Diet of Breeding White-Throated and Black Swifts in Southern California
DIET OF BREEDING WHITE-THROATED AND BLACK SWIFTS IN SOUTHERN CALIFORNIA ALLISON D. RUDALEVIGE, DESSlE L. A. UNDERWOOD, and CHARLES T. COLLINS, Department of BiologicalSciences, California State University,Long Beach, California 90840 (current addressof Rudalevige:Biology Department, Universityof California,Riverside, California 92521) ABSTRACT: We analyzed the diet of nestling White-throated(Aeronautes saxatalis) and Black Swifts (Cypseloidesniger) in southern California. White- throatedSwifts fed their nestlingson bolusesof insectsmore taxonomicallydiverse, on average(over 50 arthropodfamilies represented), than did BlackSwifts (seven arthropodfamilies, primarfiy ants). In some casesWhite-throated Swift boluses containedprimarily one species,while other bolusesshowed more variation.In contrast,all BlackSwift samplescontained high numbersof wingedants with few individualsof other taxa. Our resultsprovide new informationon the White-throated Swift'sdiet and supportprevious studies of the BlackSwift. Swiftsare amongthe mostaerial of birds,spending most of the day on the wing in searchof their arthropodprey. Food itemsinclude a wide array of insectsand some ballooningspiders, all gatheredaloft in the air column (Lack and Owen 1955). The food habitsof a numberof speciesof swifts have been recorded(Collins 1968, Hespenheide1975, Lack and Owen 1955, Marfn 1999, Tarburton 1986, 1993), but there is stilllittle informa- tion availablefor others, even for some speciesthat are widespreadand common.Here we providedata on the prey sizeand compositionof food broughtto nestlingsof the White-throated(Aerona u tes saxa talis) and Black (Cypseloidesniger) Swifts in southernCalifornia. The White-throatedSwift is a commonresident that nestswidely in southernCalifornia, while the Black Swift is a local summerresident, migrating south in late August (Garrettand Dunn 1981, Foersterand Collins 1990). METHODS When feedingyoung, swifts of the subfamiliesApodinae and Chaeturinae return to the nest with a bolusof food in their mouths(Collins 1998).
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