PARENT SESSION
Oral Session #71: Animal Population Ecology. Presiding: J. Dooley.
Thursday, August 9, 2001. 1:00 PM to 4:15 PM. Hall of Ideas J.

Conspecific attraction and site fidelity as a proximate cause of area effects in migratory birds.

Ward, Michael¹, Schlossberg, Scott¹, ¹

ABSTRACT- Area effects, the tendency of a species' density to increase with patch size, are commonly found in fragmented landscapes. The only proximal explanation suggested for area effects in migratory animals is a hypothetical preference for large patch size, though no experimental evidence for such a preference exists. Using a simulation model, we demonstrate that conspecific attraction, the tendency of individuals to settle near others of their species, and breeding site fidelity, the tendency of successful breeders to return to previously used patches, can generate area effects in landscapes where breeding success increases with patch size, a commonly observed correlation. Conspecific attraction was simulated using a novel algorithm in which individual birds sample patches and settle based on a power function of the density of individuals already present in each patch. Results of the simulation, using either three or 20 patches, revealed that breeding density increases with patch size when conspecific attraction and site fidelity are operating. Thus, the behavioral rules we modeled can generate area effects. If only one of the two behavioral rules are included in the model, there was either no relationship or a negative relationship between patch size and density. Our model suggests that area is less important than the presence of conspecifics and patch-specific reproductive success in determining settlement. We suggest that conspecific attraction and site fidelity are mechanisms by which birds "find" high quality habitat.

KEY WORDS: conspecific attraction, site fidelity, area effects, habitat selection