Wildlife biologists in northern Maine have documented unusually high mortality among young moose this year, with winter ticks identified as the primary cause. The deaths have renewed attention on how warming winters are affecting the relationship between parasites and their hosts.

Winter ticks, unlike deer ticks, do not transmit disease. But they attach to moose in large numbers and feed on their blood throughout the colder months. According to the Maine Department of Inland Fisheries and Wildlife, this year’s calf mortality was the highest recorded since tracking surveys began more than eight years ago.

The research focused on Wildlife Management District 4, a remote area northwest of Moosehead Lake. Biologists captured 70 moose calves born the previous spring and fitted them with GPS collars. By late winter, 60 of those calves had died, a mortality rate of roughly 86 percent. The deaths were attributed to a combination of blood loss, nutritional exhaustion, and the effects of cold exposure after the animals lost much of their insulating fur.

Necropsies performed on the carcasses found tens of thousands of ticks on individual animals. One adult cow examined by the team carried an estimated 90,000 ticks. The animal had died while pregnant. Examination of bone marrow showed that the moose had depleted nearly all of their fat reserves, and several organs showed signs of severe anemia.

The winter tick, known scientifically as Dermacentor albipictus, differs from many other tick species in that it completes its entire life cycle on a single host. Larvae cluster on vegetation in late summer and attach to passing moose. Once attached, they feed for several months, going through multiple growth stages. Each adult female tick consumes roughly one milliliter of blood. On a heavily infested moose, the cumulative loss can be substantial.

The feeding causes persistent irritation, which leads moose to scratch and rub against trees. This behavior damages their coats, which are normally highly effective at retaining heat. With fur compromised, the animals become more vulnerable to cold, and the time spent grooming reduces feeding. Researchers described the condition as a combination of physical stress and exhaustion rather than a single cause of death.

Observations of unusually pale moose in the region, sometimes referred to locally as “ghost moose,” are consistent with animals that have scratched away much of their dark outer coat. The exposed undercoat is lighter in color, which makes the animals appear white from a distance.

State moose biologist Lee Kantar led the investigation. His team documented the pattern across multiple carcasses and concluded that heavy tick infestation was the central factor in the deaths. The findings were consistent with earlier research linking winter tick abundance to warmer fall temperatures. Shorter, milder winters mean snow arrives later and ticks have a longer window to find hosts. Climate data from the National Oceanic and Atmospheric Administration shows that average temperatures in Maine have risen by roughly three degrees Fahrenheit since 1895.

The tick population is also affected by moose density. In the decades following extensive logging in the region, regenerating forest created abundant food for moose, and their numbers increased sharply. Higher animal density gives ticks more opportunities to find hosts. Some areas reached roughly 40 moose per ten square miles, a level that parasites can easily exploit.

Moose are considered evolutionarily naïve in this context. They migrated into North America relatively recently in evolutionary terms and have not developed the grooming behavior that other species, such as white-tailed deer, use to remove ticks quickly. As a result, a single moose can carry far more parasites than a deer of similar size.

In 2022, the state launched a management experiment in District 4, dividing the area into two zones. In one zone, hunting permits were increased, particularly for cows and calves, with the goal of reducing moose density and interrupting the tick cycle. Early results showed lower tick counts on surviving animals and improved calf survival in areas where density was reduced. The approach is not without controversy, since it requires deliberately reducing the moose population in the short term.

The situation in Maine illustrates how small shifts in climate and land use can alter the balance between wildlife and parasites. It also raises questions about how wildlife managers can respond when natural cycles become weighted against a species. The long-term outlook for moose in the region will depend on whether interventions can keep pace with continued environmental change.

The findings serve as a case study in the challenges of managing large animals in ecosystems undergoing change. For biologists, the deaths are not solely a local issue. They illustrate the wider effects of warmer winters on species that have evolved for colder conditions. The moose population in northern Maine remains under observation, and the coming winters will determine whether the current management strategy is sufficient.