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peter hayes
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From an earlier in NATURE
Bats eat birds on the wing
Migrating birds should beware of high-flying bats.
TOM CLARKE
The greater noctule bat waits for the fly-by.
As if the arduous journey between northern Europe and warmer climes weren't enough, birds migrating at night may be at the mercy of predatory bats, new research suggests1.
Although there have been isolated cases of bats taking small birds from nests or perches, they were never suspected of actively hunting birds on the wing - until now. Having sifted through 14,000 droppings of the greater noctule bat (Nyctalus lasiopterus), researchers in Seville conclude that the animals are making a meal of small birds that migrate across Spain every spring and autumn.
"It must be highly rewarding for the bats," says Javier Juste, one of the team at the Donada biological research station. "Half the year, all this food is just flying by."
Little is known about what, and when, the rare greater noctule bats eat - they feed at altitudes of up to 500 metres, out of the range of bat-detecting microphones. It had been assumed that, like all other predatory bats, they feed on insects.
But the Spanish group discovered that pellets beneath greater noctule colonies often contain feathers from a variety of small birds, as well as insect parts.
The feather content of droppings peaks when migratory bird traffic is highest - in spring and autumn. And maximum values in northern and southern Spain peak two to three days apart, which is consistent with the advance of migrating birds, says Juste.
The finding is "quite incredible," says Colin Catto, director of the UK National Bat Monitoring Programme in London. "The bats must have been catching the birds in flight," says Catto. Greater noctules are large and well adapted to fast flight in open areas; their wing structure does not equip them for the low-speed manoeuvring involved in carrying off perching birds.
Given that greater noctules weigh only around 50 grams and have a wingspan of up to 60 centimetres, "they have to be pretty tiny birds," Catto adds.
"This is certainly the first case I've heard of bats preying on active birds," says Jeremy Greenwood, who studies European bird migration at the British Trust for Ornithology in Thetford.
Fortunately, greater noctules are rare, Greenwood says, and millions of small birds travel over Spain during their peak migration period. "There are enough to overwhelm the entire Iberian bat population even if they're going at it hammer and tongs," he says.
The Spanish team now hopes to DNA-fingerprint the droppings to identify the bird species that are favoured by the bats. They would also like to borrow Spanish military high-resolution radar equipment to watch bats attacking birds under the cover of darkness. "I don't think they'd mind us using it for such a pacific purpose," says Juste.
References
Ibanez, C., Juste, J., Garcia-Mmudarra, J. L. & Agirre-Mendi, P. T. Bat predation on nocturnally migrating bird. Proceedings of the National Academy of Sciences, 98, 9700 - 9702, (2001).
Bats eat birds on the wing
Migrating birds should beware of high-flying bats.
TOM CLARKE
The greater noctule bat waits for the fly-by.
As if the arduous journey between northern Europe and warmer climes weren't enough, birds migrating at night may be at the mercy of predatory bats, new research suggests1.
Although there have been isolated cases of bats taking small birds from nests or perches, they were never suspected of actively hunting birds on the wing - until now. Having sifted through 14,000 droppings of the greater noctule bat (Nyctalus lasiopterus), researchers in Seville conclude that the animals are making a meal of small birds that migrate across Spain every spring and autumn.
"It must be highly rewarding for the bats," says Javier Juste, one of the team at the Donada biological research station. "Half the year, all this food is just flying by."
Little is known about what, and when, the rare greater noctule bats eat - they feed at altitudes of up to 500 metres, out of the range of bat-detecting microphones. It had been assumed that, like all other predatory bats, they feed on insects.
But the Spanish group discovered that pellets beneath greater noctule colonies often contain feathers from a variety of small birds, as well as insect parts.
The feather content of droppings peaks when migratory bird traffic is highest - in spring and autumn. And maximum values in northern and southern Spain peak two to three days apart, which is consistent with the advance of migrating birds, says Juste.
The finding is "quite incredible," says Colin Catto, director of the UK National Bat Monitoring Programme in London. "The bats must have been catching the birds in flight," says Catto. Greater noctules are large and well adapted to fast flight in open areas; their wing structure does not equip them for the low-speed manoeuvring involved in carrying off perching birds.
Given that greater noctules weigh only around 50 grams and have a wingspan of up to 60 centimetres, "they have to be pretty tiny birds," Catto adds.
"This is certainly the first case I've heard of bats preying on active birds," says Jeremy Greenwood, who studies European bird migration at the British Trust for Ornithology in Thetford.
Fortunately, greater noctules are rare, Greenwood says, and millions of small birds travel over Spain during their peak migration period. "There are enough to overwhelm the entire Iberian bat population even if they're going at it hammer and tongs," he says.
The Spanish team now hopes to DNA-fingerprint the droppings to identify the bird species that are favoured by the bats. They would also like to borrow Spanish military high-resolution radar equipment to watch bats attacking birds under the cover of darkness. "I don't think they'd mind us using it for such a pacific purpose," says Juste.
References
Ibanez, C., Juste, J., Garcia-Mmudarra, J. L. & Agirre-Mendi, P. T. Bat predation on nocturnally migrating bird. Proceedings of the National Academy of Sciences, 98, 9700 - 9702, (2001).