Black-chested Buzzard-Eagle

This is a huge eagle-like "buzzard" ("hawk" in American terminology). It has a total length of 62 to 76 cm (24 to 30 in) and a wingspan of 149 to 200 cm (4 ft 11 in to 6 ft 7 in). In the nominate race, males averaged 2.13 kg (4.7 lb) and females averaged 2.75 kg (6.1 lb), with a range between both of 1.67 to 3.17 kg (3.7 to 7.0 lb). In the linearly slightly smaller G. m. australis subspecies, a male weighed 1.7 kg (3.7 lb) and a female weighed 3.2 kg (7.1 lb), indicating the bulk of the two races is roughly the same.

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 colored black, with grey tips in fresh plumage. When perched, the wings cover the tail almost completely, giving the bird a unique near-tailess appearance. 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 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, the páramos at the north of its range, for example, while providing the latter, fails to provide the former, and thus it has only been recorded in the largest patches of such habitat, such as Páramo de Frontino. Most common between about 5,000 feet (1,500 m) and 15,000 feet (4,600 m) ASL, it rarely ventures into the lowlands.

It is most conspicuous in the mid-morning and afternoon when individuals will seek out places that 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 favor of simply soaring alone or in pairs in strong air currents.

The food of this carnivore consists mainly of mid-sized mammals; the introduced European rabbit seems to have become a key prey item. The black-chested buzzard-eagle is helpful to farmers by keeping down the numbers of rabbits, which can be serious agricultural pests. Native common degus also take a large part of its diet. Other mammals are also taken such as viscachas and caviid rodents. Occasionally, it will take carnivores such as Humboldt's hog-nosed skunks, lesser grisons and even larger Andes skunks and gray foxes. Its diet is rounded off with an occasional bird. Avian prey species are usually small passerines or rails but carnivorous species like the burrowing owl and sizeable prey such as Penelope guans, buff-necked ibis or the Chilean tinamou are also taken. large squamates, and if need be also arthropods and carrion will be added in their diet. 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. …