Forecasting climate impacts on select birds in the western United States

Background/Question/Methods

Global models of climate change (GCMs) predict differences in both temperature and precipitation for the future, and these different patterns are likely to affect the distribution of populations of many animals. Probabilistic predictions of future ranges of select wildlife species, linked to climate variables, can provide informed assessments of potential future distributions for species of interest. As part of a multi-faceted U.S. Geological Survey National Climate Change and Wildlife Science Center study, we forecast changes in the ranges of bird species on a broad scale at low resolution. Bird species that we examined were pinyon jay, Virginia’s warbler, pygmy nuthatch, Williamson’s sapsucker, black-throated sparrow, and gray vireo. We developed conceptual models for each species to identify important variables to include in the modeling process. We built a GIS containing current species distributions and candidate explanatory variables, and modeled current bird species ranges with and without plant variables.  We projected ensembles of future habitat and ranges expected with climate change, using six downscaled GCMs.

Results/Conclusions The explanatory variables used in our best-fit habitat models differed by species, but each one contained at least one plant species, a temperature and a precipitation variable, and sometimes a solar insolation or terrain-ruggedness variable. For example, significant variables for pinyon jay were winter precipitation, mean maximum temperatures May through September, the distribution of pinyon and Jeffrey pines, terrain ruggedness, and solar insolation. Future habitat simulations based upon an average habitat response among six GCM models revealed large differences in the amount of predicted habitat for each bird species over the next century. Three bird species are predicted to have moderate to large losses in habitat and range (pinyon jay, pygmy nuthatch, and Williamson’s sapsucker), two are expected to have a large increase (gray vireo and black-throated sparrow), while one is predicted to have only a minor decline (Virginia’s warbler). The pygmy nuthatch had the greatest predicted declines in habitat and range (81%), while the gray vireo had the largest predicted gains (58%).  Our results demonstrate that the climate change predicted for the western and southwestern U.S. will affect bird species in unique ways, based on their natural history and habitat needs.