Dark side of climate change: species‐specific responses and first indications of disruption in spring altitudinal migration in myotis bats

Abstract

AbstractIn the Rocky Mountain region of North America, climate change is occurring at an accelerated rate and its effects are already changing population and community organization. Although some data have been gathered on changes in latitudinal migration patterns of animals, almost nothing is known about altitudinal migrations and climate change. Myotis bats of the Rocky Mountains provide a good model for understanding these patterns because they undergo significant seasonal altitudinal movements between high‐ and low‐elevation. In order to test if climate change is affecting spring down‐slope migrations of myotis species, I compared May and June capture data gathered over the last 21 years from 31 survey sites located between 1650 m a.s.l. and 2250 m a.s.l. on the eastern slopes of the Rocky Mountains, Colorado. Although three of the Myotis species maintained stable or slightly increasing capture numbers, indicating typical down‐slope spring migrations, two species showed significant declines in spring captures at lower elevations. When climate data for May and June were tested against capture data, the apparent causative factors for these declines differed between species. Declines in the capture of fringed myotis did not closely track annual patterns of mean June temperatures across years. Instead a steady decline occurred regardless of yearly variation in temperatures. However, declining captures of long‐legged myotis showed clear synchrony with variations in mean June temperatures wherein more captures occurred in years having cooler temperatures, and notably fewer captures in years having warmer June temperatures. In addition, zero captures of long‐legged myotis occurred in five of the last six years when mean June temperatures have shown an average increase in 1.8°C over previous years. These data indicate species‐specific responses to climate warming for bats in the Colorado Rocky Mountains and that loss of spring down‐slope migrations from hibernacula may be how some species mitigate climate warming effects.