SAVING THE MEDIUM TREE FINCH

One of Charles Darwin’s famous 14 finches — the island-dwelling bird species that helped inspire the theory of evolution — the medium tree finch is found only on Floreana, one of the nine major islands comprising the Galápagos archipelago.

Historic threats to this finch include habitat destruction and fragmentation, but the most pressing threat today is the Philornis downsi, an introduced parasitic fly whose larvae feed on the finch’s nestlings. Causing high nestling mortality, lower fledgling success, and reduced nestling growth, the parasite appears to be hitting the medium tree finch the hardest out of all the Galápagos finches, allowing only about 6 percent of the bird’s active nests to produce fledglings. More than half the medium tree finch’s nestling mortality is attributed to the Philornis downsi.