The Breeding Status of the Snowy Plover in California
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WESTERN BIRDS Volume 12, Number 1, 1981 THE BREEDING STATUS OF THE SNOWY PLOVER IN CALIFORNIA GARY W. PAGE and LYNNE E. STENZEL, Editors, Point Reyes Bird Observatory, 4990 Shoreline Highway, StinsonBeach, California94970 The westernrace of the Snowy Plover (Charadriusalexandrinus nioosus) breeds on the Pacific coast from southern Washington to southern Baja California, inland in Oregon, California, Nevada, Utah, Colorado, New Mexico, Kansas, Oklahoma and Texas, and along the coastsof Texas and northeasternMexico (AOU 1957). For many yearsornithologists believed that the number of Snowy Plovers breeding along the Pacific coast was decliningas developmentdestroyed suitable habitat. In May, June and July, from 1977 to 1980, Point Reyes Bird Observatory(PRBO) biologistsand volunteers conducted surveys of potential breeding habitat throughout Californiato gather informationon the distributionand abundanceof Snowy Plovers.This paper summarizesthe resultsof thosesurveys and the available data on the species'past abundanceand distribution.We attempt to define suitablebreeding habitat and to describethe effectsof human activitieson it. Detailedstudies of marked birdsundertaken by John and Jane Warriner at Pajaro Dunes on MontereyBay have been very helpfulin interpretingthe surveyresults. Their informationon migrationperiods, mid-breedingseason movements and the detection rate of birds on censuses is summarized in this paper. Detailed information on the occurrence of birds at specificsites is available in a report (Page and Stenzel 1979) on file with the California Department of Fish and Game in Sacramento. If readers have information indicatinggreater breeding numbers or know of breedingsites not mentioned here, we and the Departmentof Fishand Game encouragethem to contactus. METHODS The breedingsurvey covered the coastbetween the Golden Gate and the Oregon border in 1977, the remainder of the California coastand interior in 1978, and the ChannelIslands from 1978 to 1980. A listof all sitessurveyed on the mainlandcan be derivedfrom Appendices1 and 2. SusanPeaslee and Gary Page, with occasionalhelp from others,covered the coastfrom the Golden Gate to the Oregonborder between 16 May and 11 June 1977. From USGS topographicalmaps they locatedbeaches ap- Western Birds 12:1-40, 1981 1 SNOWY PLOVER BREEDING STATUS pearingto have sand or pebblehabitat above the high water mark. They surveyedthese beaches, starting in Marin County and proceedingnorth to Del NorteCounty. Additional censuses to recheckcertain beaches during the last3 dayswere taken in HumboldtCounty. On everybeach all openhabitat was checkedand heavilyvegetated or litteredareas were sampled.Physical characteristics,vegetation, debris cover, evidence of nest predators, and level of human disturbancewere recorded. The age and sex of Snowy Ploverswere determinedwhen possible.Adult maleswere distinguishedby their blackforehead, cheek and shoulderplumage; some males also had a distinctiverusty cap whichfemales lacked. Adult females were recognized by brownerfeathering in theseregions, and juvenilesby distinctivepale edgings on wing coverts.We attemptedto find the nestsof all birdswhose behavior suggestedthey might be incubating.Descriptions of each nest includedthe presenceor absenceof nearby objects,substrate type, distancefrom water and opennessof habitatwithin a 10 m radius. Broods of chicksalso were locatedand the sizeand numberof youngrecorded. In some areasit was impossibleto detectall plovers,and estimateswere made to partiallycorrect for missedbirds. We usedfour methodsto estimate the numberof breedingpairs: 1) total adultsdivided by 2; 2) totalpairs seen; 3) total singlefemales or maleswith nestsor broods;and 4) total pairsseen plussingle adults with nestsor broods.For eacharea the methodresulting in the highestnumber of pairswas used. From 8 May to 26 June and on 9 July 1978 Lynne Stenzeland Susan Peasleemade censusesor spotchecks of beaches,lagoons, river mouths and bars, bay shores,salt pans and saltworksalong the coastbetween Border Field, San Diego County, and the Golden Gate. Suitableareas for censuses were selectedfrom USGS topographicalmaps, referencesin the literature, and many unpublishedfield observations.Only in Los Angeles County, where we assumedbeach groomingactivities precluded the possiblityof nesting,did we knowinglyexclude some sand beach from our survey.Our findingson the similarlygroomed beaches of OrangeCounty and a descrip- tion of how groomingmakes plover nestingvirtually impossible are reported in the results.Although the surveyprogressed from southto north, therewas some back-trackingor skippingahead so that censusescould be made at heavilyused areas on weekdaysand at restrictedaccess areas on weekends. Survey methods were similar to those used in 1977 except that nest descriptionswere more detailed and included information on the topographicrelief within 1 and 10 m. A searchwas made for nestsand broodsto establishevidence of breedingin each locality, but to minimize survey time and disturbance,particularly in Least Tern ($terna albifrons) nestingareas, no attempt was made to locate all nests. The interiorsurvey lasted from 26 April until 13 July 1978. PhilipHender- sonfirst checked areas in the San JoaquinValley and aroundthe SaltonSea. He thengenerally moved northward, working alone until 1 Junewhen Gary Pagejoined him in Inyo County.Potential breeding areas were selected from USGS topographicalmaps, from ornithologicalliterature and from discus- sionswith personsfamiliar with the distributionof Californiabirds. Alkaline lakesparticularly were soughtout, but if theselacked standing water they were not surveyedbecause plovers were assumedto be absent. SNOWY PLOVER BREEDING STATUS Survey methodsvaried accordingto each area's physicalcharacteristics and accessibilityby car. At each area we took many photographsand notes on vegetationand physicalcharacteristics. We recordedthe age and sex of ploverswhenever possible although sometimes glaring, midday lighting or the largenumber of ploversencountered at one time made thistask impossi- ble. We attemptedto find some nestsor broodsin each area and described nestssimilarly to thoseon the coast. NancySpear conducted surveys of the breedingpopulations on four of the Channel Islands. On 25 and 26 April 1978 she searchedbeaches on San ClementeIsland and between19 and 21 May 1978, with Hal Spearand Bob Jackman, beacheson San NicolasIsland. From 13 to 18 July 1979 the Spearsand Mike Hill coveredmost of San Miguel Island'sbeaches, and on 22 July Bud Antonelissurveyed five additionalones. From 4 to 7 June 1980 the Spears surveyed beacheson the east end of Santa Rosa Island. On all surveysthey recordedthe numberand locationof all ploversand whenever possible,their age and sex. The historicalstatus of breedingSnowy Plovers throughout the statewas inferredfrom breeding records in the literature,from unpublished field notes, and from egg and nest collectionrecords and summarizedin Appendix 1. Sourcesof unpublishedrecords are listedin Appendix3. RESULTS I. CHANNEL ISLANDS NANCY L. SPEAR Basedon my surveys,at least 130 pairsof Snowy Ploversbreed on San Nicolas,San Migueland SantaRosa islands (Table 1). The speciesalso may breed on Santa Cruz Island, althoughthe lack of nestrecords from earlierin the centurywhen the islandwas regularly visited by eggcollectors (Kill pers. comm.), as well as the low numberof wide sandybeaches, does not attest well to the species'presence there. The remainingislands probably are not used by breeding plovers. As the following accounts illustrate, habitat availabilityrather than human disturbanceappears to be the major factor limitingbreeding distribution on the Channel Islands. San ClernenteIsland. This 34 km long, narrow islandlies 69 km south- southwestof PointFermin. Sandy beaches, once reported as commonalong the westand north sides,now existonly on the north;beach areas to the south,once reportedly sandy, are now primarilycovered with rocks.The Navy maintainsa smallbase on the islandand infrequentlyconducts large- scalemaneuvers covering the islandand usingbeaches as entrypoints. Snowy Plovers probably do not breed on this island. Howell (1917) reporteda few birdsin fall 1907, but therehave been no reportsduring the breedingseason. I surveyed40% of the coastlineby foot and observedfrom a distanceanother 40%. I foundno SnowyPlovers, nor muchappropriate breedinghabitat. That habitatwhich did existis at NorthwestHarbor, a beach usedfor recreationalpurposes as well as for minormilitary maneuvers. Island Foxes (Urocyonlittoralis clementae) and Common Ravens (Coruuscorax) occurbut I doubt that their presenceis a major reasonfor the absenceof plovers. SNOWY PLOVER BREEDING STATUS Santa Catalina Island. The 30 km long Santa Catalina Island is rugged, mountainousand hasprecipitous shores with few sandybeaches. It is heavily used by the public for boating and other recreation.Although Meadows (1934) reported Snowy Ploversas common on the beach at Howland's Landing, it is now generallyagreed that they do not breed regularlythere (Jones pers. comm.). San Nicolas Island. San Nicolas, the Channel Island farthest from the mainland, lies 98 km south-southwestof Point Mugu. It is 13 km long and 5 km wide. The Navy maintainsa basewith an airstripon the northeast side. Sandy beachesare common along the perimeter and are backed by dunes, bluffs and sandstonerock. Snowy Plovers are regular breeders; evidence dates back to the early 1900s when Willett (1912) found them "fairlycommon" and Howell (1917)