A species of Darwin’s finch could face extinction in as little as four decades because of a parasitic fly, new mathematical models show.

In a study that will be published December 18 in the Journal of Applied Ecology, University of Utah researchers forecast turbulent flying ahead for the medium ground finch (Geospiza fortis), one of the most common of the dozen-plus species of Darwin's finch. (They're named for the man who first collected them, naturalist Charles Darwin, who used observations of the finches' adaptations to inform his work on natural selection. They're also known as Galapagos finches, for the islands they call home.)

The fly in question is the nest fly Philornis downsi, first documented in birds’ nests in the Galapagos in 1997. It lays its eggs in finches' nests, the larvae infesting the area and feeding, to a fatal degree, on new nestlings.

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The researchers gathered five years’ worth of data from the island of Santa Cruz, documenting the harm the fly was causing to the finch’s reproductive success. Then they used those results to help fuel mathematical models of different long-term outcomes for the finch species.

The team ran simulations based around three broad future scenarios: “good” years likely to come, where conditions such as weather and food supply were conducive to successful breeding; “bad” years ahead; and neutral years, where both bad and good conditions were equally likely.

Two of the three model runs -- "bad" and neutral -- predicted the medium ground finch's extinction. Only the "good" model showed the species able to survive.

The "bad" model predicted extinction in anywhere from 43 to 57 years, while the "neutral" model had the bird disappearing in 65 to 95 years.

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Worse still, the problem may not just apply to the medium ground finch. Study lead author Dale Clayton, a University of Utah biology professor, pointed out that the bird's other Galapagos cousins could be at risk as well.

If a species of Darwin's finch as common as the medium ground finch can face extinction because of the nest fly, "then the less common species, which have the same fly problem, are likely at risk as well," Clayton said in a release.

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Glum scenarios aside, there is still hope. The bird's extinction risk is closely tied to the fly infestation problem, so there's no mystery, and the scientists have a clear target.

“Even though these guys may be going locally extinct, the model also shows that if you can reduce the probability of infestation, then you significantly alleviate the risk of extinction,” said study co-author Jennifer Koop, a professor of biology now teaching at the University of Massachusetts Dartmouth. She said extinction could be avoided if nest infestation could be reduced by 40 percent.

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To tackle the problem, the scientists suggested several tactics to fight the fly and rescue the finch. Use of insecticides, introduction of fly-parasitizing wasps, breeding of sterile male nest flies to suppress egg production, and even the hand-rearing of at-risk chicks could each help improve matters, the scientists said.

Other good outcomes might come from the birds themselves. Clayton said a “rapid evolutionary response” by the birds could spur their immune systems to figure out how to defeat the fly.

“That happens in other animals,” he said. “The question is: Will these finches have enough time to develop effective defenses before they are driven to extinction by the fly? It’s an arms race.”