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15.7 Trends in winter tick in moose

Last Updated: 
June 10, 2015

This indicator tracks winter tick, a parasite that can have negative effects on the health of moose and other ungulates like boreal caribou.

The most obvious signs of winter tick (Dermacentor albipictus) infestation are hair loss and poor, thin body condition. Large numbers of ticks are able to parasitize individual moose and can have serious health effects on the animal. Affected moose are sometimes called “ghost moose” because of hair loss that results in white or grey patches. Winter tick is common on moose in southern Canada, but its range is thought to be limited by climate. It is not yet common in the NWT, but recent sightings of affected animals have led biologists to keep track of observations to see if this disease becomes more common in the NWT in the future. This indicator provides baseline information on the location of known observations of moose showing signs of winter tick infestation.

Surveillance for winter tick in the NWT, like other wildlife diseases, relies heavily on reports from hunters and trappers who spend time on the land. Hunters across the NWT are encouraged to report any diseases or abnormalities seen in wildlife.

NWT Focus

Some diseases and parasites are limited by climate or long periods of cold weather. Climate change may impact where these parasites can survive, or allow them to move through their various life stages more quickly. Environmental changes may have occurred, or could occur in the future, that allow the winter tick to expand its range northwards. Changes in habitat that may increase contact between individual moose may also facilitate the spread of winter tick. Monitoring winter tick on moose is important because it can provide information on changes in climate or habitat that impact the health of moose populations, an important food and cultural resource to many NWT residents.

Current view: status and trend

Historical

Traditional knowledge in the NWT suggests that moose affected by winter tick were not observed until the last several decades.

In 1987 a survey was conducted of 502 trappers representing 389 registered trap lines in northern Alberta, northern BC, NWT and the Yukon. In this survey the northern limit of winter tick-related observations in the Yukon was 62ºN (see Figure)1. The only NWT reports were anecdotal reports of moose affected by winter tick recorded from Fort Providence in 1987 and near Fort Liard and near Fort Smith prior to 19671. However, hunters north of 62º in the NWT were not surveyed in this study.

Map: Locations of trap lines where moose were [solid circle] or were not [open circle] observed in late winter/early spring with apparent tick-induced hair loss, according to a survey of 502 trappers in 19871. Source: Samuel 1989. Journal of Wildlife Diseases1.

Recent Observations

Overall, the prevalence of incidences of winter ticks in the NWT still appears to be very low, but the parasite is now established. Sightings are mostly confined to southern NWT, though sightings and cases confirmed by laboratory tests are found along the Mackenzie Valley as far north as the Sahtu region have been increasing. Observations of moose showing signs of winter tick in the NWT are reported to GNWT-ENR. There have also been two sightings of winter ticks on boreal caribou, one confirmed by lab tests.

Map of winter ticks in the NWT

Observations of moose showing signs of winter tick in the NWT and reported to GNWT-ENR.

Looking forward

Changing environmental conditions may allow the winter tick’s range to extend further northwards. Some experts think that the effects of winter ticks on moose and other ungulates across geographical regions are primarily weather-dependent2. In other parts of North America, tick-related mortality of moose sometimes occurs in many different regions in the same years, suggesting that something common is occurring in all locations. Spring has been suggested as the critical time period, when adult females drop off their host and must survive to lay eggs. Low precipitation and warm temperatures during April have been associated with increased numbers of ticks the following year, indicating this weather may support maximum survival and reproduction rates of the winter tick. April snow cover and low temperatures (less than 3-4ºC) have been linked to low tick survival.

Looking around

Moose and other ungulates throughout southern Canada are infested by the winter tick. The Yukon faced a recent tick infestation in its elk herds, causing concern for its moose population. To date, winter ticks in Yukon appear to be confined, for the most part, to two elk herds in the southwest. Yukon biologists plan to expand their surveillance efforts to get a better idea of the geographic and host species distribution of winter ticks in the Yukon.

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Other Focal Points


References:

Ref. 1. Samuel W.M. 1989. Locations of moose in northwestern Canada with hair loss probably caused by the winter tick, Dermacentor albipictus (Acari: Ixodidae). J Wildl Dis 25: 436-439.

Ref. 2. DeIgiudice G.D., R.O. Peterson, and W.M. Samuel. 2007. Trends of Winter Nutritional Restriction, Ticks, and Numbers of Moose on Isle Royale. The Journal of Wildlife Management 61:895-903.