Consumption of fipronil-treated rice seed does not affect captive blackbirds

Abstract

Fipronil is an insecticide developed for use on rice seed and other crops. In a series of cage and pen trials, we evaluated the responses to dyed, fipronil-treated rice seed of three bird species likely to encounter it in the field. Individually caged red-winged blackbirds (Agelaius phoeniceus), brown-headed cowbirds (Molothrus ater), and boat-tailed grackles (Quiscalus major) displayed no evidence of adverse reaction to treated seed. Chemical analyses of hulls from treated seeds eaten by captive birds revealed that 10-20% of the fipronil originally present was removed during feeding. In group enclosures, male red-winged blackbirds ate as much fipronil-treated rice as they did dyed, untreated seed. In four-day tests within a 0.2-ha flight pen, 10-bird blackbird flocks removed 11.4% of fipronil-treated seed from a test plot compared to 12.5% of dyed, untreated seed removed from the alternate plot. When the alternate plot contained undyed rice, however, seed removal from the treated plot averaged 2.4% compared to 28.9% from the alternative plot, suggesting that the groups of test birds avoided treated seed based on its appearance. We conclude that 325 and 500 mg kg -1 fipronil applications alone do not affect avian feeding activity.