Risk assessment of permethrin exposure on a passerine bird: Implications to protect Darwin’s Finches from an avian parasite in Galápagos

Philornis downsi is a bird-parasitic fly native to mainland South America that invaded the Galapagos Islands where it is pushing some Darwin’s Finch species over the brink of extinction. Flies lay eggs in bird nests and the larvae feed on nestlings, often killing them. Protecting Galapagos landbirds from this parasite is a conservation priority. A short-term solution involves providing permethrin-treated cotton to the finches or injecting wild nests with permethrin. However, the risk of permethrin to long-term bird health and reproduction has not been formally tested. Our experiment represents a worst-case scenario to determine the effects of exposure to permethrin in Zebra Finches (Taeniopygia guttata) across consecutive generations. The experiment consisted of two treatments. Treatment finches received nesting material sprayed with 1% solution of permethrin and control finches received nesting material sham-fumigated with water. The parental generation laid two clutches of eggs (F1.1 and F1.2). Adults reared from the F1.1 clutch were used to establish a second generation (F2). Blood was drawn to evaluate liver function by assaying aspartate aminotransferase and bile acids levels. Permethrin treatment affected hatching mass for both the F1 and F2 generations. Birds exposed to permethrin produced smaller nestlings than controls. The F2 control birds hatched all nestlings, whereas F2 treatment pairs only fledged 70% of nestlings. Treatment had no effect on liver function tests for any generation. While permethrin exposure had some detrimental effects on finch health, the risk of using permethrin on small birds in the field is minimal compared to the rate of nestling death caused by Philornis downsi.