NORTHWARD EXPANSION OF CAROLINA CHICKADEES IN THE NORTHEASTERN UNITED STATES

Black-capped Chickadees (Poecile atricapillus) and Carolina Chickadees (Poecile carolinensis) are known to hybridize along the boundary of their ranges in the northeastern United States. Between the years 1987 and 2007, that boundary moved northwards approximately 14 miles, and a larger proportion of Carolina Chickadees was found in areas previously dominated by Black-capped Chickadees. Analyzing this distribution shift can provide insight into the factors that are important to chickadee survival, as well as the spatial constraints that influence how chickadee populations respond to these factors. This study examined the relationship between temperature and large-scale patterns of chickadee species proportion between 1987 and 2007. It also sought to identify small-scale topographic and anthropogenic obstacles within the hybrid zone that may facilitate or hinder distribution shifts. Historic temperature data, chickadee population data and transect data from within the hybrid zone were analyzed using ArcGIS. The resulting spatial patterns can help in understanding hybrid zone dynamics and the way similar species respond to large-scale environmental changes.