This subject was discussed on Radio 4’s World On The Move. The story was initially released early in 2007.
The Doñana National Park, in the south west corner of Spain is the first (or last) landfall for millions of migrating birds. It is almost an island, with no residents and public access restricted to just a few days each year. It has been described as Europe’s only truly natural wild landscape.
In 2001, Carlos Ibáñez and his colleagues in the Doñana Biological Station in Sevilla, suggested that the giant noctule bat or Nyctalus lasiopterus may be hunting small migratory birds. The initial evidence came from faeces samples that contained feathers. It was accepted that this was not proof and some suggested that the bats may have mistaken falling feathers for insects. In 2003 the team in Sevilla started taking blood samples from the bats for isotope testing. Isotopes in the blood show which food has been eaten. It was found that the bats ate mainly insects, but during the spring and autumn migrations higher levels of carbon-13 and nitrogen-15 showed that they also ate birds.
It is assumed that those bird that fly at night, possibly to avoid hawks are in fact easy prey for the giant noctule. The kills appear to happen at high altitude well out of range of a detector and they appear to devour the birds whilst flying. The researchers reported a few instances where carcases had fallen out of the sky all in similar condition, with the breast torn off their body.
First published in the Autumn 08 Newsletter.