Understanding Changes in Wood Thrush and Ovenbird Populations in Virginia—The Role of Forest Fragmentation and Connectivity

Abstract

Aim: Yearly summaries of the North American Breeding Bird Survey (BBS) indicate that populations of many North American bird species are in decline. Determining the causes of these declines is the focus of much current research in avian conservation. Forest fragmentation has been linked to declines in populations of many species. In this study, the effects of forest fragmentation and connectivity as well as slope and physiographic features on two migratory bird species are explored. Location: This study area is Virginia, USA. Taxon: The species focused on are Wood Thrush (Hylocichla mustelina) and the Ovenbird (Seiurus aurocapilla). Methods: We used the Markov Chain Monte Carlo Generalized Linear Mixed Models (MCMCglmm) package with a Poisson distribution and a Bayesian data analysis model with a 95% probability interval. Using the Repeated Measures ANOVA, the independent and treatment variables included time at 3 different levels in 2001, 2006 and 2011; three different forest types—Core, Connected and Fragmented; 8 slope categories and 5 physiographic regions. Results: Results indicate that forest fragmentation has a significant impact on population sizes of Wood Thrush and Ovenbirds in Virginia and that recent changes in Virginia’s landscape have had negative impacts on the populations of these bird species. Specifically, slope characteristics that influence rates of urbanization are correlated with changes in bird populations. The Coastal Plain region in Virginia contributes significantly to the populations of both the Wood Thrush and Ovenbird currently. Main Conclusions: Core forests areas in Virginia are in decline and this process affects the populations and distributions of Ovenbird and Wood thrush in the state.