Visitation of High Mountain Bogs by Golden Eagles in the Northern Great Basin

J. Field Ornithol., 62(1):46-52

VISITATION OF HIGH MOUNTAIN BOGS BY GOLDEN EAGLES IN THE NORTHERN GREAT BASIN

DAVID A. CHARLET AND RICHARD W. RUST Departmentof Biology Universityof Nevada,Reno Reno, Nevada 89557 USA

Abstract.--Golden Eagles (Aquila chrysaetos)were observeddrinking and bathing in three high mountain bogsin the Jarbidge Mountains of northern Nevada. Six additionalsites in the Jarbidge and two in the Warner Mountains of northern California showedevidence of drinkingactivity. These "eaglebogs" all sharedfour physicalattributes that distinguished them from other high mountain bogsin theseranges. These attributeswere: (1) association with a spring abovethe highestquaking aspen (Populustremuloides), (2) presenceof an open area containingpools (without steepor undercutbanks) near the spring, (3) cover on three sidesin the form of cliffs and/or denseconiferous woodlands at least 10 m away from the pools,and (4) a narrow openingin the cover(10-30 m), on the lower side of the bogfollowed by a steepdrop. The frequencyof Golden Eagle visitationstrongly suggests that eaglebogs are an overlookedbut important habitat requirementfor the speciesin the Great Basin.

VISITA DE ANEGADOS POR INDIVIDUOS DE AQUILA CHRYSAETOS EN LUGARES ELEVADOS DE LA GRAN CUENCA DEL NORTE Sinopsis.--Se observaronindividuos de aguila dorada (Aquila chrysaetos)beber agua y bafiarseen anegadosde laselevadas montafias Jarbidge al nortede Nevada.Seis localidades adicionales,en losJarbidge y dosen las montafiasWarner del nortede California, mostraron evidenciade actividaden dondelas avesbebieron agua. Estos"anegados de aguilas"compar- tieron cuatro atributosfisicos que los distinguende otrosanegados en estasmontafias. Estos son:(1) asociaci6ncon manantialessobre los mfls altosfirboles de Populustremuloides, (2) presenciade fireasabiertas que contienenpozas (sin precipicioso bancosentrecortados) cercadel manatial, (3) cubiertaen tres de los ladosen forma de farallonesy/o densas arboladasde conlferosal menosa 10 m de las pozas,y (4) una estrechaapertura en la cubierta(10-30 m), en la parte baja del anegadoseguido por una caidaabrupta. La frecuencia de visitaspor parte de estasaves a estasfireas sugiere que los "anegadosde aguilas"son un importanterequisito de hfbitat que requierela especieen la "Gran Cuenca"y que hasta la fechahabla pasadodesapersivido.

The breeding,nesting, and feedingbehavior of Golden Eagles(Aquila chrysaetos)has beenwell documented(e.g., Beechamand Kochert 1975, Bent 1937, Boeker and Ray 1971, Brown and Watson 1964, Cameron 1905, Hanna 1930, McGahan 1968). However, observationsof Golden Eaglesdrinking or bathinghave not appearedin the literature. The only referencewe found to the drinking behaviorof eaglesstates that all liquid requirementsof eaglesare met by the ingestionof prey (Brown and Amadon 1968:49). Brown and Amadon (1968) go on to statethat a very large number of raptor speciesnever drink, that evidencefor bathing in the wild is scanty,and that little of their time is spentby searchingfor water. We presentobservational data on the frequentuse of high mountain bogsin Great Basin mountainsby Golden Eagles for drinking, bathing and preening, and describethe physicalstructure of these"eagle bogs."

46 Vol.62, No. 1 GoldenEagle Bogs [47

METHODS The JarbidgeMountains of northeastNevada (41ø50'N,115ø20'W) containsix peaksover 3200 m. They drain north,east and westinto the Columbia River, and south into the Humboldt Sink of the Great Basin. The South Warner Mountains of northeast California (41ø25'N, 120ø20'W) containthree peaks over 2950 m, and drain west into the SacramentoRiver and eastinto SurpriseValley basin.The vegetationof both rangesis dominatedby whitebarkpine (Pinusalbicaulis) subalpine woodlandsabove 2500 m (Loope 1969, Riegel 1982). The JarbidgeMountains have been visited annually from 1981-1990, and the South Warner Mountains were visited in 1988-1989. Our initial observationsof Golden Eaglesusing bogswere made incidentalto our plant collectingactivities. We later assessedthose sites for commonfea- turesto characterizewhat we call "eaglebogs." Many springs,whether associatedwith bogsor not, were then surveyedfor thosefeatures and for useby GoldenEagles to verify our characterizationand the extentof this behavior.Springs are definedas habitatswhere water emergesfrom theground, whereas bogs are habitatsof wet massesof vegetationoverlying thick layersof undecomposedsoil, or peat (Whittaker 1975:171). During 1989-1990, 54 springsabove 2450 m in the Jarbidgeand 12 in the South Warner Mountains were visited to measure and characterize their physicalfeatures, aspect and elevations.Sightings of GoldenEagles or the presenceof Golden Eagle feathersat thesesites were considered indicative of visitation. Elevationswere determinedby altimeter,calibrated at leastthree times daily from terrain featuresof knownelevation as representedon United StatesGeological Survey 7.5' topographicmaps. Springsvisited were markedon thesemaps and were later foundon National High Altitude Photographyprogram 1:24,000 scaledinfrared aerial photographsto verify their locations.A distanceof 200 m was measuredfrom eachsite alongthe steepestpossible escape route for eagles,and the drop in elevation was determinedby countingthe number of 12-m contourlines crossed in that distance.Width of the escaperoute opening, pool size, and distances from surroundingcover to poolswere measuredwith a meter tape at the site.Tree canopycover was estimatedby line intercept,and tree heights were determinedby triangulation.

RESULTS The first observationof boguse by GoldenEagles was in August1985 when two adult Golden Eagleswere seenand flushedfrom a bog at the headwatersof Marys River in the Jarbidge Mountains. In July 1987, anotherbog was discoveredat the headwatersof the East Fork of the JarbidgeRiver where two more Golden Eagleswere flushed.At both sitesthe eaglesleft the bogthrough a narrow gap in the treeswhere the bog'soutlet flowed. Numerous primaries and secondaries and muchdowny plumagewere observedthroughout each bog. Thesetwo bogshad the followingattributes in common:(1) association 48] D. A. Charletand R. W. Rust J.Field Ornithol. Winter 1991 with a springabove the highestquaking aspen(Populus tremuloides), (2) presenceof an open,fiat area containingshallow (0.2-0.4 m) poolswithout steepor undercut banks near the spring, (3) coveron three sidesin the form of cliffs and/or denseconiferous woodlands at least10 m away from the pools,and (4) a narrow openingin the cover(10-30 m), on the lower side of the bog followed by a steep drop. We call these escaperoutes "runways." Where Golden Eagleswere observedbathing, primary feath- erswere alwaysfound. Thus, we considerthe presenceof primary feathers at a bog to be indicativeof eagle bathing. Eight sites containedall or three of the four attributes, but containedonly secondaryfeathers and down. These siteswe call "drinking only" sites. Many springsoccur in both of our study areas below 2450 m, but quaking aspenat higher elevations,and black cottonwood(Populus tricho- carpa)and willows (Salix spp.) at lower elevationsdominate the vegetation of these wet areas, occludingthe pools from the view of eagles.Thus, this study was restrictedto sitesabove the elevationallimit of quaking aspen. In 1989-1990, we visited66 springs(46 associatedwith bogs),including the 2 previouslyobserved, at elevationsof 2450-3025 m (mean = 2764 m) (Table 1). The aspectsof the springsvisited are as follows:24 North, 24 East, 6 West, 2 South, 6 Northeast and 1 Southeast.Of thesesprings, 11 had Golden Eagles and/or their feathers in their associatedbogs, 6 with north aspectand 5 with east aspect.Elevation of these eagle bogs rangesfrom 2550 to 2910 m (mean = 2875 m). The surroundingcover of eaglebogs consists of a nearly closedcanopy (60-80% cover)subalpine forest of whitebarkpine and subalpinefir (Abies lasiocarpa)in the Jarbidge and whitebark pine alone in the Warner Mountains. Maximum tree heightsalong the bordersof eaglebogs typically range from 10 to 25 m. An exceptionto this is at the Marys River eaglebog, where the side abovethe spring is a snowslidetract with a tangleof downedand small trees(3-5 m tall). Despitethe smallerstature of the trees,the canopyat this height is >65%. Bogsunused by Golden Eagles have one or more sidesbordered by mountain brush or alpine plant communitiesnot exceeding0.5 m in height,or by subalpinewood- land with <25% cover. Golden Eagleswere seenon the ground on 17 d at all three bathing sites in the Jarbidge Mountains. On 3 d, five eagleswere seen at one time (two matures and three immatureson 19 July 1988 at the East Fork JarbidgeRiver bog;five immatureson 19 July 1989 at the Jarbidge Lake bog; one mature and four immatures at Marys River bog on 29 July 1990). Drinking, bathing, and preening were observedat all these sites.When the birds left they always flew out along the runway. At the six Jarbidge drinking sites,eagles were never seen on the ground, but secondaryfeathers and down were found. In the Warner Mountains, DAC's camp was serendipitouslyplaced by the Modoc National Forest Wilderness Technician next to an eagle bog near Eagle Peak to conductbotanical research. Twenty dayswere Vol.62, No. 1 GoldenEagle Bogs [49

T^BI•. 1. Physicalcharacteristics and GoldenEagle observations from all springsexamined duringJul. andAug., 1985-1990, in theJarbidge and Warner mountains.Observations were madeduring visits lasting from 10 min to 6 hr at specificsites.

Non-eagle Drinking Drinking and springs sitesonly bathing sites No. sites examined 55 8 3 % siteshaving bog and spring 60 88 100 % siteswith pools 47 75 100 % sites with cover 16 88 100 % siteswith runway 73 100 100 Mean elevation of sites (m) 2802 2833 2800 Elevationrange (m) 2450-3025 2550-2955 2765-2865 Total no. observations 459 69 28 % observationswith sightings 0 38 68 Total eaglesobserved 0 48 126 % of eaglesseen on ground 0 4 68 spent at this site (8-28 August 1989). Although no eagleswere seen utilizing the water, a pair of immature Golden Eaglescame daily (1800- 2000 hours), apparentlyfor the purposeof using it (Table 1). Each day the pair approachedfrom the high side of the spring and camewithin 20 m of the ground before seeingthe camp and departing.On three occasions,the birds then movedto a smaller spring and bog higher on the mountain,where secondary feathers and down were later found.Once, anotherpair of immaturesarrived and the four were seenengaged in aerial combatover the smaller bog. All three bathing sitesshared the four physicalattributes, whereas the 55 springsvisited that had no evidenceof eagleuse lackedone or more of the attributes.The charactersmost often missingwere adequatecover and the presenceof shallowpools without undercutbanks (Table 1). Sixteensites were missingonly one attribute of an eaglebog and showed no sign of Golden Eagle visitation. One site had pools with undercut banks, 13 had no runway, 1 had a runway that droppedonly 10 m in 200 m, and at I site the denseforest surrounding the bog was only 5 m from the pools. Nearly all of the eight sitesthat containedGolden Eagle secondaries and down but no primaries had all four eagle bog attributes(Table 1). Two of thesesites were visitedonly in early summerwhen there was still snow at the sites. Commonplants at the eaglebogs include: Kalrnia rnicrophylla,Ledurn glandulosurn,Polygonurn bistortoides, Aster occidentalis, Pedicularis groen- landica,Viola rnackloskeyi,Gentiana calycosa, Platanthera dilatata, Dode- catheonalpinurn, Carex spp. (e.g., C. scopulorurn),and Sphagnurnfirn- briaturn. No individualsof any other raptor specieswere ever observedwithin 1 km of any eaglebog. No Bald Eagles(Haliaeetus leucocephalus) were seenat any time in either mountain range. Over 450 km have been 50] D. A. Charletand R. W. Rust J.Field Ornithol. Winter 1991 traversedon foot in both ranges,and only two primarieswere ever found on dry sites.Only six secondarieswere seenon dry sites,and all of these were under whitebark pine snagswithin 0.5 km of a Golden Eagle bathing site.

DISCUSSION Golden Eagles are commonthroughout the Great Basin (Herron et al. 1985, Ryser 1985), and it is not unusualto seethem in this region. It is unusual,however, to seefive or more togetherat a time. Collectively,we have spentover 60 yr exploring the Great Basin and we have seenmore than four Golden Eagles at a time only at eagle bogs.We considerthe sightingon three occasionsof congregationsof five individualsat bogsto be significant,and further studyof Golden Eaglesat thesebogs may reveal new insightsinto their socialbehavior. Furthermore, we have observed eaglesat the first two Jarbidge eaglebogs on 17 of the 18 times that we have visited them. Therefore, we considerthe use of these bogs to be a significantfeature of the habitat requirementsof Golden Eagles in the Great Basin. During a 5-yr studyof the wild horsesof Nevada(Berger 1986), Golden Eagles were observedon four occasionsutilizing three different bogs (2500-2700 m) in the Granite Range of northwesternNevada, 41 km ESE of the Warner Mountains(J. Berger,pers. comm.). The sitesshared the features commonto the eagle bogs of the Jarbidge and Warner Mountains. Golden Eagleswere observedbathing, drinking and preening at eagle bogs,so these activities are clearly amongthe functionsof their visit. The tremendousabundance of primaries,secondaries, rectricies and down seen in and near the poolsat all of the eaglebogs strongly suggest that preening is an important activity of the birds at thesesites. Someof the siteswe designatedas "drinking only" habitat, due to the lack of direct observationof bathing and the absenceof primary feathers (Table 1), may yet proveto be bathing sites,especially the two we visited early in the season. Golden Eagle bathing sites contain bogswith shallow pools without undercut banks. Seven sites had all the attributes of a good eagle bog, exceptthat they had no bog with pools,or the poolshad undercutbanks. None of thesewere eaglebogs. If eagleswere present when we visited an eagle bog, as soon as we were detectedthey left the site through the runway. Their escapeflight was very slow, and they always lost elevationonce they flew over the drop in the runway. They typically did not regain the elevationof the bog for about 200 m. It is well known that Golden Eagleshave difficulty taking off from the ground, and particularly so when carrying prey. Similarly, we assumethat taking off is more difficult after drinking and bathing. We concludethat the escaperoute with an adequatedrop in elevation (>30 m drop in 200 m) is a very important feature in the selectionof bathing sitesby Golden Eagles.This conclusionis supported Vol.62, No. 1 GoldenEagle Bogs [51 by the characterizationof an unusedbog that had all our attributesexcept that the drop was only 10 m in 200 m. Although the presenceof a canopyover the poolsin a bog prevents GoldenEagle use,we concludethat adequatecover surrounding the bog is critically important in their selectionof a bathing and drinking site, sincethis cover preventslong distancedetection of eaglesby potential groundpredators. At 10 siteswhere all other attributeswould indicate eagleuse, there was not coveron three sidesand the bogswere not used. Alternatively,dense cover within 5 rn of poolsat one bog apparently preventedits selectionas a watering site, presumablydue to insufficient distancein the eventof predatoryambush. It is curiousthat Golden Eagles,not normally disposedto concealing themselves,invariably selectsecluded water sites.This feature of eagle bogsis probablywhy their drinking and bathingin the wild hasremained unreporteduntil now. GoldenEagles come to eaglebogs and drink, bathe and preen. These activities make the birds much more vulnerable to predatorsthan under other circumstances,hence a site with heavy cover on three sidesof the bog with a runway presenton the fourth side is advantageous.This escaperoute has a severedrop in elevationthat allows GoldenEagles a rapid departureif they encountera predator,even if the birds are heavily laden with water. We assumethat occupationof thesesites, by eitherhumans or livestock, will precludetheir useby eagles.The importanceof thesebogs for Golden Eaglesis still unknown,but if they are a habitat featurethat limits their range or reproductivesuccess, special attention should be given to eagle bogsin land managementpractices.

ACKNOWLEDGMENTS

We thank our packers,A. Smith, CottonwoodRanch, Nevada, and T. Lake, Modoc National Forest, California, for packingus into our studyareas. We thank G. Herron, nongamebiologist, Nevada Division of Wildlife, for discussionsabout Golden Eagles in the Great Basin.We alsothank R. R. Roth, Universityof Delaware, B. I. Kiefer, Wesleyen University,and S. Vander Wall, Universityof Nevada,Reno, for reviewingan earlier draft of our manuscript.DAC also thanks T. Charlet for the companionshipand nourishment providedduring the 1989 field season,and for her invaluable assistancein collectingthe data.

LITERATURE CITED

BEECHAM,J. j., ANDM. N. KOCHERT. 1975. Breedingbiology of the Golden Eagle in southwestern Idaho. Wilson Bull. 87:506-513. BENT,A. C. 1937. Life historiesof North American birds of prey. Dover, New York, New York, 891 pp. BERGER,J. 1986. Wild horsesof the Great Basin.Univ. ChicagoPress, Chicago, Illinois. 326 pp. BOEKER,E. L., ANDT. D. RAY. 1971. Golden Eagle populationstudies in the southwest. Condor 73:463-467. BROWN,L. H., ANDD. AMADON. 1968. Eagles,hawks, and falconsof the world. McGraw- Hill, New York, New York. 945 pp. --, ANDA. WATSON. 1964. The Golden Eagle in relation to its food supply.Ibis 106:78-100. 52] D. A. Charletand R. W.Rust J.Field Ornithol. Winter 1991

CAMERON,E.S. 1905. Nesting of the Golden Eagle in Montana. Auk 22:158-167. HANNA,W. C. 1930. Notes on the Golden Eagle in southernCalifornia. Condor 32:121- 123. HERRON,G. B., C. A. MORTIMOREAND M. S. RAWLINGS. 1985. Nevada raptors. Biological Bulletin No. 8. Nevada Dept. Wildlife, Reno, Nevada. LOOPE,L.L. 1969. Subalpineand alpine vegetationof northeasternNevada. Ph.D. thesis, Duke Univ., Durham, North Carolina. 292 pp. MCGAHAN,J. 1968. Ecologyof the Golden Eagle. Auk 85:1-12. RIEGEL,G.M. 1982. Foresthabitat types of the SouthWarner Wilderness,Modoc County, northeasternCalifornia. M.S. thesis,Humboldt StateUniv., Arcata, California. 118 pp. R¾SER,F. A., JR. 1985. Birds of the Great Basin. Univ. Nevada Press,Reno, Nevada. 604 pp. WHITTAKER,R. H. 1975. Communities and ecosystems.Macmillan, New York, New York. 385 pp. Received21 Mar. 1990; accepted20 Jul. 1990.

ASSOCIATION OF FIELD ORNITHOLOGISTS

ANNUAL MEETING 21-24 MARCH 1991

The annual meeting of the Associationof Field Ornithologistswill be held at Ohio Wesleyan University in Delaware, Ohio on 21-24 March 1991. A one-day Clark Fund OrnithologicalSymposium entitled, "Avian Conservation:Problems and Solutions,"will be held on Friday, 21 March, and will highlight the meeting. Speakersfor the Clark Fund symposiuminclude Scott K. Robinson, Brian A. Harrington, Tom J. Cad½, Carlos E. Quintela and FrancesC. James. On Saturday sessionsfor contributedpapers and a half- day symposiumentitled, "History of North American Ornithology," organizedby Jerome A. Jackson,will be held. Sundaywill be devotedto field trips. You may registerfor the Clark Fund symposiumonly or for the entiremeeting. For informationon registrationand accomodations,contact Edward H. Burtt,Jr., Departmentof Zoology, Ohio Wesleyan University, Delaware,OH d3015 (61d-368-3886)