Charles Darwin Foundation
August 2007

Controlling Flies to Save Rare Birds from Extinction

Baby finch killed by Philornis downsi

In the nests of Darwin’s finches and other Galapagos birds lurks a deadly intruder. Feeding on the blood of the nestlings, the larvae of an introduced fly, Philornis downsi, cause mortality of up to 76%. Although in Galapagos since 1964, P. downsi wasn’t discovered in nests until 1997. CDF volunteer entomologist and Fulbright scholar, Adair Muth, is trying to find a way to trap adult flies using attractants such as banana, urine and stale beer but the flies seem to like a mix of sugar and dry milk powder the best. The most efficient methods will be used in priority areas during the next breeding season, in an effort to increase reproductive success of rare birds such as the mangrove finch.

Muth’s research is also providing valuable clues to help identify control methods such as sterile insect techniques as a long-term solution to stop the spiral toward extinction of the rarest birds. The challenge is to find a way to rear larvae and adults on site at the research station using samples collected from active nests in Puerto Ayora. After a successful collection trip an excited Muth said “I caught a live female which laid eggs all over the inside of the collection tube! Until that moment we didn’t know if P. downsi laid live larvae or eggs. They lay eggs!”

Previous CDF studies on P. downsi showed extensive distribution in the archipelago: 11 of 13 islands sampled. Affected birds include finches, mockingbirds and flycatchers. These birds, especially the famed Darwin’s finches, show just how quickly species can be harmed when man intrudes upon Nature.