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January1985] ShortCommunications 175 lieyes this record likely refers to the Whimbrel (N. LITERATURE CITED phaeopus). As far as we know, the presentphotographic evi- AMERICAN ORNITHOLOGISTS' UNION. 1983. Check-list dence represents the first confirmed record of the of North American , 6th ed. Baltimore, Long-billed Curlew for continental South America. Amer. Ornithol. Union. One copy of the photograph has been depos- FFRENCH,R. 1973. A guide to the birds of Trinidad ited in the Colecci6nOrnitologica Phelps in Caracas, and Tobago. Wynnewood, Pennsylvania, Liv- and one is in the OrnithologicalCollection, Depart- ingston Publ. Co. ment of BiologicalSciences, University of Montreal. MEYERDE $CHAUENSEE, R. 1970. A guide to the birds We thank Gedio Marin and Rosaufo Navarro for of South America. Edinburgh, Oliver & Boyd. providing information from their field books. This ß & W. H. PHELPS,JR. 1978. A guide to the note is a by-productof ecologicalresearch supported birds of . Princeton, New Jersey, Princeton Univ. Press. by the Natural Sciencesand Engineering Research Council of Canada, the Quebec Department of Inter- Received9 April 1984, accepted27 June1984. governmentalAffairs, the Universityof Montreal,and the University of Oriente.

Survivorship in : Is Predation Important?

RICHARD $. MILLER • AND C. L. GASS2 •Schoolof Forestryand Environmental Studies, Yale University, New Haven, Connecticut06511 USA, and 2Departmentof Zoology,University of BritishColumbia, Vancouver, British Columbia V6T 1W5, Canada

The traditional optimal foraging modelsreviewed tory measurementsand experiments (Hainsworth by Pyke et al. (1977) and Krebs (1978) focusedon 1981). It is an energy-limited system(Carpenter 1978, proximal factorsthat influence energeticcosts and Gassand Montgomerie 1981) in which the amount benefits in terms of their contributions to net rate of and energy content of the food is easily measuredin energy gain. In general, these modelshave assumed the field, the food sourcesare stationary and con- that the fitness value of foraging tactics is deter- spicuous,and the foraging behavior of thesediurnal mined primarily by proximal factorssuch as quality birds is easilyobserved (Gass and Montgomerie1981). and distribution of food patches,although a variety In this paper we review the literature of predation of other factorssuch as cryptic prey, territory de- on hummingbirdsfor evidenceof consistentamounts fense, or predation risk also may significantly affect or patterns that would indicate that predation is a feeding rates (Caraco 1980). For example, stickle- significantmortality factor. backs(Gasterosteus aculeatus) alter their foraging tac- Observedpredation.--Table 1 shows the North tics and feeding rates when predators are present American recordsof predation on "adult" humming- (Milinski and Heller 1978), and feeding Blue Tits birds (of unknown age from fledging) that are avail- (Paruscaeruleus) increase their scanningrates as pre- able from the literature. This does not include 4 rec- dation risk increases(Leuchem 1983). ords of hummingbirds caught in webs In a more general context, McCleery (1978) re- (Danforth 1921, Woods 1934, Stott 1951, Hoyt 1960) viewed attemptsto study how time budgetsand be- and one attackedby wasps(Grant 1959). The 13 re- havior sequencesare influencedby costsand benefits corded instancesof predation involve 4 identified under conditions of conflicting demands. He con- speciesof hummingbirds and a variety of predators cluded that to be accurate and predictive, optimiza- (9), including insects,amphibia, and birds. Most of tion models and their associated decision rules must the instanceslisted in Table 1 occurredin flower gar- account for elements in the environment that con- dens (7) or at feeders (2). In the cases strain performance and significantly affect the of predationby frogs and birds, the hummingbirds expressionof particular choices. were eaten, but not by the mantids. An advantagein the study of the behavioralecol- It is especially noteworthy that there are only 3 ogy of -feedingbirds, and hummingbirds in recordedinstances of predationby raptors,and these particular, is the relative simplicity of the foraging caseswere distributedamong 3 raptor .When systemand the extent to which it lends itself to rea- Lowery (1938) found the remains of a -throated sonably direct and uncomplicatedfield and labora- Hummingbird (Archilochuscolubris) in the stomachof 176 Short Communications [Auk, Vol. 102

T^BLE1. North American records of predation on hummingbirds.

Predator Hummingbird Instances Source Insecta Mantidae Tenoderaardifolia Archilochuscolubris 2 Butler 1949,Hildebrand 1949 Amphibia Ranidae Ranapipiens A. colubris 3 Norris-Elye 1944 Ranasp. Selasphorusrufus 1 Morgan 1947 Aves Accipiterstriatus Calypteanna 1 Peters 1963 Falconidae Falcocolumbarius A. colubris 1 Lowery 1938 Falcosparverius A. colubris 1 Mayr 1966 Cuculidae Geococcyxcalifornianus A. alexandri 1 Spofford1976 Tyranninae Myiarchustyrannulus S. rufus 1 Gamboa1977 Icterinae Icterusgalbula Selasphorussp. 1 Ashman1977 A. colubris 1 Wright 1962

a Pigeon Hawk (Falcocolumbarius), he conductedan larger, relatively slow-flying Booted Racquet-tails extensive searchof the files of the Bureau of Biolog- (Ocreatusunderwoodii). Although this pair of falcons ical Survey and found that this was the first record killed a wide variety of mammals,birds, reptiles, am- of a hummingbird in the stomachof any , all phibia,and insects(78 species),birds constituted 71.8% raptorsincluded. It could, of course,be argued that of the species(56) and 74.8% of the individuals (163) most recorded instancesof predation on humming- in the total recorded diet. Of the total birds, 17.8% of birds are from gardens or at hummingbird feeders the speciesand 20.8% of the individuals were hum- becauseof the higher probability of predation being mingbirds. Stiles (1978) commented that Falcons observed in such situations, and that natural preda- apparentlyare generalists,with no behavioralor oth- tion is important but seldom seen. This argument is er specializations for preying on hummingbirds. not particularly convincing in view of the exponen- However, considering the fact that the single pair tial increasein field researchon hummingbirds in observedby Beebe(1950) captured 4 speciesof , the lastdecade (Montgomerie and Gass1980) and the 8 species of swifts, 2 species of swallows, and 10 lack of a correspondingincrease in reports of pre- speciesof hummingbirdsin flight indicatesthat they dation. are effectivepredators on fast-flying, small prey. The fact that there have only been 13 reports of Beebe(1950) estimatedthat this pair of Bat Falcons predation on hummingbirds since the first by Low- killed at least 600 birds and bats during his 164 days ery in 1938,that manyof theseinstances can be clas- of observation.On the basis of their proportion in sified as unusual or even bizarre, and that there is the recorded sample, this would include over 100 no consistentpattern in predator-prey relationships hummingbirds. It would seem, therefore, that Bat or amounts of predation suggeststhat these are iso- Falconscould be significanthummingbird predators lated incidents, and that hummingbirds in North in the tropics, even though they are not necessarily Americado not have "natural predators"in the usual hummingbird specialists.Bat Falconsare quite com- sense. mon over most of their latitudinal range of 48ø , from The only systematicpredation on hummingbirds central to southern and northern Ven- that has been reported in the literature is from the ezuela (Beebe1950), which includesthe geographical tropics,by Bat Falcons(Falco albigularis). Beebe (1950) distributions of many species of hummingbirds monitored the activities of a pair of Bat Falcons at (Greenewalt 1960). the Rancho Grande in the National Park at Aragua, Stiles (1978) has postulated,on the other hand, that Venezuela, for 5« months, during which time they the (Accipitersuperciliosus) may be a hum- were seento kill and/or bring to the 34 individ- mingbird specialist.This small, fast-flying uals of 10 speciesof hummingbirdsranging from the apparently locatesperches that are frequently used small Chaetocerusjourdanii (69 mm total length) to by territorial hummingbirds and waits in conceal- January1985] ShortCommunications 177 ment to capture them when they return to perch. (Parusatricapillus) based on recapturesor resightings While this hypothesisis plausible,it is basedon only and found a considerablediscrepancy between the one observation of a successful attack on tza- two sources of data; the same method of estimation catl and a few unsuccessfulattacks on Chalyburauro- gave a mean life span of 2.6 yr from resightingsand chrysia;more data will be required to establish its 1.7 yr from recaptures.They also found that older validity. There is no evidencethat predationby Bat birds tended to avoid recapture more than young Falcons,Tiny Hawks, or other predatorsin the win- birds, which could be a particularly serious factor tering areasof North American immigrantsaffects with hummingbirdsbecause they quickly learn to their mortality rates or behaviors,but this is a pos- avoid mist nets (pers.obs.). This suggeststhat the life sible factor that should be considered. spanscalculated by Calder et al. (1983)from recap- Naturallongevity.--If predation plays a minor role tures might be an underestimate. in the mortality rates of adult hummingbirds, one More importantly, the oldestbroad-tails recorded might expect that this would be reflected in their so far seem remarkablylong-lived, comparedwith natural longevities. From available equations for predictionsbased on body mass,and as it was only variablesusing hypotheticalbody massesand scaling during 1979and 1980 that mostof the local popula- components,Brown et aL (1978) calculatedthat a hy- tion was banded(Calder et al. 1983),it is likely that potheticalhummingbird weighing 3 g should have recordednatural longevity will be extended further a life spanof 5.5-5.8 yr and a 4-g bird shouldhave a in the near future. If predation on adult humming- life spanof 5.8-6.1 yr (seealso Lindstedt and Calder birds were important, we would not expect maxi- 1976, 1981).These predictions assume a balanceden- mum life spansthat are so much greaterthan phys- ergy budgetand do not includethe possiblenegative iological expectations. effects of extrinsic factors such as disease, , Other sourcesof mortality.--W. A. Calder (pers. weather, or predation on life expectancy.In other comm.) used the data in Calder et al. (1983) to cal- words,this is essentiallyan estimateof physiological culate a differenceof 6.1 yr between physiological longevity basedon energy requirementsand expen- life span and the realized longevity of the Broad- ditures,without regardto other mortalityfactors that tailed Hummingbirdsat RMBL. While there is lim- might affectlife expectancy. ited evidence of adult hummingbird mortality due Hummingbirdshave not been banded as system- to migration fatalities,disease, and accidents(W. A. atically asmost other birds, and in any caseit is high- Calder pers. comm.), nesting failure may be a very ly unlikely that band recoverieswould occurexcept important sourceof mortality in hummingbird pop- through recapture.Consequently, return rates are ulations. Baltosser(1983) monitored 148 nestsof Black- usuallylow, and relatively little is known aboutthe chinned (Archilochusalexandri), Broad-billed (Cyan- natural longevities of hummingbirds. Clapp et aL thuslatirostris), Violet-crowned (Amazilia•oliceps), and (1983) listed longevity recordsfor only 4 species:Ar- Costa's( costae) hummingbirds and found a chilochuscolubris (6 yr, 3 months),Calypte anna (6 yr), 59% failure due to nest abandonment, mortality, Selasphorusplatycercus (7 yr, 1 month),and S. sasin(3 and nestlingmortality. The mostserious factors were yr, 11 months)based on recapturesof birds of un- eggand nestlingpredation, which accountedfor 58.6 known age at the time of banding. and 25.3% of the observed losses. The most important and only systematicanalysis Calder et al. (1983) defined "nesting success"as of the natural longevity and populationdynamics of fledging of at least 1 young from a nest in which hummingbirdsis a study of Broad-tailedHumming- were laid (mean clutch size = 2). During their birds (S. platycercus)banded between 1972 and 1980 study nesting successvaried from 18 to 67% (mean = at the RockyMountain BiologicalLaboratory (RMBL) 46% of all ). at Gothic, Colorado (Calder et al. 1983). These birds There are no data available on the period between showedstrong site-fidelity,with recapturerates be- fledgingand self-sufficiency,but this couldbe an ex- tween breeding seasonsas high as 70% for females tremelycritical period in the early life of a bird with and 27%for males.During this study,2 femaleswere such high energy requirements. recapturedthat were at least8 yr old and 1 male that Conclusion.--On the basis of the available data, we was at least 5 yr old (age unknown when banded). concludethat the observedpredation on adult hum- During the 1983 field season,2 more females of the mingbirdsin temperatehabitats shows no consistent sameage were recaptured,bringing the total number amount or pattern that would indicate that predation of 8-yr-old birdsto 4 (D. Inouye pers.comm.). Calder is a significantrisk factor, and biologistshave been et al. (1983) calculatedthat the mean age of females justifiedin ignoring predationin the decisionrules recapturedin 1979 and 1980 was 3.1 yr (n = 58) and specified for these species.This conclusion ignores for males2.6 yr (n = 23). In a preliminary report on the importanceof nestling mortality (Calder 1973, the RMBL hummingbird population,Waser and In- Calder et al. 1983)and is basedsolely upon observed ouye (1977) estimateda mean life span of at least 2.5 ratesof predationon foragingadults. It is, however, yr for both sexescombined. quite possiblethat this assumptionwould be unjus- Elder and Zimmerman (1983) comparedestimates titled for hummingbirds in the Neotropics, where of the mean life spansof Black-cappedChickadees Bat Falcons,Tiny Hawks, and other predatorsmight 178 ShortCommunications [Auk,Vol. 102 imposesignificant mortalities that couldbe reflected HILDEBRAND,E.M. 1949. Hummingbird captureby in foraging strategies. a praying . Auk 66: 286. We are grateful to Karen PriceßGlenn Sutherlandß HOYT,S.F. 1960. A hummingbirdin difficulty.Bird- and StephanTatum for critical suggestionsand to Bill Banding 31: 91. Calder and Larry Wolf for helpful commentson an KREBS,J. R. 1978. Optimal foraging:decision rules earlier draft of the manuscript. for predators.Pp. 23-63 in Behaviouralecology: an evolutionary approach(J. R. Krebs and N. B. LITERATURE CITED Davies, Eds.). Oxford, Blackwell Sci. Publ. LEUCHEM,D. W. 1983. Predation risk and vigilance ASHMAN,P. 1977. Northern (Bullock's) Oriole eats in the Blue Tit (Parus caeruleus).Behav. Ecol. So- hummingbird. Western Birds 8: 105. ciobiol. 14: 9-13. BALTOSSER,W.H. 1983. Nesting ecologyof sympat- LINDSTEDT,$. L., •r W. A. CALDER.1976. Body size ric hummingbirdsin GuadalupeCanyon. Un- and longevity in birds. Condor 78: 91-145. published Ph.D. dissertation,Las CrucesßNew ß & -- 1981. Body size, physiological Mexico State Univ. time, and longevity of homeothermic . BEEBE,W. 1950. 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ELDER,W. H., & D. ZIMMERMAN.1983. A comparison Optimal foraging:a selectivereview of theory of recapturevs. resighting data in a 15-yearstudy and tests. Quart. Rev. Biol. 52: 137-154. of survivorshipof the Black-cappedChickadees. SPOFFORD,S. H. 1976. Roadrunner catches hum- J. Field Ornithol. 54: 138-145. mingbird in flight. Condor 78: 142. GAMBOA,G. J. 1977. Predation on Rufous Hum- STILES,F.G. 1978. Possiblespecialization for hum- mingbirdby Wied's flycatcher.Auk 94: 157-158. mingbird hunting in the Tiny Hawk. Auk 95: GASS, C. L., •r R. D. MONTGOMERIE. 1981. Hum- 550-553. mingbird foraging behavior: decision-making STOTT,K. 1951. An Anna Hummingbird caughtin and energy regulation.Pp. 159-194 in Foraging a spider web. Condor 53: 49. behavior:ecological, ethological and physiolog- WASER,N.M., •r •). W. INOUYE. 1977. Implications ical approaches(A. C. Kamil and T. D. Sargent, of recapturesof Broad-tailedHummingbirds Eds.). New York, Garland Press. banded in Colorado. Auk 94: 393-395. GRANT,J. 1959. Hummingbirdsattacked by wasps. WOODS,R.S. 1934. A hummingbirdentangled in a Canadian Field-Naturalist 73: 174. spider web. Condor 36: 242. GREENEWALT,C. H. 1960. Hummingbirds. Garden WRIGHT, [•. H. 1962. kills hum- City, New YorkßDoubleday & Co. mingbird. Auk 79: 112. HAINSWORTH,F.R. 1981. Energy regulationin hum- mingbirds. Amer. Scientist 69: 420-429. Received29 March 1984,accepted 5 [uly 1984.