Bats revealed as bird killers

2019-03-06 05:04:14

By Nicola Jones A rare kind of European bat regularly feasts on birds, surprised biologists have discovered. And they suspect that the large bats are capable of hunting down the birds in flight, something no researcher has ever seen. A study of faecal pellets revealed the greater noctule bat, Nyctalus lasiopterus, eats large numbers of migratory birds, called passerines. Millions of these birds pass through the Mediterranean basin on their way between northern Europe and Africa. They fly mainly at night, making them a perfect food source for bats. Some tropical species of bats are known to munch on birds, but they only eat them occasionally and catch resting prey. Carlos Ibáñez from the Doñana Biological Station, part of the Higher Council for Scientific Research in Seville, Spain, and his colleagues investigated the bird-eating habits of Nyctalus lasiopterus> by looking at their faecal pellets. They collected over 150,000 pellets from more than 200 bats throughout Spain, and analysed 14,000 of them. All of the bats were found to be eating insects. But up to 45 per cent of the pellets were also riddled with bird feathers during the migration periods in the spring and autumn. There were practically no feathers in the pellets at other times of year. “It was quite surprising to find that birds were so important in the diet of the bats,” says co-author Javier Juste, also from the Doñana Biological Station. But he says he understands why the bats might choose that food source. “In terms of energetic revenue, it is highly rewarding to switch from feeding on insects to birds.” The bats can be quite large, with a wingspan of 45 centimetres (18 inches). So the researchers suspect they should have no problems overpowering the small birds. They should also be able to sneak up on their prey, since their echolocation frequency is much higher than anything the birds can hear. Other circumstantial evidence suggests that the bats are plucking the birds out of the air rather than catching them on the ground, the researchers say. The wing shape and echolocation frequencies of the bats are best suited for long-range target detection and chase in the open air, rather than picking out prey in more crowded places on the ground. Also, the bats were not eating things like geckos and mice, which are commonly found in or near bird nesting sites. “Bats are very agile fliers,” says Barbara French with Bat Conservation International in Austin, Texas,