Scientists are helping Galapagos Island wild finches "self-fumigate" their nests by providing them with a manufactured pesticide to deal with parasites.

Rather than fumigate the nests to kill the parasitic larvae of a fly species, the researchers have set out cotton balls treated with a solution of the pesticide, which the birds are snatching as the perfect nest-building material.

Baby birds in the nests of Darwin's finches are at risk from the fly larvae, which feast on the birds' blood with sometimes-fatal results for the young finches.

The pesticide in the experiment is permethrin, a treatment for head lice found in humans, and is safe to use around the birds, University of Utah biologist Dale Clayton says.

"It might kill a few other insects in the nest," Clayton says. "This is the same stuff in head-lice shampoo you put on your kid. 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 strategy of providing cotton balls as nest material grew out of observations of the finches grabbing strands from clothing hanging on lines, fibers from towels and bits of string to build their nests.

On Santa Cruz Island in the Galapagos, the researchers made wire-mesh containers and filled them with treated cotton balls holding a weak solution of permethrin.

All four finch species living on the island readily took to using the cotton balls as nesting material. Nests built using it were subsequently found to be free of the parasites.

The flies are not natural to the Galapagos, having arrived on ships and planes, with the larvae first seen in finch nests in the 1990s.

In some years the fatality rate of nestlings because of the parasites was 100 percent, the researchers said.

"We are trying to help birds help themselves," explained Clayton, one of the authors of a study published in Current Biology. "Self-fumigation is important because there currently are no other methods to control this parasite."

It is possible the self-fumigation technique could help other birds deal with parasite threats, the researchers said, noting Hawaiian honeycreepers have been plagued by feather lice. Some Puerto Rico birds species have been attacked by flies as well as endangered scrub jays in Florida are experiencing flea infestations.

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