Foraging Efficiency, Resource Partitioning, and the Coexistence of Sparrow Species

The relationship between seed size and handling time was documented for three species of sparrows. Handling times were measured in the laboratory by presenting field—collected seeds to birds caught in the wild. Large species of sparrows were more efficient than small species at handling large seeds, but large and small sparrow species were about equally efficient at handling small seeds. Based on the relationships between seed size and handling time, a function was constructed relating profitability (measured in milligrams per second) to seed size for each sparrow species. These results with information on the abundance and size distribution of seeds in the habitats frequented by the sparrows, were used to show that different species of sparrows are likely to have broadly overlapping diets whenever seeds are scarce enough for the consumption of seeds by one species to have much impact on the availability of seeds to another species.