Research has shown that some wildlife populations are shifting poleward and upslope in the face of climate change. Although these effects can be driven by direct responses to temperature and precipitation, indirect effects via interspecific interactions complicate predictions of species responses. Several bird species in the northeastern United States are already facing climate-change related threats from increasing temperatures, changing precipitation, shifting phenology of food availability, and habitat changes. This work sought to map range changes of the American red squirrel (Tamiasciurus hudsonicus) to provide insights on potential impacts to sensitive bird species; the expansion of this nest predator that has not been present historically at high elevations has the potential to cause further negative impacts to montane bird species. Specifically, we evaluated long-term data collected through repeat point-count surveys at 469 sites across the northeastern U.S. from 1992 to 2014 to determine whether red squirrel populations have shifted in elevation and latitude over the last two decades.
Results/Conclusions
As predicted, we saw a substantial expansion into higher elevations, without a coincident contraction at the lower end of the elevational range, which extends to sea level in northern New England. Although direct effects of warming are correlated with this expansion, changes in their spruce-fir habitat may also be responsible. These results are relevant to natural resource management because red squirrels are important nest predators of montane bird populations, including the Vulnerable (IUCN 2009) Bicknell's thrush (Catharus bicknelli), and thus climate change may indirectly decrease persistence for these birds.