Rock Doc: Managing cougar populations requires reproductive math
Science often takes a lot of time and work. Those were my thoughts when I learned of all that professor Robert Wielgus has done to research the complex behavior of wild cougars.
Wielgus is a member of the School of the Environment at Washington State University. For 13 years he and his graduate students captured hundreds of cougars with the help of hounds. They attached GPS collars to the cougars and then got reports six times a day on where the cougars were – giving Wielgus good information on cougar mortality, migration, prey and reproduction. Out of all that work has come new information on how cougar populations respond to hunting. That, in turn, will now lead to changes in how the Washington Department of Fish and Wildlife manages the hunting of cougars.
One of the clear results of Wielgus’ work is the evidence that if we kill too many cougars via hunting, we can end up having more conflict with cougar populations. That’s why, starting in January, Washington officials will use “equilibrium management” on cougar populations – hunters will only harvest as many individuals as would be replaced through natural reproduction.
Research shows that whether hunters kill 10 percent or 35 percent of the cougars in an area, the total population remains the same. In the old days people explained that result by saying high rates of hunting triggered a population to increase its reproductive rates. But the work of Wielgus and company showed that isn’t the case. Instead, young cougars move around – a lot – to fill the vacuum hunting can make.
“If you kill a big adult male, three male ‘teenagers’ will come to the funeral,” Wielgus said to me.
The behavior of the youngsters is different from their older counterparts.
“They’re teenagers,” Wielgus said. “They’re sexually mature, but mentally they are not all there.”
The adolescent cougars are more likely to get into trouble with humans and our livestock than are the more mature toms that want to stay away from danger. As it happens, adolescent males have bigger territories than the adult males. This means that livestock and elk might have to cope with either one mature tom or several adolescent males that replace him. With multiple male cougars in an area, trouble is multiplied. Cougar complaints, livestock kills and pet kills all actually increase with increasing hunting mortality of cougars.
Young male cougars also change the behavior of female cougars. The adolescent males may kill a female’s kits to bring the female into heat so they can breed with her. Females may move to marginal ground like high elevations to get away from the young males. This puts pressure on sensitive and threatened game that otherwise would have little contact with cougars.
The bottom line of Wielgus’ research is that the state is going to limit cougar hunting to 14 percent of the cougar population. Once hunters have harvested that figure, hunting will be suspended in an area for the rest of the year.
“The results of this work are a win-win for cougars, livestock operators, and threatened prey species,” Wielgus said.
Dr. E. Kirsten Peters, a native of the rural Northwest, was trained as a geologist at Princeton and Harvard. This column is a service of the College of Agricultural, Human and Natural Resource Sciences at Washington State University.