Deer: Wasting disease disaster

1. Sick in the brain
2. Prion eyes
3. Disease on the move
4. Effective eradication?
5.Deer gobble plants




Epidemic proportions
While the white-tailed deer was almost absent from much of the Midwest a century ago, the population is now at record levels. The notion that hunters will stay away -- all the better not to get TSE -- has some biologists worried. How would a sit-down strike by hunters affect the ecology of Midwestern wild lands?

Forest with fence down middle shows less hemlock on side that deer can reach.The fence down the center of picture keeps deer out. Compare the dense growth of hemlocks and other trees inside the fence (left) to the sparser vegetation outside the fence. Biologists use these "deer exclosures" to study Bambi's effects on the forest. © David Tenenbaum

The Why Files asked Donald Waller, professor of botany at University of Wisconsin-Madison, who has studied the effects of white-tails on native plants (see "The White-Tailed..." in the bibliography). He was nice enough to send us a letter, which we've printed with minimal editing.

Q: Why Files: What is the likely role of deer management -- hunting policies, feeding stations, game farms, and overpopulation -- in causing CWD?

A: Donald Waller: Our current outbreak of CWD represents a complex web of interacting factors, as the question implies. Hunting policies for years were designed to protect the herd and maintain moderate to high densities of deer. This set the kindling for an epidemic. Game farms provided the match by importing animals from the West where CWD was known to occur in elk. And feeding stations [used by citizens to attract deer for viewing or, illegally, hunting] may have fanned the flames of that initial spark by encouraging close contact between animals.

Q: What are the ecological effects of deer now? And how would they change if people lose their appetite for hunting in the face of CWD?

A: Deer have a complex and diverse set of effects on wild plant and animal communities. Most obviously and immediately, our chronically high deer densities have prevented many tree species (including hemlocks, northern white cedar, and oaks) from reproducing successfully. Deer eat seedlings of these species to the point that it has become difficult to regenerate these forest types in Wisconsin.

Less conspicuously, our research shows a broad set of impacts on herbaceous species (wildflowers), including many lilies that have become much scarcer over past decades. Deer also harbor a heartworm parasite and deer ticks. The heartworm can act as a brainworm to kill moose and elk and thus prevent re-establishment of those species. Deer ticks are the primary vector for Lyme disease, a human health threat. And CWD itself could spread to other livestock species and/or infect humans -- we don't know much about these impacts yet.

Man kneels to inspect plants on forest floor. Botanist Bil Alverson, in a 1990 photo, inspecting plant growth in a forest that's full of white-tail deer. © David Tenenbaum

These impacts would also likely increase with the spread of CWD to more of Wisconsin's deer herd. Hunter's are already becoming wary of eating venison, and more than a third say they don't feel like hunting if CWD is a problem in their area. This means that deer hunting is likely to decrease.

Aside from all the economic and social impacts of that on our state, it would mean that we would have even LESS of a capability for controlling deer densities. That's a problem, as deer are already far more abundant than they should be - they are far above "goal" density in most Deer Management Units, and I hear "out of control" more and more often. As hunters represent our primary means for controlling the herd, fewer hunters means less control and yet higher deer densities, enhancing the likelihood that this, and other epidemics, will ignite further.

Donald Waller
Professor of botany and environmental studies
University of Wisconsin-Madison

Confused by CWD jargon? Indulge in our TSE glossary.




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