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Darwin's Finches, Threatened by Blood-Sucking Maggots, Get a Helping Hand

May 05, 2014 05:29 PM EDT

On the Galapagos Islands, Darwin's finches - the tiny birds that helped inspire Charles Darwin's theory of natural selection - are getting a life-saving assist by man.

It's not as ironic as it sounds, because man, who introduced a non-native species of parasitic fly to the islands, is partly responsible for the bird's life-threatening predicament. These parasitic flies lay eggs in the finches' nests and when the blood-sucking maggots hatch, baby birds in the nest are doomed.

"This parasite is not historically found in the Galapagos Islands and, therefore, Darwin's finches have not had enough time to evolve defenses against the parasites," University of Utah biology professor Dale Clayton, told Reuters.

The finches have no way to defend themselves against the parasitic flies, and some years 100 percent of nestlings are killed by bloodthirsty maggots.

Clayton and his collaborators have given the Darwin's finches on the Galapagos Islands a fighting chance for survival by soaking cotton balls in an insecticide. The researchers found that finches gathering building material for their nest would collect the cotton balls from despensers and incorporate the insecticide-laden fibers into their nests, killing the blood-sucking fly maggots and a few other insets as well.

The insecticide, permethrin, is safe for birds.

"It might kill a few other insects in the nest. This is the same stuff in head-lice shampoo you put on your kid," Clayton said in a statement. "Permethrin is safe. No toxicologist is going to argue with that. The more interesting question is whether the flies will evolve resistance, as human head lice have done."

The Darwin's finches took well to the cotton, with about 85 percent of the nests surveyed having the fibers incorporated into their nests. The fumigated cotton was found to kill, on average, about half of the maggots in an infected nest. The more treated cotton the birds used, the more parasites were killed.

"If the birds insert a gram or more of treated cotton - about a thimbleful - it kills 100 percent of the fly larvae," Clayton said.

The parasitic flies, officially known as Philornis downsi, infest the nests of all land birds on the Galapagos Islands, said lead study author Sarah Knutie, a biology doctoral student at University of Utah. The killer flies have been implicated in the species decline of two types of endangered Darwin's finch.

In the future, the researches said they want to try the same cotton ball experiment with other bird species.

"There are other species of birds that are hurt by parasites, and so if the birds can be encouraged to incorporate fumigated cotton into their nests, then they may be able to lessen the effects of the parasites," Knutie said.

Knutie and her colleagues published their work in the journal Current Biology.

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