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Home , Achilidae, Aerodramus, Aeronautes, Apodinae

DIET OF BREEDING WHITE-THROATED AND BLACK SWIFTS IN SOUTHERN CALIFORNIA

ALLISON D. RUDALEVIGE, DESSlE L. A. UNDERWOOD, and CHARLES T. COLLINS, Departmentof 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( 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 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 ,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). This bolus is passedto the nestlings.Each bolus, made up of an array of arthropodsloosely stuck together with saliva,can containonly a few large itemsor severalhundred small ones (Lack and Owen 1955, Collinsunpubl. data).We collectedfive bolusesfrom adultWhite-throated Swifts (subfamily )returning to nests in a man-madestructure in Glendale, Los AngelesCounty, California. All collectionswere madebetween 14:00 and 16:00 on 6 June 1997, 6 and 27 July 1999, and 21 June and 28 July 2000, in conjunctionwith bandingand studiesof nestlinggrowth at thissite. We collectedboluses infrequently in order to minimize disturbanceand possibleeffects on the studyof nestlinggrowth (Collinsunpubl. data). The dominantland-cover type within 15 km of the nestsite is urbanwith some areasof chaparral,coastal scrub, and montane hardwood forest (Davis et al. 1998).

Western Birds 34:209-215, 2003 209 DIET OF WHITE-THROATED AND BLACK SWIFTS

BlackSwifts and other membersof the subfamilyCypseloidinae carry a largermass of food in the esophagus,enabling them to return to provision the nestlingat longer intervals,perhaps only once or twice a day (Collins 1998, Marfn 1999). While we were bandingthe swifts,we took four samplesof this esophagealfood mass on 7 August 2000 from adults returning at dusk to nests at Lawlor Falls, located in the San Jacinto Mountainsnear Idyllwild,Riverside County, California. Foerster (1987)and Marfn (1999) previouslystudied Black Swifts at thissite. The dominantland- cover typeswithin 15 km of this site are chaparral,montane hardwood forest,ponderosa pine (Pinusponderosa), Jeffrey pine (P.jeffreyi), urban, coastalscrub, and annualgrassland (Davis et al. 1998). We storedthe food samplesin 70% ethanolfor later analysis.We sorted the samplesunder a dissectingmicroscope and, usingBorror et al. (1989), identifiedthe prey to order and, when possible,to family. Using an ocular micrometer,we measuredthe bodylength of eachprey item to the nearest 0.1 mm. Standarddeviations are reportedalong with mean values.

RESULTS AND DISCUSSION

White-throatedSwifts fed on a variety of prey with (bugs, hoppers; 41.86 %), Psocoptera(bark lice; 27.24%), and Diptera (; 21.94 %) being the dominant orders represented(Table 1). Over 50

Talkie ! ArthropodComposition of Five Bolusesof White-throated Swift Preya

Bolus

Orderand Family (or Superfamily) 1 2 3 4 5

Hymenoptera(ants, wasps, bees: 6.58%) Andrenidae -- 2 2 -- 2 Apidae 3 .... Braconidae -- -- 1 -- -- Eupelmidae -- 1 ------Formicidae -- -- 2 1 -- Halictidae -- -- 2 1 -- Ormyridae -- -- 1 -- -- Pteromalidae -- -- 10 2 -- Torymidae -- -- 1 4 -- SuperfamilyCynipoidea -- -- 1 -- -- Hemiptera(bugs, hoppers: 41.86% ) Achilidae -- 1 ------ -- 26 1 23 3 ------3 -- -- -- 4 -- -- Cicadellidae 1 -- 3 139 2 -- -- 2 7 -- -- -- 1 -- -- -- 1 ------(continued)

210 DIET OF WHITE-THROATED AND BLACK SWIFTS

Table 1 (Continued)

Bolus

Orderand Family (or Superfamily) 1 2 3 4 5

Reduviidae -- -- 4 -- -- ------1 -- -- -- 1 -- -- SuperfamilyFulgoroidea -- -- 1 -- -- Unknown -- -- 5 -- -- Diptera(flies 21.94% ) Agromyzidae -- 1 ------Bibionidae -- -- 10 -- -- Bombyliidae .... 5 Calliphoridae -- -- 1 -- -- Cecidomyiidae -- 1 ------Chloropidae ------1 -- Conopidae -- -- 1 -- -- Empididae .... 5 Muscidae -- 1 2 2 -- Oestridae .... 1 Pipunculidae -- 1 1 -- 1 Scenopinidae -- -- 2 -- -- Sciaridae ------1 -- Sciomyzidae .... 1 Simuliidae .... 1 Sphaeroceridae ------1 -- Stratiomyidae -- -- 3 -- -- Syrphidae -- -- 1 -- 3 Tachinidae -- -- 4 -- 1 Tephritidae -- -- 1 -- -- Therevidae -- -- 32 -- 31 Trixoscelididae .... 1 SectionAcalyptratae -- 1 ------Unknown -- 2 ------Coleoptera(beetles: 1.28%) Elateridae -- -- 1 -- -- Melyridae -- -- 1 -- 1 Anobiidae -- -- 2 -- -- SuperfamilyCurculionoidea -- -- 2 -- -- Psocoptera(bark lice: 27.24%) Liposcelidae -- -- 122 22 3 Unknown .... 2 Lepidoptera(butterflies, moths: 0.18%) Unknown .... 1 Thysanura(silverfish: 0.18%) Lepismatidae .... 1 Araneae(spiders: 0.73%) Unknown -- -- 3 -- 1

Total 4 38 231 208 66 aValuesare the numberof individuals(by family)for each bolus.The percentageof orders from the pooled bolusesis also given. The orders Hemiptera and Homopteraof Borroret al. (1989) are combinedunder the Hemiptera.

211 DIET OF WHITE-THROATED AND BLACK SWIFTS differentfamilies of arthropodswere identifiedfrom among the 547 prey items containedin the 5 boluses(Table 1). The mean number of individuals per boluswas 109.4 + 103.1, range 4 to 231. Taxonomicdiversity also variedfrom bolusto bolus.For example,one boluscontained three individu- als of the familyApidae (bees)and one memberof the family Cicadellidae (),while another containedrepresentatives of 33 familiesin 6 orders.Two bolusescontained many individualsbelonging almost entirely to a singletaxon (in one caseCicadellidae, in the other Psocoptera).In other bolusesthese same taxa were representedonly minimally(Table 1). The sizeof White-throatedSwift food itemsalso varied extensively. Mean bodylength of prey itemsin millimeterswas 3.9 + 2.0, range0.7 to 16.7, in the pooled sampleof 5 boluses(Figure 1). As expected,some boluses containedfewer largeinsects, while othershad many smallerones (Table 1). Large, heavy-bodied,or winglessinsects were hardlyrepresented, as all prey itemswere gatheredin the air columnby flyingadult swifts. However, two individualsof the heavy-bodiedsuperfamily Curculionoidea (weevils) were captured,as wasone smallthysanuran (silverfish), the latterperhaps having been carried aloft by wind currentsalong with a singleballooning spider. Glick(1939) foundthysanurans at altitudesof 330 m, with a singleindividual capturedat over2500 m. Many othersmall, weakly flying recorded in these bolusesmay have similarlybeen passivelycarried aloft by air currentsto the altitudesat whichWhite-throated Swifts typically forage.

2O0

18O

160

t40

120

t 00

8O

60

I I I I I I I [ I I ]]I I --I• I• I I-- I 1 2 3 4 5 6 7 8 9 10 1t 12 13 t4 15 t6 17

Pre• Length (mm) FigureI. Distributionof arthropodbody lengths in combinedfood boluses of White- throatedSwifts (n = 5) and BlackSwifts (n = 4), pooledin I-ram sizeclasses. Size classescontain prey items0.,5 mm greaterthan and lessthan the defininglength.

212 DIET OF WHITE-THROATED AND BLACK SWIFTS

The BlackSwift samples had a meannumber of preyitems of 51.5 + 9.6 and were much lessdiverse taxonomically than the White-throatedSwift boluses:94% of the prey items were of the family Formicidae(winged reproductive ants), species Solenopsis xyloni and Crernatogaster rnorrnonurn(Table 2). Also representedwere severalhemipterans (bugs, hoppers)and dipterans(flies; Table 2). The meanbody length in millimeters of all of the prey itemsin the pooledsample was 9.5 + 2.2, range 2.7 to 12.8 (Figure 1). Previousstudies of the White-throatedSwift ranked only the relative abundanceof insectorders in the diet and did not quantifythe numbersof eachprey type or provideidentification below the levelof order(Bent 1940, Hespenheide1975). The high taxonomicdiversity of prey items and extremevariation from bolusto bolusagree with datafrom previousstudies of other swifts (Lack and Owen 1955, Collins 1968, 1980, Bull and Beckwith 1993, Tarburton 1986, 1993). It also suggeststhat White- throated Swifts, like most swifts in the subfamilies Chaeturinae and Apodinae,are opportunisticforagers, quick to exploitlocalized abundances of prey, and readilyconsume any availableprey within a preferredsize range.Within the Apodinae, White-throated Swifts (body mass 32.1 g; Ryan andCollins 2000) took,on average,larger prey than the smallerHorus Swift (Apushorus: 27.9 g; Collins1980) and smallerprey than the substantially larger ( apus: 42.8 g; Gladwinand Nau 1964) and Alpine Swift (Apusmelba: 108 g; Cramp 1985). The BlackSwift appears to be a morespecialized forager, concentrating on patchflydistributed swarms of lipid-richinsects in the form of winged reproductiveants. These swarms emerge every two to fourweeks from June throughAugust, typically a few daysafter rainfall(Solenopsis spp., Hooper

Table 2 ArthropodComposition of Four Samplesof BlackSwift Preyø

Sample Orderand Family 1 2 3 4

Hymenoptera(ants, wasps, bees: 94.66%) Formicidae 51 42 38 64 Hemiptera(bugs, hoppers: 4.37%) Cicadellidae -- -- 4 -- -- -- 1 -- -- 1 -- -- Unknown 3 ------Diptera(flies: 0.97%) Culicidae -- -- 1 -- Chironomidae -- -- 1 -- Total 54 43 45 64

aValuesare the numberof individuals(by family) for eachsample. The percentageof arthropod ordersfrom the pooledsamples is also given. The ordersHemiptera and Homoptera of Borror et al. (1989) are combinedunder the Hemiptera.

213 DIET OF WHITE-THROATED AND BLACK SWIFTS

Table 3 Characteristicsof BlackSwift Prey Revealedby Four Studies

Meanprey Numberof Numberof length(mm) preyitems Range % Formicidae samples Source

9.9, 10.2a 289 7.3-12.9 98% 2 Foerster(1987) 7.4 1154 1.8-14.5 91% 10 Marin(1999) 9.5 206 2.7-12.8 94% 4 Thisstudy 8.66 276 2.0-12.0 72% 2 Collinsand Landy (1968) aSeparatemeans for each of two samples.

1995) The data from this studyare in closeagreement in both taxonomic distributionand averageprey size with previoussamples obtained at the LawlorFalls colony (Table 3) between1982 and 1985 (Foerster1987, Marfn 1999), aswell as with samples from Black Swifts nesting in Veracruz,Mexico (Collinsand Landy 1968). These data representthe first caseof replicate samplingof the diet of a swiftat the samelocation over a periodof many years. Such replicationhelps avoid misinterpretationdue to short-term seasonalor annualvariation. Other speciesof swiftsin the Cypseloidinae showa similartendency to concentratetheir foraging on lipid-richswarming reproductiveinsects like ants and termites(Collins 1968, Whitacre 1991, Marin and Stiles 1992). They may also adjusttheir breedingseasons to coincidewith the time this resourceis maximallyavailable (Marfn 1999). Additionalstudies of other speciesof swiftsare neededto clarifypossible variationin diet by season,from year to year,from locationto location,and under varyingweather conditions.

ACKNOWLEDGMENTS

We are indebtedto the severalpeople, M. Amalong, P. Collins, J. Fitch, S. Langdon,N. Mudry, and T. Ryan, who participatedin the bandingand collectingof food samples,and to Peter H. Bloom,who firstlocated the Glendalestudy site and calledit to our attention.Roy Snellingof the NaturalHistory Museum of LosAngeles County graciouslyidentified the ant speciesfound in the Black Swift samples. Studentsof John Rotenberry,University of California,Riverside, provided valuable feedbackon the manuscript.Banding activities were conductedunder masterbird- bandingpermit 08707 issuedto C. T. Collins.Evelyn Bull and Kathy Molina reviewed earlierdrafts of the manuscript.

LITERATURE CITED

Bent,A. C. 1940. Life historiesof Americancuckoos, goatsuckers, hummingbirds and their allies. U. S. Natl. Mus. Bull. 176. Borror, D. J., Triplehorn, C. A., and Johnson,N. F. 1989. An Introductionto the Studyof Insects.Harcourt Brace, London. Bull,E. L., and Beckwith,R. C. 1993. Diet and foragingbehavior of Vaux'sSwifts in northeasternOregon. Condor 95:1016-1023. Collins,C. T. 1968. The comparativebiology of two speciesof swiftsin Trinidad, West Indies. Bull. Fla. State Mus. 11:257-320.

214 DIET OF WHITE-THROATED AND BLACK SWIFTS

Collins,C. T. 1980. Notes on the food of the Apus horus in Kenya. Scopus4:10-13. Collins,C. T. 1998. Fooddelivery and chickprovisioning in cypseloidineswifts. Bull. Br. Ornithol. Club 118:108-112. Collins,C. T., and Landy, M. J. 1968. Breedingof the Black Swift in Veracruz, Mexico. Bull. S. Calif. Acad. Sci. 67:266-268. Cramp, S., ed. 1985. The Birds of the Western Palearctic,vol. 4: Terns to Woodpeckers.Oxford Univ. Press,Oxford, England. Davis,F. W., Stoms,D. M., Hollander,A. D., Thomas,K. A., Stine, P. A., Odion, D., Borchert, M. I., Thorne, J. H., Gray, M. V., Walker, R. E., Warner, K., and Graae, J. 1998. Gap analysisof mainland California: An interactiveatlas of terrestrialbiodiversity and landmanagement (compact disk). Biogeography Lab, Univ. of Calif., SantaBarbara. Available http://www.biogeog.ucsb.edu/projects/ gap/gap_cdrom.html. Foerster,K. S. 1987. The distributionand breedingbiology of the Black Swift (Cypseloidesniger) in southernCalifornia. M.S. thesis,Calif. StateUniv., Long Beach. Foerster,K. S., and Collins,C. T. 1990. Breedingdistribution of the BlackSwift in southern California. W. Birds 21:1-9. Garrett, K., and Dunn, J. 1981. Birdsof SouthernCalifornia: Status and Distribution. Los AngelesAudubon Soc., Los Angeles. Gladwin,T. W., andNau, B. S. 1964. A studyof swiftweights. Br. Birds57:344-356. Glick,P. A. 1939. The distributionof insects,spiders, and mites in the air. U.S. Dept. Agric. Tech. Bull. 673:1-150. Hespenheide,H. A. 1975. Selectivepredation by two swiftsand a swallowin Central America. Ibis 117:82-99. Hooper, L. M. 1995. The biologyof the southernfire ant, Solenopsisxyloni (McCook), and its predation of the California Least Tern, Sterna antillarum browni (Mearns).M. S. thesis,Univ. of Calif., Riverside. Lack, D., and Owen, D. F. 1955. The foodof the Swift. J. Ecol. 24:120-136. Marfn,M. 1999. Food,foraging, and time of breedingof the BlackSwift in California. Wilson Bull. 111:30-37. Marfn, M., and Stiles,F. G. 1992. On the biologyof five speciesof swifts(Apodidae, Cypseloidinae)in CostaRica. Proc. W. Found.Vert. Zool. 4:287-351. Ryan,T. P., and Collins,C. T. 2000. White-throatedSwift (Aeronautessaxatalis), in The Birdsof North America (A. Poole and F. Gill, eds.),no. 526. BirdsN. Am., Philadelphia. Tarburton, M. K. 1986. The food of the White-rumped ( spodiopygius)in Fiji. Notornis33:1-16. Tarburton, M. K. 1993. The diet of the White-rumped Swiftlet (Aerodramus spodiopygius)in Queensland'ssavannah. Avocetta 17:125-129. Whitacre, D. F. 1991. Studies of the ecology of the White-collared Swift (Streptoprocnezonaris) and White-napedSwift (Streptoprocnesemicollaris) and of patternsof adaptationamong the swifts(Aves: Apodidae). Ph.D. disserta- tion, Univ. of Calif., Davis.

Accepted 5 February 2004

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