By: John J. Ozoga
In white-tailed deer, the adult sexes live separately during
much of the year, just as they do in mule deer, red deer, elk,
moose, and many other ungulates. Scientists refer to this social
and geographical separation as ?sexual segregation" or "niche
separation" of the sexes.
Related does live in close-knit matriarchal societies, composed
of mothers, daughters, grandmothers, great-grandmothers, and so
forth. Bucks, on the other hand, form fraternal or bachelor
groups generally composed of unrelated males. In either case,
social group size and the degree of social complexity varies
depending upon many different factors that influence deer herd
sex-age composition and density.
While the female whitetail might spend her entire life on a
relatively small ancestral range, the male generally disperses
to a new range. At some point in time, the young male must leave
one societal unit to join another if he is to become a
successful breeder.
Because adult bucks and does differ so much in their behavior,
they can almost be treated as though they were different
species. Researchers around the world still debate the adaptive
advantages of the totally different lifestyles demonstrated by
the whitetail sexes. Unfortunately, their seasonal differences
in food, cover, and social requirements are seldom considered in
deer management plans.
Given the potential significance, some deer researchers question
whether current deer habitat and herd management strategies
adequately serve both sexes. We are often bound to a system that
overexploits the male segment of the population and
under-harvest the females. The goal, it seems, is to produce an
abundance of whitetails, regardless of their condition, to
satisfy steadily increasing recreational demands on this
species.
In many parts of the country, antlered bucks are currently being
harvested so intensively that mature bucks and true buck groups
are virtually nonexistent.
From the standpoint of whitetail social evolution, groups of
yearling bucks, in the absence of older bucks, do not represent
true fraternal groups. Groups of yearling deer may also include
females, and tend to occur only during late spring and summer
while does are rearing fawns. Thus, these groups of young deer
differ greatly from exclusive, age-structured groups of older
bucks.
In a natural population, only relatively few dominant bucks do
most of the breeding. A young male can only hope to become a
dominant male by engaging in competition with other bucks over a
long period. The achievement of dominant status by young males
requires outliving older, stronger males and dominating males of
similar age. It is not enough to simply maintain a rank. To
succeed, the young male must continually strive to move up in
dominance. This requires that he associate not only with animals
of lower rank, but also with those of higher rank.
 In
an age-structured male society, a high rank is not easily
attained, it requires experience and the learning of competitive
skills. Success, as in any contest of strength, skill, and
endurance, comes from long and diligent training. A young male
choosing not to join all-male groups would not be able to obtain
the necessary skills to compete successfully.
Considering that the whitetail buck's chances of breeding are
largely determined by his rank in the male dominance hierarchy,
the young buck has little choice but to associate with other
males. Although he is tightly linked to the mother-young system
early in life, he must eventually break those bonds. When
sexually mature, the buck must seek out and interact with older
males, achieve male group membership, and rise in dominance
rank. If he does not, but instead remains with female relatives,
it is my opinion that he would become a "psychological
castrate," never achieving respected breeder-status.
Even casual observers may note that, as with any behavioral
trait, the whitetail's social organization is an ada
ptation. It evolved in response to numerous environmental
stresses, including predators, diseases, climate, habitat
conditions, and hunting by Native Americans. And, as with any
adaptation, the whitetail's social organization is genetically
linked, inherited, and essential for the species' healthful
existence?it promotes social order, genetic selection and
physical fitness, and improves the prospects for survival.
Since the whitetail sexes differ in many aspects of physiology,
behavior, and anatomy, it is likely that they evolved
differently. For example, bucks and does differ in size, shape,
growth rate, metabolic rate, life span, food and cover
requirements, and in many aspects of physiology and
biochemistry.
Based upon intensive behavioral investigations conducted in
Southern Michigan's George Reserve, investigator Dale McCullough
concluded that, due to sex differences in use of space, food,
and cover, whitetail bucks and does do not compete equally for
the necessities of life on a year-round basis.
Therefore, if bucks and does evolved differently, then they must
also respond differently to environmental change. As a result,
habitat management practices that benefit does may not
necessarily benefit bucks equally, or may even be detrimental to
bucks.
Also, harvest management strategies that inflict unnatural
patterns of mortality (such as buck-only harvesting) and create
deer herds with abnormal sex and age composition could impact
the welfare of one sex, either favorably or otherwise, more than
the other.
Many hypotheses have been advanced to explain the evolution of
sex segregation among ungulates. However, two Oregon
researchers, Martin Main and Bruce Coblentz, propose that
females select habitat that is best suited for rearing
offspring. Normally, that means diversified food and cover
arrangements with ample hiding cover for both mother and young,
as a predator defense, during the critical stage of early
fawn-rearing.
By comparison, when available, males tend to select areas where
nutrition is superb, which allows for maximal body growth
necessary for the attainment of high dominance rank and improved
breeding success.
Generally speaking, both male and female whitetails in northern
latitudes subsist upon relatively poor quality forage during
winter and leave their winter ranges in depleted, poor physical
condition.
Forage and environmental conditions normally become much better
in spring and summer, allowing for fairly rapid replenishing of
energy reserves. Ungulates from northern latitudes have evolved
to give birth during this period, when conditions are most
favorable for rearing young. This is when the reproductive
patterns of the adult sexes differ the most and they show the
greatest niche separation.
The Oregon researchers emphasize that body size, physical
strength, and general body condition influence a male?s mating
success. Therefore, the ?replenishment of energy reserves should
coincide with major growing seasons, and optimization of forage
resources by males should be most evident during these periods
as they prepare for the rut. Optimal foraging by males may
require avoidance of heavily grazed areas or adoption of
foraging patterns that exploit temporal resources of high
quality. The importance of maximizing body condition for males
apparently exceeds even increased risk of predation."
When a deer population is socially balanced, my observations
indicate that adult bucks intensively scent mark their favored
summer habitat as soon as they return to it in spring, probably
as a means of reclaiming range that had been vacated during
winter. This marking, which is done primarily on overhead
branches, serves to intimidate other deer, including pregnant
females that require solitude for fawn rearing. As a result,
buck scent marking helps to segregate the adult sexes and
distribute the herd more evenly during the nonbreeding period
when does are rearing fawns and bucks are growing antlers.
In McCullough's words
, "Resource partitioning between the sexes in white-tailed deer
adds a new dimension to the role of social behavior as it
relates the animal to its environment." Indeed, if bucks differ
from does in their use or space, food, and cover resources, on a
seasonal basis, then deer herd and habitat management
considerations take on an entirely new level of complexity.
McCullough suggests that this issue should be carefully
considered especially when it comes to determining deer harvest
management strategies. As he points out, "unbalancing
populations toward females intuitively would be expected to
increase productivity, but in practice seldom does in moderate-
to high-density populations."
Clearly, poor growth rates among young deer and reproductive
failure among adult does, when associated with food competition
and malnutrition, invariably is the result of too many female
deer, not because of too many bucks.
Martin Main was probably correct in criticizing traditional deer
management practices which promote and expand female
groups?especially predator control efforts and bucks-only
harvesting?run counter to how the white-tailed deer's social
system evolved.
Wherever fawn-rearing females are overly abundant, over-browsing
and range forage deletion is likely, thereby excluding buck use
of such habitat. Conversely, female groups may be prevented from
becoming established in areas used by males, because predation
or other factors reduce fawn-rearing success.
In other words, when deer density is high, whitetail bucks often
occupy certain habitats strictly by "default." They browse
depleted areas where no does live or where does live in very low
numbers.
Today, young bucks in Michigan probably have great difficulty
finding suitable habitat during spring and summer, in an
environment saturated with too many antlerless deer. As a
consequence, many bucks are forced to occupy nutritionally poor
areas, where they grow poorly, sport undersized antlers, and may
even suffer greater than normal over-winter mortality.
John Ozoga is a former Wildlife Research Biologist for the
Michigan Department of Natural Resources where he spent more
than 30 years conducting deer research at Upper Michigan's
Cusino Wildlife Research Station. He now devotes much of his
time to consulting and popular writing and is a panel member for
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