The heads of moose living on a Michigan island are shrinking

"Decreasing skull size may be an early indicator of population change," said ecologist John Vucetich.
By Brooks Hays  |  Dec. 18, 2017 at 3:35 PM
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Dec. 18 (UPI) -- The brains and skulls of moose living on a remote Michigan island are shrinking.

According to analysis by scientists at Michigan Technological University, the skulls of moose living in Isle Royale National Park have declined in size by 16 percent over the last four decades.

The size of a moose's skull serves as a proxy for the size of the animal's brain, which in turn, can yield insights into the specimen's body size and physiology, as well as the environmental conditions the moose encountered as a juvenile.

By measuring changes in a species' skull size over time, researchers can estimate the health of a population and determine how a species is responding to changes in the environment.

"The conditions you're born into have a massive impact on not only how big you are but also how long you're going to live," Sarah Hoy, a research fellow at Michigan Tech, said in a news release. "This idea isn't new -- what we're trying to do is establish how climate warming is affecting this iconic, cold-adapted species. We found evidence suggesting that moose experiencing a warm first winter tended to be smaller as adults and live shorter lives."

In northern Minnesota, moose populations have halved over the last 12 years. Researchers believe climate change has been a major driver. Warmer winter temperatures have caused heat stress and negatively impacted the mammal's nutritional condition. Warmer temperatures have also expanded the range of white-tail deer, which carry and spread and fatal brain worm parasite.

Meanwhile, the moose population on Isle Royale has been rapidly increasing, despite a climate similar to that of northern Minnesota. Isle Royale is without white-tail deer, limiting the moose's exposure to deadly parasites.

Despite their success, the latest research suggests Isle Royale moose are being impacted by climate change. After measuring the 662 skulls, researchers concluded that the moose -- a species that evolved among the cold climes of the northern latitudes -- is being negatively affected by global warming. The moose's brain and body are shrinking and its lifespan is getting shorter.

The moose's surprising success -- detailed in the journal Global Change Biology -- is a result of the decline in the island's wolf population. Wolves, the moose's primary predator, are almost completely gone, while the moose population has tripled over the last decade.

That may sound like good news for moose fans, but the animal is likely to suffer from increased competition for limited resources. That increased competition could partly explain the shrinking noggins.

"Decreasing skull size may be an early indicator of population change," said John Vucetich, a professor of ecology at Michigan Tech. "We're likely looking at a population in transition, and the healthiest transition would almost certainly involve restoring wolf predation to Isle Royale."

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