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By targeting adult males, sport hunting is depleting populations of cougars and African lions because their cubs need fathers as well as mothers, a university-led study indicates.

In a paper published in the Public Library of Science, university lion researcher Craig Packer and his colleagues report that the vulnerability of big cat species stems from the tendency of adult males to kill cubs belonging to other males in order to bring the mothers into "season." Since fathers normally defend their families against transgressors, killing the father can lead to the death of the cubs.

The researchers studied trends in numbers of cougars and lions taken by hunters in African countries and western U.S. states. Sport hunting generates revenue that encourages conservation, but infanticidal species are vulnerable to over-harvest when wildlife managers raise quotas in response to predation of livestock, pets, or people.

"Over the past 25 years, the steepest declines in cougar and lion harvests occurred in jurisdictions with the highest harvest intensities," the researchers write. "Simulation models predict population declines from even moderate levels of hunting in infanticidal species."

In contrast, no evidence for overhunting turned up among American black bears, males of which do not routinely kill other males' cubs.

The difficulty of estimating populations of cougars and lions makes it hard to determine the number of trophies hunters can take before the populations start shrinking toward extinction, the researchers say. Their analysis suggests that wildlife management agencies often adjust quotas to control, rather than preserve, the big cats in areas where they have threatened humans or their animals.

"Unsustainable levels of trophy hunting of lions and cougars appear to be driven by conflicts with humans and livestock: the intensity of lion hunting was highest in countries with the most intensive cattle production, and wildlife managers are under similar pressure from U.S. ranchers to raise cougar offtakes," the researchers write.

The study points up the need for new ways of protecting people and livestock and preserving sport hunting without endangering vulnerable predators. Limiting hunting to males old enough to have mature offspring is one possible means. Another could be banning or limiting the use of bait and hounds, but enforcement in remote hunting areas would be difficult.

"We have an opportunity to develop new strategies that will benefit hunters, livestock owners, and conservationists," Packer says. "It's important to educate the public about the risks that these large predators pose to rural communities and to help hunters and wildlife managers develop methods to sustain healthy populations of these animals."

Packer is a Distinguished McKnight University Professor in the Department of Ecology, Evolution and Behavior, which is part of the College of Biological Sciences. He worked with an international team that included Luke Hunter from Panthera, Kristin Nowell from the International Union for the Conservation of Nature/Species Survival Commission (IUCN/SSC) Cat Specialist Group, and Dave Garshelis of the Minnesota Department of Natural Resources, who chairs the IUCN/SSC Bear Specialist Group.