Welcome to the neighborhood: Nest locations of heterospecific songbirds influence Wood Thrush (Hylocichla mustelina) nest placement

Background/Question/Methods

Heterospecific nest associations in passerines represent a fascinating case of aggregation, as territorial species choose to nest within other species’ territories and share habitat resources.  Birds may choose to aggregate because of patchily distributed habitat features, or they may experience lower predation rates through community vigilance and shared mobbing.  Heterospecific nest associations were observed in a deciduous forest in Western Pennsylvania to describe these associations and to discern whether a target species, the Wood Thrush (Hylocichla mustelina), nested in association with specific habitat features or other species of birds.  Wood Thrushes arrive later to the study location (mid-May) compared to other nesting passerines (April-early May), giving them the opportunity to nest near other species. I measured habitat variables (number and diversity of woody stems and trees and percent ground cover of herbaceous vegetation) within a 10 m radius around each nest and control location.  Additionally, I recorded the number of nests within a 50 m radius around each Wood Thrush nest or control location.  Wood Thrush territories range on average from 0.8-2.8 hectares, so any nests found within 50 meters of the focal nest were assumed to be within the territory of the focal Wood Thrush.

Results/Conclusions

Only the number of trees differed significantly between sites with and without Wood Thrush nests.  The number of avian species nesting within a Wood Thrush territory was significantly higher than that of birds nesting within the same distance from the center of the control site. Additionally, 80% of surveyed Wood Thrushes had at least one neighboring nest within their nesting territory and 42% of nesting pairs had two or more neighbors. Fifteen passerine species nested within Wood Thrush territories. Finally, Wood Thrushes increased the degree of nest aggregation in an area by nesting close to other species, thereby reducing the average nearest neighbor distance among nests.  These data suggest that Wood Thrushes select nesting habitat based on both vegetation structure and the community of potential avian neighbors.  Furthermore, the heterospecific nesting community appears to be an important influence in nest site selection for breeding passerines.