Spring is a time of rebirth. But for moose in northern New England, it's when the insidious effects of ticks can take their toll and kill their hosts.
Early results from an ongoing, five-year study in Maine and New Hampshire show that more and more moose are dying from rampant tick infestations. Tracking collars placed on 36 calves in New Hampshire show nearly 75 percent of the collared moose calves died from ticks.
It's the second year in a row that the study has shown a decline in New Hampshire moose numbers due to ticks.
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"It doesn't bode well for moose in the long term if we continue to have these short winters," Moose biologist Kristine Rines told the Portland Press Herald.
Shorter, milder winters favor winter ticks, which pile atop high plants in grotesque masses in November and wait for a moose to pass by. When the animal does walk by, the ticks latch on by the hundreds and begin a long winter feeding off the large mammal. One moose can host up to 75,000 ticks on its body.
By spring the moose have become so weakened and emaciated, many die. The ticks, meanwhile, finally drop off. Normally they would land on snow and cold conditions and then die. But shorter winters due to climate change mean they can drop off their hosts and hit bare ground – and live on to suck the life out of more hosts.
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Average annual maximum temperatures in New Hampshire have warmed 0.5 to 2.1 degrees Fahrenheit since 1970, according to a 2014 report. During the 20th century, Maine warmed by 3 degrees Fahrenheit, and "the warm season increased by two weeks," according to Maine's Climate Future, a 2015 update by the University of Maine.
Milder winters favor ticks' survival – as well as the survival of other pests, such as lungworm, which also take their toll on moose. While the results have shown an overall decline in moose numbers since the study began in 2014, last year Maine's moose actually fared somewhat better. Moose calf mortality dropped last year from 73 to 60 percent.
Part of that interruption in moose calf mortality might be linked to declining numbers of moose – since ticks depend on the animals for survival.
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About 7,500 moose were living in New Hampshire in the late 1990s, by 2013, the population there had dropped to 4,500, according to a report in Outdoor Life. In Maine, which has about 60,000-70,000- moose -- the densest population in the lower 48 states -- there's a suspected decline.
"As our moose numbers decline, the ticks will decline, as well," Rines told the Portland Press Herald. "What we don't know is at what point will things level off."