Raptor Migration in the Cauca River Valley of Northern Colombia

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We conducted full-season raptor migration counts at a watchsite in the northernmost part of the South American Andes in the Central Cordillera of Colombia from 1999 to 2004. Twenty-eight species of raptors were recorded over the 6-year period, 10 of which were migratory. Averages of approximately 21,000 and 19,000 migrating raptors were counted each autumn and spring, respectively. Two species, the Broad-winged Hawk (Buteo platypterus) and Swainson’s Hawk (Buteo swainsoni) made up > 99% of the count in both seasons. The migration of Broad-winged Hawks peaked over a 4-day period between 19 and 22 October in the autumn and between 15 and 21 March in the spring. The main migration of Swainson’s Hawks peaked a week later between 27 October and 2 November in the autumn, and 31 March and 3 April in the spring. Of the remaining eight migratory species observed, Ospreys (Pandion haliaetus) and Peregrine Falcons (Falco peregrinus) were most consistently recorded across all seasons. We occasionally observed migrating American Swallow-tailed Kites (Elanoides forficatus), Mississippi Kites (Ictinia mississippiensis) and Merlins (Falco columbarius), and a single Northern Harrier (Circus cyaneus). We made two sightings of Red-tailed Hawks (Buteo jamaicensis) which were the first records for the species in Colombia and South America. Both during autumn and spring, most raptors migrated after midday when thermals were most abundant but they migrated in all types of weather, except heavy rainstorms which they avoided.

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