Is It Possible to Kill Too Many Does?

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John Ozoga | 2007

The effects of hunting on deer populations remain a hotly debated issue. Although the detrimental effects of excessive buck harvesting are frequently addressed by those concerned with quality deer management, seldom do managers or hunters question the advisability of heavy doe exploitation.

An essential part of successful deer herd management is an adequate harvest of antlerless deer, particularly adult does. Unless natural mortality is excessive, the cropping of female deer helps maintain a healthy deer population, below range carrying capacity, in balance with available food and cover resources.

On the flip side, some scientists contend that killing too many mature does tends to remove the prime-age social leaders and disrupts the whitetail’s adaptive social system. Will a heavy harvest of these so-called “social governors” disrupt the whitetail’s complex social organization, change deer behavior, and produce biological and genetic consequences, as some claim? Can we really kill too many does?

Scientists have explored some of these questions, and new research techniques are now providing some interesting answers.

Deer Rationale: The Matriline
The basic social organization in white-tailed does is matrilineal, consisting of a family group comprised of a matriarch doe, several generations of her daughters and their fawns. Several such genetically related families share common range and associate seasonally as a cohesive clan. In such societies, close associations between mothers, daughters and other female relatives are maintained into adulthood. This assures that young individuals learn the location of food, water, cover and potential dangers. For example, some Northern deer have learned to migrate 50 miles or more between their summer and winter ranges in order to survive harsh winters.

In natural (unhunted) populations, the young and very old females normally suffer the greatest mortality. Does that survive to maturity commonly exhibit high reproductive success until they are 10 or more years old and are the least likely to die from natural causes. Heavy hunting pressure tends to remove these prime-age group leaders that would normally show high survivorship and productivity, thereby disintegrating the whitetail’s adaptive social structure.

Criticisms
Allen Rutberg, a spokesman for the Humane Society of the United States, charges that, “Rigorous scientific evaluation of the effects of sport hunting on deer behavior, population structure and population genetics are astonishingly rare,” and says “state wildlife agencies will not fund, and the cooperative research facilities will not sponsor, studies that may embarrass hunters or damage hunting interests.”

Ironically, Rutberg conveniently fails to recognize the Quality Deer Management Association and its emphasis on employing hunting strategies to help maintain natural deer population social structure, as well as nutritional balance. Rutberg also ignores the numerous published studies of white-tailed deer sociobiology — many of which involved the effects of deer-herd management strategies.

Granted, the investigation of deer sociobiology is difficult, primarily because few natural, undisturbed whitetail populations exist for study. However, Rutberg’s allegation that governmental agencies control or limit the study of hunting effects on deer welfare is pure hogwash.

Localized Management
William Porter and his students at State University of New York conducted extensive studies exploring the behavioral characteristics and dynamics of hunted and unhunted deer herds in northern New York.

Based on long-term research, Porter proposes that locally abundant whitetails can be effectively managed by removing entire family groups of deer. Because a group of related does controls and shares an ancestral range, he contends, eliminating such a group would result in a low deer density in that area for 10 years or more. That is, because surrounding doe groups are also attached to their established ranges, overflow of deer from surrounding doe groups would be gradual.

Subsequent studies have confirmed such localized deer removal might drastically reduce deer numbers in highly fragmented habitat as occurs in residential areas. Likewise, investigators believe such a surgical approach might be feasible in the central Adirondacks.

Logically, unintentional overharvesting of white-tailed does might produce similar results and, due to social disruption, cause unfavorably low deer numbers in local areas for a relatively long time. Likewise, excessive natural deer mortality, for whatever reason, in any given area, could theoretically produce similar localized consequences.

Family-Bond Deprivation
In most instances, however, it would be difficult to remove all members of a given kinship group; quite likely, even with intensive hunting effort, some females would evade harvest. If so, the obvious question is this:How do these sole remaining (socially isolated) females fare — now that they are deprived of kinship associates?

I was part of a deer research team that recognized the close kinship relationship of white-tailed does back in the 1970s, when we studied herd density effects on deer reproductive performance in Northern Michigan’s Cusino enclosure. In follow-up investigations, we sought to determine how removing doe family members influenced the behavior and productivity of those remaining does. These studies were possible because all deer in our square-mile enclosure were marked for individual recognition, and we knew female relationships from telemetry studies and intensive observations.

We also live-trapped the entire population each winter, when we Xrayed does to determine the number of fawns they carried.We also hand-picked individual deer for return to the enclosure according to study design, and had an accurate fix on newborn fawn mortality. Hence, we compared the performance of isolated does versus members of intact social groups.

Such treatment had no effect on the productivity of yearling does (11/2 years old) or those 31/2 years of age and older. However, socially isolated 21/2-year-old does outperformed their social counterparts by breeding earlier, conceiving larger litters and rearing a greater proportion of their progeny.

Therefore, heavy harvesting of doe groups did not impair reproductive performance of the survivors. In fact,we saw improved productivity among isolate does in at least one age class (21/2-yearolds). As a result, population recovery would probably proceed faster than expected if not all members of kinship groups were removed.

Whether the same outcome would prevail for deer subjected to heavy predation, acute winter malnutrition and lengthy seasonal migration remains unknown.