Midwestern winters can be tough, especially for tiny bats. Animals have evolved different ways to handle this, including hibernation (e.g. sleeping through the cold) and migration (perhaps wintering someplace warmer). But some bats do both of these things. They spend summers where food and other resources are plentiful, and then migrate to places with favorable conditions for hibernation.
In the Midwestern US, some bats use cold caves for hibernation and forests in the summer, such as the endangered Indiana bat (Myotis sodalis) and threatened northern long-eared bat (Myotis septentrionalis). They travel as far as 300 miles each year between summer maternity roosts and winter hibernation caves. The map shown here is from a paper describing Indiana bats banded in Michigan during the summer, and then later seen hibernating in locations hundreds of miles to the south. Other intermediate-range migratory bats in this area do not use caves, for example eastern Red bats (Lasiurus borealis) hibernate in trees or even in leaf litter on the ground.
While we know quite a bit about the summer and winter habits of many of these bats, we know almost nothing about how they move between those locations. Many of these bats are already under severe pressure from an invasive fungal disease called “White-nose Syndrome” which has resulted in up to 100% mortality at affected sites in the eastern US. In addition, large numbers of migratory bats are killed each year at wind turbines. So it’s urgent that we have a better understanding of what bats need during migration.
One reason we know so little about migratory bat movements is that until now the technology has not been available to cost-effectively track movements of individuals. However, a combination of new transmitter technology and easy-to-deploy open-source sensor kits has now made this research possible.
The project I’m working on is led by Dr. Justin Boyles of Southern Illinois University and Dr. Liam McGuire of Texas Tech University, and funded by a grant from the US Fish & Wildlife Service. The objectives are to answer questions about what these bats do during their migrations across the US Midwestern states. How far do they go? How fast do they move, and do they stop off at locations along the way? Do they use the fastest route, or some other path? Do the answers to any of these questions vary with age or sex? These are just a few of the things we do not know, and pretty much anything we learn will be new.