Premier Presentation: Introduced parasite causes significant mortality in Darwin’s finches: Is there an immediate solution?

Introduced parasites are a threat to biodiversity when naïve hosts lack effective defenses against such parasites.  Several parasites have recently colonized the Galápagos Islands, threatening native bird populations.  For example, the introduced parasitic nest fly Philornis downsi has may contribute to the decline of endangered species of Darwin’s finches.  Using an experimental manipulation, we demonstrate that P. downsi has a significant effect on Darwin’s finches over multiple breeding seasons.  We also present evidence that Darwin’s finches can be encouraged to “self-fumigate” nests against P. downsi with cotton fibers that have been treated with a mild insecticide.  Nests with treated cotton have significantly fewer P. downsi than control nests, and nests containing at least one gram of treated cotton are virtually parasite-free.  In turn, decreasing parasite abundance significantly increases nestling surviving.  The results from this work demonstrate that self-fumigation can be used to mitigate the effect of nest flies on Darwin’s finches.