Moose Population Plummets – But Is It Really Due to Lyme Disease?

by lmatthews on November 12, 2013

ghost moose calf lyme disease ticks

Ghost moose: A moose calf with exposed skin after rubbing off ticks on bark.

Climate change, tick population explosions, and an evolutionary quirk are being blamed for the massive moose die-off that is happening across the northern US. According to wildlife experts at Northern Wilds, moose are testing positive for Lyme disease although are not displaying symptoms, which has prompted some confusion. Are the moose dying in vast numbers because of the infection or is something else going on? As we head towards Halloween, we take a look at the strange story of ghost moose.

Moose Mortality at 25% Each Year, But Why?

Minnesotan moose appear to be disappearing at an increasingly rapid rate, with one of the two main moose populations now standing at around 100 from 4000 in the early 1990s. Experts warn that the number of moose is declining by some 25% each year in the other main moose population, up from a figure of 8% and 12% mortality in previous years. A grant of $1 million has been awarded to allow for study of the animals with rangers fitting them with tracking collars to find out what is ailing the moose. When a moose’s heart stops the rangers can track the animal’s location and quickly recover the body for examination, providing much-needed clues as to cause of death. Moose are elusive animals and so it can be hard otherwise to find their carcasses before scavengers get to work.

Ghost Moose

One thing that has become more noticeable in recent years is the increase in moose with huge amounts of fur missing and this is thought to be due to the moose trying to remove ticks from their fur by rubbing against rough bark on trees. These moose are being referred to as ‘ghost moose’ because of their exposed white skin. This bare skin then affords the animals little protection from the elements and moose can’t regulate their body temperature, becoming exhausted and dying from exposure.

Perfectly illustrating what happens when climate change and evolutionary processes intersect, moose have tended to populate areas without ticks, meaning that they have not developed the ability to groom themselves and so knock off ticks as deer and other animals can. A wild moose can, therefore, quickly become riddled with the bloodsucking pests.


Moose Being Drained of Blood

While a couple of ticks won’t make a sizeable difference to the blood supply of a large animal like a moose, thousands ticks can suck a moose dry, causing death by anaemia, particularly in baby moose. As climate change means that warmer weather is spreading north, more ticks can survive for longer and reproduce more successfully. The winter ticks present in Minnesota are much more common than in the past, and the moose have not yet learnt to contend with the parasite.

Why Moose are Vulnerable

Unfortunately for the moose, their prime mating time when they are much more mobile coincides with a surge in the tick population, meaning that they are increasingly exposed to being bitten en masse. What’s more, the larva of these ticks tend to climb vegetation to reach a certain height which perfectly corresponds with a moose’s chest, and some 300,000 larva can then jump at any one time onto a moose that has the misfortune to brush past. Ticks are not the only things that the moose must contend with, however, as liver flukes and brain worms are also being blamed for declining moose populations.


Moose in BC

One study on the moose found in the Cariboo Mountains of British Columbia, Canada, determined that it may be the loss of habitat caused by the effects of pine bark beetles on trees that is responsible for the moose die-off. One unfortunate moose in Smithers, BC, wandered into a supermarket’s flower section starving and riddled with ticks before being shot and euthanised by wildlife officers.

100,000 Ticks on One Moose

Moose may also be dying from stress and heat exhaustion as they do not fare well in temperatures above 23 degrees fahrenheit in winter, using up energy to stay cool. With the longer winters, less snow, and an increase in winter ticks, moose are simply too exhausted to defend themselves against the invading tick army. In some cases, up to 100,000 ticks have been found feeding on a single moose.

Moose-Hunting in Minnesota and Montana

In Minnesota and Montana licences to hunt moose are now being issued in much lower numbers than in previous years with last year’s rate in Montana just 362, half of that in 1995. Of course, there are those that think that unregulated hunting of moose may also be affecting the population, in addition to the possibility of wolves attacking already weakened animals.

Moose and the Ecosystem

Even for those who don’t care particularly about moose dying in vast numbers, the importance of these animals to the wider ecosystem cannot be overstated. Their grazing of shrubbery, for example, creates habitat for nesting birds, while the animals themselves are a huge boon to tourism, creating some $115 million each year in business in Minnesota. In addition, the more ticks there are feeding on moose, the more likely it is that these ticks then make contact with humans, especially if moose wander into populated areas due to starvation, confusion, or an encroachment into their own habitat by development. However, these winter ticks are not thought to carry the strain of Lyme disease bacteria that can cause the infection in humans.

Is it Lyme Disease?

The Arrowhead moose in Minnesota are testing positive for Lyme disease but veterinarians have noted that the symptoms in dying moose are not consistent with Lyme Disease. However, symptoms appear to include abnormal behaviour, excessive grooming, reduced fear of humans, confusion, weight loss, poor wound healing, and lack of appetite, all of which may well be recognisable to human Lyme disease patients. As researchers struggle to work out exactly what is killing the moose they have at least coined a new term: ‘moose wasting disease.’

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