Orientation, Animal

the ability of an animal to determine its position in space and among individuals of the same or other species. Animal orientation is a complex process that includes receiving information about the external world through various channels of communication, processing it, correlating it in the central nervous system, and forming a response. The reception and processing of signals consist of recognizing and locating an image (informational content of the signal), that is, determining by various receptor systems the source of the signal in relation to the body (biolocation).

Optical orientation is determined above all by the capabilities of the organs of sight: the eyes and other photosensitive receptors. The latter are usually capable only of recording the degree of illumination, the light’s spectral composition, and the light’s degree of polarization. For example, the lancelet, a primitive chordate animal that lives on the sea bottom, has photosensitive organs known as the Hesse ocelli. Located along the entire length of the body (along the neural tube), the organs record whether the animal’s entire body is embedded in the bottom and, thereby, protected from predators.

The ability of invertebrates and, especially, vertebrates to see individual objects makes orientation in an environment much easier. This is particularly important for very mobile animals. Invertebrates and lower vertebrates are not capable of a detailed and complex analysis of the visible world. They discern only a few biologically important signals against an undifferentiated background. Frogs, for instance, see only small moving objects—small animals that serve for food—and react to rapid darkening (“enemy”). All the rest is perceived as a hazy background. Insects, birds, and mammals are characterized by more detailed perception. Birds and mammals are capable of orienting themselves not only by numerous topographical landmarks but also by the position of the sun, moon, and stars (celestial navigation). Small crustaceans that return to the sea with the ebb of the tides also use celestial navigation. Red forest ants are able to orient themselves from the position of the moon. The homing instinct, the ability to return to one’s own district or nest even from an unfamiliar place, may be explained by memorization of topographical features and by celestial navigation. Necessary for celestial navigation is the presence of an “internal clock,” that is, the ability of the body to orient itself in time.

Chemoreception and the orientation of animals according to an environment’s characteristic chemical composition are especially common among inhabitants of water and soil. Salmon find their “native” rivers during spawning migrations by following familiar odors. Whales are guided in their migrations by the chemical composition of different sea currents. Terrestrial animals use odors when looking for food, migrating, and searching for new settling places. In the last case, the animals move predominantly against the wind and the picture of their resettlement is determined, therefore, by a wind rose. It has been shown that certain male moths (saturnids and silkworms) are able to locate a female by odor at a distance of 10 km.

Acoustic orientation of animals is an advantage in an aquatic medium and in biotopes with dense vegetation, where visibility is limited. Many predators use their sense of hearing to find and capture their prey. In such a way, an owl can locate a rodent at a distance of 15–20 m with an accuracy up to 1° (passive location). Bats and dolphins use echolocation at frequencies of 20–200 kilohertz, a process by which the animals send out sound waves that are reflected back from the target (prey) or an obstacle. Echolocation makes it possible for the emitters to orient themselves and to find and capture prey in the dark. The oilbird, a bird that nests in dark caves, orients itself by sending out sound waves at audible frequencies (in the sound range). Many lower invertebrates (such as Planaria) and insects (flies, beetles, termites) orient themselves by the earth’s magnetic pole.

Animal orientation is always the result of correlating information received through different channels of communication with the environment. However, depending on the situation, one or another receptor system plays a predominant role. Such an integrated system ensures the reliability (freedom from interference) and flexibility of orientation. At the same time, the orientation of each individual is corrected by other members of the population, herd, flock, or colony. The exchange of information among individuals further increases the reliability of animal orientation. It is precisely through this that the superiority of group life during the most important biological moments—migrations, reproduction, and growth of offspring—is demonstrated.