FALL 1984 SHORT COMMUNICATIONS 111

SHORT COMMUNICATIONS

1981- An ExtraordinaryYear for GoldenEagle "Triplets" in the CentralRocky Mountains

M. ALANJENKINS AND RONALD A. JOSEPH

The clutchsize of the GoldenEagle ( chrysaetos) and Collopy 1983). We are unableto assessthe influence rangesfrom 1 to 4 eggswith a meannear 2 (Brown 1977). of thesefactors on the high number of triplets in 1981 Clutchesof 3 are unusual,occurring less than 10% of the with the possibleexception of the influenceof high prey time (Table 1). Normally,1 to 3 youngfledge/successful densities.Clutch size, and therefore, ultimate productivity nestwith a mean of 1.2 to 1.4 (Brown 1977). (numberof fledgedyoung/successful nest), are partly in-

Table 1. Frequencyof 3-eggclutches in the GoldenEagle.

No. oF No. oF 3-EGG % OF 3-EGG STUDYAREA YEAR(S) CLUTCHES CLUTCHES CLUTCHES REFERENCE

California 21 3 14.3 Slevin, in Arnell 1971 82 8 9.8 Gordon 1955 Colorado 5 0 0.0 Jollie,in Arnell 1971 1963-1964 60 4 6.7 McGahan 1966 Montana 1963-1968 30 1 3.3 Reynolds 1969 1957-1958 5 0 0.0 Hinman [no date] Utah 1967-1968 23 1 0.4 Murphy et al. 1969 Utah 1969-1970 26 8 30.8 Arnell 1971 , 1966 15 1 6.7 Hickman [no date]

TOTALS 267 26 MEAN 9.7

Variousfactors, from failureto lay eggsto mortalityof fluencedby the quantityof food adult femaleseat before nestlings,reduce the probabilityof a pair of eaglesfledg- egg-layingaffecting her nutritionalstate of health (New- ing 3 ("triplets")from a nest.Table 2 comparesdata on the ton 1979).Newton (1979) pointedout that rodent-eating frequencyof 3 fledgling nestsfrom various studiesof raptors lay clutchesthat can vary directly in size with GoldenEagles in the westernUnited States. rodent densitiesin the nest area. This allowsraptors to In 1981, we independentlysurveyed nestsfor exploitrodent and othercyclic prey in high density productivityand recordednests with 3 nestlings.We sub- yearsby increasingproductivity. Evidence suggest that sequentlydiscovered that other investigators,in Utah this is true of Golden Eagle-preyrelationships, because especially,found 5 nestlingnests. The mean percentage the eagle's diet in is mainly (74%) (3.8%) of nestsfledging triplets in 1981 in Utah, Col- lagomorphsand rodents(Olendorff 1976) that exhibit orado, and Wyoming is significantlyhigher P < 0.10) cyclicpopulations (Murphy 1975).This relationshipmay thanthe mean percentage of tripletsfor otheryears in the be moderatedby other factors. (Table 2). We assumedthat mortal- In the western United StatesIagomorph populations ity of the nearly-grownnestling observed in 1981 appear to haveincreased in the yearsleading up to 1981. was low and that most nearly-grownnestlings fledged. In southwesternIdaho populationsof Black-tailedJack- Moststudies with whichwe compared our dataalso made (Leus californicus) reached plague proportions in that assumptionby countingnearly-grown nestlings as the winter of 1981-82, as reported in the popular press fledglings. (e.g., Trueblood 1982). Jackrabbit densitieswere the Many factors can influence productivityin Golden highestin 9 y in 1981 in the SnakeRiver Canyonof Idaho Eaglesas reviewedby Newton(1979); alsosee Edwards (Steenhofet al. 1983). In Utah,jackrabbit censuses con- 112 SHORT CO•MX•tCATtO•S VOL. 18, NO. 3

Table 2. Frequencyof three-fledgling(triplet) GoldenEagle nests in the westernU.S.

TOTAL No. SUCCESSFULNo. WITH % SUCCESSFUL STUDY AREA YEAR THROUGHOUT STUDY TRIPLETS w/TRIPLETS REFERENCE

Years Other Than 1981

Idaho, Oregon 1966 17 0 Hinman• no date Utah 1957-1958 5 0 Hinman, no date Utah 1967-1968 18 0 Camenzind 1968 Utah 1969-1970 19 3 15.8 Arnell 1971 Wyoming,Colo. 1964-1980 882 l 0.1 Den. Wildl. Res. Ctr. data Wyoming 1979 11 0* Lockhart et al. 1980 •qyoming,Mont. 1975-1978 34 0* Lockhart et al. 1978 Montana 1963- 1964 55 3 McGahan 1966 Montana 1962-1968 22 0 Reynolds1969 1974-1975 6 0 Lish 1965 Texas 1974-1975 5 0 Lockhart 1976

TOTALS !,074 7 MEAN 0.7

1981 Data

Utah 1981 95 6 6.3 Present study Colorado 1981 94 3 3.2 Pearson, Grode pers. cornYD. Wyoming 1981 46 0 0 Phillipsand Beske! 98 !

TOTALS 235 9 MEAN 3.8

*Data gatheredby personalcommunication with the author.

ductedby the Departmentof the Army (R. LeClercpers. An earlierdraft of themanuscript was reviewed and im- comm.)showed that densitieswere high(though decreas- provedby M.A. Bogan,W.R. Dryer, and R.L. Phillips. ing thereafter) in autumn 1980 at 3 northwestern Utah studysites, moderate populations at 3 others,and lowat 1 Nevada site.Data from both Steenhofet al. (1983) and the LITERATURE CITED Army showsimilar high densitiesin 1971supporting the hypothesisof a 10 yrjackrabbitpopulation cycle in these ARNELL,W.B. 1971. Prey utilizationby nestingGolden areas. Eagles(Acquila chrysaetos) in central Utah. MS Thesis. Increasedprey availability for nestingeagles is probably BrighamYoung University, Provo, Utah. an importantcause for higher than normal frequencyof BROWN,L. 1977. Eaglesof the world. UniverseBooks, tripletsin the westernUnited Statesin 1981. The only . 244 pp. otherinstance of a highfrequency of tripletsis the study CAMENZIND,F.J. 1968. Nestingecology and behaviorof of Arnell (1971) in Utah. He noted hieh lagomor_ph the GoldenEagle in westcentral Utah. Unpbl.Master's populationsin 197!, 10 yr before the high numberof Thesis.Brigham Young University,Provo, Utah. 40 triplets in 1981. PP. Acknowledgmentis due to DugwayProving Grounds EDWARDS,T.C.,JR., ANDg..w. COLLOPY.1983. Obligate (Dept. of the Army), J.M. Lockhart, E.W. Pearson,B. and facultativebrood reductionin eagles:an exami- Waddell,P.W. Wagnerand the GrandJunction office of nation of factors that influence fratricide. Auk the ColoradoDivision of Wildlife for contributingdata. 100:630-635. FALL 1984 SHORT COMMUNICATIONS 113

GORDON,S. 1955. The Golden Eagle. Collins, London. MURPHY,J.R., FJ. CAMENZIND,D.G. SMITH, AND J.B. 246 pp. WESTON.1969. Nestingecology of raptorialbirds in HICKMAN,G.L. [no date.] Life historyand ecologyof the central Utah. BrighamYoung Univ. Sci.Bull., Biol. Set. GoldenEagle in southwesternIdaho and southeastern 10:1-36. Oregon. U.S. Fishand Wildlife ServiceRep. 104 pp. NEWTON,I. 1979. Populationecology of raptors. HINMAN, R.A. [no date.] Antelope populations in Books,Vermillion, SouthDakota. 399 pp. southwesternUtah with specialreference to Golden OLENDORVV, R.R. i976. The food habits of North Eagle predation. CompletionRep., Fed. Aid. Proj. AmericanGolden Eagles. Amer. Midl, Nat. 95:231-236. W-65-R-6.61 pp. PHILLIPS,R.L., AND A.E. BESKE.1981. Golden Eagles LISH,J.W. 1975. Statusand ecologyof Bald Eaglesand and coal developmentin the eastern Powder River nestingof GoldenEagles in Oklahoma.MS Thesis. Basin of Wyoming. Unpubl. Rep. U.S. Fish and OklahomaState University,Norman, OK. 98 pp. Wildlife Service, Denver Wildlife Research Center, LOCKHART,J.M. 1976. The food habits,status and ecol- Denver, Colorado. 55 pp. ogy of nestingGolden Eagles in the Trans-Pecosre- REYNOLDS,H.V., III. 1969. Population status of the gion of Texas. MS Thesis.Sul RossState University, Golden Eagle in south-centralMontana. MS Thesis. Alpine, Texas. 65 pp. Universityof Montana,Missoula. MT. 61 pp. T.P. MCENEANEY, AND R.L. PHiL- STEENHOF, K., M.N. KOGHERT, AND J.H. LIPS. 1978. The effectsof coal developmenton the DOREMUS.1983. Nestingof subadukGolden Eagles ecologyof birdsof preyin southeasternMontana and in southwstern Idaho. Auk 100:743-747. northernWyoming. Annual Progress Rep. 1978.,Sec- TRUEBLOOD,T. 1982. The great roundup. F/e/d tion of Wildlife Ecologyon Public Lands, Denver and Stream 86(12):11,14,16. Wildlife ResearchCenter, Denver, Coloradopp. 9-14. WHITE,C.M., ANDT.L. THUROW.1984. Reproductionof D.W. , AND C.L. BE- Ferruginous exposed to controlled distur- LITSKY.1980. The statusof nesting Peregrine Fal- bance.Condor (in press). consand other selectedraptor specieson the Black Butte Mine Leaseand adjacentlands. U.S. Fish and Wildlife Service- Final Rept. to the U.S. Bureauof Land Managementand Peter Kiewit Sons'Co. 59 pp. U.S. Fish and Wildlife Service, Denver Wildlife Research MCGAHAN,J. 1966. Ecologyof the Golden Eagle. MS Center, Building 16, Federal Center, Denver, CO 80225. Ad. Thesis.University of Montana,Missoula, MT. 78 pp. dress of •econd author: U.S. Fish and Wildlife Service, Federal MURP•Y,J.R. 1975. Statusof a GoldenEagle population Building, Room 1311, 125 South State Street, Salt City, in central Utah, 1907-1973.In: J.R. Murphy, C.M. UT 84138. White and B.E. Harrell (eds.) Populationstatus of raptors.Raptor Res. Rep. No. 2. pp. 91-96 Received27 December,1983; Accepted11 June 1984.

Food PiracyBetween European Kestreland Short-earedOwl

ERKKI KORPIM/iki

I studieda raptorcommunity of the largefield plainof 1984a). Although the 4 mostcommon species comprise Alajoki in Southern Ostrobothnia,western (63ø the guild of open-terrainhunting of prey in the 05'N, 22ø55'E),from 1977through 1982(see KorpimSki, study area (KorpimSki 1978, 1981), inter- and intra- et al. 1977,1979). The mostnumerous raptor on thestudy specificfood piracyor kleptoparasitism(see Brockmann area was the Short-earedOwl (Asioflammeus)(315 total and Barnard [21979] for additional details on the terms) pairs, 39.4%), followedby European Kestrel (Falcotin- wasobserved only once.Consequently this case may be of nunculus)(36.2%), Long-eared Owl (A. otus) (20.0%), some interest. Northern Harrier (Circuscyaneus) (2.5%), Boreal Owl On 16 May 1982 at 2130 H, I sawa Short-caredOwl in (Aegoliusfunereus)(1.6%) and Sparrow (Accipiter the northern part of Alajoki flying over the field at the nisus) (0.3%); for addition details see Korpim/iki heightof about120 m and carryinga volein itstalons. The