Winter Bats

As close followers of bat behavior in the Pacific NW know, we have bats that remain in their summer locations and become active throughout the winter. A mild, dry evening produces many 'clicks' on the bat detectors, and almost always from Silver-haired and California myotis bats. The Calif. myotis bats are roosting under trim boards around our houses, barns, etc, and usually just one or two here and there. I've been watching two or three around our house since last spring, and they've been in the same spots this winter. If the daytime temperature gets into the 50s, and its not raining early evening, they are likely to go out foraging for an hour to two.

Cori, a fellow bat researcher in SE British Columbia (near Nelson) just told me she's been following some active Silver-haired bats in her area, and she has found similar behaviour. So its not just a behavior found in the 'mild Puget Sound climate zone' as some have suggested. She's recently found Silver-haireds that hang out in a cave during the sub-freezing weather, but during 'warm spells, ' they leave the cave. She put transmitters on a few in the cave, and the next time it warmed up again (above freezing), they left the cave, foraged, then would day-roost in trees until the temperatures dropped below freezing again. She said she's waiting for another warm spell, so they will go out and do their thing. Cori had a paper published in 2006 about finding recordings --near Calgary, Alberta--of Big brown bats on her 'long-term' bat detectors during the winter -- some recordings were when the temperature was as low as 20 degr. F (-6C). This is really different than what people have believed over the years, when bats were thought to either be 'hibernators' or 'migrators.' Silver-haired bats were thought to be migrators, and Calif. myotis hibernators...