Quirks & Quarks

A face-eating parasite is devastating Darwin's famous Galapagos finches

Fly larvae feed on the finch's beak, creating deformities that change their song

Fly larvae feed on the finch's beak, creating deformities that change their song

Adult Darwin's tree finch with malformed beak due to parasite damage (Katharina J. Peters )

The Galápagos finches that came to fame after their discovery by English naturalist Charles Darwin are under threat from a nasty parasite that has invaded their remote islands.

The parasite Philornis downsi, a species of fly, lays eggs in finch nests. The larvae of fly attack baby finches and feed on the keratin in their beaks. This kills many of the birds, and those that survive have disfiguring deformities of their beaks. 

Blood-sucking and beak-destroying parasites

P. downsi larvae were first discovered in Darwin's finch nest in 1997. The fly is believed to have been inadvertently introduced to the islands by humans, though when and how is still unclear.  

P. downsi's effects on nostril size in Darwin's finch chick (Jody A. O'Connor)

The adult flies are non-parasitic, but their larvae are. They live off of nestling birds until they mature into adult flies. 

The parasitic larvae start life inside baby finch's beak and eat their way out. Once they're out of the beak, they feed on the finch's blood and tissues externally. "They just suck them dry and that leads to high mortality," explained Sonia Kleindorfer, in an interview with Bob McDonald on Quirks & Quarks

"It's affecting all the finches on the islands, and it's considered the biggest risk to all the land birds on Galapagos." 

How well can you sing?

According to Kleindorfer, the larvae are responsible for 76 per cent of nestling mortality. But the male birds that survive face another problem — the holes in their beak change their mating call.

"With a gaping hole in its beak, they couldn't hit the high notes, and females are very attentive to that," explained Kleindorfer.

The team observed that about half of the birds with damaged beaks had extremely poor songs and couldn't attract any mates.

Deformed naris from P.downsi in Darwin's finch chick (submitted by Sonia Kleindorfer)

The medium tree finch had the most parasites out of all the Galapagos finch species, and as a result, were unable to create their signature song, according to Kleindorfer.

Instead, they produce songs that are similar to small tree finches, leading to mating confusion, causing some of the medium tree finch females to mate with small tree finch males and creating hybrids as a result. Over time, this will decrease the diversity of the finch populations.

"Efforts are underway to develop a biological control for the introduced parasite," said Kleindorfer. "At the same time, we are witnessing changes in both the parasite and the host."



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