February 4, 2023

Submitted by Russel Barsh, Director of KWIAHT.

It’s still cold enough to spend the evenings cozying up by the fireplace if you have one. However, should you venture outside to get some more “sticks” to feed the flames, you may be in for a surprise: a fat brown bat, sound asleep between the rails. You won’t be the first islander to find a bat in your woodpile. In fact, one of our larger island bat species is often spotted this way. It’s the silver haired bat, Lasionycteris noctivagans, or “hairy night walker.”

Silver-haired bats are the size of a vole, but they’re much lighter for flight — not quite an ounce. Like the Greater Brown Bats, which are about the same size, they have a soft brown coat but with a touch of silvery gray on their backs. Unlike the large browns, which are sociable and prefer to settle in attics and barns together with smaller bat species, the “night walker” quarters itself alone or in small family groups in tree hollows or under loose bark. And sometimes in woodpiles!

Silver-haired bats are found throughout temperate North America as far north as New Mexico and have recently been reported in southeast Alaska. Their behavior is adapted to different bioregions. In the central and eastern parts of their range, they tend to migrate up to several hundred kilometers in early fall, not as far south as at latitudes, to habitats where there are burrows or other opportunities for safe wintering.

However, silver haired bats can overwinter anywhere that has dry shelter and (mainly) temperatures above freezing. Under these conditions, these bats do not relocate their daytime quarters to hibernation, but often in very confined spaces and spend days at a time in “torpor” – deep sleep. Human houses (and woodpiles) provide excellent temporary warm winter campsites for solitary silver bats.

Here in the Pacific Northwest, these bats spend their summers in coniferous forests and may travel two or three miles from their roosts to lakes and ponds or small forest clearings to feed on swarms of insects. They are relatively slow fliers, and moths can make up half or more of their diet.

Older (“mature”), undisturbed coniferous forests with many stumps, rotten cavities, and crested woodpeckers whose neat rectangular cavities are the perfect size for arboreal bats are havens for silverhead bats. Females form small family groups in tree hollows, where in early summer they give birth to their young: often twins, which is unusual in North American bats. Even more unusually, there is evidence that mother silver haired bats move their young from one tree cavity to another nearby, perhaps to fool predators such as owls.

Bat pups, clinging to their mother’s fur, can “hang on” for a short flight of less than a minute, more than even a relatively large North American bat can afford with the extra weight of the pup!

Here on the islands we have very little “waste wood” left, and clearing should continue

avoided. Studies elsewhere suggest that selectively thinning conifers—opening the canopy a bit but leaving most trees undisturbed—may actually improve habitat quality for silver haired bats.

And if you do spot a bat in your woodpile, just leave it alone. It will likely go away on its own within hours to find another cozy place to sleep.

If you find a bat that appears injured or unable to fly, call Wolf Hollow at 378-5000. Avoid handling. Island bats do not appear to transmit rabies, but will bite when injured or frightened.

Ask a biologist!

If you have questions about protecting pest-eating bats or insect pollinators in your home, farm or garden, email: [email protected]

Check this space for future announcements of virtual and in-person learning opportunities for a healthy and productive island environment.

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