The Northern Waterthrush: Analyzing the Distribution and Abundance of a Secretive Songbird in Pennsylvania

The northern waterthrush (Parkesia noveboracensis) experienced a drastic decline between the first and second Pennsylvania Breeding Bird Atlases despite higher sampling effort during the second atlas. Atlas data suggested a slight northward range contraction and detectable increase in elevation of occupied blocks, potentially caused by climate change. This study investigates factors that may be responsible for any detected changes in distribution in northeastern Pennsylvania (Pike, Monroe and Northampton counties). In spring of 2017 and 2018, wetland surveys were conducted to detect singing males. At each of 53 sites, point counts were conducted to characterize the avian community. Vegetative, physical, and hydrological characteristics were also recorded. Sites occupied by northern waterthrush were compared to unoccupied sites in apparently suitable habitat. Shrub height and upturned tree roots were found to be significantly different between site types as was the avian community and the herbaceous plant community. It was also found that there was a range contraction at both the northern and southern end of the NOWA range between the two atlases in the study area. These results suggest that changes in vegetation structure due to deer overbrowsing and eastern hemlock decline are contributing to the decline observed between atlases.