Few bat researchers consider setting mist nets over frozen streams when temperatures are far below zero and most bats are expected to be either hibernating or enjoying the southern end of migration routes. But when graduate student Cori Lausen of the University of Calgary in Alberta set her nets in the frigid Canadian prairie, she caught bats that stayed active through most of the winter – a most unexpected discovery.
Lausen’s winter adventure at Alberta’s Dinosaur Provincial Park originally was designed to solve the long-standing puzzle of where these prairie bats hibernate in winter. Among other things, she had previously left solar-powered bat detectors at strategic locations to monitor bats’ activity by recording their echolocation calls. Lausen said she figured that when warm “Chinook winds” brought bouts of unusually warm winter temperatures to the area, bats would take wing and perhaps lead her to their hibernation sites.
“Sure enough, I found several hibernation sites,” she reports. “More importantly, I discovered that (based on recorded echolocation calls) bats were far more active during wintertime on the prairie than most biologists had imagined. In fact, bats were active in river valleys throughout the winter, not just when the warm Chinooks were blowing.”
The longest time during which the acoustic monitors detected no active bats was a two-week cold snap that dropped overnight temperatures to 49 degrees below zero F (-45 degrees C).
But as long as ambient nighttime temperatures remained at about 18 degrees F (-8degrees C) or warmer, bats were flying. In fact, she tracked one male bat as a blizzard swept the prairies the next day, and temperatures plummeted to 4 degrees below zero F (-20 degreesC).
That discovery led to the extraordinary challenges of mist netting in the Canadian winter. Lausen remained in the park for several winter months, capturing a total of nine big brown bats.
Now the question is why would bats be flying around in the dead of winter, when there are no insects around? She suspects they’re thirsty and coming out for a drink. More research may eventually solve the mystery.
BCI members can read the whole story of Cori Lausen’s suprising research results in the Spring 2008 issue of BATS magazine.