Darwin’s Finches: Bye Bye Birdie?

Female ground finch in the Galápagos Islands

Jennifer Koop / University of Utah

Female ground finch in the Galápagos Islands

Darwin’s Finches in Galápagos face possible extinction within decades, according to a new study published December 18th by the University of Utah.  Mathematical simulations show that while parasitic flies are killing the finches, efforts to eradicate the flies might hold out some hope for saving the birds.

The new research “shows that the fly has the potential to drive populations of the most common species of Darwin’s finch to extinction in several decades,” says biology professor Dale Clayton, senior author of the study published online in the Journal of Applied Ecology.

But the research “is not all doom and gloom,” he adds. “Our mathematical model also shows that a modest reduction in the prevalence of the fly – through human intervention and management – would alleviate the extinction risk.”

Several approaches may be needed, such as introducing fly-parasitizing wasps, removing chicks from nests for hand-rearing, raising sterile male flies to mate with females so they can’t lay eggs in finch nests, and using insecticides, including placing pesticide-treated cotton balls where birds can collect them to self-fumigate their nests.

Mockingbirds were more important to Charles Darwin’s theory of evolution than finches, partly because he failed to label finches he collected in the Galápagos to denote the islands where he collected the birds. Nevertheless, Darwin observed how different Galápagos finch species evolved varying beak and body sizes.

“Darwin’s finches are one of the best examples we have of speciation,” says the new study’s first author, Jennifer Koop, who did the research as a University of Utah doctoral student and now is an assistant professor of biology at the University of Massachusetts Dartmouth. “They were important to Darwin because they helped him develop his theory of evolution by natural selection.”

Darwin’s finches live only in the Galápagos Islands, off the coast of mainland Ecuador. The finches began as one species and started evolving into separate species an estimated 3 million to 5 million years ago.

The new study dealt with medium ground finches, Geospiza fortis, among the most common of at least 14 species and perhaps 18 species of Darwin’s finches. One of them, the mangrove finch, already “is facing potential total extinction because it is present in only two populations on a single island, Isabela,” Koop says.

Clayton says that if the parasitic nest fly, Philornis downsi, “can lead to extinction of such a common species, then the less common species – which have the same fly problem – are likely at risk as well.”

The study was performed on Santa Cruz Island in the Galápagos. An estimated 270,000 medium ground finches live on that island and perhaps 500,000 live throughout the Galápagos Islands, Clayton says.

Museum records indicate the nest fly arrived in the Galápagos Islands in the 1960s. They first were documented in bird nests there in 1997.