Jumat, 16 Agustus 2013

The Females of the Madagascar Sucker-Footed Bat are Missing

The Females of the Madagascar Sucker-Footed Bat are Missing

 

For the last six years, Paul Racey has been trying to find a female eastern sucker-footed bat. He has failed. The bats only live in Madagascar and since 2007, Racey’s team have tramped through the country’s eastern forests with nets, bags, and devices that detect the bats’ sonar. They’ve captured 298 individuals, some many times over. But every single one of them was male.
Where are the females? Why are they so ridiculously hard to find? And why do they segregate themselves from the males? No one knows. After so much fruitless searching, Racey doesn’t even have a good hypothesis.
All he knows is that the females must exist. For a start, a Smithsonian team once collected a female sucker-footed bat around 30 years ago, and it’s still housed in their collection. Also, Racey keeps on finding young males every year. “You can hold their wings up to the light and see bits of cartilage round their joints, which haven’t ossified fully,” he says. So, the bats must be reproducing. “There have to be females. It’s just that we can’t find them, and it’s very embarrassing.”
To put this in perspective, Racey has spent his entire career studying bats and has worked in Madagascar for 20 years. He’s vice-president of the UK-based Bat Conservation Trust, and has received a lifetime achievement award from them. He has published more than 200 papers on bats and edited textbooks about them. He even has a bat species–Racey’s pipistrelle–named after him. This is not a man who is accustomed to being unable to find a bat.
“I set out to do a study on the ecology and social organisation of [the eastern sucker-footed] bat and I’ve only done half of it,” he says. “I’m not used to that sort of failure.”
Eastern Madagascar sucker-footed bat. Credit: Paul Racey
Eastern Madagascar sucker-footed bat. Credit: Paul Racey
The sucker-footed bat (Myzopoda aurita) lives only in Madagascar and was discovered in 1878. For the longest time, people thought that it was the only representative of its family, with no close relatives anywhere in the world. Then, in 2007, Steve Goodman found another one next door. This western sucker-footed bat (Myzopoda schliemanni) lives in the island’s dry western forests while its previously known cousin inhabits the humid eastern forests. The western one poses no mystery—both sexes huddle together in the leaves of the Bismarckia palm. It’s the eastern males that lead an unprecedentedly monastic lifestyle.
Why should the females live apart from the males? “I have no credible hypothesis,” says Racey. The closest example is another bat called Daubenton’s bat. In some northern English valleys, males are found at higher altitudes and females are found lower down, although the gulf between them isn’t absolute. It also exists only in the breeding season, possibly because pregnant females struggle to cope with the harsher high-altitude environment. But this explanation can’t possibly apply to the sucker-footed bats, which live in a low valley.
The males, at least, aren’t hard to find. They roost in the Ravenala tree, or “traveller’s palm”, whose giant leaves spread out like a fan. The start as rolled-up tubes and gradually unfurl over several days, creating a hollow cavity that’s perfect for the bats. Racey once found 53 of them in a single leaf.
Over six years, he and his research assistant Mahefatiana Ralisata have tried to capture these bats by suspending huge nets between trees, and by sending climbers to the top of Ravenala plants with large cloth bags.
They mostly operated out of a coffee research station in south-eastern Madagascar, but they also carried out exhaustive searches of two neighbouring valleys. Young bats can’t fly very far since their arm bones haven’t fully hardened, so if they’re found at a specific site, their mothers are unlikely to be far away. But—aaargh!—where are they? Racey and Ralisata made 833 captures in total. They’d find the same bats again and again, but never any females. They even went back to the village where the Smithsonian found their female. Nada.
It hasn’t been a total loss. The team has learned more about the natural history of the bats. For example, they seem to be completely free of external parasites like ticks or fleas. “That’s easy to explain,” says Racey. “The roosts are spotless.” By huddling inside a rolled-up leaf, the bats protect themselves from parasites. They also stick exclusively to Ravenala. Banana leaves, while also shiny, green and coiled, never contain any bats. “I’m guessing that bananas grow too low and get hammered by rats,” says Racey. “If a rat found a bat, it’d eat it.”
The team have also shown that the bats are poorly named. They stick to leaves with tiny discs on their wrists and ankles, which were thought to act like suckers. But true suckers are held to surfaces because the air pressure outside them is greater than the pressure within their rims. That’s not how the bat’s discs work. Instead, Racey found that they secrete a sweat-like liquid that holds them against a leaf “like a licked piece of paper stuck to a window”. So, the sucker-footed bat isn’t sucker-footed. (The traveller’s palm isn’t a palm, either. Oh, you wacky biologists.)
Meanwhile, the whereabouts of the females are still a mystery. Racey suspects that they live in two very different populations—perhaps one in the high mountains and another near the coast. This would explain why the juveniles arrive in two waves every year, even though every other bat of the same size only has one annual breeding season.
We’re unlikely to find these female enclaves until our technology improves. “If I had a wish, it would be for a satellite tag that’s small enough to go on a 10 gram bat,” he says. Then, the task would be easy. You could just open a laptop and follow the males to wherever their mates are.
Suitably small trackers are probably years off and when they do arrive, someone else will have to use them. Racey is done. He’s had two grants from the National Geographic Society to fund his search, and is not planning on applying for more. “I’m 69,” he says. “We’ve done what we can, but we’ve been pissing in the wind.”
His one consolation is that he has left behind a legacy of scientists in his wake. During his stay in Madagascar, he helped to set up a non-governmental organisation called Madagasikara Voakajy,  dedicated to protecting the country’s wildlife, and training local biologists to do their own unassisted research. “It’s working,” he says. The organisation now has a female Malagasy director and Ralisata (Racey’s assistant) got her PhD on the back of the sucker-footed quest.

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