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The White-throated Hawk is a small, brown and white hawk of the Andes Mountains. An austral migrant, it breeds in central Chile and adjacent Argentina. It is now thought that birds found in the Andes from Peru north to Venezuela are entirely non-breeding visitors. It occurs in and around humid montane forests, and frequently soars high overhead. This species is dark brown above and largely white below. Unlike the similar Broad-winged Hawk (Buteo platypterus), White-throated has streaking confined largely to the sides of the breast and flanks, giving it a semi-collared appearance. The feeding and breeding behavior in this species are poorly-known. It apparently captures rodents and birds, and nests in shrubs or on cliffs.
38–48 cm, wingspan 84–102 cm (1). Smallish Buteo. Markings on sides of breast and thighs separate present species from B. brachyurus; tail noticeably longer. Brownish black above and on sides of head; white below , with sides of body chestnut, breast and belly streaked brown, and thighs barred with rufous; tail dark brown above, greyish below, with 8–10 narrow dark bands. Dark morph unknown (although suspected to occur) unlike in B. brachyurus (1). Female as male, but somewhat larger (by 2–20%) (1). Bare parts: irides brown (perhaps paler in juvenile) and cere and legs yellow (1). Juvenile similar to adult but has large blackish streaks on breast and flanks, streaked cheeks and sides of breast, and brown-barred buff thighs (1); pale-morph juvenile Geranoaetus polyosoma is larger, longer-winged, shorter-tailed, lacks hood and has more uniformly marked underparts than present species (1).
Andes from Colombia (exceptionally Mérida, in NW Venezuela) S to Bolivia, thereafter in C Chile (Atacama to Aysén (3) ) and W Argentina (S to Santa Cruz (4) ), but known to breed for certain only in the two last-named countries (5).
Generally from 1700 m to 3500 m in N half of range, but regularly at 1000–2000 m in Andean Patagonia (1), at 10–1200 m in the Chilean coastal range (6) and occasionally down to sea-level in Peru (1); humid mountain forest to stunted forest and cloudforest at higher altitudes and in adjacent open country including puna (1); frequents areas with Eucalyptus in Ecuador (though such records may only pertain to migrants) (7) and has been observed in same habitat in SW Peru (8), but mainly in Araucaria and Nothofagus (9) in S of range; however, one pair successfully nested in a pine plantation (Pinus radiata) within an urban area at Concepción, S Chile (10).
Certainly migratory from southernmost parts of range, moving lower and more specifically N in non-breeding season (commencing Mar–Apr) (9), with records down to sea-level in Peru and Chile (1) and records in NW Argentine Yungas (Jujuy, Salta, Tucumán) presumably pertaining to migrants (11). Birds return to austral breeding areas in Sept–Oct (7). Known to migrate in small flocks, sometimes with other hawks, e.g. B. polyosoma and B. ventralis (11). Although it is still unclear if the species is a total migrant (i.e. it breeds only in the far S of its range) or a partial migrant (i.e. it is resident in some other parts of the overall range), it has been speculated that all records from Ecuador pertain to migrants (12) and a satellite-tracked bird reached S Ecuador in late May (7). While it appears that the species reaches W Bolivia (e.g. La Paz) (13), presumably as an austral migrant (11), there are no definitive records in the country to date.
Diet and Foraging
Very few data available. Known to take insects, beetles (14), rodents and birds, with the following prey remains found at a nest of the species: Striped Woodpecker (Veniliornis lignarius), Austral Thrush (Turdus falcklandii), House Wren (Troglodytes aedon), Thorn-tailed Rayadito (Aphrastura spinicauda) and Black-chinned Siskin (Carduelis barbatus) (14). Observed pursuing potential prey as large as Magellanic Woodpecker (Campephilus magellanicus) (14). Males provisioned incubating females with rodents (37·5%) and lizards (25%), the remainder of the prey items being unidentified; during nestling period, 26% of prey items were birds, 16% rodents, 13% lizards and 45% unidentified (15).
Sounds and Vocal Behavior
Considered to be often silent, but utters squealing “kee-ah” during breeding season or a similar “kee-ea” that falls in pitch after first syllable when near nest (1).
Apparently breeds only in S of range (11). Until recently season unknown, but seen defending territory in Chile in Feb (1) and nest in Argentine Patagonia with young ready to fledge in late Jan (14). Overall season lasts from mid Sept until perhaps Apr, at least in Arg, but only two recorded instances of laying were 10–15 Nov; all observed copulations between mid Oct and mid Nov (15). Species has undulating display flight, although this does not appear to have been described in detail (15). Nests, which are difficult to see from the ground, constructed of both live and dead sticks, often covered in lichens, at mean height of 16 m above ground (range 13–22 m); adults continue to add material into nestling period, mostly by female during incubation (15). Nest sometimes reused in subsequent season (15). Single claim of nest on cliff in Chile, but some question as to whether species involved correctly identified (15). Two nests in Argentina were constructed on Nothofagus pumilio (Nothofagaceae) trees, 15 m and 15·5 m above ground; the platform of one measured 80 cm × 76 cm, was nearly circular, 22 cm in height at its centre and the cup measured 36 cm × 30 cm and 8 cm deep, while the other nest (1·5 km away) was oval-shaped and measured 72 cm × 68 cm, was 26 cm high in the centre and the cup was 24 cm × 25 cm and 7 cm deep (14). Overall range of measurements: platform 61–81 cm × 38–76 cm × 22–45 cm, cup 19–36 cm × 16–31 cm × 2–8 cm (15). Lays 1–2 white eggs, 50·23 mm × 39·98 mm, incubated for c. 1 month, mainly by female, with male on-bouts apparently confined to daylight hours; male entirely provisions female during incubation and brings at least 80% of food during nestling period, which occupies c. 40 days, but female principally responsible for feeding young (15). Chicks have white down. Adults may continue to provision young post-fledging (15). To date, species has only ever been recorded to fledge single young (15).
Not globally threatened (Least Concern). CITES II. Very poorly known. Generally rare and local throughout range, e.g. in Colombia, with just one record from late 1920s in NW Venezuela (16). Sometimes listed for Bolívar, SE Venezuela (1), but seems highly unlikely to occur in this region (16). Only recently discovered in C Ecuador, although these records might only be migrants (7). Considered uncommon to fairly common in C Chile and adjacent Argentina, which region represents this hawk's core (and perhaps sole breeding) range (1) and from where observations have increased dramatically in recent decades (9), spreading southwards in Aysén Province, S Chile (17). Known from relatively few protected areas across the species' range, including Fray Jorge, La Campana and Nahuelbuta National Parks, in Chile (6), and Nahuel Huapi (18), Perito Moreno, Los Glaciares (19) and Los Alerces National Parks, in Argentina (9). Preferred altitudinal range relatively less affected by human activities, especially transformation; also shows tolerance of disturbed habitat. Surveys and research required.