Moore, the Grand Portage biologist, noted that deer, while major carriers of brain worm and flukes, are not affected by the diseases. Rather, they aid in their distribution by dropping larvae-laden feces throughout the forest. The larvae in the feces are absorbed by snails and slugs, which attach themselves to plants and are ingested by grazing moose.
While not always fatal to moose, brain worm and flukes can have serious consequences on their well-being. Brain-worm-infested moose, for example, often show weakness in their hindquarters, have difficulty standing and turning their heads, and experience lethargy, blindness and even aggression.
The transmission cycle for liver flukes is similar, though it originates in a deer's liver and is spread by eggs excreted in feces and absorbed by an aquatic variety of snail. The fluke causes liver fibrosis in moose. While not fatal, it can weaken the animals, making them more vulnerable to other threats, including predators.
Ron Moen, a biologist at the University of Minnesota, Duluth, and an associate in the school's Natural Resources Research Institute, said the general consensus among scientists is that moose are taking a beating from ticks, brain worm and liver flukes. But individually or in tandem, the parasites may not be enough to cause such extensive mortality.
Increasingly, however, an additional factor is coming into play -- heat stress.
Just as a tick-infested moose that rubs off all its fur in February will die of cold exposure, the same animal is equally threatened in August by 70-degree heat, scientists say. Even a balmy January, when temperatures climb into the 20s and 30s, can trigger behavioral changes in moose.
As ruminants, moose have a complicated digestion system that affects their ability to self-cool, and their internal thermostats are triggered with even the smallest temperature shifts.
So when temperatures creep upward in spring, moose immediately begin to feel the effects, scientists say, increasing activities that cool their bodies -- like wading in lakes or lying in alder swamps -- while cutting out heat-producing activities like walking and eating.
No 'prescription' for rescue
Lenarz, the retired DNR scientist, said such behaviors can increase moose's vulnerability to other threats, especially if warm conditions persist into the fall, when the animals need to be building fat stores to maintain winter warmth and provide extra calories when foraging plants are buried under snow.
In fact, recent studies show the strongest correlation between moose mortality and warming temperatures in late January, when winter food supplies are running out, and again during the late spring months, when temperatures can rise quickly before moose have shed their winter coats.
Yet even as the evidence points strongly toward a climate-induced mortality, the state of Minnesota remains largely without policy solutions.
In December, the state released its "Minnesota Moose Research and Management Plan," the most extensive report to date on the status of the state's moose, threats to their well-being and prospects for recovery.
The report draws upon the latest scientific information about factors affecting moose. The 18-member brain trust behind the report made several recommendations to stem the population slide, but offered no solution.
In summary, the report states, "there is no cookbook or prescription for reversing a declining moose population in Minnesota. The issue is decidedly complex, and the research needed to answer critical questions will take time and will be very expensive."
But the evidence is mounting against climate change as the North Woods shift from colder to warmer, from boreal to temperate, from moose-friendly to moose-intolerant.