Antler Points

The white tail of the deer flashed at the edge of the field signals that a deer has been disturbed. The signal is very common. For people who understand deer, it means more than that there are deer present and that they have run away. A normal deer, undisturbed, will rarely run. Young ones do and seem to "play" or exercise, but old ones will rarely move fast except to move up a steep hill.

When deer are disturbed, either by predators like wild dogs or by humans, there may be six very profound effects.

1. They do not have as much time to get food or their rumination is interrupted (it takes hours for a deer to get and process the high quality food needed every day.)
2. They have elevated metabolism, using more than usual energy they have gathered at such great cost.
3. Antler development, largely a function of nutrition, will be reduced in much-disturbed populations.
4. Some people suspect that there is reduced survival of the fetuses, the fawns being carried. (There is conflicting evidence.)
5. There is movement out of preferred areas into where food quality may be less than best.
6. Accidents and injuries may occur in flight.

Three wildlife biologists studied mule deer when they were disturbed. The deer moved away when people afoot (often on snowshoes) were 656 feet (200 meters) away. They let snowmobiles get closer than people did before they moved away. They noticed the snowmobile before the people, but stayed in place longer. About 820 feet (250 meters) was about the limit for both for standing (from lying) or stopping foraging. Once they move, they do not move out of this disturbance zone an equal distance but only 623 feet (190 meters) away. There seems to be an upper limit to how far they will run.

Deer were disturbed longer by people than by the vehicle (because the people were in the vicinity twice as long). They run away at about 2.4 in./sec. or 1.6 mph.

Deer probably expend up to 5% of their daily metabolic energy when highly disturbed. Their intake of energy is reduced, the time of feeding is cut (even though only briefly). The energy cost of flight is high. The birth rate of mule deer in the Colorado study was not affected by disturbance.

As always, questions can result in answers. Answers are costly, so the deer managers' question that follows an answer to questions about disturbances is: What can we do with this? The answer to that is:

1. The disturbance zone around roads and trails can be mapped. Deer may weight more, be more productive outside of such zones.
2. Effects of poachers or recreationists can be analyzed and controlled.
3. Difference in deer in different areas can be explained, in part, not by food energy available in plants, but net energy - that in food and not lost to disturbance factors.
4. Fears of loss of fetuses may be reduced.
5. The distance at which deer run away needs further measure but it can be approximated by 627 feet (191 meters) for people afoot and 436 feet (133 meters) by people in snowmobiles. Whitetails move away from snowmobiles at 200 feet (61 meters). This is called "flight distance" and members of the R* Deer System and others need to record their experience with wild deer along with
   • Distance
   • Number of people
   • Season (date)
   • Time of day

   The same needs to be studied for vehicles of various types. The numbers will vary and the factors causing them to do so will be how large is the population, whether the population is hunted, the intensity of hunting, types and density of vegetation.

6. The effect of hunting seasons can be measured, then estimated for proposed seasons.
7. Impacts of roads or other developments can be estimated.
8. Effects of creating refuge or protected areas can be evaluated.
9. Needed removal rates may not be possible (or may be very difficult) in areas where flight distance is great. One study found antlered whitetail bucks had a flight distance of 58 yards (53 meters) in a hunted area, compared to 30 yards (27 meters) in a refuge.

"Habituation" is the tendency for a response to disturbance to decline. The deer "get used to" people or other things. Apparently deer do not habituate easily or quickly.

I asked a wildlife refuge manager in India about how he judged success of his work on the refuge. I expected comments about visitors, animals, or developments. He said he measured success in the tameness of his animals, their lack of fear of humans, how close he could get to them without their flight. (In effect the more habituated to people not likely to harm or disturb them.) The answer has many meanings; it is one to be pondered beside campfires or when the TV is off. Perhaps, just as habitat and environmental conditions can be read in the animals themselves (weight, fat, blood, urine, etc.), perhaps refuge or sanctuary quality can be read in animal behavior.

There are limits to any such statement. Perhaps one limit will be discovered in the minimum flight distance of the white-tailed deer.

All animal behavior is interesting to someone; most of it to everyone. Flight and its measure, flight distance, is one among a very few that has practical uses in managing the deer resource.

This Web site is maintained by R. H. Giles, Jr.
Last revision January 17, 2000.