Big Brown Bat (photo by Andy Reago & Chrissy McClarren)
We’re stationed in our lawn chairs outside the barn at 8:15 PM on July 23. We’re late for the post-volancy bat survey (July 14-16)—timed to count the newly flying pups before the mother bats disperse for the season—because we were in Pennsylvania the week before birding with friends from the Valley Forge Audubon Society.
Sunset today is at 8:25 PM, so we expect the bats to start appearing about ten minutes later.
At 8:15, the sky is filled with swarming, swooping swallows! At least 150 Barn Swallows are fueling up for their night roosting in the barn. They are joined in the sky by dozens of Tree Swallows that have nested in boxes and tree cavities in the nearby prairies and wetlands.
A noisy contingent of about 25 Purple Martins from the gourds near the driveway are patrolling the upper levels of the air above. We also hear one individual with a distinctive call and a short, forked tail that we’re pretty sure is a Bank Swallow. These small swallows nest around nearby Lake Koshkonong. We have seen them in previous years, flocking with other swallow species in late summer.
As the sky darkens, the Tree Swallows and Purple Martins disperse, and the net flow of Barn Swallows into and out of the barn shifts to “in.”
At 8:45, the last swallow goes in, and about 30 seconds later, the first bat flies out! The night shift is taking over! Gary and I get out our clickers and start counting. We are positioned so we can see the bats against the sky, and many fly right over our heads. Fortunately, like the swallows, they are excellent fliers and do not collide with us or anything else.
At about 9:00 PM, a large form rises over the barn roof and swoops over our heads in hot pursuit of the bats. It’s a Great-horned Owl! (Not a Galactic Empire spaceship, as we first feared.)
A Great-horned Owl with two fluffy owlets at Fair Meadows (photo by Gary Shackelford).
World-wide, owls are known predators of bats. According to The Cornell Laboratory of Ornithology, “Great-horned Owls have the most diverse diet of all North American raptors. They eat mostly mammals and birds, especially rabbits, hares, mice, and American Coots, but also many other species.” Though they prey upon bats, small rodents are a much more important food source. Other owls that eat bats are the Snowy Owl and Long-eared Owl.
Heather Kaarakka, the Wisconsin Department of Natural Resources bat specialist and coordinator of the pre-volancy and post-volancy surveys, noted, “I’ve seen owls sit on top of bat houses waiting for the bats to emerge, since I think during emergence the bats are most vulnerable to aerial predators. Owls are typically ambush predators, and I think out in the open they have trouble catching free-flying bats, but I’ve heard of it happening for sure! If there’s lots of bat activity at a roost, it might be easier for owls to capture them.”
By 9:30, we had counted 177 bats, and none had left the barn for five minutes. The count is over. According to Heather, who has visited our site, both Big Brown Bats and Little Brown Bats share the barn with the swallows. We love watching the variety of wonderful winged creatures that inhabit the world with us.
Written by Penny Shackelford, Fair Meadows Sanctuary resident manager
Cover image by Gary Shackelford. A packed mud nest contains three young Barn Swallows on a beam inside a wooden building.
