Healthy males often take chances when they're looking for mates, putting on cocky displays, for example. It makes sense that these exploits would tend to attract predators as well, thereby raising the risk of death. But there have been few data to support this theory until a new study of Utah prairie dogs published in next month's issue of the American Naturalist.
Utah prairie dogs (Cynomys parvidens) were once an abundant source of food for many grassland predators, including American badgers, coyotes, and golden eagles. But disease, poisoning, and habitat destruction have driven the prairie dogs to the edge of extinction.
Behavioral ecologist John Hoogland of the University of Maryland Center for Environmental Science in Frostburg and colleagues have been assessing the impact of predation on prairie dog survival for 11 years. They have observed a 200-member colony in Bryce Canyon National Park, where the team spends each spring perched in 4-meter-high observation towers from dawn to dusk. After marking the prairie dogs with black dye and ear tags, the researchers track their status and behaviors via binoculars and person-to-person radio communication.
Predators hardly seemed a major menace. From 1995 through 2004, they killed only 10 adult prairie dogs in their prime. But 2005 was different. Over the 17-day mating season, the team saw red fox and northern goshawk pick off 10 healthy, breeding males. "I didn't have a clue about this level of predation and susceptibility," says Hoogland, who's been studying prairie dogs for 33 years. As to why the researchers saw so few predators attack in earlier years, Hoogland believes his team's presence may have scared them away. For some reason, the fox and goshawks in 2005 were oblivious to humans and therefore were more likely to target prairie dogs, Hoogland says.
"This is by far the best documentation and quantification of selective predation," says Jerry Wolff, a behavioral ecologist at St. Cloud State University in Minnesota. Documenting patterns of predations, says Hoogland, will help wildlife managers develop plans to conserve Utah prairie dogs and other endangered species.