Biology Reference
In-Depth Information
There is no physical conflict between moose and whitetails; the two species go their separate ways
and don't bother each other. Any effect that moose have on deer, then, real or imagined, must be related
to food supplies, and there are at least two reasons why this is rarely a problem.
First, although moose and deer feed on the same species of trees and shrubs, moose mainly browse
at a considerably higher level than deer. Second, summer browse isn't usually a problem; it's browse in
the wintering areas that's critical. As already noted, moose winter in small groups at elevations higher
than most deer wintering areas, so there's seldom competition between the two species for winter food.
There have been a few documented cases of competition for winter food between moose and whitetails,
but these are very uncommon.
Then why do deer populations often decline while moose numbers rise in the same area? The answer
lies in habitat change—but change caused by humans rather than moose. As previously described,
wholesale clearcutting has benefited moose greatly by creating a sea of browse, often called “moose
pastures.” Frequently these huge clearcuts destroy deer wintering areas by removing the mature soft-
wood stands so critical to whitetail survival in severe winters. Without the shelter of these softwoods,
deer flounder in the deep snow, and many perish, while the powerful, long-legged moose continue to
move freely. As a result of this major habitat change, moose thrive and deer decline.
Far from being driven out by moose, white-tailed deer can actually have a harmful effect on moose.
Enter the villain, a diminutive roundworm with the outsized name of
Parelaphostrongylus tenuis,
better
known as the brainworm. The interrelationship between deer, moose, and brainworm is complex, yet
sufficiently fascinating to be well worth exploring.
Brainworms, threadlike parasites less than four inches long, are found in the brain covering
(men-
inges)
of the majority of deer. However, deer seem unaffected by their presence. Eggs of this parasite
travel in the bloodstream to the lungs, where they develop into larvae. The larvae then move up to the
throat, where they're swallowed and eventually pass out of the deer in the feces.
This would be the end of the cycle—and the brainworm—if it weren't for snails and slugs. These
pick up the larvae from the deer feces, and the larvae then develop further inside their new host. Even-
tually the snail or slug, brainworm larvae and all, may be accidentally ingested by a browsing moose.
Once inside the moose, the larvae migrate to the spinal cord. There they mature into adult brain-
worms and travel to the brain. Then the parasites attack the brain itself, rather than living in the men-
inges, as they do in deer. The result is a condition known as “moose sickness,” which is nearly always
fatal.
Moose afflicted by this condition display a variety of symptoms. They may act very tame and leth-
argic. (No doubt this is the source of many of the “tame” moose that people foolishly try to pet.) Later
symptoms may include such things as lack of coordination, walking in circles, and even blindness. Fin-
ally the moose becomes paralyzed and dies.
Because deer are the ultimate source of brainworm infection in moose, a high population of deer can
inhibit moose numbers. When deer populations decline as the result of large-scale clearcutting, moose
