deer ecology

Mortality & Longevity

Mortality

The major causes of deer mortality in Illinois are hunting and deer-vehicle collisions.

Other Causes

  • disease
  • train collisions
  • fence entanglement
  • poaching
  • predation—most often occurs with fawns and weakened adults
  • starvation—not serious issue in Illinois because of the generally abundant food
  • severe weather—not typically an issue with mostly mild Illinois winters

Longevity

Longevity of individual deer is influenced by a range of factors including their genetics, food availability, habitat, weather conditions, presence of predators, and the prevalence of parasites and disease in the area.

In hunted areas of central and northern Illinois, female average life span was 5½ years and 2½ years for males. Some deer do survive longer: the oldest female in one study was 18 years of age, while the oldest male was 9 years old. While survival decreases as deer age, females’ survival does not decrease as rapidly after about 6 years of age.

Aging Deer

It is possible to age deer by the number and wear of their teeth. Here the ages of five deer are shown. Top to bottom: 6 months, 1½, 2½, 3½, and 4½ years of age.
It is possible to age deer by the number and wear of their teeth. Here the ages of five deer are shown. Top to bottom: 6 months, 1½, 2½, 3½, and 4½ years of age.
Photo: courtesy of Illinois Department of Natural Resources

Aging of deer is often done by studying the teeth for eruption and wear.

Another technique using cementum annuli can give a better estimate of the age of a deer. This method analyzes the annual deposition of cementum—the calcified surface layer of the tooth root. The density of cementum varies over time and can be detected as rings denoting years of different growth. However, tooth eruption and wear are more commonly used as these are faster and less expensive to complete.

Deer use incisor teeth in the front of the bottom jaw and a hard palate on the top jaw to tear and break apart food.

Food is chewed by premolars and molars in the back of the jaw.

The large gap between the incisors and premolars is called the diastema.

Occasionally white-tailed deer possessing upper canines are reported. Researchers believe these small, peg-like teeth may be an evolutionary throwback to ancestral deer. A rare occurrence, these teeth may or may not break through the gum and are most often seen by taxidermists or those preparing a European skull mount.