Hazards to wildlife associated with 1080 baiting for California ground squirrels

Under an Environmental Protection Agency (EPA) Interagency Agreement, we evaluated the hazards to wildlife associated with aerial 1080 (sodium monofluoroacetate) baiting for California ground squirrels (Spermophilus beecheyi fisheri). We conducted the study in Tulare County, in south-central California, in the eastern foothills of the San Joaquin Valley. Vegetation is annual range grasses and associated forbs, under open stands of oak (Quercus spp.), with cottonwood (Populus spp.), California sycamore (Platanus racemosa), and California buckeye (Aesculus californica) along stream bottoms. The study monitored a large-scale operational baiting program conducted in Tulare County by the Tulare County Agricultural Commissioner. During early June 1977, (in the vicinity of the study area) about 25,000 ha (60,000 acres) were spot-treated with 0.075 percent 1080-treated oat groats at about 6.7 kg/ha (6 lb per swath acre). The actual surface area baited was about 3.4 percent of the range. California ground squirrel populations were reduced about 85 percent following baiting. Primary hazards to seed-eating birds appear minimal as indicated from intensive carcass searching and the results from 31 radio-equipped mourning doves (Zenaida macroura) and 10 radio-equipped California quail (Lophortyx californicus). One of two white-breasted nuthatches (Sitta carolinensis) found dead after treatment contained 1080 residue. One of two samples of dead ants also contained 1080 residue. Twelve cottontail rabbits (Sylvilagus auduboni) were found dead after treatment and four contained 1080 residue, indicating some primary hazard to this species. Secondary hazards to raptors and mammalian predators were evaluated by attaching radio transmitters to 24 raptors (red-tailed hawks, Buteo jamaicensis; turkey vultures, Cathartes aura; a golden eagle, Aquila chrysaetos; great horned owls, Bubo virginianus; barn owls, Tyto alba; a screech owl, Otus asio; common ravens, Corvus corax; a common crow, Corvus brachyrhynchos) and 42 mammalian predators (bobcats, Lynx rufus; coyotes, Canis latrans; gray fox, Urocyon cinereoargenteus; badgers, Taxidea taxus; striped skunks, Mephitis mephitis; raccoons, Procyon lotor; and opossum, Didelphis marsupialis) and monitoring their movements before, during, and after treatment. Five of the six radio-equipped coyotes and three of the 10 radio-equipped bobcats (one bobcat was emaciated, possibly a result of a trap injury) were found dead after treatment. Three dead striped skunks (not radio-equipped) were also found dead after treatment and one contained 1080 residue. No other treatment-related mortalities were indicated among the remaining radio-equipped birds or mammals. Also, monitoring of 58 active raptor nests indicated no treatment-related mortalities