Whitetail Insider

Who’s Your Daddy?

By: Dr. Jonathon Shaw

Most hunters can’t help but speculate about the kinship of deer. Perhaps a couple of bucks share a common antler characteristic and thus must be father and son or perhaps a yearling buck is commonly seen with a yearling doe, and thus they must be brother and sister. In reality it is extremely difficult if not impossible to determine the relatedness of deer by behavioral observations or physical characteristics. If you’re a fan of the Maury Povich Show, you already know that a DNA paternity test is the best way to determine who’s the baby’s daddy.

Prior to advances in genetic technologies, researchers relied on observations to study wildlife mating systems. Based on observation studies, deer researchers believed that a few dominant bucks monopolized breeding opportunities with females, and therefore sired most fawns. Recent genetic based research does not completely agree with this long-accepted idea.

To gain insight into the mating system of a free ranging deer herd, we conducted DNA paternity tests on harvested and captured deer at Chesapeake Farms, MD over a 4 year period. Older males, particularly males 3.5-years old or older had higher breeding success than males 2.5-years or younger. This supports the idea that breeding success is related to age, an important factor in dominance status. However, neither antler size nor body weight was related to breeding success of males older than 1.5 years of age. Also, many males successfully bred, including some young class.

As illustrated in the graph below, 38% of candidate sires were 1.5, 27% were 2.5, 20% were 3.5, and 15% were 4.5-years old or older. In comparison, 22% of offspring were sired by males 1.5, 21% by males 2.5, 30% by males 3.5, and 27% by males 4.5-years old or older. This demonstrates that individual males in older age classes have higher breeding success than individual males in young age classes. However, younger age class males, because there are more of them, collectively produce nearly as many offspring as older class males.
The table below further illustrates the importance of age in breeding success, and the ineffectiveness of older age class males to completely dominate breeding in the population. For example, the average 4.5+ year old buck is only able to successfully breed roughly 3 does in a breeding season.

Breeding Success

Sire age	Does bred	Offspring sired
1.5	1.0	1.6
2.5	1.2	1.8
3.5	2.5	3.7
4.5+	3.1	4.6

As a result of successful QDM efforts, more than 30% of antlered deer were 3.5-years old or older in the study population. Dominance hierarchies are thought to be well defined in mature male age-structured populations. While acquiring dominance rank and subsequently guarding mates may be the most effective way of maximizing breeding success, it may not be the only strategy used by bucks. While dominance may warrant privileges with receptive females, it does not necessarily guarantee breeding success.

To monopolize breeding responsibilities, dominant males must locate receptive does at the onset of the female’s 24-hr estrous period, and effectively guard them from competing males throughout estrous period. In populations with well defined short ruts, most females are receptive at approximately the same time. Given the time needed to locate, chase, breed, and tend receptive females, there are limits to the number of females a buck can breed at a given time. Sneaky fertilization of surplus females that dominant males fail to effectively locate and tend may serve as a viable alternative strategy for subordinate males until dominance status is acquired.

Multiple paternity of single litters has been documented in other populations of deer and other wildlife species. This means offspring within a single litter can have more than one father. The occurrence of multiple paternity of single litters further demonstrates the inability of dominant males to completely monopolize tending bonds with females. In our DNA research at Chesapeake Farms, we observed multiple sires in 2 of 4 sets of twins. In both cases of multiple paternity, there was a 3 year discrepancy in sire ages.

Some researchers believe displacement by dominant males is the cause of multiple paternity. Essentially, a male successfully locates and breeds a female and later is displaced by a more dominant male that successfully breeds the same female. Other researchers believe that mate selection by females plays a role in multiple paternity, as multiple fathers would increase the odds that at least one of the dam’s offspring has “quality” genes.

In the many hours spent watching deer at Chesapeake Farms, I only observed mating a couple of times. One event was a mature 10-point buck that nearly collapsed the doe beneath him, and the other was a yearling spike that wasn’t much larger than the doe he was successfully able to wear down. In essence, experience may increase the odds of success, but don’t count out youthful exuberance.

About the author: Dr. Shaw is a District Wildlife Biologist for the NC Wildlife Resources Commission. He works with landowners to manage deer and other wildlife.

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