IDENTIFICATION

The field identification of North American

A detailed, simplifiedguide takesthe puzzlesout of positive identificationof our two widespreadeagles

William S. Clark Illustrations by Brian Wheeler

INTRODUCTION DISCUSSION have found this unreliable.Many sight- ings plus a few photographsof both woSPECtES OFeagles, the Bald AGLESARE DISTINGUISHED fromother flying togetherhave shown them with the (Haliaeetus leucocephalus)and the North American raptors by their samewing attitude. Both specieshave GoldenEagle ( chrysaetos),occur greatersize, relativelylonger wings and beenseen soaring and gliding both on flat over most of North America north of overall dark coloration (Amadon 1975, and slightly raised wings. While this Mexico.The formeroccurs only in North Peterson1980), and, like mostraptors, character has been recommended for America while the latter has an extensive are generallyshy and mainly cannotbe field identification in certain locations, rangein the Nearctic,Palearctic as well closelyapproached by humanbeings. As suchas alongthe mountainridges in the as North America (A.O.U. Check-List a result,they are mostoften seeneither easternUnited States(Brett 1973, He•nt- perchedat greatdistances, or flying high 1957). Althoughthey are not closelyre- zelman 1976), its universal value is lated, their identification in the field is overhead hence the need for definitive doubtful.When gliding, the notalways simple because of thesimilar- field marks. usually closesthe primariesmore and lty in shape,size and some plumages. Bald and Goldeneagles are compara- cocks the wrist farther forward than does (Two otherspecies, the White-tailedEa- ble in size; females and more northern theGolden Eagle (Fig. 3b, upperview) gle (Haliaeetus albicilla) and the individualsof both speciesare larger. Steller'sSea Eagle (H. pelagicus)have The Bald Eaglehas a largerhead and bill BALD EAGLE beenreported in North America,the for- and longer neck than does the Golden. mer in Massachusetts and and the The Bald Eagle's wingsappear slimmer HEFOLLOWING PLUMAGE descriptions latter in parts of Alaska.) in flight with the trailingedge more near- are based on my observationsof This paperdetails field marksthat will ly parallelto the leadingedge than the known-ageBald Eagles, both in the field allowpositive identification if an eagleis 's. Immaturesof both in and from photographs. seen well, and discussesdifferences be- their first plumagehave wings slightly tween thesetwo speciesin their various widerand tails longer than in subse- Dark Immature. This is the first plum- plumages.Many of these field marks quentplumages. The Bald Eagle'slegs age, acquiredin the . The bill and havenot beenpreviously published and are unfeathered for 3 to 4 inches above cereare black, eye color dark brown. The wereidentified as a resultof the develop- the toes, whereasthe GoldenEagle's are overallplumage is mostoften uniformly ment of raptor identificationworkshops feathered to the toes, most often with darkto mediumbrown. The mostimpor- for the RaptorInformation Center. These buffy feathers.Comparing adults, the tantplumage field marksin flight are the workshopshave been presentedin many GoldenEagle has the longertail, but the whitediagonal line andwhite spoton the statesand provincesand have provided tail of the Bald in first plumageis aslong underwing.Field guideshave depicted opportunitiesfor feedbackand confirma- or longerthan the Golden's. light covertareas in the immatureplum- tion of field marks, both from the stu- Wing attitude, i.e., flat vs dihedral age, but have not fully shown these dents' and author'sexperience. (angleof thesoaring wings from the hori- marks. Table 1 briefly summarizesthe impor- zontal), has been usedas an aid in sepa- Some of the nape feathersmay have tant field marks. It refers to Figure 3 rating the two .However, after tawnytips, but these are much less exten- which illustratesflying eagles as seen extensivefield experiencewith bothspe- siveand noticeablethan the goldennape from above and below. cies in many areasof North America, I of the Golden Eagle. The primary and

822 AmericanBirds, September-October1983 Table 1. Eagle Identification Summary Bald Eagle Golden Eagle All plumages All plumages Headprojects forward of wingsmore than half the extentof the tail Head extendsforward less than half the extent of the tail.

Bill and cere are unicolored. Top of headand nape "golden."

Legsnotfeathered down to toes(only seen a! closerange). Bill andcere are tri-colored. Bill is darkat tip, horncolored at baseand cere is yellow. Immatureand subadult plumages Legsfeathered down to toes (with lightishcolored feathers in many Underwinghas diagonal white line on covertsand a whitespot where individuals.Only seen when close). wing meetsbody ("wingpit"). Tail is variablymottled, but if mostlywhitish, outer edge and tip are Immatureand subadultplumages dark. Whitein thewing is restrictedto thebase of thefiight feathers and does not appearon the underwingcoverts. Immaturewith lightupper wing coverts, darker flight feathersfrom above. Tail is white at base, with sharpdividing line with dark tip.

Subadulthas dark cheek and light tawny stripeover the eye, also Subadulthas tawny bar on upperwing. whitishtriangle on back. Adult plumage

Adult plumage Uniform dark below, but light gray barringon flight feathersand tail Unmistakablewith white head and tail. Transitionto adult produces seen at close range. unusual-lookingeagles. Tawny bar on upper wing.

secondaryflight feathersare generally mostlydark, forminga bib. Somelight characterto be acquired.The whitediag- uniform dark brown, with little or no spottingappears on the back, forming an onalline under the wing disappears early, white.The upperwing coverts are a light- invertedtriangle. There is a prominent but the white spotusually remains until er brown contrastingwith the darker buffyhne abovethe eye whichextends the is more nearly in the first-adult flight feathers. The entire coverts are ontothe nape and highlights a darkbrown plumage. lighter, whereasin the Golden Eagle areabehind the eye. Someprimaries and adult and subadultthe light area is more secondariesexhibit white areas.The bill Adult. The first adult plumageusually restrictedand forms a bar (Fig. 3). andcere have lightened to a slatecolor shows varying amounts of black or andthe eye color has lightened to hazel, brown in the white areas of the head and WhiteBelly. The next plumage is usually althoughthis is variable. The white diag- completedby the endof the first year of onalline and white spot on the underwing age. The mostprominent feature is the arestill present and are, afterthe head- whitebelly, whichhas some dark brown tail ratio, the bestfield marksin flight. markson it. The upperbreast remains Mottled. This plumage,a continuation of the previousone intothe thirdyear, has more white and mottled areas. The eyecolor is lightened to a palewhite and thebill andcere vary from horncolor to light white-yellow.The underwing marksare still present, but on somelight individualsmay be maskedby complete- ly whiteunderwing coverts (however, this will cause no confusion with the GoldenEagle). The back of mostindivid- ualswill havethe invertedwhite triangle.

Transitional. This plumage is highly variable because the subadult and adult plumagesare markedlydifferent. In gen- eral, the headbegins to lightenfirst, then the bodyand wing feathersbecome com- pletelydark. The headis usuallynot pure white, oftenwith a dark areathrough the Fig. I. ImmatureBald Eagle showingwhite eye resemblingan 's eyestripe. Fig. 2. SubadultBald Eagle showingwhite belly Photo/WilliamS. Clark. The white tail is usually the last adult triangleon back. Photo/WilliamS. Clark.

Vol. 37, Number5 823 Fig. 3a Eagles as seen from below. Top, Bald Eagle (I. to r. dark immature, white belly, mottled),below, Golden Eagle (I. to r. immature, sub-adult, adult).

824 AmericanBirds, September-October 1983 Fig. 3b. Eagles as seen from above. Top, Bald Eagle (I. to r. dark immature, white belly and mottled, adult), below Golden Eagle (I. to r. immature, sub-adult, adult)

Vol. 37, Number 5 825 Fig.4. Immatureor subadultBald Eagle. Note white underwing and Fig. 5. Immatureor subadultGolden Eagle. Note white at baseof tail. "wingpit." Photo/Harry'N. Darrow. Photo/Harry N. Darrow.

tail. In some cases, a more or less com- Sub-adult. In subsequentplumages the Wheeler and the author. I thank him for pleteterminal tail bandis present.Subse- amountof whitein the tail decreasespro- his talent, attentionto detail and pa- quentadult plumages are alike, however gressivelyuntil the 5th or 6th year when tience.Many thanksalso to the numerous even older adults can show brown and none remains. Replacementprimaries students who questioned some field black spottingin the white of the tail. and secondaries have no white. The first marks and suggestedothers. Nancy molt beginsaround one year of age, but Green made an excellent comment on Albinism. Adultshave beenreported in moltsof the flight feathersare not com- GoldenEagle bill andcere color. Appre- albinoplumage (Petit 1982, J. Hodges pleted annually (Cramp & Simmons ciationis given to JonGerrard and Peter 1979). Individuals from two to three pers. comm.).Off-white feathers replace Nye for providing photographsof the brown feathers. yearsold usuallyretain a smallamount of known-ageBald Eagles.The following white, visible from below. The upper have read drafts and providedhelpful wing coverts have a tawny area in the suggestions:Jane Church, Sidney Gauth- Vocalization.The BaldEagle is veryvo- shapeof a bar. Considerablevariation oc- reaux, Alan Harmata, Michael Harwood, cal, especiallywhen in companywith cursin the eye color, which lightensto and ChandlerS. Robbins.And finally, otherBald Eagles. amberor light brown duringthis period. thanksto JoannRodriguez for typingthe variousdrafts. The platesare the property Adult. This plumageappears uniformly GOLDEN EAGLE of the National Wildlife Federation, who brown from a distance, but, at closer graciouslygranted permission for their HEBODY AND WING coverts are uni- range,fine gray-brownbarring in the sec- use herein. form brown. There is often a some- ondariesand tail can be seen.The tawny what mottledappearance, especially on wing bar is presentin most individuals. BIBLIOGRAPHY the adult, the result of new darker feath- Vocalization.This speciesis usuallysi- AMADON, D., Chairman1975. Stickyprob- erscontrasting with the older fadedones, lemsof identification:A panel dis- lent. Many researchershave spent con- butthe mottling is neveras distinct as that cussion. pp. 118-136. In M. Harwood, of immatureBald Eagles. The golden siderablefield time studyingit and have Ed., Proc. Hawk Migr. Assoc. of N.A. naperanges from pale tawny to dark or- neverheard it call (Cramp & Simmons ConJ. 1974. angeand is presenton most individuals, 1979). However, some North American AMERICAN ORNITHOLOGISTS' UNION. individuals are vociferous near the nest 1957. Check-List of North American althoughon a few it may not be very (A. Harmam,pers. comm.). Birds. 5th Ed. Amcr. Omith. Union. Bal- obvious.The napecolor is not relatedto timore. age and probably remains constant SUMMARY BRETT, J.J. 1973. Feathers in the wind. throughoutthe bird's life. Hawk Mt. Sanct. Assoc. HETWO WIDESPREAD North American CRAMP, S., and K.E.L. SIMMONS (Eds.) eaglescan be readilyseparated in the 1979. The Birds of the Palcarctic Fauna. Immature. The tail is mostlywhite with field using the field marks presentedin Vol II. Oxford Univ. Press, Oxford. a dark terminal bar. The amount of white HEINTZELMAN, D.S. 1976. A Guide to Table I and shownin Figure3. The best variesamong individuals from the basal Eastern Hawk Watching. Penn. State field markin flight is the relativelength Univ. Press. State College. half of the tail to almostits entirety. A of the head and tail. The differences be- variable amount of white occurs at the PETERSON, R.T. 1980. A field guideto the tweenthese species are discussedin de- birds east of the Rockies. 4th ed. baseof some flight feathers, especially tail. HoughtonMifflin, Boston. the inner primariesand outer secondar- PETIT, G. 1982. Unique eagle sightedat ies.This is highlyvisible from below, but ACKNOWLEDGMENTS LBL. Tenn.Wild. Res.Ag. NEWS, Feb. 4, appearsas a much smaller area from 1982. p 1. above. The eye color begins as dark HEEAGLE PLATES were produced after --P.O. Box 1161, brown and lightens. close collaboration between Brian Annandale, VA. 22003.

826 AmericanBirds, SeptemberqDctober 1983