Footloose Bucks

young buck nestled at foot of tree
Charles Fergus

Young bucks leave their mothers when approximately one year old. Penn State biologists are conducting a trapping and monitoring program that's likely the largest study of deer dispersal ever undertaken.

When do young male deer break away from their mothers? How far do they wander? To answer those questions, Penn State wildlife biologists have begun "the largest study of deer dispersal ever undertaken," according to Ph.D. candidate Eric Long. He is supervised on the project by wildlife ecology professor Duane Diefenbach.

Deer are the main reason a million Pennsylvanians buy hunting licenses each year, hunters whose trips to deer camps and purchases of supplies and equipment generate major economic benefits in many rural areas.

And deer have a huge impact on the environment. With wolves and mountain lions gone from Penn's Woods, deer have become so plentiful that in many areas their feeding has created a distinct "browse line": the first four or so feet up from ground level, where trees' lower branches and replacement tree seedlings have all but vanished. Deer have also eliminated many forest-floor plants that provide food and habitats for songbirds, small mammals, and a host of other creatures from insects to amphibians.

It's like that in the heavily wooded mountains of eastern Centre County, one of two areas where Long and Diefenbach are working. A second research area lies a hundred miles west, near Kittanning in Armstrong County; there the rolling terrain is more agricultural, with mixed farm fields and woodlots. After two winters of work, the researchers have caught 296 juvenile bucks—called "button bucks" because of the small antler nubs that grow during their first year—as well as 32 adult bucks. Deer are nabbed mainly in corn-baited pens and beneath 70-by-70-foot nets suspended above fields. After blindfolding and sedating the captive deer, wildlife technicians attach transmitters on neck collars or clip them to the animals' ears. Teams of researchers then use radio-telemetry equipment to monitor the bucks' movements.

Preliminary observations suggest that most fawns stay with their mothers for about a year. There seem to be two main pulses of dispersal. Fewer than half of the young males strike out on their own in May and June, about the time when their mothers give birth to new fawns: in Centre County, these bucks moved an average of 4 miles; in Armstrong County, 7 miles. A second pulse takes place in autumn during the annual breeding season, or "rut," when the majority of the remaining yearlings dispersed in both areas.

"The movement of young bucks is not related to the quality of the habitat in the area where they were born," says Diefenbach. "We're seeing juvenile bucks leaving natal home ranges with good habitat and traveling to other areas of good habitat."

Some deer move from one valley to the next. Others go considerably farther. Says Long, "one buck in Armstrong county traveled more than 26 miles and swam the Allegheny River before establishing a new range." So far, the greatest movement in Centre County has been 16 miles.

Before new antler regulations went into effect in 2002, hunters were killing about 80 percent of one-year-old bucks, mainly during the two-week deer season in December. Many of those animals had by then grown single-point antlers, known as spikes, or forked antlers, although some yearling bucks in choice feeding areas, such as farmland, developed larger racks. The new rules limited hunters throughout most of the state, including Centre County, to shooting a buck only if it had three or more points on one of its two antlers; in Armstrong County, a buck had to have four points on one antler to be legal game. The regulations were designed to let bucks live longer and grow larger, increasing hunters' chances of bagging large trophy deer while allowing the fittest individuals to emerge and do most of the breeding. Simultaneously, the Game Commission allocated more permits to shoot antlerless deer, with the goal of reducing the overall size of the state's herd.

The buck study strongly suggests that the new antler restrictions helped protect many yearlings during 2002. "Of the bucks with transmitters," Long says, "only 8 percent of those killed by hunters did not meet the minimum antler requirements." The tags and transmitters are small and unobtrusive: "We don't want to bias hunter behavior to either shoot or refrain from shooting what's obviously a research animal." A message printed on the devices urges successful hunters to contact the Game Commission; the researchers find out when and where the deer was killed, and collect information on body and antler size.

Hunting is the main tool that wildlife managers can use to try to keep the deer population in check. Says Long, "From a management perspective, we've shown that you can't manage for bucks in a small area, because yearling males are likely to move out of that area and end up miles away." "We anticipated the type of dispersal that we've seen so far," adds Diefenbach. "But probably what surprised me the most was the deer densities, even after hunting season. We could go into a several-square-mile area where over 100 antlerless deer had been legally removed by hunting just a month earlier, and we could still trap a dozen young male deer."

This project is a combined effort between the U.S. Geological Survey, the Pennsylvania Cooperative Fish and Wildlife Research Unit at Penn State, and the Pennsylvania Game Commission; other collaborators include the Audubon Society and the Pennsylvania Department of Conservation and Natural Resources. Duane Diefenbach, Ph.D., is adjunct assistant professor of wildlife ecology and an employee of the U.S. Geological Survey; he can be contacted at 113 Merkle Bldg, University Park, PA 814-865-4511; drd11@psu.edu. Eric Long is a doctoral candidate in wildlife and fisheries science in the School of Forest Resources, 107 Merkle, 865-3972; esl140@psu.edu. Bret Wallingford, a Pennsylvania Game Commission biologist and a Ph.D. candidate at Penn State, is supervisor for the Centre County trapping area. Gary Alt, Ph.D., heads the gamIntimatee Commission's deer management program and plans to use the study results to further that effort.

Last Updated May 02, 2005