The Townsend’s Big-Eared Bat remains something of an enigma
By Lazo Gitchos
Sunlight poured through the south windows on the first floor of Ed Tenant’s barn near Carlton. Kent Woodruff, a retired U.S. Forest Service wildlife biologist, disappeared up a ladder and through a hole in the ceiling, careful to step only on the beams in the attic above.
The boards below collected decades of dried guano. Above, between the boards that supported the tin roof, a huddling mass of brown and gray bodies projected leaf-like appendages, rotating and squirming to hear their chirping voices reflected back from the darkness. It was a cluster of bats, each about the size of a mouse, packed very tightly together. Their tall ears reached down toward the floor.
The Townsend’s Big-Eared Bat (Corynorhinus Townsendii) lives in a wide variety of habitats throughout western North America. Although it was first observed in 1937, relatively little is known about the species. According to the National Park Service, distribution is strongly correlated to the availability of habitat, rather than climate or ecology.
“They are very adaptable,” Woodruff said. Townsend’s are considered a Candidate Species by the Washington State Department of Fish and Wildlife, a designation reserved for cases where the status of species health is not well understood; on the whole, little is known about the bat.
Townsend’s are nocturnal gleaners, foraging for moths and other insects throughout the night and resting during the day in colonies ranging in size from a dozen to a few hundred. Their exceptionally large ears are about half the length of their bodies when folded back. This extra surface area means the bats’ echolocation chirps are much quieter than most, allowing them to sneak up on insects at night.
Woodruff, who has studied the species for more than 30 years, says the Methow Valley has a very high density of these bat colonies, perhaps the highest in the western United States. He keeps a list of the dozen or so known colonies in the Methow, from Carlton to Early Winters, and checks in on them from time to time. He thinks the actual colony count could be twice as large.
Ahead, past the next rafter, Woodruff spotted another cluster, then another. With more than 200 bats, Tenant’s colony is the largest that Woodruff had ever seen.
The colony was already well established when Tenant moved onto the property near Carlton in the 1980s, though he said it was at risk from the large population of semi-feral cats fed by the neighbors.
Packrats, raccoons, and other mid-sized mammals often share habitat with the bats, and can prey on the young in springtime. Tenant regularly traps cats in his barn and relocates them, he said, but the bigger threat comes from humans — habitat loss and disturbance is a leading cause of colony disintegration and roost site abandonment among the species.
Woodruff spent a few minutes counting the tight groups of bats, and a few awoke and fluttered around the barn and down the ladder hatch. The attic was long and almost completely dark, the kind of open cavern that Woodruff said the bats prefer. Most roosts are found in old barns, mine shafts and larger caves. In the spring, females form nursery colonies separate from roosts.
Not everyone shares Tenant’s “relaxed compassion” for these bats, Woodruff said. Some are wary of rabies, or mistakenly think that bats are a threat to sensitive ecosystems. And, as new construction takes place, old buildings which make suitable roosting sites are often torn down. A study by the California Department of Fish and Game found that between 1960 and 1990, the species’ population in California declined by as much as 60%, mostly a result of habitat loss and human interference.
In 2005, Woodruff co-authored a Management Recommendations report on the Townsend’s Big-Eared Bat for the Washington Department of Fish and Wildlife (WDFW). The report notes that pesticide use may have an effect on bat populations by reducing their primary food source, and recognizes that rats and other predators have caused population pressure at roost sites. It also states that, due to a lack of studies on the matter, “a complete picture of this species’ life history is unknown.”
Abigail Tobin serves as the WDFW White-Nose Syndrome Coordinator, responsible for managing the detection and study of the fungal infection which affects bats. She says that the department tests guano from mixed-species roost sites, but does not directly survey Townsend’s populations in the Methow.
It’s likely there are more roosts between Carlton and Mazama than the dozen or so that Woodruff keeps tabs on. The bats, he said, “might be more common [in the Methow] than we think.” But, without investigating hundreds of old buildings, caves and mines, it’s impossible to know.
“[Townsend’s] are a difficult species to learn about — they’re nocturnal, they’re silent, and they’re hard to follow,” he said. And, “there’s no funding for bat research.”
Ahead in the rafters of Tenant’s barn, the bats continued to chirp and flit. They were waiting for nightfall and the moth hunt, after which they would return to the barn well-fed and just as mysterious as before they left the dark roost.
Information on making your property bat-friendly, as well as a colony reporting form, can be found at https://wdfw.wa.gov/species-habitats/living/habitat-at-home/bat-habitats#bat-help.