MONTPELIER -- Biologists are trying to determine how much moose in northern New England are threatened by a species of tick that multiplied with the help of recent warmer winters.
They estimate that 150,000 ticks -- half of which can grow to the size of a grape -- can cover a large moose.
In Vermont, biologists are concerned the ticks, which become less of a problem after long, cold winters, could be contributing to a decline in the reproduction rates and general health of the state’s moose population, said Vermont moose biologist Cedric Alexander. There are an estimated 3,000 moose in Vermont.
"They’re irritated, they’re uncomfortable, they’re not feeding," Alexander said of the moose that play host to the ticks through the winter.
In New Hampshire, biologists believe the ticks are contributing to a decline in the state’s moose population, although scientists say it’s possible there are other, unknown factors as well.
"I think the basic foundation of the concern is, in our case anyway, shorter winters, more mild winters in some regard have facilitated an increase in the abundance of the tick species, called winter tick, that is having an adverse impact on moose health and survival," said Mark Ellingwood, the chief of the Wildlife Division at the New Hampshire Department of Fish and Game.
In Vermont the moose reproduction rate is lower than biologists would like. Ideally, every four adult female moose would produce six young every year, Alexander said. Recently the number has been about three.
Newborn moose are especially vulnerable to blood-sucking ticks because the calves can scrape off their fur while trying to rub off the annoying insects.
"They can die of exposure. They don’t have any way to keep themselves warm. They are already anemic, they have no fat reserves to burn off," Alexander said.
Lee Kantar, a moose biologist in Maine, said he’s trying to determine the scope of the problem in the state. He said the ticks do not appear to be as much a problem in the northern part of the state as in the southern parts.
"Obviously science is all about identifying a problem and trying to hone that down to what that problem entails," Kantar said.
In Vermont the tick challenge comes after the state had worked for several years to reduce the size of the moose herd, which peaked in 2008, when large herds were damaging the forests. Vermont issued 1,255 moose hunting permits in 2008; this year it’s issuing about 400 regular and special permits.
Herds are smaller and the damage to the forests has been reduced, but the health of the remaining moose hasn’t improved as expected, biologists said. Alexander and others are trying to determine if the ticks are to blame.
There are about a dozen tick species in Vermont. The winter tick, also known as the moose tick, Dermacentor albipictus, is one of them, said Vermont state entomologist Alan Graham. They are not the species of tick that carries Lyme disease.
The ticks pick up their moose hosts in the fall and detach themselves in the spring to breed. The females can reach the size of a grape. Large bull moose can be covered with up to about 150,000 ticks, about half of which will be the larger females, Alexander said.
Cold weather will kill a winter tick that isn’t attached to a host, so the later-arriving cold weather in the fall gives them more time to find hosts. In years with later springs the ticks will detach themselves from their hosts and freeze to death in the snow. Dark-colored ticks on a white background are more likely to be eaten by birds, helping keep the numbers in check, Alexander said.
Extreme weather conditions during the cold months will also reduce the winter tick population.
"We haven’t had those January freezes where it goes to 25 below zero and sterilizes everything," Graham said.
Ross Stevens, of East Burke, has been a moose hunting guide in Vermont’s Northeast Kingdom for about a decade. He says he’s noticed there aren’t as many moose as there were.
"The tick problem is big. I see a lot of ticks on the moose. I think it’s taking its toll," Stevens said. "They’re the size of raisins filled with blood; they’re gross."