IV.

Communication by Visual Display

Visual displays include a rich array of facial expressions, body movements, coloration, and physical shapes, such as the male peacock’s fanned tail. Visual communication is easy to produce, instantaneous, and can be modified to carry various types of information. For example, a dog may raise its hackles (long, erectile hairs on the back of its neck) in warning when a potential enemy approaches and then lower them if the approaching animal or human appears friendly.

Visual displays can be momentary, such as raised hackles; cyclical, such as the reddened rump of a female chimpanzee that signals readiness for mating; or permanent, as evident in the scarlet and purple facial markings of a male mandrill that enhance his facial expressions. They can be as simple as a male stickleback’s reddened belly, or as complex as a mountain gorilla’s dominance ritual, which includes rising to a standing position, chest-slapping, tipping the head to one side, and tearing up and tossing vegetation.

Different aspects of an animal’s body may be used in visual display, depending on both individual anatomy and environment. Most reptiles, for instance, have body parts that inflate (the flared neck skin, or hood, of the cobra) or vibrate (the tail of the rattlesnake) to show aggression. Animals living on land, including humans and other primates, rely primarily on the head and face for producing visual displays. Fish, in contrast, use their gills and fins. Some structures used for visual display serve additional functions as well. Antlers of male deer are used both for display—signaling their gender and dominance—and for fighting other males.

Visual communication is used to some extent by nearly all animals, although those with limited vision—for example, cave-dwelling bats—do not depend primarily on this sense. Visual signals have some limitations, as they generally require light and an unimpeded view to be seen. An exception is the display of fireflies, who generate their own pulsating light to attract mates in the darkness.