The Effects of Interspecific Interactions on the Reproductive Success of Carolina Chickadees (Poecile carolinensis)

Abstract The Carolina chickadee (Poecile carolinensis) is an ideal model organism to study how interspecific interactions collectively influence fitness in a dynamic environment because the species currently hybridizes with black-capped chickadees (P. atricapillus), competes with other bird species for nesting sites, and suffers from a variety of blood parasites. I investigated how multiple interspecific interactions cumulatively affect the reproductive success of Carolina chickadees along its northern range margin. I monitored chickadees in Pennsylvania to determine breeding success, blood parasite incidence, and hybridization, while investigating potential environmental correlates. Competition with house wrens (Troglodytes aedon) had the biggest impact on reproduction, destroying 33% of nests. Presence of blood parasites reduced chick condition, but did not appear to influence adults. No evidence of hybridization with black-capped chickadees was found, although previous research has reported hybridization nearby. Understanding the cumulative effects of interspecific interactions will facilitate improved predictions of ecological responses to changes in climate.