Deadly handouts, dependent deer

by Susan Tweit

My neighbor feeds deer. He says he's actually feeding birds so that his disabled wife and her pre-teen daughter can enjoy watching them. But when he tosses chunks of stale white bread out in his front yard, it's not just crows, ravens and starlings that come to call. (And why anyone would think it was a good idea to feed any wildlife a diet known to cause diabetes, heart disease, and obesity in humans is a whole other question.)

At dusk, the street fills with mule deer, the twin bucks, each with one twisted antler, born to a scrawny mom last year; the runty triplets she had the year before, who still hang together; mom herself, looking pregnant again, one bad eye oozing; and the gimp with one back leg jutting out at an odd angle after what must have been a bad break.

Some might think this neighbor is a rescuer of sorts for giving this motley crew of deer a handout.

I think he's handing them a slow death sentence. Why? In three words: Chronic Wasting Disease, or CWD.

This mysterious brain-wasting disease, which is unique to deer and elk, was first discovered in Colorado State University's wildlife research pens in the 1960s. It has what researchers call a "density-dependent" component: The level of infection in adult animals fluctuates dramatically, from as low as 0.5 percent to over 90 percent, depending on herd density. (The higher end is generally only found in game farms.)

The more crowded the living conditions, the more chance of a chronic wasting disease epidemic. Researchers think that's because the disease is transmitted from animal to animal through contact with saliva and blood, perhaps as they nuzzle or groom one another.

Chronic wasting disease is named for what it does: Infected deer and elk lose weight, become listless and eventually waste to death. A characteristic sponge-like pattern of holes develops in infected animals' brains as protein molecules degrade for unknown reasons into misshapen "prions," damaging forms that destroy the cells and alter other proteins, thus spreading the disease. There is no cure; the disease is always fatal.

I first learned about chronic wasting disease while researching an article on Wyoming's National Elk Refuge, home to the nation's largest concentration of wintering elk. Some 6,000 to 8,000 elk, blocked from migrating downhill out of Jackson Hole in winter, crowd into feeding grounds right at the edge of Jackson. The wintering throngs are a prime tourist attraction — and, many biologists believe, a time bomb for a chronic wasting disease epidemic.

I didn't think about chronic wasting disease in relation to the scruffy mule deer herd my neighbor feeds in our small south-central Colorado city until I stumbled across a study from Boulder, where the question of how to manage the burgeoning urban mule deer herd had been contentious for decades.

"Had been," that is, before chronic wasting disease came to town. Boulder's urban deer herd, nourished by rose bushes, tulips, apple trees and other such garden delights, had gotten pretty dense by 1985, when CWD was first detected in the Table Mesa herd on the southwest side of town.

Over the next 30 years, researchers say, the number of adult deer, defined as deer older than 2 years old, in that herd dropped by 45 percent, an astonishing decrease for a herd protected from human hunting. Researchers found almost one in three adult mule deer in the herd infected with chronic wasting disease. In some age groups, infection rates were as high as 80 percent.

Infected mule deer adults were more likely to be killed in deer-vehicle collisions or by mountain lions. Researchers speculate that mountain lions somehow knew to target infected deer, even before the disease’s symptoms were obvious.

And, yes, mountain lions come through my small town periodically, usually young ones out scouting new territory and looking for easy prey.

So it's not far-fetched to imagine that while my deer-feeding neighbor may think he's simply luring wildlife into his small yard for his wife and stepdaughter to enjoy from their chairs on the front porch, what he's actually doing is setting the stage for the arrival of chronic wasting disease with all its ugly implications –- perhaps even luring mountain lions right into our downtown neighborhood to dine at the al fresco deer-bar.

However you look at those chunks of stale bread littering his front yard, they don't paint a pretty picture.

Susan Tweit is a contributor to Writers on the Range, a service of High Country News (hcn.org). She is the author of numerous books and lives in Salida, Colorado.

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