John Ozoga on large healthy fawns
Successful Deer Management Starts With Large Healthy Fawns: Importance of Birth Timing and Health of Mother
By John J Ozoga
Any successful deer management programs starts with large healthy fawns; stunted fawns reflect management failure. Small weak fawns are more likely to die soon after birth due to malnutrition or abandonment, are more likely to succumb to predators and disease, and are indicative of poor habitat and/or faulty deer population management. Those runts that do survive seldom grow up to be large productive adults.
Many factors can influence a fawn’s prospects for survival, as well as general well-being and ultimate adult stature. However, the mother’s level of nutrition (hence fetal development) during her last trimester of pregnancy is the most important factor governing the newborn fawn’s survival prospects. Malnourished does invariably give birth to small weak fawns that die within a few days.
Likewise, the young fawn’s nutritional status during spring, summer and autumn will often determine whether it survives its first winter (especially on Northern range) and will determine its stature at maturity. Given favorable circumstances, some fawns (male and female) may even achieve early puberty and breed when less than a year old.
Unfortunately, the exact nutritional requirements for favorable fawn growth are complex. Not only do the sexes differ in their dietary needs on a regional and seasonal basis, birth timing and social behavior factors can interact with nutrition to determine fawn growth and survival prospects. Understanding these relationships is essential in order to implement proper deer population and/or habitat practices.
Birth Timing
Fortunately, the whitetails’ reproductive cycle is geared to giving birth when conditions are best for newborn fawn survival. As one progresses northward, in the whitetails’ geographic range, a greater percentage of the fawns will be born during a relatively brief period in late May and early June. This is when new, lush vegetation provides excellent hiding cover for fawns and an abundant supply of nutritious forage, which is necessary if the does are to produce their maximum amount of nourishing milk. Even fawns need nutritious vegetation to supplement their milk diet at an early age.
In the North, natural selection has minimized poorly timed births. Those fawns born too early likely die from exposure. Those fawns born too late seldom achieve favorable physical size and fatness necessary to survive the hardships of winter.
In the Midwest, late-born fawns are more often the result of ideal conditions and breeding among doe fawns. In the rich farmland, where deer living at fairly low density and enjoy excellent nutrition year round, a high percent of 1 year old does will produce their first offspring. Since these precocious females tend to breed about a month or so later than adult does, their fawns usually are born in July or August.
Interestingly, fawns late-born to 1 year old mothers tend to be somewhat larger than normal at birth, as are those born to late fawning adults. Given excellent nutrition, as is characteristic of the Midwest farmland, these late-born individuals have a good chance of growing to respectable size prior to winter, and surviving to be large and productive adults.
Late-born fawns are more prevalent in southern states, where unbred adult does might re-cycle and come into estrus as often as 7 times during one season. Furthermore, many southern states have very long hunting seasons, starting in August or September. As is usually the case, bucks are preferentially harvested, which skews adult sex ratios heavily in favor of females prior to peak breeding, increasing the chances of late breeding/birthing.
With unlimited nutrition, fawns born a few weeks late will catch up over time. However, in the wild, over-browsing, poor nutrition, and density stress generally go together. As a result, late-born buck fawns, in particular, might never grow large bodies or large antlers, regardless of their genetics.
In the North, few undersized fawns survive tough winters. In the South, researchers contend such trends are self-perpetuating, even with favorable nutrition, because it takes late-born deer longer to become sexually mature.
Literature Cited
Ozoga, J. J. 1988. Incidence of “infant” antlers among supplementally-fed white-tailed deer. Journal of Mammalogy 69: 393-395.
Ozoga, J. J. and L. J. Verma. 1982. Physical and reproductive characteristics of a supplementally-fed white-tailed deer herd. Journal of Wildlife Management 46:281-301.
Ozoga, J. J. and L. J. Verma. 1984. Effects of family-bond deprivation on reproductive performance of female white-tailed deer. Journal of Wildlife Management 48:1326-1334.
Ozoga, J. J., L. J. Verma and C. S. Bienz. 1982. Parturition behavior and territoriality in white-tailed deer: impact on neonatal mortality. Journal of Wildlife Management 46:1-11.
Verma, L. J. 1988. Lipogenesis in buck fawn white-tailed deer: photoperiod effects. Journal of Mammalogy 69:67-70.
Verma, L. J. and J. J. Ozoga. 1980. Influence of protein-energy intake of deer fawns in autumn. Journal of Wildlife Management 44:305-314.
Verma, L. J. and J. J. Ozoga. 1980. Effects of diet on growth and lipogenesis in deer fawns. Journal of Wildlife Management 44:315-324.
Verma, L. J. and J. J. Ozoga. 1987. Relationship of photoperiod to puberty in doe fawn white-tailed deer. Journal of Wildlife Mammalogy 68:107-110.
Image IMG_3749.JPG Caption: The health of both the resident deer population and the habitat can clearly be seen in the quality of reproductive success of does and the health of their fawns.