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Bats Northwest

"helping bats in Washington State"

Meet the Canyon Bat (formerly Western Pipistrelle) - (Parastrellus hesperus)

By Margaret Gaspari

When we think of unusual bats, we may think of the Pallid Bat catching scorpions. When asked about rare bats, we think of the Townsend's Big-eared Bat. Yet, the tiny pipistrelle from eastern Washington is another of Washington State's uncommon bats. Indeed, as a day-flying, desert-dwelling, twin-bearing, tiny, solitary bat, it is definitely unusual.

Pipistrelles are actually found all over the world, from Tasmania to Europe and Africa and in North and South America. In fact, the Common Pipistrelle was the bat that Lazarro Spallanzani used in the experiments that led him to the conclusion that "bats see with their ears". Their name comes from the Italian word, "pipistrello" meaning "bat".

In the United States we have two pipistrelle named species, the Eastern (Pipistrellus subflavus) and the Western (Parastrellus hesperus), but they are quite different in appearance and genetics. The Eastern has a long, unkeeled calcar and distinctive tri-colored fur. The Western "pip" has a keeled calcar and fur that ranges from pale yellow and gray to red brown, with very dark face, ears and wings. It is the smallest bat in the country, weighing in at 3-6 grams with a wingspan of only 8 inches.

Our pipistrelles live in dry lowlands and desert and probably, of all our bats, are the most suited for an arid climate. They have a special adaptation, the ability to concentrate urine, which helps conserve water. They also adapt behaviorally, coming out in daylight to drink when necessary, even during hibernation. In fact, Western Pipistrelles utilize daylight hours more than any other bat. They emerge early, even before the sun goes down, rest most of the night, and then return to the air near dawn. They have even been seen feeding with violet-green swallows.

Pipistrelles have been called the "canyon bats" because of their preference for living in areas of cliffs and rocky canyons. These areas provide the roosts they need to combat the threat of dehydration. They roost in narrow rock crevices in cliffs, caves, or mines, but will also roost in burrows and even under rocks. And they normally roost alone. Little is known about where they hibernate. When found, usually in mines or caves, it is always alone.

Occasionally females will form small maternity colonies of a dozen or less, but they usually prefer to raise their young alone. Adult females are larger than males (4-5 grams vs. 3-4), a good thing since they normally have twins that weigh just under one gram at birth - an incredible investment for the mother! Lactating females have a greater need for water and will go to drink at all times of the day or night. Young grow quickly though and are flying at one month of age.

Pipistrelles, like our other Washington bats, are insect eaters, foraging on the smallest beetles, moths, caddisflies, mosquitoes, leafhoppers, etc. They often forage in swarms of insects where their slow flight is helpful. They have the slowest and weakest flight of any of our bats, a distinct disadvantage when it’s windy. But it's also a great advantage when faced with a scientist’s mist net, which they can usually avoid.

Washington is the northern periphery of the Western Pipistrelle's range and we have little information on its habits and behavior here. In fact it is listed as a "species of concern", meaning that we don't know enough to know if its populations are declining. But if you have occasion to be in the southeastern portion of the state in the summer, keep your eyes on the skies in late afternoon. You may see our country's littlest bat competing with the swallows for dinner.