Self-Fumigation? Endangered Birds On Galapagos Given Treated Cotton To Kill Parasites In Nest

By Matthew Mientka on May 6, 2014 9:32 AM EDT

A safe-for-birds pesticide may help wild finches threatened by an invasive species of nest fly, researchers say.
A safe-for-birds pesticide may help wild finches threatened by an invasive species of nest fly, researchers say.

Endangered wild finches in the Galapagos Islands are weaving cotton balls laced with pesticide into their nests, left by biologists hoping to kill a parasitic fly threatening the species.

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“We are trying to help birds help themselves," says biologist Dale Clayton, who visited Galapagos recently with colleagues from the University of Utah.

Using a pesticide called permethrin, the researchers say this method of self-fumigation is the only way of controlling the nest fly Philornis downsi, whose maggots hatch to eat eggs in the nest. The invaders likely traveled to the Ecuadorean islands sometime during the 1990s. Though the pesticide might kill a few other species of insect in the nest, permethrin is safe for birds.

“This is the same stuff in head-lice shampoo you put on your kid,” Clayton said in a press 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."

However, Clayton believes the nest fly won’t be able to develop resistance if the pesticide is used sparingly within the habitats of endangered species, rather than over a wider area. A similar lack of co-evolutionary history is what predisposed the wild finches to harm from the invasive fly.

“The birds have no history with these flies, which is why they are sitting ducks,” Clayton said. “From the perspective of the birds, these things are from Mars."

Self-fumigation with permethrin may help Hawaiian honeycreepers, the endangered Florida scrub jay, and some birds in Puerto Rico — all infected with dangerous parasites. But the method may also help prairie dogs on the Great Plains after efforts to spray burrows proved impractical. Rather, vegetation sprayed with the pesticide might be dragged into the burrows, in a way similar to the nesting bird species.

In the Galapagos Islands, Clayton and his colleagues laid two lines holding 15 cotton dispensers along each side of a road in arid woodland, with the dispensers on both sides stocked alternately with cotton balls either laced or not with the pesticide. The dispensers were spaced 130 feet apart to ensure that birds would pick their cotton from a preferred dispenser, a study control later validated with data showing none of the bird nests had contained both types of cotton.

At least four species of wild finches participated in the study, taking cotton from the dispensers to line their nests. Cameras mounted on poles recorded the medium ground finch, small ground finch, small tree finch, and vegetarian finch visiting the dispensers. After three weeks or so, the birds would leave a given nest, allowing the researchers to analyze its contents. Among 26 “active nests” found in the area, 85 percent contained cotton. Whereas 13 of the nests were found with the pesticide-laced cotton, nine contained untreated cotton, and four completely bereft of the material. Interestingly, the wild finches took about the same amount of cotton each for the construction of their nests, with no significant variation between the two types of cotton.

In a study published Monday in the journal Current Biology, Clayton and his colleagues say “self-fumigation had a significant negative effect on the parasites,” killing at least half the maggots. Nests treated with the pesticide averaged 15 maggots or so, compared to others with 30 or more fly maggots.

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

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