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Across North America - in places as far-flung as Montana and British Columbia, New Hampshire and Minnesota - moose populations are in steep decline. And no one is sure why.
Twenty years ago, Minnesota had two geographically separate moose populations. One of them has virtually disappeared, declining to fewer than 100 from 4,000.
The other population, in northeastern Minnesota, is dropping 25 per cent a year and is now fewer than 3,000, down from 8,000. Wildlife officials have suspended all moose hunting.
"Something's changed," said Nicholas DeCesare, a biologist with the Montana Department of Fish, Wildlife and Parks. "There's fewer moose out there, and hunters are working harder to find them."
What exactly has changed remains a mystery. Several factors are clearly at work. But a common thread in most hypotheses is climate change.
Winters have grown substantially shorter across much of the moose's range. In New Hampshire, a longer autumn with less snow has greatly increased the number of winter ticks, a devastating parasite. "You can get 100,000 ticks on a moose," said Kristine Rines, of the state's Fish and Game Department.
In Minnesota, the leading culprits are brain worms and liver flukes. Both spend part of their life cycles in snails, which thrive in moist environments.
Another theory is heat stress. Moose are made for cold weather, and when the temperature rises above minus 5 Celsius, as has happened more often in recent years, they expend extra energy to stay cool. That can lead to exhaustion and death.
In the Cariboo Mountains of British Columbia, a recent study pinned the decline of moose on the widespread killing of forest by an epidemic of pine bark beetles, which seem to thrive in warmer weather. The loss of trees left the moose exposed to human and animal predators.
"It's complicated because there's so many pieces of this puzzle that could be impacted by climate change," said Erika Butler, until recently the wildlife veterinarian at the Minnesota Department of Natural Resources.
The stakes go beyond the moose. The animals are ecosystem engineers; when they browse shrubs, for example, they create habitat for some nesting birds. And moose contribute to the economy. In New Hampshire, for instance, moose-watching tourism is a US$115 million-a-year business.


Moose disappearing, and scientists point finger at climate change

Moose populations are in steep decline. Photo: Shutterstock

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