The potential of fenthion to act as a secondary poisoning hazard to birds of prey was investigated using American kestrels (Falco sparverius) and house sparrows (Passer domesticus) as a representative model of a naturally occurring predator-prey interaction. Kestrels were presented with live sparrows previously exposed to perches containing Rid-A-Bird 1100$ sp circler$ solution (Rid-A-Bird, Inc., Muscatine, IA), 11% fenthion active ingredient, under simulated field conditions. All 14 kestrels tested died following ingestion of fenthion-exposed sparrows. Decreased brain cholinesterase activity and residue analyses of kestrel gastro-intestinal samples confirmed secondary fenthion poisoning. / Prey selection trials were conducted in the laboratory to determine the response of kestrels to a mixed flock of contaminated and uncontaminated sparrows. Kestrels captured fenthion-exposed prey significantly more often (12 out of 15 trials) than normal, unexposed prey. / These results suggest that avian predators and scavengers in the wild are at risk from contact with fenthion-exposed prey in areas where Rid-A-Bird perches are in use.

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