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After three years of “mugging deer,” Colorado State University Prof. Tom Hobbs has reached some preliminary conclusions from his study of chronic wasting disease in local deer populations.
“The presence of CWD in an area will limit the population of deer, but will not cause that population to go into decline. Next year we will be able to report a lot more,” Hobbs said, referring to the completion of the study with more data.
In an extensive epidemiological study funded by the National Science Foundation, Hobbs and his team of CSU graduate students have captured, studied and released more than 450 deer, mostly females. Many of these are recaptures of deer studied in previous years.
Each deer is captured by helicopter net-gunning and quickly transported to an improvised medical site where many biological samples are taken. The deer are then equipped with a GPS device and a radio transmitter on a collar, allowing the students to track the animals, and investigate the cause of death whenever possible.
Overall, they have experienced a 3 percent rate of mortality from capture-induced trauma, and found that in 2012 the rate went up to over 6 percent. Hobbs attributes this partially to the winter drought and partly to the use of a new crew of helicopter “muggers.”
CWD is a prion disease spread by feces, urine and saliva. It is extremely persistent in the environment despite temperature fluctuations and UV rays. In this latest year they have discovered what appears to be a relationship to clay soils. That is, the prion seems to have the ability to protect itself by binding with clay. Areas that have higher levels of clay soil have a higher prevalence of CWD in the local deer population.
In general, a healthy female deer has a 5 percent chance of contracting the disease in any given year. After that, the mortality rate is about 50 percent per year. The bucks are less fortunate; a male deer has a 20 percent chance of infection in any given year. Some deer will die within one year of contracting the disease, but most deaths will occur in year two or three. The average age of female deer in the study is six years.
In the genetics portion of their studies, the researchers have identified two genetic strains of the disease. One strain produces a more mild form of the disease.
Hobbs points out that an infected animal cannot be identified visually. That is, even if they look sick one cannot be sure they have CWD. Oddly, though, their study of animals that die by predation reveals that mountain lions eat a higher share of diseased deer than chance would dictate. Maybe the lions know something, or know what signs to look for.
Known as the Laramie Foothills Mule Deer Project, the study has focused on the area along U.S. 287 from Owl Canyon to the Wyoming border. Most deer captures occurred east of the highway. The researchers have noted that some young females stay year-round within as little as 2 square kilometers of their home range, while some males range throughout the area and roam well into Wyoming before returning home.
The study has important implications for wildlife management decisions. It is doubtful that culling operations, such as one previously conducted by Colorado officials, will ever be used again.
Residents of the area who spot a radio-collared deer are encouraged to report the sighting on the team’s web site at http://www.nrel.colostate.edu/projects/modelingCWD/. These site also contains full information on the study and a video of the helicopter operations.