Who's Doing the Breeding?
Breeding success of individual male white-tailed deer greatly interests deer managers. Which bucks are successfully breeding has significant implications on deer management in general and buck harvest strategies in particular. At the Noble Research Institute Wildlife Unit (NFWU), we are in the process of addressing the "breeding success" question in a collaborative project with researchers at Mississippi State University, Texas A&M University, and the King Ranch, Inc. The project is not completed, but the preliminary results are very interesting.
Conventional wisdom, based on very limited information, often assumes that a few mature bucks dominate breeding and that young bucks, particularly yearlings, do little, if any, breeding when some mature bucks are present in the population. In spite of limited information, some buck harvest strategies advocate protecting large-antlered bucks as "breeder" bucks. Other strategies include introducing "superior" bucks in an effort to boost overall antler quality by impacting the population gene pool. These strategies, however, are valid only if the effective male breeding population is small and predictable.
Research in other species has shown that male breeding success may vary among populations depending on population sex ratio and male age structure. A variety of management strategies are used to manage white-tailed deer across their range, resulting in very diverse populations with respect to sex ratios and age structures. To address this variance, we are documenting and evaluating male breeding success in three discrete populations with different population parameters. The population on the Noxubee National Wildlife Refuge in Mississippi is being used to represent an area that has been subjected to heavy buck harvest. Areas such as this typically have unbalanced sex ratios (< 1 male: 4 females), the majority of the antlered bucks are yearlings, bucks > 3.5 years old are relatively uncommon and doe harvest traditionally has been light or non-existent. The NFWU population is being used to represent a herd under "quality management." Populations under quality management usually have sex ratios ranging from 1:1 1:2.5 (M:F), < 50 percent of the antlered bucks are yearlings, bucks 3.5 years old are not uncommon and does are harvested to control deer numbers. The deer herd on the Laureles Division of the King Ranch, Inc., is serving as a population under "trophy management." Populations under trophy management usually have very tight sex ratios (around 1:1 (M:F)), the majority of the bucks are usually > 3.5 years old and does are harvested to control deer densities.
Our specific objectives are:
- to determine the age classes of bucks that are siring fawns in each of the populations;
- to compare the age distribution of successful sires to the age distribution of bucks in the populations and
- to compare the distribution of breeding success in the three populations.
In the "heavy buck harvest" population (Fig. 1), bucks > 3.5 years old made up less than 20 percent of the potential male breeding population but accounted for 32 percent of the fawn production. The 2.5-year-old bucks accounted for an even more disproportionate amount of the breeding. While yearling bucks did not breed in proportion to their numbers, they did account for 32 percent of the breeding.
Breeding in the "quality management" population (Fig. 2) was distributed somewhat differently. Bucks > 3.5 years old made up 30% percent of the antlered buck population, but accounted for 2/3 of the breeding. The 2.5-year-old bucks essentially bred in proportion to their numbers. The breeding contribution of yearling bucks was not great, but they did account for 11 percent of the breeding.
In the "trophy management" population (Fig. 3), bucks > 3.5 years old made up more than 50 percent of the antlered buck population and accounted for the bulk of the breeding, however, not to the exclusion of the other age classes. The 2.5-year age class essentially bred in proportion to their numbers. Even though older age-class bucks were plentiful, yearling bucks were still able to account for 14 percent of the breeding.
Age does appear to be an important factor in breeding success. In all populations, bucks > 3.5 years old accounted for a disproportionate amount of the breeding. They did not, however, completely dominate the breeding. Even in the "trophy management" population, it appears that almost 1/3 of the breeding is being done by younger age-class bucks.
Additionally, our data indicate that, in all populations, more bucks are breeding than was previously thought. No individual dominates breeding. This suggests that selective harvest or introduction strategies will be inefficient at producing genetic changes at the population level because too many bucks are breeding and exactly which individuals are breeding is unpredictable.
Disclaimer for Demonstrations and Preliminary Research Results
Information reported from demonstrations is for illustration purposes only and should not be taken as conclusive evidence. Demonstrations are conducted in such a way that definitive statements about differences or similarities among factors or treatments cannot be made with any level of certainty. In a similar way, preliminary results from designed experiments are subject to conclusions that could differ dramatically from year to year or location to location. Therefore, information from demonstrations and all preliminary results should be viewed with a degree of caution.