by Hannah Staab
Over the past few decades, warmer winters have been associated with major declines in the moose population. These massive and majestic animals are dying across the U.S.—from Maine, New Hampshire and Vermont to Michigan and Minnesota—as well as throughout Canada. Twenty years ago, for example, two separate moose populations roamed Minnesota, but since the 1990’s one of the moose populations has essentially vanished, plummeting from 4,000 to fewer than 100. The other moose population in Minnesota has declined from 8,000 to fewer than 3,000.
What are the reasons for this decline? Among other factors, warmer winters have caused spikes in the winter tick population. Many of the moose in the areas experiencing population decline are seen covered in Dermacentor ticks— sometimes as many as 100,000 ticks. The insidious pests attach themselves to the moose and feast on their blood, leading to anemia. The tick-infested animals are called “ghost moose” because in an attempt to dislodge the ticks they scratch, bite, and rub at their fur, exposing a pale undercoat and bare skin. If the moose loses too much of its fur, it can lead to hypothermia, reduced fat stores, and a compromised immune system.
Moose are not the only large mammals that ticks attach themselves to, so it is important to consider why tick infestations have such severe consequences on moose compared to other animals. For example, deer experience tick attachment to their fur, and yet they do not experience the same deadly symptoms as moose. It has been suggested that deer cope with ticks more efficiently because deer have lived among ticks for a longer period of time, and therefore have adapted grooming strategies that effectively remove ticks. On the other hand, moose habitats have only been exposed to ticks recently, leaving moose unprepared to handle ticks and their associated damage.
Moose habitats are being exposed to an increasing number of ticks due to the effects of climate change. Climate change is allowing more ticks to survive the warmer winters, and expand their range into more northern territories. Ticks attach to moose in the fall, remain dormant until January or February, feed on the moose until March or April, and then drop off. With warmer and shorter winters, more ticks are able to remain attached to the moose throughout the winter, increasing blood and hair loss. Moose are also most likely to be found dead in March or April, after the most tick–related damage has been done.
Concomitantly, Canada, a country that was never previously vulnerable to ticks and their diseases, is seeing a rising number of Lyme disease cases in humans and animals. Regions like Canada that are facing their first exposure to ticks are both less aware of, and less equipped to handle the health hazards that ticks bring to a habitat, and therefore are more heavily affected.
In addition, moose are often co-infected by brainworm, a worm parasite that is associated with severe neurological illness. The cumulative stress imposed by brainworm and tick infestation, especially for calves, may be overwhelming.
It is important that we remain aware of the tick impact on moose. Hopefully, with more research and information, climate change mitigation, and conservation efforts, we will preserve and perhaps restore populations of this iconic symbol of the American wilderness.
For more on Lyme disease and climate change, click here.
