Family Hawks, Eagles (Accipitridae)

Least Concern

Variable Hawk (Geranoaetus polyosoma)


Taxonomy

French: Buse tricolore German: Rotrückenbussard Spanish: Busardo dorsirrojo
Other common names: Gurney's Hawk (poecilochrous)
Taxonomy:

Falco polyosoma

Quoy and Gaimard

, 1824,

Falkland Islands

.

Genetic data indicate that this species is closest to G. albicaudatus#R#R, which it may replace at medium elevations. Formerly placed in Buteo and thought, mistakenly, to be close to Buteo galapagoensis (which see) and to include Buteo ventralis as colour morph (see that species). Long-standing problem of status of form poecilochrous, frequently treated as a full species (e.g. in HBW), requires resolution: one study#R failed to find any reliable diagnostic plumage and measurement differences from nominate, and genetic data#R further supported treatment as conspecific, whereas other studies proposed that the two differ in morphology and body size (from analysis of external measurements of specimens and of live birds), in plumage details (from analysis of plumage sequences) and in ecology, behaving as separate species with no intergradation or clinal gradient between them#R#R#R; detailed study examining displays and vocalizations along the long boundaries where the two taxa supposedly come into contact has been called for, and, pending this work and its findings, the view that a single species is involved#R is accepted here. (If poecilochrous treated as a full species, it would presumably include the newly described fjeldsai#R as a race.) Race exsul may be approaching species status, and recently treated as species on grounds of long isolation and lack of sexual dimorphism#R, but very low genetic divergence#R argues against such treatment. Proposed races peruviensis (Ecuador, Peru), aethiops (C Chile) and erythronotus (S Chile) all included in nominate. Four subspecies recognized.

Subspecies and Distribution
  • G. p. polyosoma (Quoy & Gaimard, 1824) – Red-backed Hawk – C Andes of Colombia S through Andes to Patagonia and Tierra del Fuego, also Falkland Is; winter visitor to NE Argentina and Uruguay.
  • G. p. poecilochrous (Gurney, Sr, 1879) – Puna Hawk – Andean páramo and puna in S Colombia (C Andes and Cauca) and Ecuador.
  • G. p. fjeldsai (J. Cabot & de Vries, 2009) – puna of Andes from N Peru S to N Chile (Tarapacá) and NW Argentina (Jujuy).
  • G. p. exsul (Salvin, 1875) – Juan Fernandez Hawk – Alejandro Selkirk I (Más Afuera), in Juan Fernández Is, off SC Chile.
  • Introduced (exsul) to Robinson Crusoe I, in Juan Fernández Is.

    Descriptive notes

    45–62 cm; 660–1300 g; wingspan 113–151 cm. True to its English name, a highly variable, polymorphic hawk with longish wings and legs and medium-length tail... read more

    Voice

    Gives loud “keeow-kyow-kyow” while soaring and especially when disturbed at nest; poecilochrous... read more

    Habitat

    Occupies open and semi-open habitats across broad range of elevations and topographies, from... read more

    Food and feeding

    Nominate race a generalist mammal predator, taking most prey roughly in proportion to its relative abundance; e.g. at low elevations in C... read more

    Breeding

    Few data. Nests Dec–Jul in Ecuador; Sept–Jan in mainland Chile, Argentina and Falkland Is; Nov–Feb on Alejandro Selkirk I... read more

    Movements

    Some populations composed of residents, others of partial migrants. In Bolivia, birds in valleys... read more

    Status and conservation

    Not globally threatened (Least Concern). CITES II. Status poorly known, but in general appears to be relatively secure, and locally common, although thought to be declining... read more

    Recommended citation

    Bierregaard, R.O., Jr, Marks, J.S. & Kirwan, G.M. (2019). Variable Hawk (Geranoaetus polyosoma). 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/53131 on 23 April 2019).