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How Does Habitat Quality Affect Deer?
Deer biology is very closely linked with habitat quality. Many of the most important factors influencing deer populations—average weight, antler development, age first bred, number of fawns per doe, and fawn mortality—vary with the quality of deer habitat. Equally importantly, these same factors vary with the relationship of the deer population to the carrying capacity of the habitat. Just as average weight and age first bred will be lower in poor habitat than they will be in high-quality habitat, these factors will be lower when population density nears carrying capacity than they are in the same herd when the deer density is lower and well below carrying capacity.
In this article, we use the term “carrying capacity” as used by George McCullough in his studies of deer in the George Reserve in Michigan. In these studies, carrying capacity, or K carrying capacity, means the density of deer in a given habitat where productivity declines to zero – that is the mortality in the population in any given year is exactly equal to the number of fawns that survive into their first winter, so that population growth each year at carrying capacity is zero. Deer can sometimes exceed carrying capacity and cause enough damage to habitat to actually reduce its carrying capacity.
When deer densities are well below carrying capacity, and in high-quality habitats, average body weight and antler development are both greater than they are in poor quality habitat or when deer densities approach carrying capacity. While there is a significant genetic component to antler development, diet is also extremely important. In fact, antler development in autumn is a good index of the animal’s later winter condition, and is better on high quality habitat with deer densities well below K carrying capacity.
Verme2 found that poorly nourished white-tails began breeding several weeks later and were much less likely to bear twins than does on an adequate ration. Similarly, several studies have shown that female fawns in very good habitat can reach puberty near the end of the rut, before they reach one year in age. On submarginal range or in conditions where deer densities are near the K carrying capacity of the habitat, it is not uncommon for yearling does (1.5 years old) to remain sexually immature. In northern regions, cold weather causes a fawn’s metabolism to shift, with survival taking precedence over reproduction, reducing the proportion of even well-fed doe fawns in these regions.
In another study, Verme3 showed that both age and nutritional status affected white-tailed deer productivity. He produced this table to show these relationships:
Relationship of autumn nutritional plane to whitetail doe productivity
| Fawns per doe | ||||
|---|---|---|---|---|
| Nutritional Plane | Yearling Does | Two-year Does | Prime-age Does | All Does |
| Low | 0.05 | 0.50 | 1.31 | 0.54 |
| Moderate | 0.84 | 1.40 | 1.85 | 1.43 |
| High | 1.18 | 1.53 | 1.78 | 1.50 |
These results can be confounded by fawn survival data. Lactation stress can modify productivity, with does who successfully nurture twins through to the rut entering the run at a later date and in poorer condition.
Finally, as noted in the habitat quality article, fawn survival tends to be higher in better habitat, or habitat where deer densities are well below the K carrying capacity of the habitat.
1 Taber, R.D. 1958. Development of the cervid antler as an index of late winter physiological condition. Proc. Montana Acad. Sci. 18:27-28.
2 Verme, L.J. 1965. Reproduction studies on penned white-tailed deer. J. Wildl. Manage. 29(1): 74-79.
3 Verme, L.J.; Ullrey, Duane E. 1984. Physiology and nutrition. In: Halls, Lowell K., ed. White-tailed deer: ecology and management. A Wildlife Management Institute book. Harrisburg, PA: 91-118.