In the dead of night, when it's dark enough that you or I might not be able to see our hands in front of our faces, some bats have no trouble tracking down a small, flitting insect and making a meal of it. Their secret? A biological sonar called echolocation.
By pushing air through their larynxes and out of their mouths or noses, echolocating bats generate ultrasonic "chirps." The echoes that bounce back to their ears give the bats the lay of the land and the sky, revealing obstacles and prey.
Bats that hunt like this are usually classified in one of two groups. There are the "gleaners" that use quiet echolocation calls to pluck prey off the ground, and the "aerial-hawkers" that use louder calls to find and catch flying insects mid-air. In other words, "whisperers" and "screamers." Some bats, though, aren't so easily pigeonholed, and can go from a whisper to a scream if they need to.
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Hemprich's long-eared bats (Otonycteris hemprichii) have traditionally fallen into the gleaner camp. Flying low through the deserts of North Africa and the Middle East, the bats use quiet calls to hunt large bugs, spiders, and scorpions on the ground. So when Talya Hackett and Carmi Korine, a pair of biologists who study desert bats, noticed Hemprich's bats calling louder and deviating from their normal flight patterns — acting more like aerial-hawkers — they were understandably puzzled.
Could Hemprich's bats be trying to have it both ways, hunting on the ground and in the air? The two groups of hunters aren't mutually exclusive, the researchers say, and "at least some species are able to use different tactics when necessary." Even bats that usually feed on fruit or nectar have been known to catch insects mid-flight if there's an opportunity. But the same features that make Hemprich's bats good gleaners — long ears that can pick up faint echoes and large wings that allow them to carry off heavy prey — are a strike against them when it comes to hunting in the air; they're slower and less agile than bats that specialize in aerial-hawking.
To see if the bats were really switching between hunting tactics, Hackett, Korine and fellow bat biologist Marc Holderied studied them as they hunted in deserts and gardens in Israel. They recorded the bats' flight paths and the echolocation calls they used, and collected their post-meal droppings to see what they were eating.
The bats they watched sometimes flew higher and slower than they usually did when hunting on the ground. They also called longer and louder than they did when gleaning, "screaming" at almost the same decibel level as aerial-hawkers and showing off what the researchers say is the largest range in call intensity they've seen in a bat.
And the droppings? They were loaded with bits and pieces of flies, butterflies, bees, wasps, and other flying insects, instead of the usual ground-bound spiders, beetles, and scorpions.
All of this suggests that the bats aren't just grabbing a flying insect here and there if they have the chance while gleaning. They're completely switching from one mode of hunting to the other, and changing their flight behavior and echolocating chirps to do it. They ramp up the intensity of their calls and fly even slower than they usually do so they can make tighter turns and track with their targets. The whisperer can scream when it needs to, indicating that bats might be more flexible hunters than we'd thought.
Why would the bats both hawk and glean? The researchers think that it may have to with the weather and the menu available to them. When the desert is especially hot and dry during the summer, the bat's usual prey tend to hide themselves away, forcing the hunters to go after different prey and change up their tactics.
Hemprich's bats are not only versatile hunters, but fearsome ones. In his time studying the bats, Korine has seen them dive-bomb and attack Israeli yellow scorpions, also known as "deathstalkers," a nickname that should give you a hint about their toxicity. While getting stung in the head and the face, the bats gobble down the scorpions whole, including stingers and poison glands, seemingly without a care in the world.
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