Moose in northern New England are dying off in startling numbers. In New Hampshire, 70 percent of moose calves died in 2014 and 2015, according to Kristine Rines, wildlife biologist and Moose Project leader at the New Hampshire Fish and Game Department.
The decline is associated with a trend toward shorter winters, with later starts and earlier thaws. Scientists think the weather is helping deadly parasites flourish and spread, with different parasitic species thriving in different areas.
In New Hampshire south of the White Mountains, a large deer population is prospering, in part because of the shorter winters, Rines says. Many of these deer carry brain worm, a microscopic parasite that doesn’t bother them. The brain worm travels through deer droppings to a secondary host, the land snail, which it also does not harm.
When a moose eats an infected snail, however, the brain worm larvae travel to the moose’s spinal cord and brain, causing abnormal behavior. The moose may die from malnutrition or paralysis.
In northern New Hampshire and Maine, winter ticks seem to be more of a problem for moose, Rines says. The ticks thrive with shorter winters due to their life cycle. Tens of thousands can latch on to a single moose in autumn—as many as 30 ticks per square inch. They engorge themselves on their host’s blood all winter and fall off in spring. If they land on snow, they’re likely to die, but if they land on the ground, they lay eggs and repeat the cycle.
More dense moose populations, such as those in parts of New Hampshire and Maine, lead to greater transmission of parasites from moose to moose. Winter ticks may also be more deadly if they occur alongside a third parasite that can kill moose, the microscopic lungworm.
Moose that are irritated by winter ticks will rub off their fur, exposing a pale stubble of broken hair shafts next to the skin, earning them the name “ghost moose.” These animals can lose all of their insulating hair, which can lead to hypothermia. If exposure doesn’t kill them, they may die of anemia.
The tormented moose leave a trail in the woods. “If you’re a winter hiker, you might see blood spattered where moose have walked through,” Rines says.
The ghost moose are visible in late winter and early spring, when they have lost the most fur. Those that survive will molt in spring and replace their tick-ravaged winter coats with new black coats by midsummer.
Scientists in New Hampshire and Maine are working together to collar moose and study their causes of death. In the meantime, the states are adjusting hunting seasons to protect the moose population. In New Hampshire, permits to hunt moose have been reduced to 105 per year (down from a high of 675 in 2007) and may be scaled back even more if the population declines further, Rines says. “We’re trying to see if there’s a moose density where tick impacts will be reduced.”
To fully protect the iconic animal, she says people must address climate change. “If our winters continue to stay short or shorten, I don’t know what the future holds for moose.”