Winter ticks becoming a drain on health of Colorado’s moose populations |

Winter ticks becoming a drain on health of Colorado’s moose populations

A moose in Silverthorne with bare patches in its coat in April showed signs of being afflicted by winter ticks. The malady can lead to an animal's death due to lower energy levels from substantial blood loss and already coming off one of the toughest times of the year for survival.
Courtesy of Fiona Kennard |

North America’s moose are under siege from a silent assassin, and the high country population is not immune.

The winter tick, a common parasite throughout the continent, has grown in both force and impact throughout the past handful of years, and it’s begun to take a toll on these creatures. This bloodsucking scourge infests its unsuspecting host at a time of year when the animal is at its weakest and, during the course of several months, can drain a moose to the point of death.

The clearest sign of a moose affected by ticks are patches of hair missing from its dark brown coat, exposing the animal’s bare skin. To rid itself of the irritant, a moose will rub its neck and body up against trees and reveal its pale undercoat, earning the condition a nickname of “ghost moose.”

The effect of the winter tick on a moose is threefold: The animal is already coming out of a period where food is least available, it’s being sucked dry of its blood to the point of anemia and it’s spending more of its day grooming rather than eating to rebuild its strength following winter. The deadly combination may leave moose lethargic, malnourished and rail thin.

“They can look like skin and bones, almost like a walking skeleton with skin on it,” said Jeff Yost, a veteran terrestrial biologist with Colorado Parks and Wildlife. “Coming out of winter, it’s springtime when we notice it and you see the white and patches of hair.”

Moose are most prevalent in parts of Canada and the northern New England states of Maine, New Hampshire, Vermont, Connecticut, Massachusetts and Rhode Island, but reside in Colorado, too. Steamboat Springs is believed to have the state’s largest herd, but the region that includes Summit and Grand counties isn’t too far behind, with roughly 400 animals.

‘hasn’t been an extreme issue’

Despite its name, the winter tick does not take to frigid climates. The elevation of Colorado’s Western Slope, and its associated temperatures, has kept the pest from being the growing problem it is in those northeastern states where annual mass moose die-off is becoming a norm.

“It hasn’t been an extreme issue for us,” Yost said of the state. “Ticks survive better under warmer conditions, and that’s probably why we have not seen a lot of incidents so far, because it’s cold enough in the winters with the ice and snow that ticks don’t do well.”

A New York Times article from January stated that recent studies have determined the tick has killed about 70 percent of the calves previously tagged for research in certain areas of New England. The warming of the planet due to climate change, which is producing warmer and shorter winters across the United States, is increasing the tick’s chances of survival beyond the typical single winter.

The winter tick hatches in the fall and the larvae find their way onto plants to await these 1,000-pound herbivores. When the chance is right, they latch on, sometimes with as many as tens of thousands of their closest friends and relatives, and ride out the cold-weather season, eating their fill before detaching in the spring.

CPW encourages anyone spotting a moose with the listed symptoms to call in and report it. Often nature is simply taking its course and local district wildlife managers may not be able to do anything to help save the animal if it is on the verge of death. But because of the scarcity of the illness in Colorado moose, those that do expire can be brought in for further study in a health lab to learn more about this blight.

Even though many scientists theorize the winter tick is the primary cause, definitive conclusions about what may be causing a rising mortality rate in the nation’s moose population remain elusive. Additional parasites such as the lungworm could be playing a role, and the grouping of these ailments might also be the root cause.

“Winter ticks could be a factor in moose declines, in conjunction with another disease or malady as one or two or three things wrong with an animal,” said Yost. “Potentially as we have warming temperatures and winters, it may become more and more prevalent. It’s one of the concerns of moose researchers across North America, and it’s on everyone’s radar.”

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