October 18, 2011
Most does breed for the first time when they are 18 months old (yearlings) and produce a single fawn. From then on, they typically produce twins. However, access to abundant, high quality nutrition can greatly influence fawn production. For example, in the most productive habitats, up to half of all female fawns breed their first year when they are only 6 to 8 months old. Additionally, yearling does often produce twins, and mature does occasionally even produce triplets. Given the above, it’s easy to see why whitetails are one of the most widespread and prolific big game animals in the world.
While today’s deer hunter is far more knowledgeable about whitetail biology and behavior than ever before, two common myths surrounding does and fawns remain. First, many hunters believe that once a doe reaches a certain age she becomes “barren” and stops producing fawns. During my tenure as a graduate student and a Deer Research Coordinator at The University of Georgia I worked with dozens of mature whitetail does including several ranging from 10 to 17 years of age. All remained productive until their deaths. Numerous deer managers and researchers have reported similar results.
The second myth commonly repeated by hunters is that fawns don’t have any scent, at least during their first month of life. While it is true that fawns have less scent than adults, they do have a scent. Many hunters are surprised to learn that bucks are not the only deer in the herd that rub-urinate on their tarsal glands, and that this behavior is not confined to the breeding season. Does and even day-old fawns rub-urinate daily on their tarsals throughout the year. This activity is what gives each deer its individual scent. In fact, this scent is the primary mechanism by which does identify their fawns.
In recent years, studies involving modern DNA techniques have shed light on many previously unknown aspects of whitetail reproduction including whether a set of twin fawns can have different fathers (multiple paternity) and which bucks in a given herd are responsible for siring the most fawns.
Studies in Michigan and Texas have now confirmed that multiple paternity in whitetails is not only possible, but it actually is fairly common. In both studies, approximately 25 percent of all sets of twins had different sires. One theory regarding how this occurs in the wild is that a dominant buck displaces a lower-ranking buck that was breeding and guarding an estrous doe. These studies confirm that a set of twin fawns is not necessarily a set of “twin” fawns. This also could help explain differences in body size, growth rate, and antler size at maturity of two seemingly “twin” male fawns.
Another recent study led by Dr. Randy DeYoung, now at Texas A&M Kingsville, used DNA techniques to determine which bucks in a given deer herd were responsible for breeding which does and siring which fawns. The study was conducted at locations in three states – Mississippi, Oklahoma, and Texas – and it revealed some very interesting information. First, the results shattered the myth that a small number of mature, large-antlered bucks dominate the breeding duties in a given area, thereby relegating younger, smaller-antlered bucks to watching from the sidelines. At all three study sites, even one on the famed King Ranch where more than half of all bucks were 3.5 years old or older, approximately one-third of all fawns were sired by 1.5- and 2.5-year-old bucks. The study did reveal that, on average, individual mature bucks sired more fawns than younger bucks, but they didn’t monopolize this activity.
Another major finding was that fewer fawns were being recruited from individual bucks than previously believed. I’ve heard hunters proclaim that a mature buck can breed 20 to 30 does each year, thereby producing 40 or more fawns annually. While this may be possible in a pen, studies with wild deer indicate that far fewer fawns survive and are recruited into the population. Nevertheless, this logic has led some hunters to consider purchasing large-antlered “breeder bucks” to improve the genetics of their deer herds (though illegal in most states). In addition, many hunters involved in management programs are becoming concerned about removing mature, poor-antlered “cull bucks” from their herds because of the perceived negative genetic impacts if they are allowed to breed. According to Dr. DeYoung’s research, neither approach is likely to impact genetics in free-ranging whitetail herds because the average buck in his study sired less than three fawns that survived and were recruited into the herd during their life. In fact, the top breeder sired only 13 fawns over a six-year period.
When you examine the whitetail’s breeding strategy, these findings begin to make sense. Unlike a herding deer species like elk, where one male gathers and defends a group of females, whitetails work solo. They must spend considerable time locating, courting, breeding and defending a single receptive doe. Once a receptive doe is located, the tending and mating process can take up to 48 hours and it greatly limits the number of potential breeding opportunities, especially in deer herds with short, compact ruts. One unexpected finding from the study was that nearly 60 percent of all bucks, even some mature bucks with large antlers, did not sire any fawns that survived to be recruited during the 11-year study. It is not known whether these bucks did not participate or if their offspring were simply unlucky and did not survive. Unquestionably, we still have much to learn.
For hunters, the most important take-home message from this article relates to genetics. These and other studies confirm that whitetail fawns are the product of a highly evolved breeding strategy in which many bucks participate and compete for mates, though none completely dominate. This is a good news / bad news story for hunters. The good news is that it is very difficult to genetically “damage” a deer herd through unselective harvest because so many individual bucks (and does) are contributing from a genetic standpoint. However, the bad news is that it is equally difficult to improve genetics through protection of “superior” bucks and/or culling of “inferior” bucks – at least in free-ranging herds. In simple terms, don’t fret over genetics. Instead, focus on what research has repeatedly demonstrated that you can impact – a herd’s sex ratio, buck age structure, and habitat quality. If you manage these variables, Mother Nature will do the rest and bless you with a healthy fawn crop, a quality deer herd and great hunting experiences.
Brian Murphy is an avid hunter, wildlife biologist and CEO of the Quality Deer Management Association (www.QDMA.com). He has worked exclusively in deer research and management for 25 years during which he has presented more than 600 lectures and authored more than 125 popular and scientific articles, book chapters and other educational materials designed for deer hunters and managers.