This colonyextends the species'successful breeding range some650 km southinto one of the world'shottest nesting environments (Grant 1982). I alsodescribe recent nesting attempts by LaughingGulls, including one at the northend of the sea,extending that species'breeding range 50 km northto RiversideCounty, California. While the SaltonSea supportslarge numbers of winteringRing-billed (L. clelawarensis),Herring (L. argentatus),and CaliforniaGulls, the recentcolonization by the lastrepresents the sea'sfirst significantcolony of breedinggulls.

CALIFORNIA GULLS

On 4 May 1997 I noted an aggregationof 40-50 California Gulls apparentlynesting on a smallunvegetated islet just offshoreof Obsidian Butte,approximately 8 km northwestof Calipatria,Imperial Co. (Figure1). This site had been used previouslyby nestingGull-billed Terns ($terna nilotica), CaspianTerns ($. caspia), Black Skimmers(Rynchops niger, Molina 1996), and, mostrecently, Brown Pelicans [Pelecanus occidentalis; nest-buildingattempts by three pairsin 1997, SaltonSea NationalWildlife Refuge(NWR) files]. The islet'slow-lying western perimeter forms a narrow peninsulacomposed largely of smallboulders and rocks.Along this stripI

106 Western Birds 31:106-111, 2000 RECENT BREEDING OF CALIFORNIA AND LAUGHING GULLS AT SALTON SEA

Figure 1. The T-shapednesting islet (upper left) near ObsidianButte, ImperialCo. The CaliforniaGull colonyforms along the islet'sseaward edge. Photo courtesySalton Sea National Wildlife Refuge found22 active(plus three abandoned)gull nests on my firstvisit on 15 May. The colonywas orientedlinearly along the rockyperimeten and the distance from the neststo water'sedge rangedfrom 1 to 4 m. Many of thesenests were within the spray and surge zone during the strong winds prevalent in spring.Placed in relativelyflat areas betweenrocks, the nestswere com- posedof dried cane (Phragmitessp.) and linedwith filamentousalgae and feathers. The mean clutchsize [+ standarderror (SE)]for the 22 active nests was 2.1 + 0.2. The abandonmentof three nestswith eggsmay have been due to inundationby waves. To minimizedisturbance to the colonyI monitoredits progressfrom the mainlandshore at weeklyintervals until fiedging was complete. I surveyedit from a kayak on 19 June and 5 July (Figure2). when I recorded8 and 12 chicks, respectively,seeking shelter among the low boulders.This rocky, uneven substratehelped to conceal chicks, and the observednumber is a conservativeestimate of nesting success.On 19 June the chicksranged from recent hatchlingsto near fledging,suggesting marked asynchrony within the colony.On 31 July, my lastvisit, ! noteda solitarynearly fledged chickswimming away from the isletbut no furthernesting activity. At ObsidianButte in 1998• ! observedcopulation and nest buildingby 2 May, althoughgulls in high breedingcolor were at the site in late April. I confirmed 37 active nestsand the onset of hatchingon 6 June. Using an interval from egg laying to hatching of 30-33 days (Winkler 1996), I estimatedthe earliestdate of egg layingas 2-5 May for thisyear. The mean

107 RECENT BREEDING OF CALIFORNIA AND LAUGHING GULLS AT SALTON SEA

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Figure2. CaliforniaGulls with juvenile(second from left) alongrocky perimeter of ObsidianButte islet, 5 July 1997. Photo by Kathy Molina clutch size (+ SE) of 37 active nestsin 1998 was 2.2 + 0.09. On 28 June I countedthe highestminimum of 15 chicks.In 1999 1noted nest building at this site by 16 April and confirmed 40 active nests (plus 5 abandoned attempts)on 21 May. Hatchinghad alreadycommenced by my visiton 10 June. The mean clutchsize (+ SE) for 40 nestsin 1999 was 2.5 + 0.11. On 15 June I countedthe highestminimum of 24 chicks. The colony'sorientation and nest compositionin 1998 and 1999 were similarto thoseof 1997. Despiteall nestsin bothyears being farther from the water (> 5 m) than in 1997. shallowpuddles persisted among many of them in late May, indicatingthat they were stillwell withinthe inundationzone. Earliernesting attempts by CaliforniaGulls have been reportedfrom the SaltonSea. Small(1994) citedan undocumentedand apparently unsuccessful attemptby one pair in the early 1970s. More recentlyI recordedthe nesting attemptsby one or two pairson 7 June 1996 at the JohnsonStreet tern and skimmercolony (site described by Molina 1996) at the north end of the sea, RiversideCo. Here nest composition(dried cane, feathers,and a few twigs) was similarto that at ObsidianButte, but nestingsubstrate and distanceto water differed.One nest containingtwo eggswas placedon top of a bare earthenlevee 3 m from the sea'ssurface. The secondnest was placed on the floorof a dry and sparselyvegetated impoundment surrounded by an earthen wall 2 m high. The singleegg in this nest was obviouslyabandoned when I foundit. By 28 Junethe leveenest contained two recentlyhatched nesfiings: I estimatedthe largest,at 44 g, to be < 2 daysold. By 12 July I foundone desiccatedchick (LACM 110635) at the leveenest and no further evidenceof

108 RECENT BREEDING OF CALIFORNIA AND LAUGHING GULLS AT SALTON SEA the otherchick or the adults;I presumedthat thisat-tempt was unsuccessful. I estimatedan egg-layingdate between25 and 27 May, nearlya monthlater than the successful nests at Obsidian Butte. Additionalattempts by CaliforniaGulls to nestat the Rock Hill tern and skimmercolony at the SaltonSea NWR (threeto four attemptseach during May of 1998 and 1999) havebeen discouragedby the refuge'spersonnel since in recent years California Gullshave begun to prey on tern chicks (pers. obs.).

LAUGHING GULLS

Millerand van Rossem(1929) describedthe firstnesting of severalpairs of LaughingGulls at the SaltonSea on 9 June 1928. A few pairscontinued to nest sporadicallyup until the late 1950s, when AmericanWhite Pelicans (Pelecanuserythrorhynchos) and CaspianTerns alsoceased to nest along the southend of the sea (Remsen1978). While visitingthe JohnsonStreet colonyon 5 August1994, Ken Sturm and I discovereda large sticknest underan Allen rolfea shrubcontaining two recentlyhatched Laughing Gulls, one of whichwas freshly dead (LACM 108310). The largerchick survived until at least 12 August, when it regurgitatedtwo small Tilapia during examination.By 23 AugustI could find neither it nor mobbingadults. I encounteredno furtherbreeding evidence for this speciesuntil 27 May 1999, when a singlepair nestedat Salton Sea NWR. This two-eggclutch failedto hatch, althoughthe adultscontinued to attend it until 15 July.

DISCUSSION

With the recentestablishment of the ObsidianButte colonyat the Salton Sea, the CaliforniaGull has expanded its breeding range south into the one of the world'sharshest nesting environments (Grant 1982). Althoughat the Salton Sea eggsand hatchlingscan be vulnerableto even brief periodsof exposureto the sun,and thusrequire nearly constant attendance, a variety of charadriiformbirds nests successfully at the sea.The proximityof nest sitesto water for brief episodesof bellysoaking and adequateexposure to breezesare believedto enhanceevaporative cooling for adultstilts, avocets, plovers,and ternsat the SaltonSea, where ambienttemperatures during the nestingseason commonly exceed birds' body temperature (Grant 1982). At RockHill off-dutymates of nestinggulls, like thoseof ternsand skimmers, often restedat the shorenear their nests,with legsand feet submergedin water.Although Gull-billed Terns and BlackSkimmers frequently, but briefly, left their neststo drink and wet their extremitiesand bellies(Molina 1999) I have not observednest-attending gulls to interruptincubation to do so. Gulls at Obsidian Butte nested on a low windward strip of rocks and boulders,often subjectedto floodingduring high winds. The near-water placementand phenologyof nestsat ObsidianButte differedfrom the unsuccessfulattempts at JohnsonStreet. At the latter, two of the three unsuccessfulattempts by gullsoccurred at the baseof an impoundmentand were surroundedby a wall 2 m high that blockedthe wind. Additionally, incubationat ObsidianButte was predominantly in May, whereasat Johnson

109 RECENT BREEDING OF CALIFORNIA AND LAUGHING GULLS AT SALTON SEA

o 3o

^ 25

= 10

0 i i i i April May June July August Figure3. Mean numberof daysper month (__standard deviation) in whichambient temperaturemaxima (measured at ImperialAirport) reached or exceededa gul]'s mean bodytemperature (41øC), 1995-1998. it was in June and July, monthsin which the numberof dayswith ambient temperaturesreaching or exceeding41øC, a mean body temperature calculatedfor larids on the basisof McNab (1966), increasedthree- and eightfold,respectively, over that for May (Figure3). Hand et al. (1981) believedthat proximityto water with unobstructedexposure to convective air currents ameliorated the effects of intense solar radiation for Yellow- lootedGulls (L. livens),nesting in the Gulf of California.Variation in chick mortalityamong nestingsubcolonies of WesternGulls (L. occidentalis)on the CaliforniaChannel Islands during an unusualheat wave was thought to be dueto variationin nest-sitemicroclimate (Salzman 1982). However,Jehl and Mahoney(1987) believedthat predationrisk, rather than variationin nest-sitemicroclimate, was responsiblefor CaliforniaGulls' selection of nest sitesat Mono Lake. Althoughquantitative data for the Salton Sea gull- nestingsites are lacking,differences in nestsubstrate and locationand the timingof nestingcould lead to importantdifferences in exposureto windand sun. Becausemicroenvironmental variation may have important conse- quencesfor adults' and chicks' thermoregulationand, ultimately,nest successat the Salton Sea, nest-siteselection by larids deservesfurther investigation.

ACKNOWLEDGMENTS

I am gratefulto KimballGarrett, Jihadda Govan, Fritz Hertel, and Eric Mellinkfor their fieldassistance, and especiallyto Ken Sturmfor alsoproviding logistic support. Kimball Garrett, Joseph R. Jehl, and Philip Unitt made helpfulcomments on an earlier draft.

110 RECENT BREEDING OF CALIFORNIA AND LAUGHING GULLS AT SALTON SEA

LITERATURE CITED

AmericanOrnithologists' Union. 1998. Checklistof North AmericanBirds, 7th ed. Am. Ornithol. Union, Washington,D. C. Dawson, W. L. 1923. The Birds of California, vol. 4. South Moulton Co., Los Angeles. Garrett, K., and Dunn, J. 1981. Birdsof SouthernCalifornia: Status and Distribution. LosAngeles Audubon Soc., LosAngeles. Grant,G. S., andHogg, N. 1976. Behaviorof late-nestingBlack Skimmers at Salton Sea, California. W. Birds 7:73-80. Grant,G. S. 1982. Avianincubation: Egg temperature, nest humidity, and behavioral thermoregulationin a hot environment.Ornithol. Monogr. 30. Hand, J. L., Hunt, G. L., Jr., and Warner, M. 1981. Thermal stressand predation- Influenceson the structureof a gullcolony and possibly on breedingdistributions. Condor 83:193-203. Howell, S. N. G., and Webb, S. 1995. A Guide to the Birds of Mexico and Northern CentralAmerica. Oxford Univ. Press,Oxford, England. Jehl, J. R., Jr., and Mahoney, S. A. 1987. The rolesof thermal environmentand predationin habitatchoice in the CaliforniaGull. Condor89:850-862. McNab,B. K. 1966. An analysisof the bodytemperatures of birds.Condor 68:47- 55. Miller, L., and van Rossem,A. J. 1929. Nestingof the LaughingGull in southern California. Condor 31:141-142. Molina,K. C. 1996. Populationstatus and breeding biology of BlackSkimmers at the Salton Sea, California.W. Birds27:143-158. Molina,K. C. 1999. An explorationof parentalinvestment hypotheses using Gull- billedTerns and Black Skimmers(Aves: Laridae) at the SaltonSea, California. M. S. thesis,Calif. StateUniv., Northridge. Palacios,E., and Mellink, E. 1992. Breeding bird recordsfrom Montague Island, northern Gulf of California. W. Birds 23:41-44. Reinsen,J. V., Jr. 1978. Bird speciesof specialconcern in California.Calif. Dept. Fish& Game NongameWildlife Invest. 78-1. Salzman,A. G. 1982. The selectiveimportance of heat stressin gullnest location. Ecology63:742-751. Small,A., andPyle, R. L. 1952. SouthernPacific Coast Region. Audubon Field Notes 5:308. Small,A. 1994. CaliforniaBirds: Their Statusand Distribution. Ibis Publ., Vista, CA. Winkler, D. W. 1996. California Gull (Larus californicus),in The Birds of North America (A. Poole and F. Gill, eds.),no. 259. Acad. Nat. Sci., Philadelphia.

Accepted 13 March 2000

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