Woody cover and proximity to water increase American black bear depredation on cattle in Coahuila, Mexico

摘要

American black bear (Ursus americanus; hereafter, bear) depredation on cattle is a rare occurrence. Our study population of bears normally coexists with cattle ranching operations in Serranias del Burro, Coahuila, Mexico. However, we observed unusually high incidences of depredation upon cattle during a severe drought in 1999-2000. We documented 60 reports of calf kills among 3 herds; we were able to locate exact kill-site locations for 16 of these cases. Of the 16 kills, 15 were of calves and 1 was of a cow giving birth, which resulted in the death of both cow and calf. We used logistic regression to quantify how landscape features (i.e., grassland vs. woody habitats, distance to screening cover, and distance to water source at 16 kill sites and 26 random sites) influenced probability of cattle kills. Of known kill locations, 88% of kills (n = 14) took place in woody vegetation while 12% (n = 2) took place in grassland. Our analysis indicated that habitat type (woody vs. grassland) and distance to water source were important factors in predicting bear depredation on cattle. Mean probability of depredation was 2-3 times greater in woody vegetation than in open grassland and was highest near water tanks. The probability of encounter between bears and cattle likely increased as they localized movements around watering areas, which happened to coincide with calving areas and season. Bears utilized screening cover to approach and drag off calves while mother cows were foraging. Supervising and keeping cattle in grassland areas until calves are = 1 month old and providing alternate water sources outside of calving areas may reduce the potential for conflict. Drought may increase the potential for conflict, so cattle management strategies during periods of low rainfall should be altered to minimize losses.