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Gray-backed Hawk
Leucopternis occidentalis

Status: Endangered

Population Trend: Declining.

Other Names: Grey-backed Hawk.

Leucopternis occidentalis
click to enlarge
Distribution: Neotropical.  Western ECUADOR and extreme northwestern PERU. more....

Subspecies: Monotypic.

Taxonomy: Using sequences from four mitochondrial genes, Amaral et al. (2006) found that the genus Leucopternis, as traditionally arranged, is not monophyletic and that it is a composite of three independent lineages. The predominantly black and white plumage shared by several species has evolved at least twice. The Gray-backed Hawk has sometimes been considered a race of L. albicollis (Stresemann and Amadon 1979). The recent phylogenetic studies of Lerner et al. (2008) showed a close relationship between the trans-Andean (west of the Andes) races of the White Hawk, L. albicollis, and L. occidentalis. They suggested that the northern subspecies, L.albicollis ghiesbreghti, forms a clade sister to L. occidentalis, but the nominate race, L.a. albicollis is more closely related to L. polionotus.

Movements: Non-migratory (Bildstein 2006).

Habitat and Habits: Chapman (1926) described the ecological range as deciduous and evergreen forests from 100 to 2,100 m elevation. Vargas found the species from 100-1,300 m in his study areas in western Ecuador, where it occurred in Tropical Dry Forest, Tropical Moist Forest, and Tropical Cloud Forest, but not in the wetter lowland tropical forests of Esmeraldas. In some areas, it occurs in a mosaic of forest patches and agricultural lands, and it is not found in the interior of dense forest. This species is said to be very confiding and easily approached, a behavioral trait that probably contributes to its scarcity. In northwestern Peru, Weidenfeld et al. (1985) almost always saw this species perching quietly in the middle level of open trees.

Food and Feeding Behavior: Vargas (1995) identified a total of 246 food items delivered by males to females, nestlings, and fledglings. Prey, in decreasing order of frequency, were reptiles (59%), mammals (13%), birds (10%), crustacea (9%), amphibians (7%), and earthworms (3%), with the two main prey types being snakes (48%) and rodents (13%), mostly rice rats (Oryzomys). He did not record insect prey, but local farmers informed him that the species eats large grasshoppers during the rainy season, and a beetle and a katydid were found in the stomachs of collected specimens (Robbins and Ridgely 1990). Collar et al. (1992) listed small frogs as prey, and Williams and Tobias (1991) recorded one taking a thrush. Overall, Varga concluded that this species is primarily a snake-eater, but that it is opportunistic and will usually take the most available prey in the habitat.more....

Breeding: Vargas (1995) made a detailed study of this species in western Ecuador from 1992 to 1994, and the following summary is from his work: Breeding apparently occurs throughout the year, since nests with eggs were found in eight different months. Ten nests were generally small, well hidden structures of fresh and dry sticks, lined with green sprigs or green leaves, and placed from 14-35 m in a tree 20-45 m tall. All of the nest trees were growing on steep slopes and were relatively close to streams. Based on observations at five nests, clutch size is apparently one unmarked, bluish-white egg, and one measured 54.7 x 46.3 mm. Egg mass of 62 g (n = 1) was 8.3% of female body mass. The incubation period was 36 days at one nest. Only the female incubated, and the male provided her with food. In Vargas's study, two nestlings fledged at 84 and 76 days, respectively, and another chick left a nest that had disintegrated at 56 days.more....

Conservation: This species now survives in only a few remnant forest patches in western Ecuador (Robbins and Ridgely 1985, Best et al. 1993, Vargas 1995) and northwestern Peru (Wiedenfeld et al. 1985), one of the most heavily deforested areas in the world. Vargas (op cit.) estimated a population size of about 500 breeding pairs in Ecuador, the stronghold of the species, and additional habitat loss has occurred since his study. Categorized as Endangered by BirdLife International (2006).more....

Important References: 
Amaral, F.S., M.J. Miller, L.F. Silveira, E. Bermingham, and A. Wajntal.
  2006. Polyphyly of the hawk genera Leucopternis and Buteogallus (Aves,
  Accipitridae): multiple habitat shifts during the Neotropical buteonine
  diversification. BMC Evolutionary Biology 6:1-10.
Bierregaard, R.O. 1994. Grey-backed Hawk. P. 170 in del Hoyo, J., A.
  Elliott, and J. Sargatal (eds). Handbook of birds of the world. Vol. 2. New
  World vultures to guineafowl. Lynx Edicions, Barcelona, Spain.
BirdLife International. 2000. Threatened birds of the world. Lynx
  Edicions, Barcelona, Spain, and BirdLife International, Cambridge, UK.
Collar, N.J., L.P. Gonzaga, N. Krabbe, A. Madroņo Nieto, L.G. Naranjo,
  T.A. Parker, III, and D.C. Wege.
1992. Threatened birds of the America: the
  ICBP/IUCN Red Data Book. International Council for Bird Preservation,
  Cambridge, UK.
Ferguson-Lees, J., and D.A. Christie. 2001. Raptors of the world. Houghton
  Mifflin, Boston, MA.
Lerner, H.R.L., M.C. Klaver, and D.P. Mindell. 2008. Molecular
  phylogenetics of the buteonine birds of prey (Accipitridae). Auk
Ridgely, R.S., and P.J. Greenfield. 2001. The birds of Ecuador: status,
  distribution, and taxonomy. Cornell University Press, Ithaca, NY.
Robbins, M.B., and R.S. Ridgely. 1990. The avifauna of an upper tropical
  cloud forest in southwestern Ecuador. Proceedings of the Academy of Natural
  Sciences of Philadelphia 142:59-71.
Vargas, H. 1995. Food habits and breeding biology of the Gray-backed Hawk
  Leucopternis occidentalis in western Ecuador. M.Sc. thesis, Boise State
  University, Boise, Idaho.
Wiedenfeld, D.A., T.S. Schulenberg, and M.H. Robins. 1985. Birds of a
  tropical deciduous forest in extreme northwestern Peru. Pp. 305-315 in P.A.
  Buckley, M.S. Foster, E.S. Morton, R.S. Ridgely, and F.G. Buckley (eds.),
  Neotropical Ornithology. Ornithological Monographs no. 36. American
  Ornithologists' Union, Washington, D.C.

Sites of Interest:
BirdLife International
Details on status and conservation needs.

Vargas, Hernan

Last modified: 10/9/2010

Recommended Citation: Global Raptor Information Network. 2017. Species account: Gray-backed Hawk Leucopternis occidentalis. Downloaded from http://www.globalraptors.org on 23 Feb. 2017

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