Evening is showtime for owls and bats

Western pipistrelle Photo courtest of National Park Service

Western pipistrelle
Photo courtest of National Park Service

Great horned owl in hiding.  She squawked and now hoots.

Great horned owl in hiding. She squawked and now hoots.

Coming home is always a relief, even when the vacation was wonderful. After a two week road trip we unpacked bags, fixed a simple dinner and retired to the back yard to relax. There we discovered that wildlife had moved in while we were away. The afternoon shadows were long as a party of bats swooped and fluttered like gauzy bow ties above the melon patch. And from the enormous shoestring acacia tree nearby came an intermittent squawking. As dusk drew down, a great horned owl launched from the acacia and skimmed low over the yard, a fleeting presence on broad wings. Each evening since, we’ve tried to be outside after sunset for the show.
The owl sets out reliably from the shaggy tree, sometimes flying west over the yard, and sometimes perching first on the rocky slope behind our home. (Happy hour prices on rock squirrels?) Perhaps this new neighbor is a juvenile establishing a territory. I was on the patio at 5:30 in the morning when she hurtled past like a dark ghost, barely clearing the block wall before disappearing behind the curtain of green acacia leaves.
We usually see the bats at dusk, and their numbers vary. The bugs that drew so many that first afternoon may have been winged ants hatched in recent rains. Western Pipistrelles are the smallest bat in the United States. The furry critters weigh just 1/10 of an ounce, with a wing span of 7-9 inches. Pipistrelles are known to utilize daylight, sometimes hunting in late afternoon, resting through the dark night and feeding again at dawn. They eat swarming insects, and can determine the size, shape, and even the texture of the insects by use of echolocation. Pipistrelle flight is erratic and fluttery, as they tilt and careen to scoop up their prey.
Also known as the Canyon bat, these mammals roost in rocky crevices by day, generally alone or in small groups. The bats mate in the fall, but the female holds the sperm and does not ovulate and become pregnant until after winter’s hibernation. The babies are born in June or early July, usually coming as twins and always as breech births. The females hang from their thumbs to deliver and catch the newborns in their tail membranes. In about ten days the young bats will begin to fly. Pipistrelles live 10-13 years. One of their primary predators is the owl, which may explain the low flight pattern of our great horned neighbor.


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