White-tailed deer, it seems, are homebodies.
That is the upshot of an intensive study of the traveling behaviors of 173 radio-collared white-tailed deer in south central Wisconsin. The new results, which surprised researchers by revealing how little deer move about the landscape, are important because they may help researchers and wildlife managers better understand how chronic wasting disease (CWD) spreads.
“They are using small home ranges and not traveling long distances,” says Nancy Mathews, a wildlife biologist at UW-Madison’s Gaylord Nelson Institute for Environmental Studies. “The only dispersers are young males, and they only go five to seven miles before setting up a new home range.”
The results of the study are both encouraging and confounding, says Mathews. On the one hand, knowing more about how deer move about the landscape may help scientists home in on how CWD spreads among wild deer. On the other hand, the findings contradict the idea that deer are great travelers, moving long distances and possibly taking the disease with them.
“Based on the behavior of these deer, we cannot account for the distribution of CWD on the landscape,” says Mathews who, with her students, conducted intensive, year-round telemetric studies of deer fitted with radio transmitters for the past two-and-one-half years.
“Adult does and their female fawns establish home ranges in the same location where they were born and stay there for their entire life,” Mathews explains. “Once young bucks have dispersed, they too establish small home ranges and rarely leave them, even during the rut. Deer are not moving long distances, except for young bucks.”
First identified in Wisconsin deer in 2001, CWD is a fatal brain disease found in deer and elk. It is transmitted through an agent called a prion, an abnormal protein that causes brain damage and, subsequently, the characteristic symptoms of the diseases: staggering, shaking, and excessive salivation, thirst and urination. There is no cure or treatment.
Nor do scientists know how the disease is transmitted from one animal to another. Understanding how deer use the landscape may help answer that question, says Mathews, by providing insight into the movement and behaviors of animals in an area where the disease has gained a toehold.
Scientists have generally assumed that deer transmit the infectious prions among themselves through direct contact. One alternate hypothesis is that areas where deer congregate – mineral licks, for example – may become hotspots for the disease. In those areas deer frequently lick the soil. They leave behind saliva that may also contain prions. Whether that behavior and the consumption of contaminated soil is at all associated with transmission is speculative, Mathews emphasizes, “but we can’t rule out deer congregating around hot spots as another means of transmission.”
In their new study, what the Wisconsin scientists found to their surprise was that deer in south central Wisconsin use very small home ranges, about one-half square mile in size. These ranges tended to be smaller in areas with a higher amount of forest edge. It may be, she says, that deer in the area have an abundance of high quality resources – food, water, mates – and do not need to travel long distances to find those resources on the south central Wisconsin landscape. The study also shows that the size of deer home ranges was not related to the number of deer harvested or deer density.
In general, according to the study’s results, females and adult males stay close to home. Young bucks travel on average five to seven miles from their home range to establish new territories.
Young deer of both sexes, says Mathews, do tend to go on “exploratory” excursions lasting for less than a week, but they eventually return to their home range and family groups.
“They always come back and the females never leave, so it is unlikely they are contributing to large-scale transmission of CWD,” says Mathews. “A big key for understanding transmission is young bucks. They are the only segment of the population that makes permanent movement out of their home ranges.”
Mathews also found that even after one CWD positive doe was found in a social group of females, other females in the group continue to test negative. She says this suggests that CWD is not spreading rapidly among females within social groups.
The study was initiated in January of 2003 and results through June of 2005 constitute the data in Mathews and Skuldt’s new report. Deer were fitted with radio collars and tracked intensively with each animal’s range on the landscape being determined a minimum of 37 times a season or 148 times a year. Deer were located at all times of the day with the exception of midnight to 3 a.m.