170 ShortCommunications [Auk,Vol. 102 tive parametersof this species.We recommendspe- KADLEC, J. A., & W. H. DRURY. 1968. Structure of cial care in employing these methods for nest ex- the New EnglandHerring Gull population.Ecol- amination and suggest that other types of nest ogy 49: 644-676. perturbationin other speciesmay have similar, but M¾1•ES,M.T. 1957. Clutch size and laying datesin as yet unquantified, results. Cliff Swallow colonies. Condor 59: 311-316. We thank the Texas Memorial Museum and De- NEWNAM,J. C. 1980. The breeding biology of the partment of Zoology of The University of Texas at Cliff Swallow (Petrochelidonpyrrhonota) in Burie- Austin and the National GeographicSociety for fi- son and Washington counties, Texas. Unpub- nancial support. We also extend gratitude to the Rob lished M.A. thesis.College Station, TexasA&M and Bessie Welder Wildlife Foundation and its direc- Univ. tor, Dr. JamesG. Teer, for providing housingaccom- NXCE,M.M. 1937. Studiesin the life history of the modations.J. Ollason,C. Brown, J. Reddell, A. Rug- Song Sparrow, I. Trans. Linnaean Soc.New York: gles, J. Wiens, and an anonymousreferee contributed !-247. to the development of the manuscript. OLLASON,J. C., & G. M. DUNNET. 1980. Nest failures in the Fulmar: the effect of observers. J. Field LITERATURE CITED Ornithol. 51: 39-54. PARSONS,K. C., & J. BURGER. 1982. Human distur- CAIRNS,D. 1980. Nesting density, habitat structure bance and nestling behavior in Black-crowned and human disturbance as factors in Black Guil- Night-Herons. Condor 84: 184-187. lemot reproduction. Wilson Bull. 92: 352-361. ROBERT,H. C., & C. J. RALPH. 1975. Effects of human CHAPMAN,B. R. 1973. The effectsof nest ectopara- disturbance on the breeding successof gulls. siteson Cliff Swallowpopulations. Unpublished Condor 77: 495-499. Ph.D. dissertation. Lubbock, Texas, Texas Tech SAFINA,C., & J. BURGER.1983. Effects of human dis- Univ. turbance on reproductive successin the Black ELLISON, L. N., & L. CLEARY. 1978. Effects of human Skimmer. Condor 85: 164-171. disturbanceon breeding of Double-crestedCor- $IKES, P. J., & K. A. ARNOLD. In review. Movement morants. Auk 95: 510-517. and mortality estimatesof Cliff Swallows in Tex- EMLEN,J. T., JR. 1952. Socialbehavior in nesting as. Cliff Swallows. Condor 54: 177-199. TREMBLAY,J., & L. N. ELLISON. 1979ß Effects of hu- ß 1954. Territory, nest building, and pair for- ' man disturbanceon breedingof Black-crowned mation in the Cliff Swallow. Auk 71: 16-35. Night-Herons. Auk 96: 364-369. GILLFIT, W. H., Jß L. HAYWARD, JR., & J. F. STOUT. WELTY,J. C. 1975. The life of birds. Philadelphia, 1975. Effectsof human activityon eggand chick W. B. Saunders Co. mortality in a Glaucous-winged Gull colony. WERSCHKUL,D. F., & E. MCMAHON. 1976. Some ef- Condor 77: 492-495. fects of human activities on the Great Blue Her- GOERING,D. K., & R. CHERRY.1971. Nestling mor- on in Oregon. Wilson Bull. 88: 660-662. tality in a Texas heronry. Wilson Bull. 83: 303- WITHERS,P.C. 1977. Energetic aspectsof reproduc- 305. tion by the Cliff Swallow. Auk 94: 718-725. HUNT, G. L., JR. 1972. Influence of food distribution and disturbanceon the reproductive successof Received7 February1984, accepted7 June1984. Herring Gulls. Ecology 53: 1051-1061.

Snail Kite Kleptoparasitismof Limpkins

BRUCE W. MILLER • AND RONALD Lß TILSON 2 •OklahomaCity Zoo,Oklahoma City, Oklahoma73111 USA, and 2MinnesotaZoological Garden, Apple Valley,Minnesota 55124 USA

Kleptoparasitismis defined as the stealing of food port our observationsof kleptoparasitismof Limpkins from an individual by another individual (Roth- (Aramusguarauna) by Snail Kites ( Rostrhamussociabilis) schild and Clay 1952). Interspecifickleptoparasitism at shallow lagoons near Crooked Tree (17045'N, occurs in many animal groups but is particularly 88ø35'W),Belize, Central America,from 7 to 21 May widespreadamong birds, especiallywhen individu- 1983. We relate the occurrenceof this parasitic be- als of different speciesregularly congregateat feed- havior to an apparently diminishing resourcebase ing areas(Brockman and Barnard1979). Here we re- shared by these two species. January1985] ShortCommunications 171

SnailKites feed almost exclusively on Pomaceasnails kleptoparasitism.During the period when Snail Kites (Beissinger1983, Snyder and Kale 1983)captured in werepirating snails, they alsowere searchingfor and flight by extendinga foot and grabbingthe mollusk finding snails in the shallow waters. near the water surfacewith their long toes.The kite A general model (Brockmann and Barnard 1979) then perchesto extractthe body from the shell with for the ecologicalconditions that facilitate the evo- its thin, sharplyhooked bill. Two modesof hunting lution and expressionof kleptoparasitismrequires a havebeen described (Snyder and Snyder1969, Hav- large number of availablehosts; food itemsto be pi- erschmidt1970, Beissinger 1983). Still-hunting kites ratedshould be relativelylarge, numerous, and high- visuallysearch from a perchand capturesnails after ly visible; the host should have predictablehabits; a short,quick flight; course-huntingkites fly 3-5 m and kleptoparasiticbehavior should occurmore fre- abovethe water, usuallyfacing into the wind, and quently when the food resourcebase is decreasing scanfor prey. Course-huntingwas the prevalentfor- in availability.At CrookedTree theseconditions were aging pattern of the kite population (>50) at Crook- met by the presenceof numerousLimpkins, the rel- ed Tree Lagoon. When the lagoon's water level atively large size and conspicuousnessof Pomacea dropped dramatically during a 2-week period, leav- snails,the visibility of foraging Limpkins and their ing an estimatedone-third to one-half of the surface prolongedextraction procedure once a snail was cap- areadry, kites useda third, and previouslyunre- tured, and the suspecteddecrease in food availability ported,hunting method:kleptoparasitism of Limp- when the water level of the lagoon dropped. Most kins. studiesof kleptoparasitismhave been made at or near Many aquatic and shore birds occur in Crooked breeding colonies (Brockmann and Barnard 1979). Tree Lagoon(Tilson and Miller 1983).Limpkins were Theseobservations support the contention that food especiallyabundant and were widely distributed thievery may emerge whenever individuals of dif- alongthe lagoon'sedges and islandscreated by the ferent speciesregularly congregate at feedingareas. lower water level. At these sites,Limpkins fed in We were supportedby the Oklahoma Zoological typicalmanner (Snyder and Snyder1969). Trust,the OklahomaCity Zoo,and the Vulture Study As the lagoondried, the availabilityof snailsmay Group. We thank J. Jex for field assistanceand S. R. havedeclined. We basethis assumptionon the ob- Beissinger, J. Clinton-Eitniear, E. Henckel, and D. servationsthat the Limpkins spacedthemselves at Mock for commentson this manuscript. greater distances (50-60 m) from each other and showedmore aggressiveinteractions when individ- LITERATURE CITED uals approachedeach other. We did not measuresnail availabilityat the lagoon(e.g. Beissinger1983), but BEISSINGER,S. R. 1983. Hunting behavior,prey se- the frequencyof probing appearedto increaseand lectionand energeticsof Snail Kitesin Guyana: successfulextraction of snailsby Limpkinsdecrease consumerchoice by a specialist.Auk 100:84-92. aswater levelsdropped, possibly indicating reduced BROCKMANN,H. J., & C. J. BARNARD.1979. Klepto- food availability. parasitism in birds. Anim. Behav. 27: 487-514. At this time we first noted kleptoparasiticinterac- HAVERSCHMIDT, F. 1970. Notes on the Snail Kites in tions. On 8 separateoccasions we observeda Snail Surinam. Auk 87: 580-584. Kite perchingon a smallsnag and surveyingthe for- ROTHSCHILD,M., & T. CLAY. 1952. Fleas, flukes and agingLimpkins. When a Limpkin pickedup a snail, cuckoos. London, Collins. the kite swoopedin from behind,struck the Limp- SNYDER,N. F. R., & H. W. KALE, II. 1983. Mollusk kin, and stolethe snail from the Limpkin'sbeak or predation by Snail Kites in Colombia. Auk 100: pickedit up when droppedon the vegetativemat. 93-97. The kite immediatelyflew back to its perch and ex- ., & H. A. SNYDER.1969. A comparativestudy tractedthe snail.Limpkins reacted by callingloudly of mollusk-predationby Limpkins, Everglade and flapping their wings but never attemptedto re- Kites, and Boat-tailedGrackles. Living Bird 8: trieve the snail. Kites were unsuccessful in a dozen 177-223. piracyattempts when they flew towardsa Limpkin TILSON, R. L., & B. W. MILLER. 1983. Field recon- fromthe frontor theside. On eachattempt the Limp- naissanceof the Lesser Yellow-headed Vulture, kin sawthe oncomingkite and escaped.Snail Kites centralBelize. Vulture StudyGroup, Spec. Rept. did not pursuefleeing Limpkins. This suggeststhat surprisefrom behind may be essentialto effective Received7 February1984, accepted 19 June1984.