Famously formidable, wolverines require a springtime "refrigeration zone" home to feed their cubs, biologists report.
"Wolverines are unique mammals, they fill a niche that a lot of other creatures couldn't survive," says Robert Inman of the Wildlife Conservation Society's wolverine program in Ennis, Mont. Famously, 1,000 pounds of attitude stuffed into 30 furry pounds, wolverines range across the Canada, Scandinavia and Siberia, patrolling ranges hundreds of square miles in size in snowy places. "They are carnivores but not top predators, often scavengers that benefit from other's kills," he says.
In an upcoming study in the Journal of Mammalogy, Inman and colleagues look at one mystery about these formidable carnivores, why they bear their young as early as February, a time when there isn't a lot of food. Bearing and weaning a cub can take more than 100 times more calories than normal daily living for carnivores, the study notes:
"The timing of reproductive events in relation to food availability may be particularly critical for the wolverine. The wolverine's large feet are a morphological adaptation that allows it to travel easily over deep snow, and the species is distributed in circumpolar fashion across the tundra, boreal, and montane biomes (regions). Throughout its distribution, the wolverine displays extremely large home ranges, territoriality, low densities, and low reproductive rates. These adaptations are necessary for exploiting a cold, low-productivity niche where growing seasons are brief and food resources are limited. Starvation is a significant natural cause of wolverine mortality."
"What advantage do they receive by bearing their young in February, ahead of other animals, when their isn't a lot of food," Inman asks. "Any why do they live in rocky terrain that other creatures avoid."
To figure it out, the researchers used reproductive data on wolverines, their own and others, from 1955 to 2011, along with similar data about food resources, carcasses of everything from reindeer to ground squirrels "habitually" cached by wolverines.
The data suggest that female wolverines are preferentially caching carcasses near the dens where they bear young, the researchers report, to later feed their tots:
"We expect that the limits to wolverine distribution are ultimately related to the species' ability to avoid competition by existing in cold, low productivity environments and accumulating (caching) the limited food resources present therein. As such, we propose a ''refrigeration-zone'' hypothesis as a food/competition-based explanation for the observed correlation between wolverine distribution and the area encompassed by persistent spring snow cover."
The "refrigeration zone" regions needed for wolverines may shift due to global warming, Inman says. "A warming climate is not good for wolverines, they are adapted to cold conditions."
Only about 250 to 300 wolverines live in the Lower 48 states, he adds, about half as many as the region could support, the subject of proposed rule-making under study by the U.S. Fish and Wildlife Service. "They are hard creatures to track and study," he adds. "We don't know a lot of things about wolverines, which might be surprising for such a famous animal."