Invasive parasites in the Galápagos Islands may leave some Darwins tree finches singing the blues.
The nonnative Philornis downsi fly infests the birds nests and lays its eggs there. Fly larvae feast on the chicks blood and tissue, producing festering wounds and killing over half of the baby birds. Among survivors, larval damage to the birds beaks may mess with the birds songs when theyre older, possibly affecting their appeal to potential mates, researchers report June 12 in Proceedings of the Royal Society B.
“Whats heartbreaking, when youre walking through this beautiful forest, is to hear these medium tree finch males just singing and singing and not being able to attract a mate,” says Sonia Kleindorfer, a behavioral ecologist at Flinders University in Adelaide, Australia and the University of Vienna.
The fly arrived in the Galápagos probably in the 1960s. The researchers studied two finch species on Floreana Island that the fly larvae plague: the critically endangered medium tree finch (Camarhynchus pauper) and the related small tree finch (C. parvulus).
In one life stage, the larvae reside in the birds beaks, where they chew up the keratin and soft tissue, enlarging the birds nostrils, called nares. Kleindorfer and colleagues wondered how this impacts the birds song and the sexual selection that results from it.
So the scientists captured finches, measured their nares and then tagged and released them back into the wild. Then, the researchers recorded and analyzed the songs of 77 birds.
The medium tree finch usually makes a more metallic bell-like sound, while the small tree finches lower-pitch tune sounds like “cha cha cha,” Kleindorfer says. But in both species, birds with the most deformed beaks sang at a lower pitch than birds with normal beaks.
The song of the medium tree finch normally sounds bell-like (first sound clip). But those with parasite-deformed beaks tend to make lower-pitched sounds (second sound clip), more similar to the related small tree finch.
S. Kleindorfer/Flinders Univ.
“If you have a beak with a gaping hole, you cannot hit the high notes,” she says. For medium tree finches, the deformity meant they sounded similar to a small tree finch with a healthy beak. That may explain why scientists had previously had observed female medium tree finches choosing small male tree finches as partners, instead of males from their own species. The researchers did not observe female small tree finches choosing medium tree finch mates.
The research also suggests that the parasites impact on birdsong is affecting the birds success in finding a mate. From 2004 to 2014, the researchers tracked the courtships of 52 males, watching the birds during two-week stretches in FebruaRead More – Source