Many critics of antler restrictions are quick to dismiss the program as a gimmick or another “flavor of the month” for deer management. However this notion ignores the basic breeding ecology of deer and the impacts that can affect a white-tailed deer herd when that ecology is compromised.
Deer numbers and distribution are a direct reflection of their environment. The deer herd we have today is a result of management practices instituted to restore deer numbers during the last century. Following the era of exploitation, game laws were established to allow the return of a variety of wildlife species, including white-tailed deer. Complete protection of all female deer was necessary to achieve this, and the three-inch antler statute was an effective mechanism to protect female deer. However under the three-inch legal antler statute, we have been targeting almost every yearling buck within shooting range for almost 100 years. As a result, our current deer population in most of New York State consists of primarily older females, a few young males and a scarcity of adult males. This is not a normal age structure for a mammal population with a relatively high reproductive capacity. The present imbalance in both the sex ratio and the male age structure has had a profound impact on the deer herd and it’s habitat in NY and many northeastern states with similar hunting statutes.
We must not forget that hunters directly control three components of the deer herd: adult sex ratios, age structure, and overall density of the herd. The quality of our deer herd today is the by-product of agency policies that failed to recognize the need to refine deer management strategies as deer numbers recovered following World War II.
White-tailed deer are promiscuous, seasonal breeders. Breeding occurs in late fall, when both bucks and does are in their best physical condition of any time throughout the year. The fall breeding period or “rut” typically begins in early to mid November. White-tailed deer have approximately a 200 day gestation period and all does bred in the normal rut will drop their fawns in late spring when natural vegetation has it’s peak nutrition.
Any does that are unbred after the initial estrus, will have a second estrus period about 28 days later and if still not bred, can continue to ovulate additional times. However, does that are bred later in the year will ultimately drop their fawns later in the summer, and these late births will have a difficult time reaching an adequate body size to survive their first winter. White-tailed deer fawns are born in about a 1:1 male to female sex ratio, but with intense selective harvesting of young males that now occurs, that ratio no longer exists in older age classes in the wild.
Folklore has long advocated that mature bucks do most of the breeding when does are in estrus. However, recent DNA analysis has shown that older bucks do not dominate breeding, and younger bucks equally partake in breeding. Interestingly, it has also been documented that about 25% of the twin fawns that you see have different sires in spite of the fact that does are only in estrus for a brief 24 to 36 hour period.
Although yearling bucks are physically capable of breeding, they lack the maturity for signpost behaviors (rubs and scrapes) and pheremone production (a hormonal attraction mechanism) of mature bucks. Yearling bucks also lack the body size to have a full compliment of fat reserves stored in their body and an extended rutting period can drastically reduce their survival chances during a harsh winter.
Complications to the Fall Rut
Numerous studies have shown that when does outnumber bucks and the herd’s buck-to-doe ratio is out of balance, deer reproductive behavior and activities are extended over a period of two or more estrus cycles. Prolonged breeding activities take their toll on the buck’s body condition and fat reserves and as a result, can also compromise survival in harsher winters. However when a high proportion of the does are bred in the first estrus, both sexes of deer can revert to normal feeding and behavior patterns and their chances for survival through the winter will greatly increase.
These extended periods of rut are commonly referred to as “trickle ruts”, implying that instead of a normal, relatively brief intense period of breeding, we see breeding and conceptions “trickling” on well into second and third estrus periods. Trickle ruts are simply a direct reflection of a poor buck to doe ratio. The prolonged breeding activity of a trickle rut needlessly burns up considerably more fat and energy reserves needed by deer for the upcoming winter.
Trickle ruts also result in an extended period of fawn drop in the late spring and into early summer. Fawns that are born over an extended period of time experience significantly greater losses from predation. A comprehensive fawn survival study conducted by the Pennsylvania Game Commission in 2001-02 showed that predation is a primary form of mortality for newborn fawns. Fawns are most vulnerable to predation during the first two weeks of their life when they have limited mobility. Up to six weeks of age, fawns also avoid danger by remaining immobile. Once they become fleet afoot, the incidence of predation declines.
The research conducted in PA before the implementation of their antler restriction program demonstrated that only about 50 % of the fawn crop survived to eight months of age. Predation by coyotes, black bears, bobcats accounted for their losses during the period of greatest vulnerability.
Predation is a density-dependent form of mortality. If there is a long, drawn-out period of fawn drop, then there will be a longer period of fawn vulnerability, higher levels and longer periods of heavy predation, and ultimately less recruitment to the deer population. Similar studies in other states have demonstrated that in locations with a better-balanced buck-to-doe breeding ratio there was a more intense, shorter rut, resulting in a shorter period of fawn drop. When a greater number of fawns hit the ground in a relatively short period of time, this results in what is appropriately described as “prey saturation”. Prey saturation consists of simply having more potential food for the predators than they can possibly consume.
Prey saturation is a direct outcome of a short, intense rut and direct result of a buck-to-doe ratio that allows most of the breeding activity to occur in the first estrus. Having a larger number of fawns susceptible to predation for a brief period of time results in increased overall fawn survival.
Conversely, a trickle rut creates an extended period of fawn mortality, and ultimately greater numbers of fawns are lost and recruitment suffers.
Examining reproductive tracts and embryos of winterkilled deer is one of the standard techniques used by deer biologists to determine herd health. It allows them to pinpoint the timing and duration of the rut and fall estrus period of deer.
By measuring the crown-to-rump length of each fetus recovered from dead does in the winter, deer biologists can determine the age of each fetus within a couple of days. By subtracting the age in days from the date of death, they can then determine date of conception. With an adequate sample size, they have fairly accurate snapshot of the timing of deer breeding activity during the previous fall.
The last comprehensive statewide effort to determine the reproductive status of white-tailed deer in NY was in the early 1970′s. Recently NYSDEC completed a study of deer reproduction in smaller selected areas of Central and Western NYS (See: http://www.dec.ny.gov/docs/wildlife_pdf/deerrepro09.pdf .)
An examination of the DEC’s data from this recent study gives us insight into the present breeding ecology of deer in the portions NYS that were sampled. As expected, conceptions gradually build up during the first week of November and reach a peak in mid-November, from about November 14th to 20th. That period is aptly referred to as “the peak of the rut” and has long been of key interest to deer hunters because of the amount of overall deer activity that they observe in the field during this time.
Following the graph, the number of conceptions decreases daily following the peak of mid-November breeding. However conceptions continue into early December, and a small but steady number of conceptions occur until almost January 1. And finally, some of the past years fawns reach puberty, enter estrus and are bred from late December until the end of January.
As shown by the graph of conception dates, this extended pattern of breeding of adult females continues for more than 60 days. A direct result of this extended breeding activity is an extended period of fawn drop during the next spring that will also continue for a 60-day period of time. Worse yet, fawns born to last year’s fawns (now yearlings) will be born in August. This is a classic “trickle rut” as described in previous paragraphs and ultimately is a reflection of an unbalanced adult sex ratio. Similar research completed by Dr. Grant Woods of Woods and Associates, Inc in the early 1990′s in northern NY demonstrated that ruts in some locations in NY can last as long as 110 days.
It is important to never lose sight of the fact that having a trickle rut is a direct by-product of a poor adult buck to adult doe ratio. There are several ways to possibly address this imbalance, however, it comes down to the simple case that there either needs to be more bucks or fewer does.
Removing females in several southern locations prior to the rut has successfully reduced the overall duration of the rut. However the concept of an early antlerless season has not been readily accepted by NY deer hunters and justifiably so, given that 41% of the WMUs are currently 10% or more below desired deer levels.
The flip side of the coin is that protecting yearling bucks can result in the creation of a segment of the male population that is not subject to harvest and is available for breeding throughout the duration of first estrus period. In the Southern Zone, as many as 45% of the bucks that will be taken during the regular season will die on opening day. By the end of the first full week of the regular season, as many as 75% of the bucks that will be taken during the regular season are either on a meat pole or in the freezer. Yearling buck numbers are rapidly reduced throughout the first week of the regular season by the intense hunting pressure.
However, by protecting yearling bucks with antler restrictions, most of them would remain available for breeding activities through out the duration of the first estrus. Conserving the standing crop of yearling bucks each year could easily reduce the intensity and/or eliminate second and third estrus periods of a trickle rut. And again, having a shorter estrus period results in short fawning periods, better fawn survival and ultimately better overall recruitment to the deer population.
Bucks can still lose up to 30% of their stored fat reserves in a short rut. However, a shorter, more intense rut will also allow surviving bucks of all ages to return to normal late fall feeding patterns, instead of expending energy participating in extended breeding activities. With a short rut, they will be in better physical condition heading into the rigors of the upcoming winter, and this can be a key factor in winter survival during especially severe winters.
Animal husbandry is in fact a science, and there is no reason not to apply sound breeding practices to our free ranging herd of white-tailed deer in NY. In many areas hunters often observe fewer deer than meets their satisfaction and it’s easy to blame this on a number of things. We must not overlook the fact that every time a NY hunter pulls the trigger or releases an arrow, he or she is making a decision that will determine the herd’s characteristics for the next season. When a poor buck-to-doe ratio exists, we will experience a trickle rut. A breeding chronology that is extended as it appears to the case in some areas of NY is something that hunters can control. Only our stubborn adherence to outdated hunting traditions that results in annually clear-cutting the yearling buck population prevents us from refining deer breeding ecology.
Yearling bucks are capable breeders, and DNA analysis has shown that in white-tailed deer populations with a well-balanced age structure, yearlings will breed about 1/3 of the does. However, in unbalanced herds such as NY and other northeastern states with a poor buck age structure, yearlings by default are forced to conduct the bulk of the breeding over an extended period of time. This immature age class of male animals with the smallest physical stature, the poorest stored fat reserves, and the most inept breeding behaviors are forced to be the primary breeders over a needlessly long breeding season. It defies the basic logic of animal husbandry practices, yet is a time-honored scenario that currently plays out every fall, to the chronic long term detriment of overall deer herd health in NY.
By simply restoring a balanced age and sex structure to our deer population with antler restrictions that protect a majority of the yearlings bucks, New York hunters can finally begin to experience a deer herd structure that none of us, or many generations of our forefathers have ever seen.
More importantly, we owe future generations of deer hunters a better legacy than 100 years of tradition, unhampered by progress, lacking in scientific support and devoid of common sense.