Habitat Associations of Migrant and Resident Vultures in Central Venezuela

Abstract

We investigated spatial and temporal differences in the habitat associations of five New World vulture taxa (family Vulturidae auct. Cathartidae) in the Llanos of central Venezuela. Overall numbers of vultures were higher over open or semi-open savanna habitats than closed canopy riverine gallery forest. Black Vultures Coragyps atratus brasiliensis and Lesser Yellow-headed Vultures Cathartes burrovianus foraged principally in open habitats at all times. Although King Vultures Sarcoramphus papa were counted mainly over gallery forest they also sometimes foraged outside the forest area. During the wet season, resident Turkey Vultures Cathartes aura ruficollis foraged in all habitats but highest densities occurred over gallery forest, east of the main highway. This indicated that, to some extent, vulture species were ecologically segregated by habitat. During the dry season, a larger, dominant, migratory race of Turkey Vulture, C. a. meridionalis, coexisted with the resident subspecies. Migrants foraged at highest densities over open and semi-open habitats, but they also occurred in low numbers over gallery forest. When sympatric with these migrants, resident Turkey Vultures foraged almost exclusively in closed gallery and semi-deciduous tropical forest to the east of the highway, and, in contrast to the wet season, avoided open habitats. At the end of the dry season (March to April), migrant Turkey Vultures departed for North America to breed, resulting in a dramatic reduction in densities of Cathartes vultures. Despite the absence of migrants, densities of Cathartes vultures remained higher in open and semi-open savanna habitats than the gallery forest area. Support for a possible niche shift came from the proportion of carcasses visited in different habitats by resident Turkey Vultures, habitat sightings of wing-tagged birds and radiotracking studies.