Ruffed grouse population declines after introduction of West Nile virus

The abundance of ruffed grouse (Bonasa umbellus) has declined over a broad region in the Appalachian Mountains in the last 3 decades. We determined empirical support for different hypothesized causes of declines: habitat loss, forest maturation, and the introduction of West Nile virus (WNV) in the early 2000s. We examined how these factors relate to declines observed in 2 data sets: changes between 2 Breeding Bird Atlas (BBA) surveys in Pennsylvania conducted in the 1980s and 2000s and a 48-year time series of flush rate data. Initial occupancy of BBA blocks was positively related to the amount of available forested habitat, and persistence and colonization probabilities were negatively related to WNV intensity and positively related to available forest and to increasing trends in early successional habitat. Flush rates dropped in most regions after the arrival of WNV, but trend estimates were imprecisely estimated, and there was considerable uncertainty about whether or how the slope of annual trends in flush rates changed. Our results provide support for the importance of forest and early successional forest, but taken together with other supporting evidence for the presence of WNV in wild ruffed grouse populations and mortality in ruffed grouse chicks caused by WNV infection, our results also suggest that ruffed grouse populations might have been affected by mortality from WNV. In the face of WNV, managing habitat may be insufficient to sustain ruffed grouse populations. (c) 2017 The Wildlife Society. Based on our results and corroborating evidence, we conclude that West Nile virus likely contributed to ruffed grouse population declines in Pennsylvania, notwithstanding the well-known and equally negative effects of habitat loss and forest maturation. West Nile virus might thus complicate efforts to increase grouse populations in the short-term, until and unless resistance emerges in grouse populations.