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How Accurate is Aging Deer on the Hoof?

Posted Aug. 1, 2010

As managers and sportsmen become more aware of the importance of age in antler production, selective harvest management programs become increasingly popular. The use of physical characteristics to estimate ages of deer in the field is often the basis of harvest decisions. This aging technique is commonly referred to as "aging on the hoof" (AOTH). AOTH receives a lot of press; however, prior to a study by the Noble Research Institute, there have been no scientific evaluations of this aging method.

To evaluate the method, we developed a quiz consisting of photographs of 70 wild, known-age, antlered male, white-tailed deer ranging in age from 1.5 to 7.5 years. We administered the quiz to 108 deer biologists who use AOTH. The results are given in Table 1. The average percentage of correct estimates was 36 percent, with a range of 15 to 56 percent.

The yearling age class had the highest accuracy rate (62 percent), but accuracy was less than expected by the deer biologists. Specific year-class accuracy rates for deer 2.5 ranged from 15 to 43 percent. In addition to low accuracy rates, there was also significant overlap among year-classes. For example, 2, 16, 20, 17, 12 and 9 percent of the 3.5-year-olds were incorrectly estimated to be 1.5, 2.5, 4.5, 5.5, 6.5 and 7.5 years old, respectively. Similar overlap was found for other age classes.

Much of the inaccuracy of the AOTH method can be attributed to two factors. A lack of quantitative estimation criteria makes consistent application difficult and very subjective. Variability of characteristics within specific year-classes also hurts accuracy. For example, all of the deer in the photos are 3.5-year-olds, but they share few physical similarities.

Using AOTH to make year-class specific management decisions may not yield desirable results. However, using AOTH to identify some age groups may have some management utility. For example, our data indicate that if the management goal is to protect deer 3.5 years old, placing AOTH deer 4.5 years old off limits for harvest will protect 100, 94 and 62 percent of the 1.5-, 2.5- and 3.5-year-olds, respectively. The downside is that 38 percent of the 3.5-year-olds with the most promising size and antler quality are placed at risk. Placing AOTH deer 5.5 years old off limits will protect 79 percent of the 3.5-year-olds. Results in Table 1 may help you determine where to draw the line for harvest management.