Moose in Northern Michigan have more ticks during winters after particularly warm summers, according to a study published in the journal Frontiers in Ecology and Evolution.

Infested moose often host tens of thousands of ticks, which burrow into their skin to suck their blood. The moose try to get rid of the pests by rubbing against trees so aggressively that their fur wears away. The infestation is usually survivable for adults but less so for calves.

Scientists who collected data over 19 years at Michigan’s Isle Royale National Park reported Monday that climate change may lead to worse infestations.

That’s presumably because higher temperatures quicken the development of tick eggs, boosting the number surviving to hatch, said author Sarah Hoy. She is 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 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 longest-running 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.

Winter tick life cycles begin in June as each female lays several thousand eggs in soil. They hatch a few months later. Larvae crawl up forest and meadow plants and wait for hosts to brush by so they can latch on.

The ticks feed on their hosts’ blood through winter, then detach and reproduce. Males die, as do females if they fall onto snow-covered ground. If the ground is dry, females survive and lay eggs to start the next generation.

Previous studies of how climate change might affect tick-moose interaction have focused on milder winters, which give ticks more time to find hosts while boosting their prospects for successful egg laying by reducing snow cover.

“But this new paper says, ‘Not so fast — these subtle changes during summers can be exacerbating some of these effects and you need to pay attention to that as well,’” said Michelle Carstensen, wildlife health program supervisor with the Minnesota Department of Natural Resources.

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