Study: Warmer summers worsen tick infestations for U.S. moose

TRAVERSE CITY, Mich. — It’s a ghastly sight: ticks by tens of thousands burrowed into a moose’s broad body, sucking its lifeblood as the agonized host rubs against trees so vigorously that much of its fur wears away.

Winter tick infestation is common with moose across the northern U.S. — usually survivable for adults but less so for calves, and miserable either way. And climate change may make it worse, scientists reported Monday.

Data collected over 19 years at Michigan’s Isle Royale National Park shows moose have more ticks during winters following particularly warm summers, according to a study published in the peer-reviewed journal Frontiers in Ecology and Evolution.

That’s presumably because higher temperatures quicken the development of tick eggs, boosting the number surviving to hatch, said author Sarah Hoy, a research assistant professor of animal ecology at Michigan Technological University.

“We usually think about winter having a big impact on moose, but growing evidence suggests summer might be even more important,” Hoy said.

In addition to the partial loss of their bristly winter coats, tick infestation makes moose anemic and less able to reproduce, she said. It’s a leading cause of recent population declines in the Northeast, where summer temperatures have been surging more than in the Upper Midwest.

The findings underscore the varied ways global warming can affect wildlife, said co-author John Vucetich, a professor of population ecology at Michigan Tech.

Much research on that topic has involved predator and prey relationships, he said. Vucetich, Hoy and colleague Rolf Peterson have led the world’s longestrunning predator-prey study in a closed ecosystem. It features moose and wolves on Isle Royale, a Lake Superior island park.

“But parasites are at least as important as predation,” Vucetich said. “To be a parasite is an easy way to make a living in the natural world.”

Previous studies have predicted wildlife migrating to different areas because of climate change will encounter parasites to which they haven’t developed immunity. Warmer temperatures are expected to help parasites develop faster and survive longer.

The Michigan Tech team estimated year-to-year levels of tick infestation for hundreds of Isle Royale moose using photographs showing hair loss between 2001 and 2019.

The researchers developed models with those figures, plus temperature and snowfall data and other information, to draw conclusions about climate change’s role.