1 week Ago By Ruth Schuster
Once upon a time, people assumed that bats were blind, mainly because of their beady little eyes and nocturnal lifestyle. The discovery that bats "see" prey using echolocation did nothing to dispel that myth. First of all, many fruit bats have huge soulful eyes you could get lost in.
Second, insect-eating bats may only have "pinhole" eyes but they can see, science has proven. The assumption had been that bats' sonar skills only apply to hunting at short distances, not long-distance navigation. Is that so? Now the intrepid bats team at Tel Aviv University has demonstrated that wild Kuhl's pipistrelle microbats ( Pipistrellus kuhlii ) driven a few kilometers from the roost can find their way home with their eyes closed.
They apparently achieve this by creating sonar-based maps in their little heads. Microbats are usually insectivores. They weigh about the same as a cigarette but average a decent wingspan of 25 centimeters (9.
8 inches). Flying foxes, which are fruit bats, can weigh as much as nine cartons of cigarettes and reach almost 2 meters in wingspan. The experiments on navigation in the Kuhl's pipistrelle by Aya Goldshtein, Lee Harten, Prof.
Yossi Yovel and colleagues were described in the latest journal of Science . How does one investigate what bats can do with their eyes closed? By isolating auditory input and frustrating other sensory input, including by blindfolding them. Since the blindfolded bats made it home, the team concluded that they were achieving "acoustic cognitive map-based navigation.
" Whether microbats normally use echolocation to find their way home, or just can do it, isn't clear. But here we are and a large-scale echolocation model the team created suggests the microbats make acoustic maps of their environment. Separate work led by Yovel has shown that Egyptian fruit bats navigate with their eyes much like we do, helped by conspicuous landmarks such as skyscrapers.
They build mental maps and even take shortcuts, suggesting that once they have the map in mind, they don't necessarily need the landmarks anymore . Now Yovel and the team suggest mapping in blindfolded microbats whose sense of sight, smell and personal compass were reversibly impaired. How was this achieved? The wild bats were caught at the roost using nets.
Then they were chauffeured to a new location about 3 kilometers (1.8 miles) away, sequestered inside in a darkened container, isolated from the outside – no sights, no smells. Before their release, the scientists glued felt around their eyes, Yovel says.
"They can't remove it in flight but can the moment they land, scratching it off with their hind feet," he stresses. He adds that they'd never have done this experiment on fruit bats because, their lack of sonar-aided hunting aside, "vision is so important to them that they'd go crazy." Pipistrelles, on the other hand, can and will fly in the pitch dark, which is why they were chosen.
They presumably hated the experience but they also seemed to have been unfazed, he says. The scientists also glued tiny trackers onto the microbats to see in real time that they got home. We just note that cats removed from home, shouting from a closed cat carrier on the car floor and unable to see the route, may also return.
We don't know how. Cats may tap into geomagnetism in some form. Here, the team disabled potential geomagnetic aid by gluing a tiny magnet to the microbats' little heads.
However, while geomagnetics may explain homing in cats (or not), Yovel doesn't think it plays a role here because of scale. Magnetism may provide a compass, but not coordinates. "We didn't completely eliminate a magnetic hypothesis, but I think it's unlikely," he says.
All this gluing was done using surgical cement that disintegrates in a couple of days, leading the tracker and magnet to fall off. As said, the bats removed the felt blindfold the moment they got home. Or rather, the 95 percent who got home did.
Why the attrition, we do not know. Maybe some changed roost, he says. How does echolocation work? Bat squeaks.
The sound wave travels through the ether until encountering an object. It bounces off the object and the bat hears it return. The bat can identify prey type, location and even trajectory based on the characteristics of the echo: the prominent body parts of a flying bug such as head, wings and thorax return discrete echoes (called "glints").
Apparently bats can differentiate between insect-sized virtual objects and other-sized virtual objects . And skyscrapers. The bottom line is, eyes are good.
Control microbats without blindfolds got home more quickly or efficiently than their peers with the blindfolds. But now the team has shown that in insectivorous bats, echolocation may not only allow for local navigation to the nearest mosquito, but may also – surprisingly – serve to build a sort of acoustic map that helps navigate long distances. Yovel adds about homing cats that many animals "home," and we don't know a thing about their path home.
Maybe they wandered for a month before encountering something familiar. This is not the case of our tough little Kuhl's pipistrelles who beetled straight for home with their eyes shut – not that they had a choice in the matter. And once home, they ripped off that damn blindfold.
Why didn't they stop on the way to do that? Maybe they couldn't be sure where they could land safely because they were blindfolded..
