Family Hawks, Eagles (Accipitridae)

Endangered

Black-and-chestnut Eagle (Spizaetus isidori)

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Taxonomy

French: Aigle d’Isidore German: Isidoradler Spanish: Águila poma
Other common names: Isidor's Eagle
Taxonomy:

Falco Isidori

Des Murs

, 1845,

Bogotá, Colombia

.

Previously placed in monotypic genus Oroaetus, but recent phylogenetic study found this species to be nested among the New World Spizaetus group#R. DNA studies indicate that this species and S. ornatus are sisters, and that S. melanoleucus is sister to this pair#R#R#R. Monotypic.

Distribution:

Coastal ranges of NE Colombia (Santa Marta Mts) and N Venezuela (Carabobo and Aragua), also Sierra de Perijá (on border of those two countries), and Andes of NW Venezuela (Mérida and Trujillo) S on both slopes through Colombia, Ecuador and extreme NW Peru, then along E slope through Peru, Bolivia and NW Argentina (to Jujuy and Catamarca)#R#R.

Descriptive notes

60–80 cm, wingspan 144–166 cm#R. Large, stocky eagle with relatively short tail but long wings#R. Head, crest, neck and upperparts black, below chestnut streaked with black; thighs black, feathered tarsi chestnut; tail greyish, with thick black subterminal band; underside of primaries whitish with black tips, contrasting sharply with chestnut secondaries and underwing-coverts. Crest seems to be erected when relaxed; held erect even in flight, and lowered in stressful situations. Female similar to male, but significantly larger (by up to 14%#R) and also relatively longer-tailed#R. Iris orange-yellow, cere yellowish horn, feet yellow. Immature fuscous-brown above; head, neck and underparts white; tail with two visible blackish bands above broader subterminal band; hindneck and mantle streaked dusky, crest tipped black. Gradual transition to adult plumage, with progressive darkening over four years; underparts become streaked with chestnut and dusky brown; iris blue-grey in juvenile, becoming yellowish in older immature birds.

Drawing by Ian Willis
Descriptive notes:

60–80 cm, wingspan 144–166 cm#R. Large, stocky eagle with relatively short tail but long wings#R. Head, crest, neck and upperparts black, below chestnut streaked with black; thighs black, feathered tarsi chestnut; tail greyish, with thick black subterminal band; underside of primaries whitish with black tips, contrasting sharply with chestnut secondaries and underwing-coverts. Crest seems to be erected when relaxed; held erect even in flight, and lowered in stressful situations. Female similar to male, but significantly larger (by up to 14%#R) and also relatively longer-tailed#R. Iris orange-yellow, cere yellowish horn, feet yellow. Immature fuscous-brown above; head, neck and underparts white; tail with two visible blackish bands above broader subterminal band; hindneck and mantle streaked dusky, crest tipped black. Gradual transition to adult plumage, with progressive darkening over four years; underparts become streaked with chestnut and dusky brown; iris blue-grey in juvenile, becoming yellowish in older immature birds.

Drawing by Francesc Jutglar
Descriptive notes:

60–80 cm, wingspan 144–166 cm#R. Large, stocky eagle with relatively short tail but long wings#R. Head, crest, neck and upperparts black, below chestnut streaked with black; thighs black, feathered tarsi chestnut; tail greyish, with thick black subterminal band; underside of primaries whitish with black tips, contrasting sharply with chestnut secondaries and underwing-coverts. Crest seems to be erected when relaxed; held erect even in flight, and lowered in stressful situations. Female similar to male, but significantly larger (by up to 14%#R) and also relatively longer-tailed#R. Iris orange-yellow, cere yellowish horn, feet yellow. Immature fuscous-brown above; head, neck and underparts white; tail with two visible blackish bands above broader subterminal band; hindneck and mantle streaked dusky, crest tipped black. Gradual transition to adult plumage, with progressive darkening over four years; underparts become streaked with chestnut and dusky brown; iris blue-grey in juvenile, becoming yellowish in older immature birds.

Voice

Usually silent, except in breeding season. Then, most common vocalization is a series of a few piercing monotonous whistles “KEEEuw...KEEEuw..”. Fledged young are quite vocal, and utter a series of yelping whistles “yeEEW..yeEEW..yeEEW”.

Habitat

Heavily forested mountain slopes in subtropical and lower temperate#R zones (exceptionally to up upper tropical zone#R), probably occurring mostly in large valleys; usually at 1500–2800 m, but recorded from 150 m#R up to 3800 m#R.

Food and feeding

Most data are based on heresay#R. Large birds (e.g. guans) and arboreal mammals, from squirrels (frequently delivered to young for first 2 months of life#R) to monkeys (Lagothrix); sloths (Choloepus/Bradypus), tree porcupines and coatis also reported#R. Observed attacking group of Sickle-winged Guans (Chamaepetes goudotii)#R. Thirty-four prey items identified at nests in Colombia dominated by Penelope montagnii but also included domestic chickens and turkeys#R; 29 prey items identified at nest in Argentina consisted of 14 guans (Penelope sp.), four diurnal raptors (including Caracara plancus), one Tinamou (Tinamidae), two domestic chickens and eight other unidentified birds#R. Powerful legs and talons specialized for taking large prey. Hunts primarily in the canopy; soars frequently and is rarely seen perched.

Breeding

Few nests found. No description of any aerial displays#R. In Venezuela and Colombia#R, nest building Feb–Mar, hatching May, fledging probably Aug; in Bolivia, nesting in Aug; at first nest known from Argentina, egg laid in late May or early Jun, chick hatched on 9 Jul, and nestling fledged in mid- to late Oct#R. Very large stick nest, up to 2 m wide and 1 m deep#R; built in emergent tree, or in tree on side of ravine; in Venezuela, prefers oaks, and perhaps east-facing valley slopes; greenery brought to nest from time to time; nest placed up to 22 m above ground#R#R. Clutch size probably only 1 egg; chick has white down; fledging estimated at 4 months, although chick at first nest in Argentina fledged at about 3·5 months#R. Male provides most of food until young well developed; noisily announces arrival at nest; will feed young if female away from nest.

Movements

Presumably sedentary.

Status and conservation

ENDANGERED. CITES II. Rare and patchily distributed along a 6000 km linear range from Venezuela to Argentina; status very poorly known. Population estimated to number fewer than 1000 mature individuals in 2001#R, and more recent reassessments of national populations appear to confirm that it is scarcer than previously thought. Not considered of conservation concern until 2004; indications that the population is smaller than previously assumed, and declining, led to classification as Endangered in 2014#R. A few hundred are perhaps present in Venezuela, up to 200 in Ecuador. Despite the absence of documented records in NW Argentina in the decades following its discovery in 1954#R#R, more than a dozen sightings have been reported since the 1980s, especially in Calilegua National Park#R, and a nest was documented in Feb 2014#R. Probably susceptible to loss of continuous forest habitat; observed in some partially logged tracts of forest, but perhaps as direct result of loss of extensive primary forest in subtropical zone. In Colombia and Ecuador it is also persecuted as a predator of chickens, with eight cases of eagle persecution and killing documented in one Colombian study#R. Surveys conducted in rural area of Gachalá‐Cundinamarca, Colombia, estimated an annual loss of one to two domestic fowl per household, with 57% of owners surveyed claiming to have suffered losses; inhabitants preferred not to have eagles breeding close to their houses (< 10 km) and would consider killing eagles that preyed on more than five domestic fowl per year#R. Likely highly dependent on protected areas, e.g. Podocarpus National Park in S Ecuador#R. Considered nationally Near Threatened in Venezuela#R, Endangered in Colombia#R and Argentina#R. Given the growing concern over the true status of this large eagle, reliable population estimates are urgently needed. Further research is required to determine ecological requirements and tolerance of habitat fragmentation, and to identify key threats and quantify their relative contribution to population declines#R.

Recommended citation

Bierregaard, R.O., Jr, Kirwan, G.M., Boesman, P., Sharpe, C.J. & Marks, J.S. (2017). Black-and-chestnut Eagle (Spizaetus isidori). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from https://www.hbw.com/node/53185 on 13 December 2017).