The outline of an animal is not the only feature that might give it away. Often some part of it, perhaps its eyes or its legs or its tail, also might be a clue. In this activity, these parts are called give-away parts. Their concealment often involves special features.

Eye Concealment

In some environments, round objects are unusual and likely to attract attention. In nature, this characteristic of a round object is quite likely an advantage to many flowers whose round blooms must be visited by nectar feeders if the flower is to reproduce. It may also be an advantage to certain plants whose round, brightly colored fruits and berries attract animals that disperse the seeds in their droppings. It may be a disadvantage, however, when the object is the eye of an animal, as many hunters can attest.

In many animals, the conspicuousness of the eye is diminished if there is a match of the color of the iris to the color of the head. However, this still leaves the pupil, which is usually round and black, as a potential give away feature.

A few animals, such as many geckos (small harmless lizards) and some snakes, not only have an iris that blends with the color of the head, but also a pupil that closes down to a narrow inconspicuous slit during the daytime. Since such animals are primarily nocturnal, their need for vision during the day is small. Therefore, the size of the pupil would not affect its vision and may prove advantageous for concealment.

Most animals have round rather than slit pupils; therefore, if they are to see, they must expose a black, round spot. Many variations in color appear to make the black spot of the pupil and the rest of the eye structure less conspicuous, or at least less recognizable as part of an animal.

One of the most common features that effectively conceals the eye is the eye stripe. Note the stripe runs through virtually unrelated structures. Besides the pupil, it can involve a portion of the iris and the skin, scales, feathers, or hair on the body. In view of the involvement of such different structures, the incidental occurrence of such stripes seems unlikely. Their functional character is further suggested by their occurrence in many diverse animal groups.

The presumed advantage of the stripe is it replaces a small but circular spot with a larger but ambiguous stripe. Often the stripe acts as a disruptive mark, obscuring the profile of the animal. Dark stripes harmonize with many features of the environment and their shadows—rock crevices, fissures in bark, twigs and slender leaves.

There are several other kinds of eye concealment. Often the eye is hidden in a black patch as with the American Kestrel (Figure 6b). The mask of a raccoon may be advantageous in concealing its eyes.

Protection of the Eye

Besides being a possibly conspicuous spot, the eye is also a vulnerable spot. Therefore, features of coloration that hide the eye may also serve primarily to protect the eye. In some instances, concealing the eye may be at the expense of revealing the animal. The butterfly fish, for example, is made conspicuous by a larger than life “eye” toward its tail. Possibly such a marking misleads an inexperienced predator that, responding to the spot as an eye, miscalculates the direction in which the prey will flee. The true eye is hidden by a stripe. There is also the possibility the marking may function in species or sex recognition.

Coloration protecting the eyes is often advantageous for predators that prey on animals that can retaliate—particularly those that might peck the predator’s eyes. The eye stripe of the Shrike may have evolved as a result of its predatory habits. The Pygmy Owl and the American Kestrel (Figure 6b) also prey on smaller birds and may owe the eye like marks on the backs of their heads to this feature of their existence. Should an owl or hawk be attacked by other birds, their chances of losing an eye would probably be less because of the deceptive markings.

Leg Concealment

A frog’s leg, very useful in jumping, may be an obstacle to concealment. The unfolded leg might be recognized as a part of a frog and thus be a give away part. For concealment, therefore, hiding of the legs may be advantageous.

As might be expected, frogs in general are observed to fold their legs when resting. Although such behavior greatly reduces the conspicuousness of the legs, some frogs also have disruptive marks that slash across the folded legs. These marks may provide an advantage to the frog as they help to obscure the still discernible outlines of the legs. Like the eye stripes previously discussed, these markings run through several distinct structures—in this instance, three parts of the leg and foot. Disruptive patterns that join up different parts of the body in this way are often called “coincident disruptive coloration” or joining patterns.

Wing Concealment

The wings of moths also often exhibit coincident disruptive coloration. Again, pattern elements run through more than one structure. In the moth, markings often cut across both pairs of wings, sometimes involving the back of the abdomen as well.

Coincident disruptive markings are observed on a great variety of animals. Since such marks appear impossible to explain as incidental (or physiological) coloration, they offer some of the best arguments that the coloration evolved as a result of their visual effect.