20 Million Bats

Okay, I know this is totally weird, but this post is not about Sean (with apologies to those of you who tune in regularly specifically to read posts about Sean).

Back in August, I went to the Ecological Society of America meeting, which, as luck would have it, was in Austin. This is the premier meeting in the U.S. (and perhaps the world) of ecologists and I generally enjoyed watching talks about the cools stuff that is going on in ecology. There were also various workshops and field trips, but I couldn’t attend most of them because I was still in vacation in Maine (not that I’m complaining). There was one field trip, however, that looked interesting and was held the Tuesday evening of the conference instead of the weekend before it. So I signed up.

And on Tuesday, about 100 other ecologists and I took a bus for the several hour drive to the outskirts San Antonio — more specifically, to Bracken Cave. Bracken Cave is the summer roost of about 10 million Mexican free-tailed bat moms and their offspring, for a total of about 20 million bats. This is the largest congregation of bats known anywhere. We got a tour from some scientists from Bat Conservation International, which owns and protects the property, and then we got to watch the evening exodus of bats pour out of the cave. For hours. Millions and millions of bats going out for the night to eat insects. It was amazing. Here’s a taste:

The cave is huge and so is its entrance

Bats flying out of the cave

The view from on top of the cave, with millions of bats spiraling out and up

Bat bodies almost mask the view of the cave entrance at peak exodus

They spiral up out of the depression where the cave mouth is, until they’re above the treetops. Then they all head off in one direction, a river of bats in the sky.

They spread out more as they get farther away, creating an undulating celestial ribbon

Up a bit closer

And closer still

Here I photographed them just a couple meters over my head

The sound of thousands of flapping wings:

And some artsy photos, because I could.

Zoom

Backlit

Tree

Moon

And so here’s some cool ecology. With 20 million bats flying out every night, and half of them being new fliers, you might wonder: don’t they ever crash into each other or the rocks or trees? The answer is, yes, they do. Not very many, but a few get blown by a gust of wind and collide with something. And there’s a panoply of cave entrance dwellers that know it. We watched a coachwhip snake emerge and head up the cliff face to a small shrub that jutted out from the wall. It waited. We wondered what it was doing. Then a bat got snagged in the bush and the snake wasted no time in gathering its evening meal. It knew what it was doing.

Coachwhip snake photo and video