Townsend’s Big-Eared Bat: Species of the Week

On our Northeast Oregon property, we have an old house that’s rotting.  It has little historic or architectural value, so we’ve been leaning towards tearing it down. Then my nephew, Gerek, found the bat in the closet.

Townsend's Big Eared Bat

Twitter pal Chris Clarke as well as experts associated with Bats Northwest (Meg, Aimee Hart and Pat Ormsbee) helped me identify it as a Townsend’s big-eared bat (Corynorhinus townsendii), a species that ranges throughout North America.

Such a lovely creature: I’d like to gaze at it for a few moments at least once or twice a week. But I don’t. Why? Because every glance (or photo) we sneak risks pressuring this sensitive and threatened species to abandon its roost. The stress of looking for another of the same quality might kill it or at least prevent it from breeding this season.

Over the last few years, I’ve been meditating more and more on what it means to measure the worth of nature encounters by senses other than sight.  Now the Townsend’s big-eared bat is teaching me how to appreciate a presence that, if I respects its needs, provides little sensual entertainment at all.  And it may teach me more than that.  This tiny creature may dictate big decisions Jerry and I make about our old buildings and the surrounding habitat.

Given bats’ nocturnal habits and sensitivity to human disturbance, research on them isn’t easy. But what research has been done on the Townsend’s big-eared bat suggests that the greatest factor for survival and reproductive success is the availablity of roosting sites.  They need caves or cave-like structures (old mines, abandoned buildings) with internal complexity and low to moderate airflow.  They need to hide from predators and find spots that are consistently cool enough in summer and warm enough in winter.  What this means at different latitudes or elevations varies.  If the bats can’t find a single roosting site to meet year-round needs in a particular climate, they will move short distances with the seasons to take advantage of several.  They may have different sites for breeding, hibernating and summer foraging as well as some transitional roosts in between.  Males and females may occupy different roost sites at different times of year but return to the same places every year and pass on information about good roost sites to the next generation.  They also need water and forage nearby and prefer forest edges over dense canopies or open grasslands.

In Oregon and Washington (as well as other states), Townsend’s big-eared bats are listed as a species of concern.  Over the last 200 years, human activities across North America have probably increased the number of roosting sites available to this picky species by providing mine shafts and buildings and then abandoning them.  However, the species still appears to be in decline. Reasons may include various human activities: poisoning the insects they eat with pesticides, closing old mines and trapping bats inside, and the growing popularity of caving.

I can see why a Townsend’s big-eared bat might like the canyon where we live.  There aren’t many people out here. It can take advantage of differing elevations to warm up or cool off.  There are plenty of abandoned homesteads around.  The canyon walls are littered with basalt rockfalls that may offer cave-like dwellings.  There are also plenty of springs, small ponds and marshy areas nearby.  There’s a creek at the bottom of the canyon (a steep climb for us two-legged creatures but a short flight for one with wings).  There are also many edge areas between grassland and forest.

The old house on our property sits in a south-facing hollow just below a spring and small marsh.  Before I found the bat, I had been fantasizing about tearing down the house and digging out a pond.  The Townsend’s big-eared bat might appreciate more wetlands; they’re often associated with beaver activity.  But to be a good neighbor, I would have to leave them a closet to roost in or provide an alternative.  Bat boxes won’t work. They need bigger structures that are just right (and of course, it’s hard for humans to figure out what “just right” means to a finicky bat).

We’d like to know more.  How many bats use the old house?  It is a roost one or more return to year after year or is it transitional? Is it a bachelor pad or do females use it too? Do they roost in some of the other outbuildings nearby?  Could those be alternatives if we tear down the house?   Or do we have to build a new structure just for the bats?  Of course, to answer these questions, we ‘d have to do like the foolish monkeys in one of my favorite South Asian tales.  To make sure the garden trees had sufficient water, they pulled each one up to look at the roots.

For now, we’re striving not to be foolish Homo sapiens.  We’ve reduced our activity around the house, propped the closet doors open so the wind doesn’t blow them shut and trap the bat inside.   We content ourselves with the photo I took before I knew how sensitive these bats were.  We consider ourselves lucky that, despite the flash photo, the bat continues to live in the house (though it did move to another closet).

For the future, I’ll be researching if and how one can monitor bat populations without disturbing them and how to build low-cost, alternative “caves.”  If anyone has any ideas, I’d love to hear them.

Resources:

“Townsend’s Big-eared Bat (Corynorhinus townsendii): A Technical Conservation Assessment,” Prepared for the USDA Forest Service, Rocky Mountain Region, Species Conservation Project, October 25, 2006, by Jeffery C. Gruver1 and Douglas A. Keinath (with life cycle model by Dave McDonald3 and Takeshi Ise).

Bats Northwest (this organization has a great website.  Meg also responded promptly to my email asking for help in identifying the bat and put me in touch with Aimee Hart and Peg Ormsbee, who provided invaluable information).

Cross-posted at The Clade.

If you enjoyed this post on appreciating nature we can’t (or shouldn’t) see, you might like  “Looking for Black Gibbons,” published in In the Mist.