Desert bighorn sheep mortality due to presumptive type C botulism in California

During a routine telemetry flight of the Mojave Desert (California, USA) in August 1995, mortality signals were detected from two of 12 radio-collared female desert bighorn sheep (Ovis canadensis) in the vicinity of Old Dad P eak in San Bernardino County (California). A series of field investigations determined that at least 45 bighorn sheep had died near two artificial wat er catchments (guzzlers), including 13 bighorn sheep which had presumably d rowned in a guzzler tank. Samples from water contaminated by decomposing bi ghorn sheep carcasses and hemolyzed blood from a fresh bighorn sheep carcas s were tested for the presence of pesticides, heavy metals, strychnine, blu e-green algae, Clostridium botulinum toxin, ethylene glycol, nitrates, nitr ites, sodium, and salts. Mouse bioassay and enzyme-linked immunosorbent ass ay detected type C botulinum toxin in the hemolyzed blood and in fly larvae and pupae. This, coupled with negative results from other analyses, led us to conclude that type C botulinum poisoning was most likely responsible fo r the mortality of bighorn sheep outside the guzzler tank.