The Magic of Bats: Not Just for Halloween
Posted by Richard Conniff on October 31, 2013
When it comes to bats, a lot of people go a step beyond Ronald Reagan’s notorious remark about trees. They think that if they’ve seen one bat, they’ve seen one too many. And let’s admit up front that some bats aren’t much to look at it, unless you are partial to hairy carbuncles, scrunched-up noses, and needle-sharp teeth. Bats tend not to get much public love, except around this time of year, and then only as one of the little horrors of Halloween.
But the recent discovery that bats use a kind of natural megaphone to amplify their voices reminds me that amazing and often ingenious behaviors seem to be a bat specialty. This probably shouldn’t be too surprising. The 1240 bat species described so far represent about a fifth of all known mammals, meaning plenty of diversity. Their fossil record also dates back more than 50 million years, meaning lots of evolutionary time to develop strange behaviors.
Let’s start, for instance, with that megaphone behavior. Naturalists already knew that in New World rain forests, Spix’s disc-winged bats like to make their homes in the furled leaves of Heliconia and Calathea plants. These bats get their name from the little suction cups on their wrists and ankles, which enable them to stick to the leaves (and also to your fingernails, a juice glass, etc., says one bat biologist who has studied them).
The leaves have an annoying habit of unfurling, with the result that the bats must frequently relocate. When they arrive in a new home, these bats make a call to help strays find their way back to the group—and it turns out that the trumpet shape of the leaf amplifies this call by 10 decibels. Researchers at North Dakota State and the Universidad de Costa Rica hope to find out next whether these bats select real estate based on amplifying power, or if they modify their calls according to the acoustic qualities of the leaf.
Echolocation—the ability to fly by night through tangled forests and precisely target insect prey—would of course also rate as an amazing bat behavior. But it’s old news, and we are jaded. Likewise is the discovery that certain moths put out signals to jam a bat’s radar so it cannot find and eat them.
Bats have, however, also evolved in this aerial arms race. Barbastelles are medium-sized European bats that live by hawking for their insect prey by night, and they specialize not just in moths, but in moths with ears—moths that should normally be able to hear them. So barbastelles actually reduce the intensity of their echolocation call, making them less efficient at finding pretty, but also much harder for their prey to detect. In one experiment by University of Bristol researchers, a moth could spot a conventional bat approaching at a distance of 33 meters, leaving time to begin evasive maneuvers. Barbastelles, on the other hand, could sneak up close enough—1.9 meters—to whisper “gotcha” in the ears of their oblivious prey. They have invented “stealth echolocation.”
Another adaptation to insect defenses isn’t really fair play, old man, but a bat has to live. Researchers from the Max Planck Institute spent four years studying houseflies and Natterer’s bats in a cowshed near Marburg, Germany. The problem for the bats was that houseflies hardly ever fly by night. Instead, the flies hang around on walls and ceilings, where the massive background echo masks the faint echo of the houseflies, preventing the bats from zeroing in on them.
The bats, already hungry and a little annoyed, soon realized that the houseflies were not only lounging about, but also having sex. And it was noisy sex, at that. The fluttering of wings. A burst of broadband click-like signals. What sounded to human ears like a low-frequency buzzing. You know the kind of thing. So the bats began to eavesdrop. They also realized that they could target this sound, hover just above the happy but distracted couple like demons in a Hieronymus Bosch painting, then pick them both off and gnash them between their teeth, all in one quick swoop. The result was that 26 percent of flies engaged in sex were attacked by bats. Or as the researchers (who were, after all, German) put it: “Sex kills.”
But let’s end on a happier note, and an even more colorful behavior. Chinese researchers were studying the short-nosed fruit bat (Cynopterus sphinx), in which a single male frequently lives with a harem of females. When the male mounts a female from behind, she apparently wants sex to last for a reasonably long interlude.
To their astonishment, the researchers realized that she was keeping the male engaged by performing oral sex. Acrobatic oral sex, at that, since she had to bend over and lick the base of the male’s penis as he was copulating with her. But as long as this was happening, the male continued happily copulating.
The scientists go into way too much detail about how and why this might be so. There’s even a video. For the purposes of this article, let’s just say that bats are wonderful.