By Matt Walker
Editor, Earth News
Melting away with the snow?
The wolverine, a predator renowned for its strength and tenacious character, may be slowly melting away along with the snowpack upon which it lives.
Research shows wolverine numbers are falling across North America. Their decline has been linked to less snow settling as a result of climate change.
The study is the first to show a decline in the abundance of any land species due to vanishing snowpack.
Details of the wolverine's decline are published in Population Ecology.
The wolverine lives in boreal forest across Scandinavia, northern Russia, northern China, Mongolia and North America, where it ranges mostly across six provinces or territories of western Canada.
This largest member of the weasel family eats carrion and food it hunts itself, including hares, marmots, smaller rodents and young or weakened ungulates.
It has evolved for life on the snowpack, having thick fur and outsized feet that help it move across and hunt on snow.
Wildlife biologist Dr Jedediah Brodie of the University of Montana, in Missoula, US, wondered how climate change might be having an impact on snowpack levels, and on the animals that depend on it.
He had previously researched how declining levels of snow in the US Yellowstone National Park, caused by climate change, was changing the abundance of aspen trees and how elk feed on them.
Dr Brodie and his colleague, Professor Eric Post of Pennsylvania State University, at University Park, US, gathered data on snowpack levels across six provinces or territories of Canada: Alberta, British Columbia, Manitoba, the Northwest Territories, Saskatchewan and the Yukon Territory.
In all bar the Yukon, he found that snowpack depth declined significantly between 1968 and 2004.
Other studies have shown corresponding rising temperatures and declining precipitation across much of the western US.
"It occurred to me that a good first place to look for ecological impacts of that snowpack decline would be with a snow-adapted species like the wolverine," Dr Brodie told the BBC.
"Fortuitously, Canada has good records of both snowpack trends over time as well as trends in the harvest of all sorts of fur-bearing animals."
So Dr Brodie and Professor Post examined the records of wolverine numbers caught by fur trappers over the same period.
They found a striking correlation between declining snowpack and falling numbers of the predator.
"In provinces where winter snowpack levels are declining fastest, wolverine populations tend to be declining most rapidly," the researchers wrote in the journal article.
"Spring snowpack also appears to influence wolverine population dynamics."
The researchers found only one territory, the Northwest Territories, where wolverine numbers are increasing. There, snowpack levels are declining but they remain much higher and less variable than in most other provinces.
Dr Brodie cannot be sure why wolverine numbers are falling, but he has his suspicions.
"Recent work shows that wolverines appear to use areas with deep snowpack for dispersal. So reduced snowpack could make dispersal more difficult or dangerous, potentially reducing the success rate with which individuals can establish new home ranges," he says.
"Reduced snowpack may also make it harder for wolverines to get food, for several reasons.
"First, harsh winters and deep snow are major causes of mortality for ungulates like elk, moose, deer and caribou.
"If milder winters mean that fewer of these animals die over the course of the winter, then there will be fewer carcasses for wolverines to feed on," he explains.
"Wolverines also hunt rodents, and this food source may be important for wolverine reproductive success in some areas.
"But shallower snowpack is bad for a lot of rodents because it provides less insulation from the cold.
"So if declining snowpack reduces rodent abundance, that could be bad for wolverines."
Dr Brodie believes that his is the first study to show a decline in species abundance due to a reducing snowpack - for any land animal, not just those in North America.
But he says there are interesting parallels in marine systems.
"For example, sea ice is critical for polar bear foraging."
Polar bear body condition, reproductive rates, and survival have declined significantly in Hudson Bay as sea ice breaks up earlier in the spring, he says.
"At the other end of the globe, Antarctic sea ice has increased over recent decades.
"This may have negative impacts on adelie penguin populations that depend on ice-free areas for breeding and foraging.
"But we don't have to just sit back and watch climate change drive animals extinct," he says.
"As climate change worsens, we should reduce trapping levels and also disturbance to boreal forest habitats.
"Reducing the impact of these anthropogenic stressors could help 'offset' the impacts of climate change on wolverines."