Arkansas Nature Trivia

The Purpose of Spots on Baby Deer

By Renn Tumlison

Anyone familiar with the story of Bambi knows that baby deer have white spots scattered over their otherwise brown backs and sides. The pattern is an important adaptation for their survival. For most life-threatening situations, such as the risk of being caught by predators, the pattern of spots actually breaks up the pattern of the deer.

Speed is the primary adaptation of deer to avoid danger, but young deer do not have the muscle strength or the longer legs that allow escape by running. During the first few weeks after birth, a baby deer that is in danger automatically drops to the ground and lies motionless in a curled position, even when a predator is almost on top of it.

 The baby deer has no scent, so predators that may depend on their sense of smell have difficulty finding the young deer. The mother, always close at hand, tends to circle back toward where her baby lies, to get the attention of the predator. With the predator’s attention refocused on her, she runs and leads the predator away from her baby, typically outrunning it. After a failed chase by the predator, the mother comes back to her baby. The lack of an odor made the sense of smell of no use for the predator. Still, why didn’t the predator see the baby - which would be easy prey and a good meal for most large predators, such as wolves, coyotes, bobcats, or mountain lions?

The answer is in the spotted pattern of the fawn. As sunlight falls between the leaves and branches of the plants in the forest, a dappled pattern of light and dark spots are spread across the ground. The outline of the baby deer could be seen among the vegetation, except that the spotted fawn itself looks like its surroundings. It also is important to know that mammals, with the exception of primates (including humans), do not see color. Light receptors in the back of the eye called cones allow an animal to see color. Most mammals lack the cones, so other receptors called rods allow excellent distinction of shades of gray. Thus, the brown coat will not stand out against green grass or leaves in the eyes of the mammalian predator. Notice that it is more difficult to see the fawn in the black and white photograph as compared to the color image. Birds, lizards, and other vertebrates can see the color of the deer, but they are of no importance as predators, so their ability to see the color of the fawn is irrelevant. Those large mammalian predators that are a threat to the young deer have difficulty seeing the broken pattern, which has saved many fawns from the jaws of an enemy. As the young deer gets older, it becomes larger and stronger and relies on speed for escape. When molting replaces its hair, it no longer will be spotted.