Vulnerability Assessment of Forest Birds in the National Capital Region

Hostetler, Jeffrey; Sillett, T.

Considerable evidence has accumulated that birds can be vulnerable to climate change. However, this vulnerability must be put into context of the species’ baseline vulnerability (vulnerability to other threats in the absence of climate change) and overall vulnerability (combined vulnerability to climate change and other threats). The objectives of this study were to estimate the baseline, climate change, and overall vulnerabilities of migratory forest birds breeding in National Parks in the National Capital Region. We estimated these vulnerabilities first with a qualitative index using a survey of ornithologists. We then developed a quantitative, model- and data-based approach that uses long-term avian point count and weather data to assess the effect of seasonal weather on bird population dynamics. Using those results and downscaled climate projections, we projected bird populations into the future and estimated vulnerabilities in terms of population size declines and probabilities of local extirpation, while accounting for uncertainty. Species were ranked differently for baseline and climate change vulnerability by the survey, population size, and probability of extirpation approaches, highlighting that these measures capture different aspects of vulnerability. However, a few species, such as Louisiana Waterthrush, were consistently identified as highly vulnerable to climate change. Our results suggest that baseline vulnerability may be a greater concern for most species in these parks than climate change vulnerability, and that some of the same approaches, such as habitat protection and restoration, may be able to address both types of vulnerability.