AUSTRALIAN 212 DEBUS, EDELST AM & MEAD BIRD WATCHER The Black Morph of the Chestnut-shouldered (Burger's) Goshawk Erythrotriorchis buergersi The New Guinean Chestnut-shouldered (or Burger's) Goshawk, formerly Accipiter buergersi, is a 'sister' species to the Australian Red Goshawk Erythrotriorchis radiatus. Recent work has shown that the Chestnut-shouldered Goshawk should be classified with the Red Goshawk in an endemic Australasian genus, namely Erythrotriorchis (Debus 1991, Schodde 1993), a move adopted by the most recent, authoritative text on the world's raptors (Ferguson-Lees et al. in press). This book has also dropped the 'gos' from the vernacular names of these species, thus removing the misleading implication that they belong in the genus Accipiter. The Chestnut-shouldered Goshawk has been said to have a black colour morph (e.g. Rand & Gilliard 1967, Coates 1985, Beehler et al. 1986). One of us, echoing Brown & Amadon (1968), is on record as casting doubt on the existence of a black morph in this species, because of potential confusion with the black morph of Meyer's Goshawk Accipiter meyerianus (Debus 1985; 1987a,b). A black morph of the Chestnut­ shouldered Goshawk was described at a time when Meyer's Goshawk was not known to occur in mainland New Guinea. It is now clear that the two species are sympatric, hence the need for a reassessment of their colour morphs. Although Wattel (1973) described a specimen of the black morph of the Chestnut-shouldered Goshawk and thus effectively removed any doubt about its existence, SJSD was not aware of this at that time. Also, Wattel did not provide a detailed diagnosis, enumerate its differences from Meyer's Goshawk, nor address the question posed by Brown & Amadon (1968) on the true identity of the black New Guinea specimen. We examined the following specimens. Chestnut-shouldered in normal plumage: one fresh juvenile male in the American Museum of Natural History, New York (AMNH 532451: CE); two immatures (male and female) in the Museum fiir Naturkunde in Berlin, Germany (nos 50.103, 30.2001: CE); two adults (male and female) in the British Museum (Natural History), Tring (BMNH 98.11.20.2 and no reg. no.: CE, DAM); two adult males in the Queensland Museum, Brisbane, and a worn juvenile female in the Australian Museum, Sydney (QM 0.17191, QM 0.17192, AM 0.40285: SJSD). Chestnut-shouldered in melanistic plumage: adult female in Berlin (BM no. 63.164: CE). Meyer's in normal plumage: immature male, two juvenile females in Berlin (nos 19.351, 50.102 and 63.165: CE); immature male, adult female in the British Museum (BMNH 88.2.7.10 and 1939.12.9.1561: CE, DAM); adult male in New York (AMNH 53.2449: CE). Meyer's in melanistic plumage: adult female in New York (AMNH 333704: CE), the bird described by Mayr (1934) . In addition, we examined colour prints of all the remaining AMNH specimens of Meyer's in normal plumage (adult male and female, juvenile female nos 812149, 220666, 532448) and Chestnut-shouldered in normal plumage (juvenile male and female? nos 532452, 802008). We can confirm that the dark Berlin bird (Plate 29) is indeed a black Chestnut­ shouldered Goshawk, and is the specimen discussed as such by Wattel (1973; J. Wattel pers. comm.). It was collected by S. Biirger on the middle Sepik River on 6 December 1912 and is an adult female just completing its second (or later) moult: wing quills new except S7 right and S8 left which are moderately worn; rectrix 6 is growing on both sides, and R4 left and R5 on both sides have not yet been shed. This bird is jet black above with only the slightest bluish sheen, and jet black below except that the greater unde:-wing coverts are dark grey and all flight and tail feathers have pale grey cross-bars below, somewhat more narrow than in normal plumage. There is no visible white on the nape. VOL. 15 (5) MARCH 1994 Black Morph of Chestnut-shouldered Goshawk 213 The melanistic Chestnut-shouldered Goshawk differs from melanistic Meyer's Goshawk in at least two ways (see Plates 29, 30): (a) tail barring. The nature of rectrix barring is similar to that of normally plumaged Chestnut-shouldered Goshawks, i.e. 9-10 narrow bars. This contrasts with the fewer (5-6) and much wider bars on the rectrices of Meyer's Goshawk (which may be more distinct on melanistic than normal Meyer's, cf. Mayr 1934). The immature male normal Meyer's (with adult quills) in the BMNH has an unbarred tail, as does one of the two adult males in the AMNH. (b) remex barring. This is again similar to that of normally plumaged Chestnut­ shouldered Goshawks, i.e. primaries and secondaries are clearly banded with narrow, evenly spaced pale bars. This contrasts with the broad and diffuse banding on the quills of Meyer's Goshawk. However, we note that a melanistic Meyer's had banding on the primaries as pronounced as in normal Meyer's, or more so (Mayr 1934), although not reaching the outer vane, as it may do in normal birds (CE). This may be an age character, as juveniles have bold primary banding in normal Meyer's (from specimens; see Plate 29). One normal adult male Meyer's in the AMNH is entirely devoid of remex or rectrix barring. A further difference between the two species is primary formula (shape of the wing tip as determined by the relative lengths and emargination of the outer primaries). The Chestnut-shouldered Goshawk, like the Red Goshawk, has a 'six-fingered' wing (P7 is longer than P6 and 8, which are longer than P5 and 9) whereas Accipiter species have a 'five-fingered' wing (Corben 1982). This may be a useful diagnostic character on birds in the hand, and in the field if soaring birds can be viewed at length or photographs obtained for later consultation. We note that neither melanistic specimen (i .e. Chestnut-shouldered and Meyer's) has visible white on the nape (cf. Mayr 1934), but there are hidden white feather bases that may show up if the bird raises a ruff when agitated. Also, toe proportions may not be diagnostic (cf. Wattel 1973): it is not clear whether the two species differ in the relative length of the middle toe, given the difficulty of correctly measuring toe length in old skins. All specimens examined by CE, of both species, have a markedly long second toe and heavy feet for their size. Unlike the black Chestnut­ shouldered Goshawk, the black Meyer's has (mostly basal?) white speckling on the uppertail coverts (as noted by Mayr 1934), but it is probably not visible in the field . The quickest way to tell the two species apart is by the banding on the tail, which in Meyer's Goshawk is much broader and sparser (e .g. Plate 31) , though in melanistic individuals this does not show up dorsally and so is less useful in the field. It does, however, provide safe identification in the hand. Another character, at least in adults, is eye colour, which has been described for some of the specimens examined. Normal Meyer's have reddish-brown irides (immature male) or dull orange-red irides (adult female), and the black bird (adult female) had dark red irides; Diamond & LeCroy (1979) listed iris colour for these and some other specimens as brown, dark red, reddish-brown and orange-brown, with one bird from the Moluccas as 'chromeous'. This last bird is an adult male (AMNH 532449, perM. LeCroy). Irides of Chestnut­ shouldered are yellow or greenish yellow. Juveniles of both species have pale eyes. Given that Meyer's and Chestnut-shouldered Goshawks co-exist in New Guinea, there is an obvious need for great care in separating the black morphs of the two species in the field. A major gap in knowledge is the juvenile plumage of the black morphs of both. The presence of a black morph in the Chestnut-shouldered Goshawk may have no taxonomic significance (cf. Debus 1985), because melanistic morphs are common in other tropical raptors, including the African Black Sparrowhawk Accipiter AUSTRALIAN 214 DEBUS,-EDELSTAM & MEAD BIRD WATCHER Ventral (upper) and dorsal (lower) views of Meyer's Goshawk Accipiter meyerianus and Chestnut-shouldered Goshawk Erythrotriorchis buergersi skins in the Museum fu'r Naturkunde, Berlin. Left to right: immature male and juvenile female (x2) Meyer's; adult female melanistic, immature female and immature male Chestnut-shouldered. Plate 29 Photos: C. Edelstam VOL. 15 (5) MARCH 1994 Black Morph of Chestnut-shouldered Goshawk 215 Ventral (upper) and dorsal (lower) views of Meyer's Goshawk Accipiter meyerianus skins in the American Museum of Natural History, New York. Left to right: juvenile female; normal adult female and male (x2); melanistic adult female. Plate 30 Photos: Photography Studio, AMNH, per M. LeCroy AUSTRALIAN 216 DEBUS, EDELSTAM & MEAD BIRD WATCHER Ventral (upper) and dorsal (lower) views of normal adult Chestnut-shouldered Goshawk and Meyer's Goshawk skins in the British Museum (Natural History). Left to right: male and female Chestnut-shouldered; female and male Meyer's. Plate 31 Photos: D.A. Mead VOL. 15 (5) MARCH 1994 Black Morph of Chestnut-shouldered Goshawk 217 melanoleucos, Ovarnbo SparrowhawkA. ovampensis and Gabar 'Goshawk' Micronisus (or Melierax) gabar. Other examples could be cited among endemic Latin American raptor genera. Some Australasian accipiters also have melanistic morphs (Solomon Islands Pied Goshawk Accipiter albogularis and Imitator Sparrow hawk A. imitator). Even in the Australasian endemic raptor clade, there is a tendency to melanistic plumage in the New Britain Buzzard or Black Honey-Buzzard Henicopemis infuscatus [an insular allospecies of the New Guinean Long-tailed (Honey-) Buzzard H.