Organophosphate Insecticide (Famphur) Topically Applied to Cattle Kills Magpies and Hawks

Abstract

A systematic field study of a black-billed magpie (Pica pica) population revealed that magpies and red-tailed hawks (Buteo jamaicensis) were killed by famphur (=famophos, Warbex?) used as a pouron to control cattle warbles (Hypoderma sp.). Magpie mortality began on treatment day and continued for more than 3 months (38 found dead); mortality peaked between Day 5 and Day 13. Estimates of magpie density (based on transects) decreased in both the control and treatment areas, but the decrease was greater in the treatment area. A red-tailed hawk found dead on Day 10 had eaten a famphur-contaminated magpie. Another red-tailed hawk was found alive but immobilized, and a third died outside the study area. Brain cholinesterase (ChE) activity was 70-92% depressed in all dead birds examined; famphur residues were detected in all 17 magpies and the 2 hawks analyzed. The amount of famphur obtained by the dead magpies was estimated at 5.2-6.1 mg/kg (based on residue concentrations in the gizzard), which was above the acute oral LD, for several bird species. The cow hair portion (12%) of the pooled gizzard contents from 13 other dead magpies produced extremely high famphur residues (4,600 ppm). The residues persisted on cattle hair for more than 90 days post-treatment. Magpie populations in the far western states declined between 1968 and 1979, which corresponds with widespread use of famphur, although other factors may be involved. J. WILDL. MANAGE. 49(3):648-658 Organophosphate (OP) insecticides are now used extensively in agriculture. The topical use of famphur (O,O-dimethyl O-[p-(dimethylsulfamoyl)phenyl] phosphorothioate) in the autumn as a systemic insecticide for control of warbles in cattle was recommended in 1970 (Every et al. 1970). Famphur can be administered to livestock dermally as a pour-on (the only method we observed), orally (mixed with feed), or by intramuscular injection (Ivey et al. 1976). The larvae are killed within the animal during the autumn before they develop into grubs the following year. Grubs emerging on the backs of untreated cattle during the spring may be eaten by magpies (Bishopp et al. 1926), but this is not an adequate control. Observations of magpies dying after famphur use on cattle were reported by ranchers as early as 1973 (unpubl. data, Oreg. Dep. Fish and Wildl., La Grande). Magpies and other species of birds were found dead after cattle were treated with famphur in the United Kingdom (Felton et al. 1981). Magpie brain ChE activity was severely depressed and famphur was identified in the gizzard contents. Another organophosphate (fenthion), also used as a pouron to control Hypoderma larvae in cattle, was implicated in magpie mortality in Canada (Hanson and Howell 1981). Despite relatively rapid degradation in the environment and tissues of homeotherms, some OP insecticides are highly toxic to wildlife for varying periods of time after application (Zinkl et al. 1978, White et al. 1979). The degree of exposure of nontarget wildlife species to OP insecticides can be assessed by measuring ChE activity in tissues and blood (Bunyan et al. 1968, Ludke et al. 1975, Hill and Fleming 1982). The depression of brain ChE activity by 20% or a decrease of 2 SD in wild birds (relative to species baseline data or concurrent controls) has been used as a co servative criterion to indicate absorption of OP chemicals. Depression of brain ChE activity by >50% and confirmation of suspected OP residues in tissues or ingesta are criteria for cause-effect diagnosis of death in birds exposed to anti-ChE chemicals. We studied a magpie population that lived on or near seven ranches where 535 cattle were treated with Warbex? (13.2% famphur). Warbex? was poured along the back line of the cattle at the recommended rate of 0.326 ml/kg body weight, not to exceed 118 ml/animal. The field study was prompted by: (1) reported magpie mortality in Oregon and the United Kingdom; (2) a magpie population decline in the far