Courting costs: male prairie dogs seem too busy mating to dodge predators.

Mating season makes the normally fast and tough male prairie dog so preoccupied that he's easy pickings for predators, researchers find.

In a study of prairie dogs in the wild, a fox and a few goshawks caught adult males only during the short breeding season, says John L. Hoogland of the University of Maryland Center for Environmental Science in Frostburg. In those 17 days, though, predators picked off enough adult males to account for almost 40 percent of all captures observed during a 4-month period.

Other vulnerable adult groups were pregnant females, recent immigrants, and prairie dogs with edge territories, says Hoogland.

"Perhaps our most important finding is that nonjuvenile victims of predation were not the old and the weak, but rather young and middle-aged adult Utah prairie dogs in excellent condition," he and his colleagues conclude in the October American Naturalist.

The study took advantage of a rare opportunity to see prairie dog predators in action, says Hoogland. The results convinced him that the presence of researchers often scares away such animals.

Since 1995, Hoogland and his crew have spent months at a time, dawn to dusk, watching a colony of a hundred or so Utah prairie dogs (Cynomys parvidens) in Bryce Canyon National Park. The rarest of the five prairie dog species, it has such small populations that common perils, including "varmint shootings," threaten its existence, says Hoogland.

In 2005, a fox that had gotten used to people lunched frequently at the colony. Also, at least one goshawk made unusually common strikes. In 4 months, the crew saw these predators kill 26 prairie dogs. During the entire previous decade, the team had observed only 7 such deaths.

Seeing so many kills "has forced me to rethink what I know about prairie dogs," says Hoogland. He hadn't ranked predators as a major risk before. Several lines of evidence, however, suggest that the predation tallied in 2005 was not a fluke, he says.

The problem for the adult males that predators captured "was mostly just total preoccupation with sex," says Hoogland. A female prairie dog becomes fertile for at most 5 hours once a year.

The numbers in the new prairie dog study are small, cautions Peter Neuhaus of the University of Neuchatel in Switzerland. In his studies of Columbian ground squirrels, he, too, has seen high mortality among breeding males. Yet he couldn't tell whether predators, disease, or overexertion claimed them.

Neuhaus says that he observed predators catching his study animals, but he adds that "the main problem" with some other longterm studies is the rarity of reported predator attacks.