Forest structure affects resource partitioning between pygmy and white-breasted nuthatches

Abstract

Ecologically similar, sympatric species will theoretically drive one or the other extinct unless those species can divide their resources. Resource partitioning is a common way to avoid competitive exclusion and these differences in resource utilization often represent the “ghost of competition past.” I studied how two closely related species, pygmy (Sitta pygmaea) and white-breasted (Sitta carolinensis) nuthatches, divide tree space. Furthermore, I tested whether pygmy and white-breasted nuthatches foraged in different areas on large- and small-diameter trees and whether pygmy nuthatches foraged more frequently on small-diameter trees. Finally, I tested whether each nuthatch species foraged less frequently in forests where most of the small-diameter trees have been removed. I found that in large trees, pygmy nuthatches foraged higher up in the tree and on the branches than white-breasted nuthatches. White-breasted nuthatches foraged low in the tree and on the trunk. In small-diameter trees, pygmy nuthatc...