The Black-chested Buzzard-Eagle (Geranoaetus melanoleucus)

Jan 12, 2014 Features / Columnists, Interesting Creatures in Guyana

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The Black-chested Buzzard-Eagle (Geranoaetus melanoleucus) is a bird of prey of the hawk and eagle family (Accipitridae). It lives in open regions of South America. This species is also known as the Black Buzzard-eagle, Grey Buzzard-eagle or analogously with “eagle” or “eagle-buzzard” replacing “buzzard-eagle”, or as the Chilean Blue Eagle. It is sometimes placed in the genus Buteo.
This is a huge eagle-like “buzzard” (“hawk” in American terminology). It has a total length of 24–32 in (about 60–80 cm) and a wingspan of 58–79 in (149–200 cm). In the smaller G. m. australis subspecies, the weight is 3.7–7.1 lb. (1.7–3.2 kg), with no reported weights on the nominate subspecies. It is noted for its bulky, powerful-looking build. It is rather long- and broad-winged and the slightly tapering tail is short by comparison and coloured black, with grey tips in fresh plumage.
When perched, the wings cover the tail almost completely, giving the bird a unique near-tailless appearance when perched. The adult has a white underside, sometimes with fine blackish stripes; its upperparts are dark grey with a blackish, brownish or bluish hue. The feathers of the neck and the lowest dark feathers of the breast are somewhat elongated. Adults have an ash-grey-and-white zone on the wings, the silvery white seen clearly from afar. The female is distinguished by a reddish-cinnamon hue to the upper- and underwing secondaries and is considerably larger than the male.
The immature plumage is reminiscent of that of the Great Black Hawk (Buteogallus urubitinga). Its upperparts are deep brown, sometimes almost black, and it has no light wing patch. The underside is white or light buff with heavy dark streaks on the breast and dark bars on the belly and thighs. It does not acquire the full adult plumage until 4–5 years old.
It is not very vocal, calling usually in flight and when close to the nest. Some calls resemble a wild human laugh; others are a curlew-like whistle. Occasionally flying birds give a high-pitched vocalization “kukukukuku”.
The Black-chested Buzzard-Eagle is readily identified in flight by its short wedge-shaped tail scarcely protruding from its long, broad wings. It is usually easy to make out the generally white underparts with the dark chest-band and tail if the birds are adult. Yet as this bird is usually encountered in the wild when it soars, you are less likely to see its grey upperparts.
The Black-chested Buzzard-Eagle is found in mountainous or hilly terrain with sparse vegetation, shrubland or (in the south of its range) Nothofagus forest, where it spends a lot of time soaring in thermals and vertical drafts while looking for prey. It requires large territories with suitable habitat.
It is most conspicuous in the mid-morning and afternoon, when individuals will seek out places which provide the best soaring conditions, such as north and west facing slopes and ridges. Apparently, their main interest at these times is aerial play and display; they tend to ignore places where food is more plentiful or easily hunted in favour of simply soaring alone or in pairs in strong air currents.
The food of this carnivore consists mainly of mid-sized mammals. The Black-chested Buzzard-Eagle is helpful to farmers by keeping down the numbers of the rabbits, which can be serious agricultural pests. Its diet is rounded off with an occasional bird – including carnivorous species.
While not aggressive under normal circumstances, the Black-chested Eagle-buzzard will fiercely attack humans if it considers itself or its offspring threatened. It is near the top of the avian food chain in its range, in part since it is the only Andean eagle found outside forest habitats.
It nests in high trees or on rocky cliffs, or if these are not available on high trees or even cacti. If no appropriate high place is available this species will nest in bushes or even on the ground.
The nest is a huge mass of sticks about 85 centimetres (33 in) in diameter; the Black-chested Buzzard-Eagle is just as likely to reuse an existing nest as to build a new one, and several abandoned nests are often found in the vicinity of an active one. The male and female engage in courtship flights, and copulate over a prolonged time of several weeks as the pairs bond. Little is known of the actual nesting; the clutch contains usually but sometimes one or three eggs, which are incubated for about a month. The nestlings presumably are covered in white down like in its relatives.
This bird species is considered a Species of Least Concern by the IUCN. While it is rare and declining in places – e.g. in Rio Grande do Sul and Santa Catarina states in Brazil, or in parts of Argentina – its habitat requirements mean that it will to some degree benefit from deforestation.
(Source: Wikipedia – The Free Online Encyclopedia)

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