Warmer summers exacerbate tick infestations for moose
Travel City, Michigan. – It’s a horrific sight: ticks in the tens of thousands pierce the body of a vast moose, sucking up its lifeline while the ailing host rubs trees so hard that much of its fur is eroding.
Winter tick infestation is common with moose throughout the northern United States – usually surviving to adults but less so for calves, and miserable either way. Scientists reported Monday that climate change could make matters worse.
Data collected over 19 years in Isle Royale National Park in Michigan shows elk have more ticks during winters than during particularly warm summers, according to a study published in the peer-reviewed journal Frontiers in Ecology and Evolution. .
This is likely because higher temperatures speed up the growth of tick eggs, which increases the survival of tick eggs to hatch, said Sarah Hoy, a research professor of animal ecology at Michigan Technological University.
“We usually think of winter as having a major impact on moose, but mounting evidence suggests that summer may be even more important,” Hoy said.
In addition to the partial loss of their coarse winter coats, infestations of ticks make anemic moose less able to reproduce, she says. It’s a major cause of recent population declines in the Northeast, where temperatures have been warmer in summer than in the upper Midwest.
Co-author John Vucic, professor of population ecology at Michigan Tech, said the findings underscore the diverse ways global warming could affect wildlife.
He said that much of the research on this topic has involved relationships between predator and prey. Vucetich, Howe and colleague Rolf Peterson led the world’s longest study between predator and prey in a closed ecosystem. It features moose and wolves at Isle Royale, the Lake Superior Island park.
“But parasites are at least as important as predation,” Vucetich said. “Being a parasite is an easy way to make a living in the natural world.”
Previous studies predicted that wildlife migration to different regions due to climate change would encounter parasites to which they had not developed immunity. Warmer temperatures are expected to help parasites develop faster and survive longer.
The Michigan Tech team estimated annual levels of tick infestation for hundreds of Isle Royale deer using images showing hair loss between 2001 and 2019.
The researchers developed models with these numbers, as well as temperature and snowfall data and other information, to draw conclusions about the role of climate change.
Winter ticks’ life cycles begin in June as each female lays several thousand eggs in the soil. They hatch after a few months. The caterpillars crawl over woodland and meadows vegetation and wait for hosts—preferably members of the deer family, which includes moose—to clean them up so they can catch them.
Deer do a better job of cleaning themselves than moose, the paper said, possibly due to evolutionary differences.
The tick feeds on the blood of its host during the winter, then separates and reproduces. Males, as well as females, die if they fall on a snow-covered ground. If the land is dry, the females live and lay eggs to start the next generation.
Previous studies of how climate change affects tick reaction have focused on milder winters, which give ticks more time to find hosts while enhancing their odds of successful egg-laying by reducing snow cover.
said Michelle Carstensen, wildlife health program supervisor for the Minnesota Department of Natural Resources.
It’s helpful, said Carstensen, who was not involved in the study, but noted that Isle Royale has unique properties.
Its only predators are wolves, which were nearly extinct before officials began restoring the population in 2018 with mainland surrogates. Isle Royale doesn’t have any deer, so moose have not been exposed to the brainworm, a deadly parasite carried by deer. Fishing is not allowed there.
That helps explain why the Isle Royale deer population has risen to about 1,800 in recent years, despite ticks.
Mainland moose are not protected. Little remains in northwest Minnesota, where thousands roamed a few decades earlier. In the state’s northeast, the population has fallen from over 8000 in the mid-2000s to 3000-4000 today.
Climate change may be impairing their ability to deal with diseases and parasites, Carstensen said, although ticks have played only a minor role in the decline.
But the tick is prevalent in New England, which has the highest population of moose in the lower 48 states. This caused about half of calf deaths between 2014 and 2020 in Maine and New Hampshire, said Pete Pickens, a retired wildlife biologist at the University of New Hampshire.
“It’s like the worst vampire Halloween nightmare you could possibly imagine,” he said.
Pickens, who was not involved, said that because of the environmental differences between regions, the conclusions of the Isle Royale study should be applied with caution elsewhere. But it does illustrate the impact of global warming on parasites and other dangers to popular wildlife, including moose.
“Maybe this is where we can reach people and make them understand that climate change is real,” he said. “Winter ticks win the arms race and your distinct species lose.”
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