Plumages and Moult of the Little Eagle Hieraaetus Morphnoides

VOL. 13 (4) DECEMBER 1989 103 AUSTRALIAN BIRD WATCHER 1989, 13 , 103-113 Plumages and Moult of the Little Eagle Hieraaetus morphnoides by S.J.S. DEBUS, P.O. Box 1015, Armidale N.S.W. 2350 Summary The plumages, age criteria and moult of the Little Eagle Hieraaetus morphnoides were investigated from museum skins, captive birds and field studies in north-east New South Wales. Characteristics of juveniles, second-year birds and adults of both morphs are discussed: these relate mainly to the colour of the head and underparts (juveniles more rufous than adults of their respective morphs); the amount of black streaking on the crown, crest and underparts (heaviest in adults); the colour and contrast of the median upper-wing coverts and scapulars (paler and more prominent in adults); the presence of a uniform translucent trailing edge to the wings and tail in juveniles; and the colour of soft parts (irides changing from dark brown to reddish brown or orange-brown; cere, gape and feet tending to fade from cream or pale yellow to off-white). First-year birds show no wing or tail moult until c. 12 months old. Older birds show descendent, interrupted, symmetrical primary moult and convergent, symmetrical retrix moult, or jumbled and sometimes asymmetrical primary and rectrix moult. A rare, previously undescribed rufous morph in adults is a 'red' version of the dark morph but with the under wing pattern of the light morph. The proportion of dark and light birds varies geographically, with the highest proportion of dark birds on the humid east coast of Australia. Light x light adults produce light young, and dark x light adults produce light or dark young. It is suggested that light birds are homozygous, most (moderately) dark birds are heterozygous, and the few exceptionally dark ('black') birds are also homozygous. Introduction The plumage stages, age criteria and moult of many Australian raptors, including the Little Eagle Hieraaetus morphnoides, are poorly understood. The ability to distinguish age classes in raptors is useful for conservation purposes (e.g. Ridpath & Brooker 1986), and the study of moult reveals the time taken to attain each plumage class (e.g. Brooke et al. 1972). Such knowledge enables population trends to be monitored from the proportion of birds in each age class. This paper presents data on plumages, age criteria and moult of the Little Eagle derived from studies of birds in the field, in captivity and in museum collections, and supplemented by the literature and by data generously provided by colleagues. Methods Field studies Since 1980 I have observed eight fledgling Little Eagles of the light morph (all progeny of light x light parents), and one fledgling of the dark morph (progeny of light male x dark female), at distances down to 15m through 8 x 40 binoculars. Since 1980 I have also kept a tally of sightings (total 300) of each morph of the Little Eagle. This is based on casual observations and transect counts in the north-eastern part of New South Wales bounded by the Queensland border, Warialda, Narrabri, Coonabarabran, Singleton and Sydney (effectively from the North-West Slopes and Hunter Valley eastwards to the coast). Museum studies I examined 70 Little Eagle specimens from collections in eastern Australia (Queensland Museum, Australian Museum, Museum of Victoria, South Australian Museum, Australian National Wildlife Collection in Canberra, and University of New England, Armidale). Sixteen of these were identifiable as juveniles including six (5 light, 1 dark) that were clearly fledglings from their collection dates and plumage AUSTRALIAN 104 DEBUS BIRD WATCHER condition. Details of plumage and soft parts (if described by the collectors) were noted for each specimen. Moult details were noted for 48 post-juvenile specimens. Captive studies In March 1986 I obtained an injured female Little Eagle for rehabilitation after it had received veterinary treatment at Taronga Zoo, Sydney. This bird had accidentally lost (and regrown) several tail feathers in January, but it had all the characteristics of a juvenile (first-year) bird including symmetrical fault bars across all its original rectrices, fresh, evenly worn primaries and secondaries and no sign of moult. It was released in April 1987 after it moulted. Details of plumage, soft parts and moult were kept from written descriptions, colour photographs, the collection and labelling of moulted flight and tail feathers, and examination of the bird in the hand for missing or growing feathers. In June 1987 I received an injured adult male Little Eagle. It was in the final stages of regrowing several flight and tail feathers; it moulted one dorsal and one ventral body feather during the following two months before it was transferred to another facility. Terminology Because it was clearly established that Little Eagles are either light or dark at fledging and remain so after moulting, the term 'morph' (a lifelong condition) is used in preference to 'phase' (a transitory stage); the criterion for classification as dark or light is the under-wing pattern (see Debus 1984). A rare rufous morph in adults (not to be confused with juveniles of the light morph) is described. A standardised terminology for colour description is desirable, therefore where possible the names of colours used here are those in Smithe (1975) with identifying numbers. Primary feathers are numbered from the innermost (1) to outermost (10), and rectrices are numbered from the central (1) to outermost (6) on right (R) and left (L) sides. Moult terminology follows Brooke et al. (1972). Results First-year plumage Light morph: The juvenile plumage of the light morph is described in some detail by Whitlock (1909) and Hall (1974), and illustrated by colour photographs in Cupper & Cupper (1981, p. 173), Egerton (no date, p. 26) and Trounson & Trounson (1987, plate 7, p. 10). Juveniles differ from adults of the light morph by their more rufous head and underparts, 'warmer' rufous cast to the upperparts and darker, less contrasting 'shoulder' band (median upper-wing coverts) and scapulars. Many juveniles have a rufous wash to the oblique band on the under-wing (museum specimens). Juveniles have little or almost no black streaking on the head (cheeks, crown and crest), and have thin streaks on the underparts (dark feather shafts only). They also have pale tips to the secondary coverts, secondaries, inner primaries and rectrices. Some juveniles have pale rufous terminal spots on the lesser upper-wing coverts. At fledging, the iris is dull, dark brown (grey-brown in nestlings), and the cere, gape and toes cream to pale yellow. In some older first-year birds, the cere and toes are pale blue-grey (museum data). Some fledglings are rufous to the under-tail coverts (pers. obs.), whereas some museum specimens, the nestling described by Hall (1974) and the juvenile photographed by Trounson & Trounson (1983, Plate 7, p. 10) are paler on the belly. The captive bird held by me was at c. 7 months old paler on the belly than wild fledglings I have seen. These differences may be a result of feather wear and/or individual variation. VOL. 13 (4) DECEMBER 1989 Plumages and Moult of the Little Eagle 105 Dark morph: There are no detailed descriptions of the juvenile plumage of the dark morph, but a colour photograph of a feathered nestling is provided in Morcombe (1986, p. 138). This bird is darker reddish brown (amber, colour 36) on the head and underparts than juveniles of the light morph (cinnamon-rufous, colour 40); it has less streaked head and underparts and darker, less contrasting upper-wing coverts than adults of the dark morph. The juvenile dark morph observed by me resembled fledglings of the light morph but was slightly darker and duller rufous (tawny, colour 38) on the head and underparts and had dark brown (not white) wing linings. Compared to the adult dark morph, it had a darker (though still discernible) fawn band across the upper-wing coverts and more rufous, less heavily streaked head and underparts. It was no darker below than some adults of the dark morph, and in fact it was not as dark on the breast as its mother. A juvenile male of the dark morph agrees with the above dark juveniles in its rich tawny (colour 38) head and underparts and dark (fawn, colour 25) upper wing coverts; it had little black on the head and crest but it had more prominent dark shaft streaks on the underparts than juveniles of the light morph (P. Slater unpubl. photographs). Two juvenile females of the dark morph were not as 'red' as this bird (P. Slater unpubl. data). Museum specimens reveal that dark juveniles may have prominent (though narrow) breast streaks, pale rufous spots on the lesser upper-wing coverts, and pale tips to the secondary coverts, secondaries, inner primaries and rectrices. None of these specimens was any darker on the breast than dark adults of the same sex in museum collections. A colour photograph of a dark bird of the New Guinean form H.m. weiskei in flight (Pruett-Jones & Pruett-Jones 1981, p. 21) appears to show a juvenile: it has an unmarked tawny head, yellow gape and feet and uniform translucent trailing edge to wings and tail. This bird, misidentified in the caption as a Whistling Kite Haliastur sphenurus, resembles dark juveniles of the Australian form except that it appears to have a zone of heavier black streaks on the breast. Second-year plumage Light morph: After moulting, the captive female held by me had changed little in colour except that there was more black on the crown; her median upper-wing coverts were still dark although each feather had a small pale area at the tip, and she had lost most of the rufous spotting on the lesser upper-wing coverts.

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