By Dr. Christopher S. Rosenberry, Wildlife Biometrician -
A buck quietly walks past a hunter as the early rays of sunlight mark the opening of another season. The hunter does not shoot, however, because this particular buck is a button buck. The little "buttons" on his head came nowhere close to meeting the 3-inch minimum antler length.
Many hunters have experienced such a situation. If only the buck had been a year older. But all is not lost, the hunter thinks, because the young deer will be in the same area when the next buck season rolls around.
Actually, though, what are the chances a hunter will see the same button buck a year later? This is the question I intend to answer over the course of this 2-part series on the lives of bucks from buttons to antlers. This first part will cover the movements and the social environment of young bucks, and what causes them to do what they do. The second part will incorporate information on deer behavior into applications landowners and others might consider for managing deer on areas of varying size.
A timeline and some definitions of terms will help clarify important factors in the life of young bucks. In Pennsylvania, most fawns are born in late May or early June. During buck season, most male fawns, or button bucks, will be about six months old. When the buck reaches its first birthday, it will begin to grow its first set of antlers. When buck season rolls around again, the young buck will be about 18 months old and have its first set of antlers.
For the purposes of this article, "yearling buck" will refer to a buck between 7 and 18 months of age. "Natal range" describes the area where a fawn is born. Most young bucks will still be on their natal range at six months of age. "Dispersal" refers to the movements of yearling bucks away from their natal ranges.
What is the chance of seeing the same button buck a year later?
Generally speaking, the chances are not good. First, a button buck must survive the hunting seasons. In Pennsylvania, 25 percent of the antlerless deer harvest consists of button bucks. Second, a button buck that does survive the hunting seasons will probably be miles away from that location by the time the next buck season arrives. Research conducted across the country indicates 50 to 80 percent of young bucks will disperse an average of about five miles from their natal ranges. Dispersal distances of 30 to 100 miles have been reported, but such long distance movements are less common. Although little is known about exact movements during dispersal, dispersing yearling bucks have been known to swim across big rivers and other large bodies of water.
When do yearling bucks disperse?
Although young bucks may disperse at any time, most dispersal occurs during two periods: spring fawning season (May-June) and fall breeding season (September-November) (Figure 1). From birth to about one year of age, a buck lives with his mother and siblings. As the fawning season approaches, a yearling buck's mother reduces her movements, becomes less tolerant of him and other deer, and prepares to give birth to new fawns. Some yearling bucks will disperse during this time of family group separation.
In many areas, dispersal occurs more frequently during fall breeding season. In Maryland, for example, fall dispersal began in mid-September and concluded in early November, prior to the peak of the breeding season. Once breeding peaked, in mid-November, dispersal movements stopped.
Following dispersal, the area where a yearling buck settles is likely to be his home range for life. Studies from many areas report this common pattern of dispersal. A yearling buck seen during buck season is probably going to be in the same area for the rest of his life.
Why do yearling bucks disperse?
Social pressures probably influence dispersal of yearling bucks. Competition from other bucks and maternal aggression are two prominent ideas to explain dispersal. Early deer research noted dispersal during the breeding season and speculated that aggressive competition from older bucks caused yearling bucks to disperse. A more recent study investigated another possibility - a yearling buck's mother. In this study, yearling bucks maturing with their mothers were more likely to disperse than yearling bucks that were orphaned before one year of age. From these results, it was concluded that adult does cause dispersal of yearling bucks, and that orphaning a button buck reduces his chance of dispersal. These results have been incorporated into quality deer management strategies where hunters are encouraged to harvest adult does. By harvesting more adult does, it's expected that more young bucks will be orphaned and, therefore, stay in the area.
Unfortunately, reducing dispersal may not be as simple as increasing adult doe harvests.
In a study I worked on, competition with other yearling bucks appeared to influence dispersal more than aggression from adult does. In this study, yearling bucks were captured and marked with solar-powered ear tag transmitters and color streamers. The combination of transmitters and color streamers permitted visual identification of individual bucks and monitoring of long distance movements. Social behavior of yearling bucks was observed throughout summer and fall. After fall dispersal, behavior of yearling bucks that dispersed was compared to behavior of those that did not. Behavioral comparisons suggested that dispersing yearling bucks appeared more subordinate in competitive interactions (antler sparring) with other bucks than yearling bucks that did not disperse.
There was no evidence that adult females influenced dispersal of yearling bucks. Thus, in this study, it appeared that competition with other yearling males influenced dispersal.
Social behavior of white-tailed deer varies in different areas, and the two most investigated causes of dispersal (male competition and adult female aggression) are based on social behavior. Thus, it is likely that causes of dispersal could vary according to changes in social structure and behavior of different deer populations. Although current research provides insights into the social environment of dispersing yearling bucks, it has not identified a universal cause of yearling buck dispersal.
Dispersal is a significant part of the lives of most yearling bucks. Next month I'll discuss the impacts of dispersal on deer management decisions on areas from hundreds of acres to a hundred thousand acres or more. Below is a summary of main points of dispersal:
Chances of seeing a yearling buck a year later are not high because some will be taken during deer seasons, and of those that survive, most will disperse miles from their natal range by the next deer season.
Dispersal is likely to occur during spring fawning and fall breeding seasons, when yearling bucks experience social changes.
The reason why bucks disperse is not likely to be a single factor. Studies with conflicting results emphasize that deer behave differently in different areas.
Once a yearling buck has chosen an area to live after dispersal, he will probably remain in that area for the rest of his life.