Use of communal roosts by Andean Condors in northwest Patagonia, Argentina

ABSTRACT.   Andean Condors ( Vultur gryphus ) are endangered in the northern portion of their South American range, but populations are larger further south. However, throughout their range, little is known about current population sizes and dynamics. Andean Condors use cliffs with shelves as communal roosts and, from 1999 to 2001, we surveyed three of these roosts in northwestern Patagonia, Argentina, to estimate population sizes and trends. The minimum population of Andean Condors in our study area was 196, one of the highest populations recorded for this species. The maximum number of condors observed increased during our 3-yr study. However, there was a strong seasonal pattern in roost use and use also varied among roosts, possibly due to differences in their environmental characteristics, size, and room available for roosting, as well as proximity to nest sites and stage of the breeding season. In 1999 and 2000, more adults were observed than juveniles, but proportions were similar in 2001. Because we observed differential use of roosts among age classes, spatial segregation seems probable. We conclude that intensive censuses of communal roosts can provide useful information about the size, status, and dynamics of local populations. However, the large aggregations we observed may represent a potential risk for the conservation of the species because a single threat could affect multiple individuals. We suggest that a suitable conservation strategy for condors must involve the design and protection of a network of communal roosts.