Darwin Finch Die-off

Parasitic flies on the Galápagos Islands threaten Darwin's famous finches.

When Charles Darwin disembarked the Beagle and waded ashore the Galápagos Islands in 1835, he strolled among bathtub-sized tortoises, three-foot-long basking lizards, and strange seabirds with sky blue beaks and scarlet-red feet. Yet the animals that would have the longest-lasting impression on Darwin back in England were some of the islands' least charismatic residents. The 13 species of Darwin's finches all had beaks of different designs depending on their diet, a phenomenon that helped shape Darwin's theory of evolution.

Now these famous finches are under attack by a most unforgettable foe: blood-sucking flies. Birgit Fessl and Sabine Tebbich of the Konrad Lorenz Institute in Vienna report in the journal Nature that parasitic flies have infested the islands. The fly larvae live in the birds' nests, emerging at night to feed on chicks, sucking their blood and burrowing into their flesh. The flies seem to thrive in the highlands, where on some islands larvae can be found in nearly every nest. About one-quarter of the nestlings die; however, it is unclear what the long-term impacts on finch populations may be.

The alien pests are thought to have arrived in shipments of fruits or vegetables from the Ecuadorian mainland. While treating nests with insecticides kills most larvae, the tactic is not a long-term solution. The researchers hope the finches will do what they seem to do best: adapt.

A small tree finch (Camarhynchus parvulus) photographed at the Charles Darwin Research Station. Photo: Barbara West

Typical desert finch habitat with cactus in the Galapagos Islands off Ecuador. Photo: Gerald and Buff Corsi