From the Vault: Anabat

By Eilene Lyon

At the end of my freshman year at Fort Lewis College, in 2005, I did a 10-week internship in the Natural Resources department at Mesa Verde National Park. One of the full-time employees, Marilyn Colyer, invited me to join a bat survey in the La Plata Mountains.

Though wandering the forest at night is not my favorite thing, bats became a bit of an obsession. The principal tool we used was an Anabat, which allowed us to record echolocation calls, rendering them audible and visual, in the form of a graph. Part of my job was to study the graphs and determine which species we had observed.

Bats fascinate me for several reasons. They are the only mammals capable of true flight. Like us, they have a low reproductive rate, generally no more than one pup per year. They are long-lived, as much as 25 years in the wild. No mammalian order other than Rodentia boasts as many species, and bats (Chiroptera—“hand-wing”) are more varied in morphology and life strategies.

Large, diurnal fruit-eating bats, aka flying foxes, use their eyesight exclusively to forage. Smaller, nocturnal bats use echolocation—a high-volume, high-frequency burst of sound—to forage, but their eyesight in daylight is as good as ours. Hence the phrase “blind as a bat” is patently ridiculous.

There are 18 species of bats known to live in or migrate through Colorado. All are insectivorous and nocturnal. Of these, the most common are Mexican free-tailed (Tadarida brasiliensis), big brown (Eptesicus fuscus), little brown (Myotis lucifugus), and silver-haired (Lasionycteris noctivagans).

The most endangered is the Townsend’s big-eared bat (Corynorhinus townsendii). White-nose syndrome, a deadly fungal disease, finally reached southern Colorado this past summer. A single bat at Bent’s Old Fort tested positive. The disease has killed millions of bats nationwide, thus we need to be concerned.

The summer before my senior year, my field ecology class had the opportunity to camp out for a night, just across the state line in New Mexico. We observed a scientist mist-netting bats near a stock pond in the desert. When bats leave their roost at night, their first task is getting a drink of water. Though we were not permitted to participate in the mist-netting, one lucky volunteer (me!) got to briefly hold and release a silver-haired bat.

With Marilyn’s encouragement, I decided to do a bat study for my senior thesis project. To do so, I needed an Anabat of my own, since the college did not have one. Fortunately, I got some grant money to help purchase this one. The technology has improved since 2007, so it is essentially obsolete. And software now does the work of “reading” the graphs to determine species.

What the machine is still good for is listening to bats in real-time. Their echolocation calls fall in the 20–100 kilohertz (kHz) range, while our hearing is in the 20 Hz–20 kHz range. It’s actually a good thing we can’t hear them, because the volume would be deafening. Bats avoid injuring themselves by dislocating the bones in their inner ears when they call. By instantly analyzing the echo, they can detect an object no bigger than the width of a human hair.

The Anabat uses a division process to bring the bat calls into our hearing range. The microphone is so sensitive that it will pick up the sound of your fingerprint whorls rubbing together. It’s fun to take along on a camping trip, or even using here at home in the summertime when I see bats foraging in the dusk near our deck.

As with any other being, the more we know and understand about bats, the more likely we are to fight for their conservation. Though they offer services that make the world better for humans (like eating mosquitoes!), they deserve to live their lives for their own sake, without interference from us, without our destroying their habitat.

For more on bat sounds, visit this Ohio State University page.

Feature image: The Anabat II with separate recording unit.

Sources:

Feldhamer, George A., Lee C. Drickamer, Stephen H. Vessey, and Joseph F. Merritt. Mammalogy: Adaptation, Diversity, Ecology. 2nd ed. New York, NY: McGraw-Hill, 2004.

Adams, Rick A. Bats of the Rocky Mountain West: Natural History, Ecology, and Conservation. Boulder: University Press of Colorado, 2003.

Colorado Public Radio news

Colorado Parks & Wildlife: Bats in Colorado