Climate change projected to alter Indiana bat maternity range

Research by US Forest Service scientists forecasts profound changes over the next 50 years in the summer range of the endangered Indiana bat. In an article published in the journal Ecology and Evolution, Forest Service Southern Research Station researchers Susan Loeb and Eric Winters discuss the findings of one of the first studies designed to forecast the responses of a temperate zone bat species to climate change.

The researchers modeled the current maternity distribution of Indiana bats and then modeled future distributions based on four different climate change scenarios. "We found that due to projected changes in temperature, the most suitable summer range for Indiana bats would decline and become concentrated in the northeastern United States and the Appalachian Mountains," says SRS research ecologist Loeb. "The western part of the range (Missouri, Iowa, Illinois, Kentucky, Indiana, and Ohio)—currently considered the heart of Indiana bat maternity range—would become unsuitable under most climates that we modeled. This has important implications for managers in the Northeast and the Appalachian Mountains as these areas will most likely serve as climatic refuges for these animals when other parts of the range become too warm."

In general, bat species in temperate zones such as Indiana bats may be more sensitive than many other groups of mammals to climate change because their reproductive cycles, hibernation patterns, and migration are closely tied to temperature. Indiana bat populations were in decline for decades due to multiple factors, including the destruction of winter hibernation sites and loss of summer maternity habitat.

Due to conservation efforts, researchers saw an increase in Indiana bat populations in 2000 to 2005, but with the onset of white-nose syndrome populations are declining again, with the number of Indiana bats reported hibernating in the northeastern United States down by 72 percent in 2011. The study predicts even more declines due to temperature rises from climate change, with much of the western portion of the current range forecast to be unsuitable for maternity habitat by 2060.

"Our model suggests that once average summer (May through August) maximum temperatures reach 27.4°C (81.3°F), the climatic suitability of the area for Indiana bat maternity colonies declines," says Loeb. "Once they reach 29.9°C (85.8°F), the area is forecast to become completely unsuitable. Initially, Indiana bat maternity colonies may respond to warming temperatures by choosing roosts that have more shade than the roosts that they currently use. Eventually, it is likely that they will have to find more suitable climates."

The models the researchers produced provide resource managers guidance on areas that are likely to contain maternity colonies now and in the future, depending on the availability of suitable habitat in those areas. "Managers in the western parts of the range should be aware of the potential changes in summer distributions due to climate change and not assume that declines are due to habitat loss or degradation," says Loeb. "Management actions that foster high reproductive success and survival will be critical for the conservation and recovery of the species."