Is It Possible to Kill Too Many Does?

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John Ozoga | 2007

The tendency for white-tailed does to form cohesive social groups of related individuals is probably an adaptation to exploit patches of ideal food and cover, and to maximize offspring survival. The close alignment of fawn-rearing territories, as occurs among related does, assures the harmonious use of available space and provides an effective defense against marauding predators.

Mature, maternally experienced does exhibit superior predator-avoidance skills and invariably rear a greater percentage of their offspring, as compared to younger ones. This is especially evident when faced with effective predators, such as the coyote, black bear and gray wolf — as I discussed in the December 2006 issue of Deer & Deer Hunting.

Young does fawning for their first time tend to set up and defend fawning territories border-to-border with their mothers’ territories. As a result, the young inexperienced mother can reap certain benefits. Because a doe cannot distinguish the calls of her own fawns from those of strange fawns, it’s not unusual to see two or more does rush to defend a bawling fawn.

Such behavior likely proves especially beneficial to the inexperienced young mother and her offspring, as the matriarch sometimes inadvertently lends defense against predators.

On Northern range, associating with an older deer helps the young ones to learn lengthy migratory routes, to locate favorable wintering areas, and survive the threat from predators. Also, there is definite safety in numbers when deer are subjected to harsh winter conditions and potential threat from predators.Multiple deer also do a better job of maintaining packed trails, which are critical to the whitetail’s mobility and escape from predators.

Because older does are better able to protect their newborns from predators — and provide critical guidance for younger deer during harsh winter weather — this adaptive advantage is lost when the bulk of the mature does are removed from the population.

Genetic Effects
Hunting-induced mortality ranks as one of the potentially most important factors that might disrupt whitetail social organization and impact herd genetics, because it can be highly selective. Employing DNA analysis, in South Carolina, Chris Comer and other researchers demonstrated that many related does established home ranges farther apart than expected on a Savannah River study site where antlerless deer were intensively harvested. Many unrelated does also had overlapping home ranges.

Overall, their results indicated a low degree of genetic structuring, suggesting young female deer on the Savannah River area were inclined to disperse from their natal range. As a result, does were less likely to form cohesive social groups of related individuals.

Studies in Minnesota and Illinois have also demonstrated unnaturally high dispersal rates among young does in areas where mature does experience high mortality. In Mississippi, DNA studies conducted by Randy DeYoung also showed that intensive harvesting of bucks and does can disrupt normal social behavior patterns and alter herd genetics. He postulates that harvesting of females fragments female kinship groups and leads to greater spacing of related females. In addition, orphaning of male fawns tends to reduce male dispersal and contributes to genetic substructuring.

Young does (fawns and yearlings) seem to have a strong drive to achieve compatible associations with other mature does. If their mothers or other close female relatives are not available, then they might disperse considerable distances to find these associates. On the other hand, does 2 years and older tend to remain on their established home ranges.

Conclusions
Harvesting some adult does is generally desirable. In fact, killing a large percentage of the prime-age individuals can produce certain short-term biological benefits — at least in mild environments. However, overwhelming evidence indicates that excessive doe harvests can disrupt adaptive female organization, fragment cohesive social groups of related does, and cause adverse biological consequences in harsh Northern environments.

Findings also indicate that such social disruption can alter herd genetics. However, the exact long-term genetic consequences, if any, are still obscure and will likely require long-term research to clarify.

Meanwhile, at least one researcher advises that we manage deer hunting “so that the age-specific survival pattern (and thus age-specific structure) emulates that occurring in the absence of hunting.”

In other words, we should attempt to inflict natural-type mortality — by killing the young and very old — in an effort to maintain natural population social structure.