Darwin's Finches' Biology Provide Insights to the Theory of Evolution with How They Evade a Parasitic Fly

Darwin's finches are being attacked by a parasitic avian vampire fly. According to Knowable Magazine, swarms of hungry parasitic fly maggots wriggle up through the bird's nest once the chicks have nestled for the night. Maggots feed on the blood and tissue of Darwin's finches every night, and they squirm back to the nests where they wait for the night.

Chicks can lose 18% to 55% of their blood due to these nightly raids. Unfortunately, over 50% of the nestings in an infested nest die because of the parasitic ly larvae. Those who survive often end up with a hole in their beak.

Now, two studies from Flinders University investigate how Darwin's finches in Galapagos Islands deal with a parasitic fly, giving new insights into the theory of evolution.

Hybrid Darwin's Finches Host Fewer Parasitic Fly

According to Science Daily, the avian parasitic vampire fly (Philornis downsi) was accidentally introduced to one island in Galapagos back in the 1960s and since then has fed on offsprings of Darwin's finches.

One of the two studies, titled "Avian Vampire Fly (Philornis Downsi) Mortality Differs Across Darwin's Finch Host Species" published in Scientific Reports, investigated which species of Darwin's finches proved to be the most successful in dealing with the parasitic fly.

Lauren Common, Ph.D., Candidate in the Flinders University BirdLab and lead author of the study, and her team found that the larvae of the parasitic fly had the best survival rates in the nests of medium tree finch, which only lives on Floreana Island. However, the larvae had the least success rate in the nests of hybrid tree finches.

The hybrid population is a product of the interbreeding between medium tree finches and small tree finches who started interbreeding when the parasitic fly arrived on the island.

"We found that nests belonging to these hybrid finches played host to fewer flies and had the lowest parasite survival rate, suggesting that hybridization between the small and medium tree finches may be their defense strategy against this invasive parasite," says Miss Common, as quoted by Science Daily.

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Darwin Finches' Nestling Behavioral Type Matters

The second study, titled "Nestling Behavior Predicts Naris Deformation in Darwin's Finches Parasitized by the Avian Vampire Fly," published in the journal Biological Journal of the Linnean Society, looked at how infected birds cope up.

Researchers led by Dr. Andrew Katsis from the Flinders University BirdLab measured each nestling's behavioral type by recording how much it struggled when humans handle them and compare it to how much damage the chicks sustained from being infected with the parasitic fly.

The team found that nestings that struggle more during human handling have more deformed nostrils from being infected. Although they do not know the exact reason, they think that more vigorous nestlings attract parasitic larvae by moving inside the nest. They added that more docile nestlings tend to survive to adulthood at greater risks in the future, which could change how Darwin's finches behave at a population level.

In 2019, Bird Watching reported that an enlarged naris produced indistinguishable songs from other finches. This might be evidence that parasite-induced decoration can disrupt the mating signal and result in the ongoing hybridization of the medium tree finch and the small tree finch.

Researchers from the two Flinders University studies believe that studying the biology of finches would help understand how they evolve to deal with the parasitic fly and develop new strategies for dealing with parasites worldwide.