Cougar Predation

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Cougar Depredation on Feral Donkeys, California

"Predation is an understudied aspect of burro ecology, Lundgren maintains. Several publications have pegged burro population growth directly to birth rates, without recording how many foals actually survive to adulthood. “Only three of 10 peer-reviewed demography studies on horses and burros mention if there are predators in the system or not,” Lundgren says. “The lack of predation is an assumption that’s carried around without anyone explicitly testing it.”

In the course of the 2018 and 2019 field seasons spent monitoring Death Valley field sites in areas like Willow Canyon and Mesquite Spring, Lundgren says he has found considerable evidence of predation: around 33 burro carcasses in the riparian vegetation, half of which he characterizes as undeniable kills from mountain lions. (The other half are less conclusive, but were found in close proximity to lion scat and tracks.)

Some mountain lion trails contain skeletons from two or three burros, he adds, and the dense vegetation that springs up in the groves during the growing season may be hiding more remains. While such kills might be attributable to just a few lions, Lundgren argues, they might also be a signal that the lion population is adapting to target the largest available prey in the ecosystem, which would provide a natural check on burro populations. Some studies suggest that high levels of mountain lion predation essentially negate population growth in some wild horse herds.

IN ORDER FOR THIS kind of natural check on burros to work, Lundgren points out, lion populations have to be healthy. In some areas of Nevada where burro populations are skyrocketing, mountain lions are shot at a certain age to protect bighorn sheep or livestock, he adds, meaning that cubs often don’t have exposure to more challenging prey. The young and inexperienced lions that remain have a hard time going after wild burros. In addition, burro herds in the park tend to shield themselves by clustering around areas of heavy human habitation, which lions tend to avoid. All these factors make it appear as if the burros have no predators, Lundgren says, but actually point to a more complicated dynamic."

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