Invader threatens Darwin's finches with extinction

The finches of the Galapagos Islands – which are said to have inspired Charles Darwin's theory of evolution – are being attacked by an invading parasite, scientists have found.

Many of Darwin's finches, which include some of the most vulnerable birds in the world, are threatened by the blood-sucking larvae of alien flies that were accidentally introduced to the islands.

Conservationists are very concerned about the mangrove finch, Camarhynchus heliobates, which is represented by less than 100 breeding pairs and is the most threatened of the 13 species of Darwin's finches.

Birgit Fessl and Sabine Tebbich of the Konrad Lorenz Institute in Vienna analysed 177 nests of 12 species of Galapagos birds, including seven types of finch, and found that virtually all of them were heavily infested with the larvae of a warble fly called Philornis downsi, which was unheard of in the Galapagos before 1989. The larval parasite sucks the blood of fledglings and the fear is that this could seriously weaken young birds.

Dr Fessl and Dr Tebbich found that heavily infested nestlings were more likely to die and many dead birds had holes drilled through their flesh. The scientists analysed the nests of the estimated 30 to 70 breeding pairs of mangrove finch on Isabella, the only island where this critically endangered species exists.

"We confirmed the presence of Philornis at these sites in March 2000. A decline in nestling survival related to fly-larvae parasitism would be a severe threat to it," they write in the journal Ibis.

Nigel Collar, an adviser to Birdlife International, said the emergence of this alien parasite in the Galapagos was extremely worrying.

"A decline in nestling survival resulting from these new parasitic fly larvae would severely threaten this already critical species with extinction," he said.