Effects of Organophosphorus Insecticides on Sage Grouse in Southeastern Idaho

Abstract

Die-offs of sage grouse (Centrocercus urophasianus) were verified in southeastern Idaho in 1981. We captured 82 apparently healthy grouse to quantify the effects of organophosphorus insecticides (OP's) and other pesticides on sage grouse in sagebrush (Artemisia spp.) bordering agricultural lands in July 1985 and 1986. Grouse were fitted with radio collars and tracked through part of each summer. At least 18% of 82 radio-tagged grouse in 1985-86 subsequently occupied fields at the time they were sprayed with OP insecticides dimethoate or methamidophos. Cholinesterase (ChE) assays of brains and residue analysis of crop contents indicated that 5 and 16% of the marked sample died from OP's in 1985 and 1986, respectively. Approximately 200 sage grouse were present in a block of alfalfa sprayed with dimethoate; 63 of these were later found dead and ChE activity in 43 brains suitable for assay were depressed >50%. Maximum residues in crop contents of dead grouse were 18 Ag/g methamidophos and 30 g/g dimethoate. Intoxicated or dead grouse were observed in or near 6 fields sprayed with dimethoate or methamidophos in 1985-86. Twenty of 31 intoxicated grouse radiotagged after being found in dimethoate-sprayed (1986) alfalfa died. Our study indicates that certain pesticides have the potential for adversely affecting grouse populations. J. WILDL. MANAGE. 53(4): 1139-1146 Replacement of organochlorine insecticides (OC's) with shorter-lived chemicals such as organophosphorus (OP), carbamate, and other compounds alleviated many problems with persistence and bioaccumulation of lipid-soluble OC's (Blus 1982, Wiemeyer et al. 1984). Additional research revealed that serious effects, resulting from different modes of action, are also associated with use of the newer compounds, particularly from a short-term perspective where acute or subacute toxicity (Hill and Fleming 1982, Grue et al. 1983, Henny et al. 1985) and reduction in the food base are major concerns (Rands 1985, Potts 1986). Initial evidence that OP's caused mortality of sage grouse was noted in 1981 when a die-off occurred near a potato field sprayed with methamidophos. Brain ChE activity of 5 sage grouse collected when intoxicated (sick, immobile, and showing signs of OP poisoning) and later sacrificed ranged from normal to 61% inhibition (E. F. Hill, Fish and Wildl. Serv., pers. commun.). Data collected in 1983 indicated depression of 40 to 65% in brain ChE activity of grouse collected in a potato field shortly after spraying with methamidophos. These preliminary findings and previous unverified reports of die-offs suggested a potentially serious situation and led to radio-telemetry studies in southeastern Idaho in 1985-86. The purpose of our study was to determine and quantify effects of OP's on a population of sage grouse. We thank K. L. Stromborg, D. H. White, and B. A. Rattner for reviewing the manuscript; the many individuals assisting with field work including C. R. Breckenridge, M. C. Mondecar, and R. K. Sherwood; and J. W. Connelly, Jr. and other members of the Idaho Department of Fish and Game for ideas and assistance. This study was partially funded by the U.S. Environmental Protection Agency (Interagency Agreement DW89931370-01). STUDY AREA AND METHODS The study area was located in southeastern Idaho near Mud Lake, Monteview, Hamer, and Camas in Jefferson County and Arco in Butte County (Fig. 1). This area provided summer range for sage grouse (Gates 1983, Connelly et al. 1988). Major agricultural crops included small ' Present address: Oak Ridge National Laboratory, P.O. Box 2567, Grand Junction, CO 81502.