NESTING HISTORY OF GOLDEN EAGLES IN MALHEUR-HARNEY LAKES BASIN, SOUTHEASTERN by StevenP. Thompson• U.S. Fish and Wildlife Service P.O. Box 113 Bums,Oregon 97720 and RichardS. Johnstone 604 Yama Street Yreka, California96097 and Carroll D. Littlefield U.S, Fish and Wildlife Service P.O. Box 113 Burns,Oregon 97720

Abstract Historically,the GoldenEagle (Aquila chrysaetos)was a commonbreeding species andpermanent resident of Malheur-HarneyLakes Basin since at least1875. Incidental recordson breedingterritories were available from 1875to 1980.Data were available frompreselected breeding territories from 1966to 1980.Eaglets fledging per occupied breedingterritory fluctuated annually from 0.20 to 1.67.A total of 179 breedingterri- torieswere examinedon or adjacentto Malheur National Wildlife Refuge.Our data agreewith studieselsewhere which suggest a relationshipbetween Golden Eagle repro- ductivesuccess and abundanceof their major prey species,the black-tailedjackrabbit (Lepuscalifornicus). Nesting and fiedgingsuccess are summarizedfor 1940,and 1966 through1980.

Introduction Severalunpublished Golden Eagle studies have been conducted in the Malheur-Har- neyLakes Basin in southeastOregon. Here we attemptedto summarizepast studies and presentthe nesting status for the species in thebasin. Nesting surveys were conducted in 1940,and from 1966-1980.Incidental records on specificnests were availablefrom 1875-1980.In 1966, The U.S. Fish and Wildlife Serviceinitiated a studyof Golden Eaglesin southwestIdaho and southeast Oregon. This preliminary field work (Hickman 1968)began long term data collection on and adjacentto MalheurNational Wildlife Refuge(NWR), Harney County, Oregon.

lAddressall correspondenceto: StevenP. Thompson

116 RaptorResearch 16(4): 116-122 Winter 1982 Thompsonet al.--OregonGolden Eagles 117

StudyArea Malheur-HarneyLakes Basin is in the northwestextremity of the .It is composedof the High LavaPlains and Basin and Range Physiographic Provinces (Franklin and Dyrness 1973). The High Lava Plains Provinceis characterizedby extensivebasalt-rhyolite rimrock formations, while the Basinand RangePro- vinceconsists of fault blockmountains enclosing internal drainage basins. Elevation varies from 1227-1586m (4025-5200ft.). The relativelyflat lowlandsare a mosaicof shrubuplands, freshwater marshes, seasonally wet meadows andalkali playas. Within the shrubupland native and introducedgrasses are common.Dominant shrubs in- chde big sagebrush(Artemisia tridentata), low sagebrush(A. arbuscula),black greasewood (Sarcobatus ver- miculatus)and rabbitbrush(Chrysothamus spp.). Freshwater emergents grow adjacent to the shrubupland in marshes.Wet meadowsare composedof meadowgrasses including timothy (Phleumpratensis), wildryes (Elymusspp.), meadow barley (Hordeurn hystrix), and red top (Agrostisalba ). A uniquefeature of the basinis the extensiveecotone between the seasonalflooded wetlands and shrubuplands. Low rimrockcliffs 5-70 m highprovide a sharpecotone between sagebrush and wetlandplant communities.Generally, the regionre- semblesthe GreatBasin of northernNevada and western Utah. Vegetationin someareas has been converted to alfalfa,cereal grains and crestedwheatgrass. Many of the crestedwheatgrass monotypic seedings range from 800 to 3200 ha. The climateis semi-arid,typical of the coolerportions of the IntermountainWest. Most precipitationoc- cursfrom November through January principally in the form of snow.Water on all lakesand ponds,except thosewith warmsprings, is usuallyfrozen from late Novemberthrough early February.

Methods Data were collectedannually on an averageof 11 (range5 to 18) breedingterritories from 1966-1979.In 1980,33 territorieswere surveyed,15 of which were associatedwith predominantlysagebrush and grease- woodplant communities.Another 15 were associatedwith varyingdegrees of wetlandhabitat. Three were not usedin the analysiscomparing wetlands and rangelandsbecause they couldnot be clearlyclassified into eithercommunity. Breeding territories were recordedas active or inactive.Breeding territories were consid- eredunoccupied when no signof territorialdefense, courtship, or other relatedreproductive activities were notedafter several visits. Both traditional and alternativenest sites were plottedon topographicmaps and all knownnests within a territorywere examinedannually. Most surveys were conductedon foot andby vehicle, but fixed-wingaircraft and helicopterswere usedat leasti time a year.Field workbegan in Februaryand continuedthrough August. Additional observations were also noted for the remainderof the year,but not on a regularbasis. Terminology used to describereproductive success follows the definitionsas defined by Postø upalsky(1974). Data collectedin 1940,and 1966-1976were analyzedby us. Additionaldata were collectedby us during 1977-1980.Oologist records of eggsets and nestsite descriptions were providedby the WesternFoundation of VertebrateZoology (Lloyd Kiff pers.comm.). Field notesof William E. Griffeewere alsoincorporated into thisreport.

Results and Discussion Historically,Golden Eagles have been a commonbreeding species in the basinsince at least1875 (Bendire1877). The first nestingrecord was by Captain CharlesBendire (1877).He stated,"Golden Eagles are moderatelyabundant throughout the mountainous portionsduring the greaterpart of the year.Each pair appearsto confineitself to a cer- tain districtand no othersbreed there. I haveheard of severalother nests in thisvicinity at intervalsof abouttwenty milesfrom the other. They are generallyseen hunting in pairsin the early spring,chasing ducks, geese, and sagehens,and mostsuccessfully." CaptainBendire took eggs from a nestlocated in a ponderosapine (Pinusponderosa) on 9 April 1877and 4 April 1878. Willett (1919)also reported Golden Eagles as rather commonin the mountainoussec- tionssurrounding the lake in 1918.In 1936,Jewett (Lloyd Kiff pers.comm.) located 2 large,downy young on 15 May 1934near the presentsite of KrumboReservoir. Jewett alsorecorded the speciesas common on SteensMountain (Jewett 1936). 118 RAPTOR RESEARCH Vol. 16, No. 4

WilliamE. Griffeecollected Golden Eagle egg sets annually within the basinfrom 1937-1942.In 1940,only 2 of the 7 neststhat Griffeevisited contained eggs. Two sites hadsingle birds near their nests, but no eggswere present, and no nestingactivity was notedat 3 othertraditional sites. In 1941, of 6 neststraditionally visited, 4 contained eggs;I wasdecorated and ready for eggs with both birds in attendance;and 1 appeared deserted.Of the 4 occupiednests, 3 heldsets of 3 eggs,while I had 2 eggs.He alsore- cordedan unusuallylarge number of 3 eggclutches in 1942.Black-tailed jackrabbits wereextremely common in thespring of 1941(Griffee). The firstdocumented study on GoldenEagles in the basinwas conducted by Frank W. Groves(Refuge files). In 1940,Groves found all 7 siteshe examinedto be active. Four of the 7 sitesfledged 6 young(0.86 fledged/occupiedbreeding territory; 1.5 fledged/successfulnest). Althoughfew data were collected from 1950 to 1966,Golden Eagle populations were apparentlylow. John Scharff (Refuge files) stated, "There has been a 75 percentreduc- tionin the GoldenEagle population in the MalheurNWR areasince 1950." He postu- latedthat the localpopulation reduction was probably due to low jackrabbitpopu- lations,with a few eaglesbeing shot. A large"jackrabbit crash" was recorded in 1950 (Refugefiles). Since1966, traditional sites have been examined every year except1975. Food habit data collectedin 1940, 1966 and 1967 indicatedGolden Eagles depend heavily on black-tailedjackrabbits astheir primary prey during the nesting season (Table 1). Ga- brielsonand Jewett (1940) reported, "The Golden Eagle feeds largely on jackrabbits, but alsotakes waterfowl and otherbirds, all kindsof rodents,and possiblyoccasional lambs and fawns."

Table1. Percentfrequency of preyremains at GoldenEagle nesting sites in southeastOregon (Malheur- HameyLakes Basin).

%Frequency %Frequency PreySpecies 1940(Groves) 1966-67(Hickman) Mammals 78 69 black-tailedjack rabbit 69 49 (Lepuscalifornicus) Nuttall's cottontail 4 12 (Sylvilagusnuttallii) yellow-belliedmarmot 5 2 (Marmotaflaviventris) Other Mammals 0 6

Birds 22 29 dabblingducks 20 9 (Anasspp.) Other Birds 2 20

OtherSpecies 0 2

TOTAL 100 100 Winter1982 Thompsonet al.--OregonGolden Eagles 119

McAdooand Young (1980) stated that jackrabbitpopulations are cyclic.Wagner and Stoddart(1972) reported that black-tailed jackrabbits normally experience cyclical pop- ulationfluctuations with 4 or 5 yearsof populationdecline (1962 to 1967),followed by 3 successiveyears of populationincrease. In west-centralUtah, Murphy (1075)reported that rabbitdensities were moderately low in 1967,rose to a peakin 1969,then began a precipitousdecline falling to very low levelsin 1973. Kocherr(1980) assumedthat in southwestIdaho jackrabbit numbers peaked in 1970 or early 1971. Jackrabbitpopu- lationsin southwestIdaho declined in 1972 and reached a low level in 1973, 1974, and 1975.By 1976-1978,their numbershad increasedbut were still below 1971 levels.The timingof our subjectiveiackrabbit "highs" and "lows"approximate those of Murphy andKochert. A "iackrabbitcrash" occurred in the Malheur-HarneyLakes Basin during the winter of 1972-1073(Littlefield 1976). Severalinvestigators (Palmer 1897; Nelson 1000;Clark 1972;Wagner and Stoddart1972; Newton 1979;McAdoo and Young1980) suggesta 7-10 yearjackrabbit population cycle. Low and high populationsare evident by their marcityand abundance.Our subjectiverabbit estimatessuggest that 7-10 year cyclesalso occur in the Malheur-HameyLakes Basin. Murphy(1975) and Kocherr (1980) found that fledgingrates in Utah and Idahoclosely followedfluctuations in jackrabbitpopulations. Kocherr (1980) foundnestling survival declinedmarkedly from good to poorjackrabbit years. Kocherr reported decreases in the percentof successfulpairs, number of youngfledged per successfulattempt, and numberof youngfledged per pair. In southeastOregon, we believethe mostreliable in- dicatorsof GoldenEagle production were fledglingsper pair and the percentof tradi- tionaleyries which were successfulin fledgingat least1 young(Table 2, Fig. 1). Eagle reproductivesuccess closely paralleled our subjectiveestimates of jackrabbitfrequency.

Table2. GoldenEagle breeding data 1940,1966-80 in southeastOregon; sample size (n) in parentheses.

# Successful Nests Year # FledgedPer # FledgedPer # BreedingTerritories Occupied BreedingTerritory SuccessfulNest Checked 1940 0.86 (7) 1.50 (4) 57% (7) 1966 1.00(6) 1.50(4) 57%(7) 1967 1.40(10) 1.75 (8) 73% (11) 1968 1.60(5) 2.00 (4) 57% (7) 1969 1.67(6) 1.67 (6) 66% (9) 1970 1.00(8) 1.60 (5) 45% (11) 1971 0.89 (9) 2.00 (4) 40% (10) 1972 0.50 (10) 1.67 (3) 27% (11) 1973 0.20 (10) 2.00 (1) 8% (la) 1974 0.55 (11) 2.00 (3) 25% (12) 1975 1976 1.00(8) 1.60 (5) 55% (9) 1977 1.50(8) 2.00 (6) 60% (10) 1978 1.62(13) 1.75 (12) 75% (16) 1979 1.06(16) 1.42 (12) 71% (17) 1980 1.39(18) 1.67(15) 83%(18)

Pooled Mean 1.08(145) 1.70 (92) 51% (179) 120 RAPTOR RESEARCH Vol. 16, No. 4

GOLDENEAGLE BREEDING DATA 'GO90 t IN SOUTHEASTOREGON 80-

JACK RABBIT CRASH I I

4O- I I 30-

10-

66 67 68 69 70 71 72 73 74 76 77 78 79 80

YEAR Figure1. Golden Eagle reproduction data, Harney Co., Oregon. Percentage ofGolden Eagle pairs fledging at leastone successful young from 1966-1980. The percentageof breedingterritories which were successfulin fledgingat leastone ydungwere higherin year• when jackrabbitpopulations appeared high] In contrast, eagleswere lesssuccessful when jackrabbitsappeared scarce (Fig. 1). Murphy (1975) foundin lowprey years, even though fewer pairs-breed, there is a highpotential for sue- cesson the part of thosewhich do nest. Our data support Murphy's conclusions. Within the basin,approximately 50,587 ha of nativerange have been converted to crestedwheatgrass (G. Wingpers. comm.). For the past7 years,approximately 1215 ha peryear, of sagebrushand greasewood, have been cleared and converted to cerealcrops or alfalfa(Paul Friedricksen pers. comm.). Brush species provide escape cover to jack- rabbitsfrom aerial predators such as Golden Eagles. The abilityof brushspecies to store water duringwinter and early spring months may be asimportant to jackrabbitsurvival asescape cover. Water is knownto be important,with mostworkers agreeing that jack- rabbitsselect succulent vegetation (Hansen and Flinders1969). In northernUtah, West- oby(1980) found shrubs, such as sagebrush and greasewood, were commonlyselected in the jackrabbit'sdiet becauseof their relativelyhigh water content.Sagebrush was a largeproportion of theirdiet fromthe beginningof shrubdormancy (November) until new growthbegan in April. Thismay explainwhy breedingterritories associated with largeblocks of monotypicvegetation, such as crested wheatgrass and agricultural areas, were not as successfulas siteswith a mosaicof native vegetation.Because Golden Eaglesare permanent residents within the basin, it is importantthat substantialareas re- Winter 1982 Thompsonet al.--OregonGolden Eagles 121 mainin nativevegetation. Small monotypic stands of agricultureand crestedwheatgrass withina breedingterritory may increase diversity, thereby increasing the prey base. Severalworkers (Perrins 1969; Krapu 1979;Newton 1979)have discussedthe needfor propernutrition of adult birdsbefore egg laying and incubation.It seemslogical that pairsassociated with wetlandhabitat should have an availablefood supplyto exploit duringthe criticalwinter months prior to egglaying and incubationthat is not available in the shrubuplands. In 1980, additionalbreeding territories were examined,bringing the total checkedto 33. Fifteenwere associatedwith predominantlysagebrush and greasewoodplant communitiesand another15 were adiacentto wetlandplant commu- nities.In 1980,the meannumber of fledglingsper occupiedbreeding territory was 1.07 in sagebrushand greasewoodcommunities as comparedto 1.67 fledgedper occupied territoryassociated with varyingdegrees of wetlandhabitat. These data were significant (t = 2.40; p<.05) indicatingeagles were more productiveadjacent to wetlands.The low elevationwetland areas attract migratory waterfowl, upland game birds, mule deer (Odocoileushemionus), jackrabbits, and usually large populations of winteringlivestock (Refugefiles). The amountand qualityof wetlandswithin breedingterritories varied. During win- ter, prey appearedto concentratenear wetland lowlands.Thus, pairsassociated with wetlandhabitat may have an abundantfood supply prior to egglaying. When jackrab- bit numberswere low or decliningGolden Eaglespairs in territoriesassociated with sagebrushand greasewood plant communitiesand no wetlandswould be forcedto exert moreenergy to obtainfood. The apparentdifference in potentialprey frequencyis one possibleexplanation for the differencesnoted in reproductivesuccess between occupied breedingterritories adjacent to wetlandsand thoseinhabiting homogeneous rangelands in 1980. Of data collectedon 179 breedingterritories over a 15 year period,the fate was de- terminedon 145 (Table 2). Ninety-two(63%) of the 145 of known fate were successful in raisingat least I young.In our studyarea, 156 eagletsfledged from 107 occupied breedingterritories (1.46 eaglets fledged/occupied territory). Eaglets fledged per suc- cessfulnest was slightlyhigher, with 1.70 fledgedper successfulnest (156 eaglets fledged/92successful nests). These data are verycomparable to otherlong term studies in Scotlandand (Watson 1957, USDI 1979).

Acknowledgements In a longterm studyyou accumulatea largelist of peoplewho haveassisted in data collection.We thankBurns District Bureauof Land Managementpersonnel Ginny Ro- senburg,Guy Sheeter,Larry Todd and Gary Wing. Personnelof the OregonDepart- mentof Fishand Wildlife were helpful, especially Ellis Masonand Jim Totland. We ap- preciatethe severalbiologists associated with MalheurNWR. Significantcontributions were receivedfrom JohnComely, Larry Ditto, Harold Duebbert,Frank Groves,Gary Ivey, Gene Kridler,Dave Marshall,Eldon McLaury, Larry Napier, JohnScharff and Dick Siostrom.We thankLloyd Kiff of the WesternFoundation of VertebrateZoology for dataon specificnests. William E. Griffee'sfield notesand personalcommunications providedspecial insights. We thankJohn Coruely, Brad Ehlers and Joe Mazzoni for re- viewingand improving this manuscript and Ruth Warneke for typing.This manuscript was improvedby the commentsof refereesMark Fuller, JosephMurphy, and David Ellis. 122 RAPTOR RESEARCH Vol. 16, No. 4

Literature Cited Bendire,C. E. 1877.Notes on someof the birdsfound in southeasternOregon, particu- larly in the vicinityof Camp Harney,from November1874 to January1877. Boston Soc. Nat. Hist. Proc. 19:109-149. Clark, F. W. 1972. Influenceof jackrabbitdensity on coyotepopulation changes. ]. Wildl. Mgmt.36:343-356. Franklin,J. R., andC. T. Dyrness.1973. Natural vegetation of Oregonand Washington. USDA, ForestServ. General Tech. Rep. PNW-8. Pac. NorthwestForest and Range Exp.Stat., Portland, Oregon, 322pp. ' Gabrielson,I. N., and S. G. Jewett.1940. Birds of Oregon.Oregon State Coil., Corvallis, Oregon,650 pp. Griffee,W. E. 1941.Large sets of GoldenEagle eggs. Murrelet 22:40-41. Hansen,R. M., and J. T. Flinders.1969. Food habitsof North Americanhares. Colo. StateUniv. RangeSci. Dep. Sci. Ser. 1, 18 pp. Hickman,G. L. 1968.The ecologyand breeding biology of the GoldenEagle in south- westernIdaho and southeastern Oregon. USDI, Fishand Wildlife Serv.,Unpub. rep. Jewett,S. G. 1936.Bird notesfrom HarneyCounty, Oregon, during May 1934.Murrelet 17:41-47. Kochert,M. N. 1980.Golden Eagle reproductiveand populationchanges in relationto jackrabbitcycles: implications to eagleelectrocutions. In Workshopon raptorsand energydevelopment. Boise, Idaho. Krapu,G. L. 1979.Nutrition of femaledabbling ducks during reproduction. Proc. 1977 Symp.,Madison, WI. NC Sect.,The Wildlife Society,T. A. BoohoutEd. pp 59-70. Littlefield, C. D. 1976. Productivityof Greater SandhillCranes on Malheur National Wildlife Refuge,Oregon. Proc. Int. CraneWorkshop 1:86-92. McAdoo,J. K., andJ. A. Young.1980. Jackrabbits. Rangelands 2:135-138. Murphy,J. R. 1975. Statusof a GoldenEagle populationin centralUtah, 1967-1973. RaptorRes. Rep., No. 3. Vermillion,South Dakota. Nelson,F. W. 1909.The rabbitsof North America.U.S. Dept. Agr., Bur. Biol. Survey, N. Am. Fauna29. 314 pp. Newton,I. 1979.Population ecology of raptors.Buteo Books, Vermillion, South Dakota. 300 pp. Palmer,I. S. 1897.The jackrabbitsof the UnitedStates. Revised ed. U.S. Dept. Agr., Div. Biol.Survey, Bull. 8.88 pp. Perrins,C. M. 1969.The timingof bird'sbreeding seasons. Ibis 12:242-255. Postupalsky,S. 1974. Raptor reproductivesuccess: some problems with methods,cri- teria,and terminology. Raptor Res. Rep., No. 2. Vermillion,South Dakota. USDI. 1979.Snake River birds of preyspecial research report to the Secretaryof the In- terior. Bureauof Land Manage.,Boise District, Idaho. Wagner,F. H., and L. C. Stoddart.1972. Influence of coyotepredation on black-tailed jackrabbitpopulations in Utah.1. Wildl.Mgmt. 36:329-342. Watson,A. 1957. The breedingsuccess of Golden Eaglesin the northeasthighlands. Scottish Nat. 69:153-169. Westoby,M. 1980.Black-tailed jackrabbit diets in CurlewValley, northernUtah. 1. Wildl. Mgmt.44:942-948. Willett, G. 1919.Bird notesfrom southeasternOregon and northeasternCalifornia. Con- dot 21:194-207.