Bare Parts in Honey Buzzards


Literature on Bare Parts Colouration


Forsman (1999) attaches considerable significance to bill patterns.


p.33 for Honey Buzzard, adults have yellow eyes and a dark cere, which is unique among European buzzards. Juveniles have dark brown eyes, like many other species, but the bill is diagnostic: cere and base are bright yellow with black only at the very tip. The juvenile Honey Buzzard shows much more yellow and less black in the bill than any other species – a useful character also on flying birds. The feet are yellow at all ages.


p.268 for Common Buzzard, feet and cere yellow at all ages, deeper in adults than in juveniles; bill dark. Iris pale grey, brownish grey or light brown in juveniles with black pupil clearly visible. Adults show a very dark brown iris and the pupil is not discernible in the field.


Earlier, Forsman & Shirihai (1997) made a similar point:


p.5 for Honey Buzzard, at close range, the bare parts provide another important clue when separating juveniles and adults. Juveniles have all-dark eye and the basal portions of the bill and gape, including cere, are bright yellow. The bill, also unlike Buteo buzzards, is extensively yellow with only a small dark tip.


The Collins Bird Guide (2001) mentions the cere of juvenile Honey Buzzards as being yellow but does not mention the bill colour (p.90).


Ferguson-Lees & Christie (2001) mention at p.339: Common Buzzard has less extensively yellow bill than juvenile Honey Buzzard.


Literature on Bare Parts Dimensions


Baker (1993) brings together clearly statistics from BWP (Cramp, 1980) with Honey Buzzard at p.160-162 and Common Buzzard at p.176-179. To a large extent the tarsus has been over-looked before in Honey Buzzard identification, except perhaps in perched birds. The length of the tarsus varies a lot from raptor species to species.

Kites in particular have short legs for the size of the bird. The table below shows how similar the tarsus length for Honey Buzzard is to that of the kites. The tarsus is short for the kite family, indeed being no longer than that of the much smaller Sparrowhawk. It should also be noted how the Common Buzzard tarsus is much longer than that for Honey Buzzard by about 50%.


Species

Male mean (mm)

Female mean (mm)

Honey Buzzard Pernis apivorus

51.9

53.6

Black Kite Milvus migrans

55.2

55.9

Red Kite Milvus milvus

53.2

52.8

Sparrowhawk Accipiter nisus

53.4

61.0

Common Buzzard Buteo buteo

75.0

76.5

Table showing Variation of Length of Tarsus in selected Raptor Species



Discussion


Bare parts are perhaps slightly underrated for identification of birds of prey. With buzzards and Honey Buzzard, the bill and cere may be useful in photographs of birds soaring overhead at fairly close range as the light catches the top of the bill and the cere well while the underside pattern of the wings may be underexposed. The largely yellow bill and all-yellow cere on a juvenile Honey Buzzard is very useful support for the identification.


For identification purposes the length of the tarsi is significant when Honey Buzzard are seen perched in the open (Forsman 1999, p.33) but this is rare so not of much use in everyday fieldwork. In flight if the underside of the bird is seen clearly or photographed with some detail then the length of the legs relative to the length of the tail is significant. This is because the Common Buzzard has a shorter tail but longer legs so in this species the legs extend about half-way along the tail. In the Honey Buzzard the tail is longer and the legs shorter so the legs only extend about 25-30% along the tail. The plates in Forsman (1999) for the two species confirm these relative lengths. This feature should be used with caution on birds that have a spread tail while soaring as the length of the tail appears to be much shorter then. On birds with folded tails though the difference in this feature is very significant.


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