THE BLACK SKIMMER IN CALIFORNIA: AN OVERVIEW

CHARLEST. COLLINS, Departmentof BiologicalSciences, California State Univer- sity,Long Beach,California 90840 KIMBALL L. GARRE'FESection of Vertebrates.Natural History Museum of Los AngelesCounty, 900 ExpositionBlvd., Los Angeles. California 90007

Althoughmany avian speciesin westernNorth Americahave suffered recentpopulation declines, a few have increasedover the sameperiod of time (Jehl and Johnson1994). Many of the increases,such as parrots' (Psittacidae),can be attributedstrictly to anthropogenicinfluences (Johnston and Garrett 1994). Among thosespecies showing apparent natural popula- tion increasesin Californiais the BlackSkimmer ( niger), which first occurredin the state in 1962 (Small 1963, 1994) and is now a resident breederwith a populationin 1995 of about 1200 pairs. Recentstudies in this region have documentedits nocturnalactivity pattern in the breeding season (Wilson 1995) and winter (Gazzaniga1995, de la Cueva and Fern/•ndez1996), food habits(Wilson 1995), and pattern of chick growth (Schewand Collins 1990, 1991). In this paper we review the statusof the Black Skimmer in California with emphasison the size and locationof breeding colonies and overwintering aggregations(Figure 1). We also includea list of museumspecimens of Black Skimmerstaken in California (Appendix). The first Black Skimmer recordedin Californiawas a singleindividual observedat the mouth of the Santa Ana River in coastalOrange County on 8 September1962 (Small1963). The realinvasion began 6 yearslater with the sightingof five skimmerson the Salton Sea at the mouth of the WhitewaterRiver, Riverside County, on 3 July 1968 (McCaskieand Suffel 1971) and the discoveryof five nestsat the southend of the SaltonSea in 1972 (McCaskieet al. 1974). Although the skimmer populationsat the SaltonSea havefluctuated since then, approximately487 pairsbred there in 1995 (Molina 1996; Table 1). Skimmers spread to the Pacific coast beginningin 1971 and bred in southSan Diego Bay in 1976 (Unitt 1984). They spreadnorthward in the ensuingyears as regularsummer visitors and occasionalsmall overwintering groups (Unitt 1984, L. Hays pers. comm.) beforeestablishing a breedingcolony at the BolsaChica Ecological Reserve, OrangeCounty, in 1985 (McCaskie1985, Collinset al. 1991, L. Hays and D. Yparraguerrepers. comm.) and Upper NewportBay Ecological Reserve, Orange County,in 1986 (McCaskie1986). Thesetwo coloniesnow each supportan annualbreeding population of greaterthan 200 paris(Table 1). The increasein the breedingrange of the BlackSkimmer has continued with the documentationof breedingon San FranciscoBay in 1994 and 1995 (Layneet al. 1996) and the formationof a new colonyat BatiquitosLagoon in northernSan Diego Countyin 1995 (Whelchelet al. 1996) (Figure1). A singlepair nestedat an inlandsite in the Tulare Lake basin,Kings County, in 1986 (Ericksonet al. 1986, Small 1994); four birdsappeared at this site againin 1993 butapparently did not nest(Yee et al. 1993). Six pairsbred at Western 27:127-135, 1996 127 BLACK SKIMMER IN CALIFORNIA theSeal Beach National Wildlife Refuge in AnaheimBay, Orange County, in 1987 (McCaskie1987, B. Masseypers. comm.). Documentationof colonysizes has varied in detailfrom year to year.In California,Black Skimmers have a prolongedbreeding season lasting well into Augustand September in someyears (Grant and Hogg 1976, Schew andCollins 1991, Stadtlander1994, Konecny1995, Molina1996), andat leastsome but not all (Collinspers. obs.)of the late-seasonnests are the resultof renesting.However, no detailed information on the rate of renesting isavailable. Thus, an exactcount of the numberof nestingpairs at eachsite

ß Breeding Sites e Imp.o.rtant.. winter sites

View

ß Tulare L.

Barbara

Lo..ng.Beach/ Chica ,•eal Bati½

Mission Bay San Diego Ba Montague I. Ensenada/ Punta Banda SanQuintin• Figure1. Breedingcolony sites (filled circles) and important winter concentration sites (hatchedcircles) of the BlackSkimmer in Californiaand northernBaja California.

128 BLACK SKIMMER IN CALIFORNIA is usuallynot possible,and only crudeestimates have been reported.We regardthe numberof nestsinitiated as the most consistentyear-to-year indexof the sizeof the skimmers'breeding population, even thoughit will

Table ! Number of Pairs or Nest Initiations(*) by Black Skimmers in California Breeding Colonies 1972-1995

Year

1972 5 1973 3 1974 10 1975 9 1976 25 1 1977 100 3 1978 100 6 1979 ND f 14 1980 0 30 1981 0 25 1982 0 35 1983 0 50 1984 0 ++g 1985 47 150 10' 1986 300 130 60* 2 1987 500 ++ 106' ND 1988 100 200 150' 15 1989 0 ++ 112' 45 1990 100 ++ 338* 14 1991 80 >157 h 398* 40 1992 100 ++ 278* ++ 1993 300 326 284* ++ (473*) 1994 450 310 353* ++ 2* (420') 1995 487 >200 h 201' 451' 2* 14'

ødata from Molina (1996). bdatafrom H. R. Carter et al. (unpubl.data), Stadtlander (1994), Konecny(1995), and F. Schaffner,E. Copper,and D. Stadtlander (pers.comm.). CDatafrom E. Burkett,L. Hays, K. Gazzaniga,and M. Taylor(pers. comm.). dDatafrom Layne et al. (1996). eData from Whelchel et al. (1996). )'ND, no data available. •++, birdsseen, possibly in largenumbers, but no nest-censusdata available. hMinimalcount; entire colony not censused.

129 BLACK SKIMMER IN CALIFORNIA almostcertainly exceed the actualnumber of breedingpairs by an amount yet to be determined.This is the value,when known, listedin Table 1. The breedingpopulation of skimmersat the Salton Sea has shownthe mostdramatic fluctuations, with more than 100 nestsreported by 1977, few if anynests from 1980 to 1983, anda reboundto a highof over500 nests in 1987 (Molina 1996, Table 1). Most of the coastalcolonies have shown a nearly steadyyear-to-year increase in numbersof nestswith occasional spurtssuch as that noted at BolsaChica, from 112 nestsin 1989 to 338 in 1990 (Table 1). The statusof the BlackSkimmer in adjacentBaja California, , has been summarizedby Palaciosand Alfaro (1992). Skimmershave been recordedregularly in BajaCalifornia since 1979 (Wilbur1987) andare now "considereda locallycommon on the northwesterncoast of Baja California,not only in winterbut year round"(Palacios and Alfaro 1992). There havealso been winter and breeding-seasonrecords of skimmersin BajaCalifornia Sur since1985,(Palacios and Alfaro 1992, Carmonaet al. 1995). The onlyknown Baja California breeding colony is on Montague Islandin the northernmostGulf of Californiain the ColoradoRiver delta; breedingwas suspected in 1992 (Palaciosand Mellink 1993) andconfirmed (14 nests)in 1993 (Peresbarbosaand Mellink1994); 21 nestswere found in 1994 (Peresbarbosa1995)• Someof the skimmerswintering in northwest- ern Baja California and nestingon MontagueIsland were bandedin southern California colonies as chicks (Palaciosand Alfaro 1992, Peresbarbosaand Mellink 1994). Althoughno nestinghas been noted, skimmershave been observedsince 1994 in springand summerin man- made pondsat Cerro Prieto, in the MexicaliValley (K. Radamakerpers. comm.).The skimmersin Baja CaliforniaSur may have originatedfrom mainlandcolonies in Sonora or Sinaloa,Mexico (Palaciosand Alfaro 1992, Carmona et al. 1995). Awayfrom the breedingcolonies and known coastal wintering sites, Black Skimmersare noted regularlyalong the coastfrom San Diego north to Monterey Bay. For example, there are 37 recordsof singleskimmers or smallgroups (up to four)in coastalSan LuisObispo County since 1977, all butseven of whichwere between March and October (T. Edellpers. comm.). The firstsighting in northernCalifornia was of a singlebird at BodegaBay, Sonoma County, 24 July 1971 (DeSante and LeValley 1971); more recently,birds have also reachedcoastal San Mateo County (Yee et al. 1995b,c), Marin County (Yee et al. 1993, 1994, 1995a), and coastal SonomaCounty again (Bailey and Fix 1994), aswell as a numberof siteson San FranciscoBay. All recordson the immediatecoast of northernCalifor- nia are from 22 May to 14 August.The only Channel Islandsrecord is of four individualsseen on Santa Catalina Island,28 June 1995 (McCaskie 1995b). Rosenberget al. (1991) summarizedfive records (involving six individuals) for the lower ColoradoRiver valley; the firstrecord for that regionwas in 1977, and all recordsfall between16 May and 3 September.Other inland sightingsfor southernCalifornia are of a juvenilenear Lakeview and at Lake Elsinore,Riverside County, 27 Augustto 4 September1978 (Garrettand Dunn 1981), two at TwentyninePalms, San BernardinoCounty, 25 August 130 BLACK SKIMMER IN CALIFORNIA

1994 (McCaskie 1995a), and two at China Lake Naval Weapons Center, extreme northeasternKern County, 28 July 1990 (McCaskie1990). At leastthe firstof theseinland records suggests an occasionaloverland route from the Salton Sea to the coast. Additional records of Black Skimmers at inlandsites, in Durangoand Jalisco,Mexico, have been reportedby Williams (1982). UnlikeAtlantic-coast populations nesting north of North Carolina(Burger and Gochfeld1990, Gochfeldand Burger1994), BlackSkimmers breeding in California are not all long-distancemigrants; many winter locally in southernCalifornia (Gazzaniga 1995, 1996). Winteringconcentrations of skimmershave been noted at Santa Barbara, Santa Barbara County, Seal Beachand Upper Newport Bay, OrangeCounty, and MissionBay and San Diego Bay, San Diego County (Gazzaniga1995, 1996) (Figure1). More distant locationsinclude Ensenadaand San Quintin in Baja California, Mexico (Palaciosand Alfaro 1992). Observationsof banded birds have indicated that a few skimmers from the Salton Sea winter on the coast (Molina 1996). Individualsbanded at Bolsa Chica have been observed in winter flocksfrom Santa Barbarasouth to San Quintin (Gazzaniga1995, 1996), and birdsfrom San Diego havebeen observed in both Long Beach and Santa Barbara (M. Taylor and C. Collinsunpubl.) and Ensenada(K. Molina pers. comm.). Two of the chicksbanded in San FranciscoBay in 1995 (Layneet al. 1996) have been observedin winter flocksin southern California:one was observedin Santa Barbaraon 11 February1996 (K. Molinaand K. Garrettpers. obs.),another in Long Beach4-21 April 1996 (Taylorand Collinspers. obs.).Observations of uniquelybanded skimmers havedemonstrated a degreeof year-to-yearoverwintering site fidelity as well as some intraseasonalmovements between sites (Gazzaniga 1995, 1996). Furtherobservations of theseuniquely color-banded birds will aid in quanti- fyingthe patternof juvenileand adultsurvival during the winter(Gazzaniga 1995, Taylorand Collinsunpubl.). Skimmers banded as chicks at Bolsa Chica have been observed as breedersin coloniesat San Diego (J. Konecnypers. comm.), Seal Beach(B. Massey pers. comm.), and Montague Island (Peresbarbosaand Mellink 1994). Althoughthe coloniesare occupiedannually, these observations of bandedbirds suggest reduced philopatry, at leastamong prebreeders, and a noticeableamount of mixingof birdsamong the severalbreeding colonies. Breedingat two yearsof agewas documented for a bandedskimmer nesting at Seal Beach in 1987 (B. Masseypers. comm.). The BlackSkimmer is now a well-establishedresident breeding species in southernCalifornia and Baja California. Further populationincreases at both some of the well-establishedcolonies and also at the three newly colonizedsites (Layne et al. 1996, Whelchel1996) overthe next few years seemlikely. The formationof additionalbreeding colonies, however, is more apt to dependon the availabilityof suitablesites sufficiently protected from human disturbance. Black Skimmers on both the Atlantic and Pacific coasts frequentlynest in associationwith variousspecies of (Sterna spp.) (Gochfeldand Burger 1994, Collinset al. 1991), and suchan association may proveto be a pre- or co-requisitecondition for the establishmentof new skimmercolonies in Californiaand Baja California. 131 BLACK SKIMMER IN CALIFORNIA

ACKNOWLEDGMENTS

We are gratefulfor the permissiongranted us to monitorskimmer populations in the several breeding colonies. We are also indebted to the numerous individuals mentionedabove, and particularlyGuy McCaskie,who have so freely sharedtheir fieldobservations of skimmerswith usand therebymade this a muchmore complete overview.Kathy Molinaand PhilipUnitt made helpfulcomments on earlierdrafts of this paper,and Mark C. Wimer preparedFigure 1.

LITERATURE CITED

Bailey,S. F., and Fix, D. 1994. The winter season.Middle Pacific Coast region. Natl. Audubon Soc. Field Notes 48:337-339. Burger, J., and Gochfeld, M. 1990. The Black Skimmer: Social Dynamics of a ColonialSpecies. Columbia Univ. Press,New York. Carmona, R., Fernbndez,G., Brabata,G., and Arvizu, E. 1994. Variaci6ntemporal en la abundanciadel Rayador,Rynchops niger (:) en Baja CaliforniaSur, M•xico. Rev. Biol. Trop. 43:313-315. Collins,C. T., Schew,W. A., andBurkett, E. 1991. ElegantTerns breeding in Orange County,California. Am. Birds45:393-395. De la Cueva,H., andFernbndez, G. 1996. Nightfeeding of BlackSkimmers at Estero Punta Banda, Baja California,Mexico. W. Birds27:162-163. DeSante, D., and LeValley, R. 1971. The nestingseason. Middle Pacific Coast region.Am. Birds33:899-904. Erickson,R. A., Bailey, S. F., and Barron, A.D. 1986. The nestingseason. Middle PacificCoast region. Am. Birds40:1248-1254. Garrett,K., and Dunn, J. 1981. Birdsof SouthernCalifornia. Los Angeles Audubon Soc., Los Angeles. Gazzaniga,K. T. 1995. Distributionand dispersalof Black Skimmers(Rynchops niger)in southernCalifornia. M. S. thesis,Calif. StateUniv., Long Beach. Gazzaniga,K. T. 1996. Overwinteringof BlackSkimmers in California:Site fidelity and inter-site movements. W. Birds 27:136-142. Gochfeld,M., andBurger, J. 1994. BlackSkimmer (Rynchops niger), in The Birdsof , no. 108 (A. Poole and E Gill, eds.). Acad. Nat. Sci., Philadel- phia. Jehl, J. R., Jr., and Johnson,N. K. (eds.).1994. A centuryof avifaunalchange in western North America. Studies Avian Biol. 15. Johnston,R. E, and Garrett, K. 1994. Populationtrends of introducedbirds in western North America, in A centuryof avifaunalchange in western North America (J. R. Jehl, Jr., and N. K. Johnson,eds.). StudiesAvian Biol. 15:221- 231. Konecny,J. 1995. Colonialseabirds and the WesternSnowy Ploverin southSan DiegoBay 1994. Bayand Estuary Program, U.S. Fish& WildlifeService, 2730 Loker Ave. W., Carlsbad,CA 92008. Layne,V. L., Richmond,R. J., and Metropulos,P. J. 1996. Firstnesting of Black Skimmerson San FranciscoBay. W. Birds27:159-162. McCaskie,G. 1985. The nestingseason. Southern Pacific Coast region. Am. Birds 39:961-963.

132 BLACK SKIMMER IN CALIFORNIA

McCaskie G. 1986. The nestingseason. Southern Pacific Coast region. Am. Birds 40:1254-1257. McCaskie.G. 1987. The nestingseason. Southern Pacific Coast region. Am. Birds 41:1486-1489. McCaskie.G. 1990. The nestingseason. Southern Pacific Coast region. Am. Birds 44:1184-1188. McCaskie.G. 1995a. The fall season.South PacificCoast region. Natl. Audubon Soc. Field Notes 49:99-103. McCaskie,G. 1995b. The summer season.Souther Pacific Coast region. Natl. Audubon Soc. Field Notes 49:979-983. McCaskie.G., Liston,S., and Rapley,W. A. 1974. Firstnesting of BlackSkimmers in California. Condor 76:337-338. McCaskie,G., and Suffel, S. 1971. Black Skimmersat the Salton Sea, California. Calif. Birds 2:69-71. Molina, K. 1996. Populationstatus and breedingbiology of BlackSkimmers at the Salton Sea. W. Birds 27:143-158. Palacios,E., andAlfaro, L. 1992. Occurrenceof BlackSkimmers in Baja California. W. Birds 23:173-176. Palacios,E., and Mellink, E. 1993. Additionalrecords of breedingbirds from MontagueIsland, northern Gulf of California.W. Birds24:259-262. Peresbarbosa,E. 1995. Fluctuacionesespaciales y temporalesde lasaves que anidan en la Isla Montague, Golfo de California, M•xico. M. S. thesis, Centro de Investigaci6nCientifica y de Educaci6nSuperior de Ensenada. Peresbarbosa,E., and Mellink, E. 1994. More recordsof breedingbirds from MontagueIsland, northern Gulf of California.W. Birds25:201-202. Rosenberg,K. V., Ohmart, R. D., Hunter, W. C., and Anderson,B. W. 1991. Birds of the Lower ColoradoRiver Valley. Univ. Ariz. Press,Tucson. Schew,W. A., andCollins, C. T. 1990. Age andsex determination in BlackSkimmer chicks. J. Field Ornithol. 61:174-179. Schew,W. A., and Collins,C. T. 1991. Annualand within-year variability in growth patternsof BlackSkimmer (Rynchops niger) chicks. Proc. Int. Symp. Mar. Biol. 8:87-94. Small, A. 1963. The fall migration.Southern Pacific Coast region. Audubon Field Notes 17:66-71. Stadtlander,D. 1994. Colonial seabirdsand the Western Snowy Plover nestingin southSan Diego Bay 1993. Bay and EstuaryProgram, U. S. Fish & Wildlife Service, 2730 Loker Ave. W., Carlsbad,CA 92008. Unitt, P. 1984. The birdsof San Diego County.San Diego Soc. Nat. Hist. Memoir 13. Whelchel,A. W., Keane, K. M., and Josselyn,M. N. 1996. Establishmentof a new BlackSkimmer colony in southernCalifornia. W. Birds27:164-167. Wilbur,S. R. 1987. Birdsof BajaCalifornia. Univ. Calif. Press,Berkeley. Williams,S. O., III. 1982. Black Skimmerson the Mexican plateau.Am. Birds 36:255-257. Wilson, J. E 1995. Diel periodicityand dietary breadth in the Black Skimmer: Implicationsfor coexistencein a mixed-speciescolony of .M. S. thesis, Calif. State Univ., Fullerton.

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Yee, D. G., Bailey,S. F., and Deuei,B. E. 1993. The springseason. Middle Pacific Coastregion. Am. Birds47:449-452. Yee,D. G., Fix, D., andBailey, S. F. 1994. The summerseason. Middle Pacific Coast region.Natl. AudubonSoc. FieldNotes 48:984-987. Yee, D. G., Bailey,S. F., Fix, D., and Singer,D. S. 1995a. MiddlePacific Coast region.Natl. AudubonSoc. Field Notes 49:95-99. Yee,D. G., Bailey,S. F., andSinger, D. S. 1995b.The winterseason. Middle Pacific Coastregion. Natl. AudubonSoc. FieldNotes 49:304-307. Yee,D. G., Bailey,S. F., andSinger, D. S. 1995c.The summerseason. Middle Pacific Coastregion. Natl. AudubonSoc. Field Notes 49:975-979.

Accepted 27 April 1996

Appendix.Specimens of the Black Skimmerfrom California.CSULB, CaliforniaState University, Long Beach; CSUN, CaliforniaState University, Northridge;LACM, Natural History Museumof Los AngelesCounty; SBCM, San BernardinoCounty Museum; SDNHM, San Diego Natural HistoryMuseum. Inquiries to LouisianaState University, the Museumof VertebrateZoology, University of California,Berkeley, and the Universityof California,Los Angeles, revealed no BlackSkimmer specimens.

South end Salton Sea, Imperial County 28 Apr 1979, adult, mount, SBCM M50894 19 Jul 1991• juv., studyskin, LACM 106066 19 Jul 1991, chick, in alcohol, LACM 106446 31 Jul 1991, chick, in alcohol,LACM 106447 31 Jul 1991, chick, in alcohol,LACM 106448 31 Jul 1991. chick, in alcohol,LACM 106449 31 Jul 1991. chick, in alcohol,LACM 106450 31 Jul 1991. chick, in alcohol,LACM 106451 31 Jul 1991 chick, in alcohol, LACM 106452 31 Jul 1991 chick, in alcohol,LACM 106453 4 Jun 1993 adult, skeleton,LACM 107571 17 Jul 1993 chick, studyskin, SDNHM 48801 19 Sep 1993, juv., fiat skin/skeleton,LACM 107762 13 Aug 1994, juv., studyskin, LACM 108428 3 Sep 1994, juv., studyskin, LACM 108429 3 Sep 1994, juv., studyskin, LACM 108430 12 Aug 1994, adult,skeleton, LACM 108447 12 Aug 1994, adult,skeleton, LACM 108448 3 Sep 1995, juv., studyskin, LACM 108946 North end SaltonSea, RiversideCounty 3 Jul 1968, adult, studyskin, LACM 76788 17 May 1970, adult,mount, SBCM S33298 24 Jul 1993, juv., studyskin, LACM 107763 7 Aug 1993, juv., studyskin, LACM 108431 7 Jul 1994, adult, skeleton,LACM 108446

134 BLACK SKIMMER IN CALIFORNIA

San Diego Bay, San Diego County 31 Jul 1977, adult,study skin/partial skeleton, SDNHM 40388 6 Jul 1978, imm., skeleton, SDNHM 42107 22 Jul 1990, postjuv.,study skin/partial skeleton, SDNHM 47409 5 Jul 1994, adult, skeleton, SDNHM 49011 MissionBay, San Diego County 22 Mar 1989, adult,study skin/partial skeleton, SDNHM 45694 Jan 1994 (exactdate unknown),age?, skeleton,SDNHM 48839 BolsaChica, Orange County Date unknown, chick, in alcohol, CSULB 6465 Date unknown, chick, in alcohol, CSULB 6466 28 Jun 1986, chick, studyskin, CSULB 6482 10 Sep 1987, juv., studyskin, CSULB 6783 16 Jun 1989, adult, skeleton, CSULB 7617 15 Aug 1989, adult, skeleton,CSULB 7166 20 Aug 1989, adult, skeleton,CSULB 7188 20 Jul 1990, adult, skeleton,CSULB 7398 31 Aug 1991, chick, studyskin, CSULB 7555 5 Jun 1994, adult, skeleton, CSULB 7600 TerminalIsland, Los AngelesCounty 10 Mar 1993, adult, studyskin, CSUN 1282

Black Skimmer Sketch by Tim Manoils

135