As female deer wander, fatal disease goes with them

(Credit: Jacob Enos/Flickr)

New research looks at dispersal, the permanent movement of juvenile white-tailed deer away from where they were born.

The study finds that fewer female white-tailed deer disperse than males, but when they do, they typically travel more than twice as far, taking much more convoluted paths and covering larger areas.

The findings could be significant, especially in states where chronic wasting disease infects wild, free-ranging deer, wildlife experts say.

“Dispersal of female deer is density dependent, meaning that higher deer densities lead to greater dispersal rates,” says Duane Diefenbach, adjunct professor of wildlife ecology at Penn State. “Therefore, reducing deer density will reduce female dispersal rates—and likely will reduce disease spread.

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“Containing the spread of chronic wasting disease is going to be difficult when female deer disperse. Although not as many females disperse in Pennsylvania—8 to 24 percent of females versus 50 to 75 percent of males—there end up being more of them, because they live longer than males and they disperse an average of 11 miles compared to 5 miles for males.”

Chronic wasting disease

Commonly referred to as CWD, chronic wasting disease affects the nervous system of deer and elk and is always fatal. Wildlife managers are scrambling to find a way to slow or stop the spread of the disease, which has been discovered in free-ranging and captive populations of deer and elk in 23 US states and two Canadian provinces.

Dispersal is an important behavior because it affects the rate at which genetic traits are transferred through the population, can influence population growth, and can spread disease, Diefenbach says.

Wildlife biologists believe that dispersal, from an evolutionary perspective, can benefit individuals by reducing inbreeding and competition for mates and local resources. Juvenile white-tailed deer usually are “motivated” to disperse by social cues, such as aggressive behavior directed toward them by older, socially dominant does or maternal abandonment.

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Documenting and understanding deer-dispersal behavior and identifying factors that influence that behavior are important to understand the basic ecology of the species and to provide critical information for its conservation and management.

277 radio collars

For the study, published in the Journal of Wildlife Management, researchers fitted 277 juvenile female deer in Pennsylvania with radio collars.

  • Dispersal occurs at one year of age, coinciding with the fawning season.
  • Dispersal paths generally are nonlinear.
  • Dispersal takes on average two days but can take weeks.
  • Roads, rivers, and human development cause females to change direction and sometimes inhibit dispersal.
  • About 50 percent of yearling females travel several miles from where they are born, even if they don’t ultimately disperse.

One particular GPS-collared doe stood out, says lead researcher Clayton Lutz.

“On May 25, she left her natal home range for good, and she kept going for 55 days and 10 hours. She traveled 160 miles, crossed Interstate 80 twice, and crossed three major rivers four times. Despite all of this effort, she did not end up that far from home—only about 20 miles.”

This deer is a great example of how complex dispersal behavior can be and how it makes controlling disease spread so difficult, Lutz says. When it comes to females, biologists can’t predict the direction they will travel. Also, while roads and rivers stop some deer from dispersing farther, they don’t stop all of them.

Beyond disease control, knowledge of female dispersal also is important for localized management of deer population densities, says Christopher Rosenberry, chief of the Game Commission’s deer and elk section. Managers increasingly are looking for methods to control deer densities in areas closed to hunting, such as parks and areas of suburban development.

“For any population-control method to be effective, it must consider the effect of immigration from dispersing females on the target population.”

The Pennsylvania Game Commission and the US Geological Survey supported this work.

Source: Penn State