Mixed-Species Aggregations of Waterfowl
Tuesday, June 8, 1999 - 2:45pm - 3:00pm
Emily Silverman (University of Washington)
Many species of waterfowl aggregate together outside the breeding season. These aggregations can be used to study the interactions between individuals of different species, the species-specific roles of ducks in their community, and the extent to which interactions among species determine community composition. I considered a simple deterministic model and an analogous stochastic model for the formation of mixed-species aggregations, testing the fit of the models to field observations. These models do not differentiate between species or include interactions between individuals. Although clearly overly simplistic, the models' inability to reproduce observed patterns point to critical interactions and species-specific behaviors. Results indicate that a description of aggregative behavior must incorporate the movements of groups of birds, not simply movement by individuals. Large numbers of single-species groups suggest that species moved separately; nonetheless, individual species behaved similarly. Birds with few conspecifics traveled in large groups with other species, joined aggregations in a confined location in relatively greater numbers than numerous species, and initiated aggregations more often than their representation predicts. The formation of waterfowl aggregations does not appear to be a complex process, but conspecific density affects social behavior.