This delicate species’ association with manmade structures makes some biologists think bats exist in northern Alaska only because of us: our houses and sheds have made a marginal area to hibernate slightly more safe and warm.
But Reimer and other biologists recently found bat maternity colonies away from buildings. In the Copper River Valley, Reimer and her co-workers in summer 2017 radio-tagged mother bats at their cabin roost. When later tracking them with handheld receivers, they found the mother bats did not return to the cabin.
Instead, they tracked the bats to an old cottonwood tree that had a foot-high pile of bat guano at its base. They counted more than 100 bats flying out of a crack in the tree.
There was a natural bat nursery, which suggests to Reimer that little brown bats don’t need buildings, or humans, to thrive. Maybe they just roost in cabin crevices because they resemble the tight, dark spaces they rely upon in nature.
“Large maternity colonies in trees shoots down the theory that bats only came to Alaska as buildings went up,” she said.
As Reimer was making her discovery, Colorado State University scientists working on Fort Wainwright lands were finding the same thing. Sound detectors they installed in likely bat spots away from buildings picked up bat echolocation. Biologists radio-tracked bats to several dying or dead poplar and birch trees on Army lands near Fairbanks. They also tracked them to buildings.
One of those researchers, Garrett Savory, thinks their recent findings give a clue to one of the biggest mysteries surrounding far-northern bats:
“I think bats do hibernate in Interior Alaska, given that we have detected bats in early April, when there is still snow on the ground, and have detected bats late into September,” he said. “We still don’t know where bats hibernate, however.”
Reimer agrees that far-northern bats must be hibernating north of the Alaska Range, rather than migrating south through the mountains.
From the Kenai Peninsula to Fairbanks, in spring bats seem to all appear at their roost sites the instant the average air temperature gets above freezing. If they were migrating from farther south, there would probably be a time lag in the date the farthest-north bats arrived in Fairbanks compared to when they appeared on the Kenai.
“It seems to suggest that they are spending the winter nearby,” she said.
No one seems to know where those northern bats are right now. GPS transmitters are still not small enough to fit on a bat, Reimer said, and the radio tags biologists have used last only a week or two before they fall off.
Scientists want to know the location of northern Alaska’s bats because white nose fungus has killed so many little brown bats in the Lower 48. Alaska bats have shown no sign of it yet, but the disease has reached Washington state after devastating bats in the eastern part of the country.
Reimer is now looking at genetic samples of Alaska little brown bats to compare them with farther-south populations.
“If they are meeting up (with Lower 48 bats) at some point, the likelihood of sharing the fungus is great,” she said.
But so far, so good. Alaska’s little brown bats may be saved from the disease because their adventurous ancestors chose extreme isolation.
Since the late 1970s, the University of Alaska Fairbanks’ Geophysical Institute has provided this column free in cooperation with the UAF research community. Ned Rozell is a science writer for the Geophysical Institute.