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Vargas, Hernan F. – Food habits, breeding biology, and status of the Gray-backed Hawk (Leucopternis occidentalis) in western Ecuador. 1995.

Photo of a Gray-backed Hawk.                       Photo courtesy of Susan Brown.

Gray-backed hawk. Photo courtesy of Susan Brown

I studied the breeding biology, feeding habits, and relative abundance of the gray-backed hawk (Leucoptemis occidentalis), in western Ecuador from 1992 to 1994.

This research was mainly conducted in Pias (400 – 1300 m. elevation, El Oro Province) and Cerro Blanco (100 – 400 m. elevation, Guayas Province) where eight and two nests were respectively located and monitored.

Hawks constructed nests near forest edges (7 nests) and within interior forest (3 nests). Nests were placed in tall trees averaging 31 m in height (mean DBH = 111 cm) at an average height above ground of 24 m (n = 10 trees). Nests averaged 78 cm in greatest diameter, 54 cm in smallest diameter, 37 cm in outside depth and 14 cm in cup depth (n = 5 nests).

Gray-backed hawks bred almost year round. Two apparent groups of breeders were identified: six pairs nested during the rainy season, (January to June) and four during the dry season (July to December). Clutch size was one egg for all nests (n = 10). One bluish white egg weighed 62.0 g and measured 46.3 mm in width and 54.7 mm in length. The incubation period at one nest was 36 days, and the young fledged at an average age of 72 days (range = 56 – 84 days, n = 3). Fledging occurred in May and June (n = 5) for the birds nesting in the rainy season and February and March (n = 3) for birds breeding in the dry season. Nine eggs hatched (90%) from the 10 observed nests and 8 nestlings (80%) fledged. One nest failed because the two-week-old chick was taken by a farmer, in the belief that he could cross it with his fighting cocks and a second was abandoned during the incubation period.

Diet was determined from 246 identified prey items recorded at seven nests. Observations of prey brought to the nests showed that reptiles (59%) were the primary food, followed by mammals (13%), birds (10%), crustaceans (9%), amphibians (6%) and earthworms (3%). Snakes (49%) and rats (31%) were the main prey recorded. In terms of biomass, I estimated that reptiles accounted for 53%, and mammals 30% of the diet during the breeding period. Average prey length was 51 cm (range = 11 – 82 cm) and average prey mass was 40 g (range = 5-95 g).

During surveys, I documented that gray-backed hawks persist in several small patches of forest, which are threatened by deforestation. The most significant Gray-backed Hawk population was found in southwestern Ecuador.

I recommend the creation of a reserve in Buenaventura (Pias) and the expansion of Bosque Protector Cerro Blanco to ensure the conservation of gray-backed hawks in western Ecuador.

Thesis Abstract

Where Are They Now?