September 9, 2009

Songbird Feasts On Bats

Researchers have found that a species of bird known as the great tit (Parus major) has been found feeding on hibernating pipistrelle bats in a Hungarian cave, BBC News reported.

The team discovered that the birds were systematically hunting bats by sight and sound as they hibernated through the cold months over two winters.

The scientists wrote in the journal Biology Letters that it was the first proof of bat hunting in songbirds. Great tits usually dine on smaller prey such as insects and seeds.

However, it was noted that the birds seemed to prefer other food when they could find it.

Bjorn Siemers from the Max-Planck-Institute for Ornithology in Seewiesen, Germany, one of the members of the research team, said the occurrence doesn't look like an overwhelming thing that threatens the bat population.

"So then the question to ask is 'how do they invent it?', and so far we can only speculate - it could be a kind of cultural learning," he told BBC News.

Researchers have reported finding dead or injured bats outside caves in Sweden and Poland over the last couple of decades.

The team noted one particular case where a bat had been eaten by a great tit, while others had wounds that could have been inflicted by a tit's beak.

However, they say there is no definitive proof that the birds had hunted or killed them.

But Siemers said that if the tits did indeed inflict the wounds on the bats, it raises the possibility that the habit or skill of bat hunting was carried along migration routes.

The researchers documented 16 cases of great tits hunting, killing and eating a hibernating bat in the one cave during two field seasons in the Bukk Mountains of northeastern Hungary.

Pipistrelle bats (Pipistrellus pipistrellus) are about one-quarter of a great tit's size.

The team watched as the birds flew close to the cave walls, landing frequently and often disappearing into crevices where they would either eat the bats there or carry them away for feeding.

The bats squeak in the audible range for humans and great tits when their hibernation is disturbed.

The birds may have learned to listen for these squeaks, according to the researchers, who said they recorded some and played them back and the birds responded with interest about 80 percent of the time.

It is suspected that the birds can only bat-hunt when they are able to visually identify their prey.  But lots of light penetrates the wide-mouthed cave, suggesting it would be a rarely found behavior for the species of birds.

Meanwhile, one experiment showed that the birds would leave the bats largely untouched when scientists provided other food such as sunflower seeds and bits of bacon, which the birds preferred to eat over the bats.

Siemers said it raised the suggestion that bats are a food of last resort in a harsh winter.

This type of behavior in large tits is new to Graham Madge, a spokesman on conservation issues for the UK's Royal Society for the Protection of Birds (RSPB).

He said great tits are normally feeding on things like insects, beetles, spiders, seeds and maybe fruit in winter.

"There's no indication they'd be able to predate something like a bat. It's incredible behavior," he added.

In the UK, the blue tit -- a close relative to the large tit -- has also been quick to take advantage of novel foods, Madge noted.

"There was this phenomenon where blue tits learned how to open the foil tops of milk bottles, and quickly this behavior spread through the population; so they're quick learners," he said.


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