One of the great joys of my writer-in-residence “position” is the opportunity to explore some wonderful aspects of the Great Basin with National Park Service biologists. Last night was one those occasions, when I tagged along with a crew headed to a nearby cave to band bats. The cave is a well-known roost for migrating Mexican free-tailed bats, where they collect in the millions before departing for more southerly wintering sites. We arrived at the cave entrance before sunset, which we reached by an easy scramble up a limestone outcrop. At the lip of the cave there was a broad bench overlooking the Spring Valley. It was a beautiful evening: calm and mild, with wonderful views of “typical” Basin and Range topography (a great gulp of valley-space, cupped by fringing ranges of 11,000-foot-plus mountains, snow on the highest peaks in an autumn of early storms). But what dominated the ambiance of the place was the powerful odor of ammonia. The smell was as much like gauze as air; it settled in my mouth and nose, wrapped me in its sweetly acrid stench. The odor wafted up from the portal of the cave, where the bats would soon emerge, rising up out of the darkness in a counterclockwise spiral before launching themselves over the valley to hunt for insects. To catch the bats, we erected a harp trap at the entrance to the cave. The trap consisted of a metal frame supporting a series of vertical monofilament lines; when a bat hit the monofilament, it tumbled into a canvas pouch, where plastic sheets funneled it into dead-end spaces on opposite sides of the trap. It then was easy for one of the biologists to grab the bat, note its sex, age, tooth wear, and reproductive condition for the data recorder, and attach a numbered aluminum band to its forearm. In this way, scientists working the cave have banded 30,000 Mexican free-tailed bats over a three-year period. Thirty thousand bats sounds like a lot (and it is)—but it is only the tiniest fraction of the estimated two to three million Mexican free-tailed bats that use the cave over the course of four months, from June until mid-October. Two to three million bats, each weighing about 12 grams—or in my favorite units, about 15 to 20 raisins—roosting in densities of about 170 bats per square foot. Imagine the impossibly claustrophobic, hot and crowded and fetid cave-darkness, which is their bat-home—and so the wonder of that….and then the explosion of bodies pouring into the gathering dark, up to 2,000 per minute, which would mean 120,000 per hour, or 240,000 in the two hours that we were banding at the cave. The bats were everywhere, flying within inches of our bodies, hitting the harp trap, pulsing out into Spring Valley, silhouetted by the setting sun: a great and lovely shivering of wings streaming out of the cave, the numinous, bat-quick air suffused with light and life. And in some years a pair of peregrine falcons wait above the cave and plunge into the swirling mass of exiting bodies; they take what they can, but the bats keep coming. No one knows where these Mexican free-tailed bats come from, or where they go. Of the thirty thousand bats banded at the cave, handfuls have been recaptured at the cave entrance, a few elsewhere. They are present in the Spring Valley for four months and then they vanish into the ether. Perhaps many head towards Mexico, as one banded at the cave was later captured in Arizona. They colonize the night and unknown, distant caves. But the bats of the Spring Valley also colonize our imagination: an aerial river of life, millions of creatures, so alien in how they make their way through the world. Yet they remain our hairy, milk-drinking kin, our brothers and sisters, and they speak to us in a language as mysterious and potent as the ultrasonic clicks with which they hunt their prey. . . . We left the cave entrance around eight o’clock, down-climbing the small outcrop in the dark, and then heading back to Baker. On the way home I thought about the bats, of course, but also the opening lines from a poem by Gerard Manley Hopkins that a friend had sent me a few days before: Let me be to Thee as the circling bird, Or bat with tender and air-crisping wings That shapes in half-light his departing rings. . . Those “air-crisping wings”: millions of them, flowing out into the Nevada night, a motion and a presence that haunts my heart and mind, and which will be with me always. PS: Thanks to the NPS biologists who let me tag along with them, and get in the way: Bryan, Kathleen, Joey, and Kelsey. They are doing good work.
31 Comments
Rob Mrowka
9/28/2017 07:09:40 am
I know that cave well. I fought (and lost) a wind farm being constructed in the valley mere miles from the cave. We did win concessions on turbine speed, installation of bat radar so turbines could be turned off, and five years of mortality monitoring.
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Chris
9/28/2017 09:08:24 am
Hi Rob - I checked with a NDOW biologist and they are not using the radar system any more, as it has not worked well with bats, because of small target size. Instead they have installed an IR beam break system that monitors bat out- and in-flights. from the cave. The system tells the wind turbines when to curtail night activity, due to high numbers of bats in the air. Monitoring of wind farm mortality indicates that mortality is well below the thresholds.
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AuthorI am a professor emeritus of Environmental Science and Ecology at SUNY Brockport. What began in 2017 as a sabbatical blog continues in a haphazard way, as the spirt moves me and time allows. The focus, though, remains the same - the natural world, in all of its complexity and beauty, and our relation to it. Archives
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