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POTENTIAL HAZARD TO EASTERN SCREECH-OWLS AND OTHER RAPTORS OF BRODIFACOUM BAIT USED FOR VOLE CONTROL IN ORCHARDS

1988; Wiley; Volume: 7; Issue: 3 Linguagem: Inglês

10.1897/1552-8618(1988)7[245

1552-8618

Paul L. Hegdal, Bruce A. Colvin,

Forest Insect Ecology and Management

During the fall and winter of 1981–82, a study was conducted to evaluate the secondary poisoning hazards associated with a proposed anticoagulant rodenticide, Volid® (10 ppm brodifacoum), when used to control voles (Microtus spp.) in apple orchards. Radio transmitters were attached to 38 eastern screech-owls (Otus asio), 5 barred owls (Strix varia), 3 red-tailed hawks (Buteo jamaicensis), 2 great horned owls (Bubo virginianus) and 2 long-eared owls (Asio otus), and the birds' movements were monitored before, during, and after rodenticide applications. Screech-owls selected woods over alternate habitats for day-roosting; 73% of daytime locations were in woods. At night, screech-owls generally were located in woods, orchard, and field-pasture proportional to their availability, while they avoided cropland. The home ranges of 32 screech-owls tracked posttreatment included brodifacoum-treated areas; the proportion of home range treated and habitat use varied among individuals. Minimum mortality was 58% among screech-owls for which more than 20% of home range was treated, as compared with 17% among those for which less than 10% of home range was treated. Secondary brodifacoum poisoning was the most probable cause of death in six screech-owls. Of five other screech-owls found dead posttreatment, four had been consumed by predators and one died of unknown causes. Of six radio-equipped screech-owls collected one to two months posttreatment, four contained detectable brodifacoum residue. The fate of 14 of the 32 screech-owls tracked posttreatment was unknown at the conclusion of radiotracking efforts (63 d after treatment began) because radio contact was lost or the transmitter was dropped; one of these owls was encountered alive in May. Four barred owls tracked posttreatment showed strong selection for woodland habitat and used orchards limitedly; none was found dead posttreatment. One long-eared owl found dead (not radio-equipped) was probably killed by secondary brodifacoum poisoning. The results indicate a hazard to screech-owls and a potential risk to other raptors, given this use pattern and formulation of brodifacoum bait.