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Predation by coyotes (Canis latrans) on domestic sheep is a problem for many livestock producers throughout the United States Intermountain West. We examined whether surgical sterilization of coyote packs would modify their predatory behavior and reduce predation rates on domestic sheep as compared to coyote packs with pups. From June 1997 to December 1997, we gathered baseline information on coyote pack size and movements. In winter 1998, we surgically sterilized and radio-collared members of 5 coyote packs. We also captured and radio-collared members of 6 packs that remained intact (i.e., reproductive). During summer 1998, only 1 sterile pack killed a lamb, while 3 intact packs killed 11 lambs. When only sheep-killing packs were included, sterile packs killed an average of 0.35 lambs/week, while intact packs killed 1.53 lambs/week in 1998. During winter 1999, we monitored 4 sterile and 8 intact packs. In summer 1999,3 sterile packs killed 3 lambs, while 4 intact packs killed 22 lambs. Considering only sheep-killing packs, sterile packs killed on average 0.38 lambs/week, while intact packs killed an average of 2.95 lambs/week in 1999. Coyotes were more likely to kill lambs that were on the edges of coyote territories as compared to core areas. Lambs of less than average weight were also more likely to be killed by coyotes. The available rodent biomass in each territory was not an influence on the differential kill rates exhibited between sterile and intact packs, nor did the amount of available alternate prey influence annual coyote predation rates on sheep. We conclude that we could use surgical sterilization to modify the predatory behavior of coyotes associated with pup production and provisioning of pups. Sterilization successfully reduced, but did not eliminate, coyote predation on domestic sheep. The amount of losses averted in the first year exceeded the costs associated with surgically sterilizing a coyote pack, which indicates that surgical sterilization could prove beneficial on small-scale livestock operations.