Blind as a Bat? The Sensory Basis of Orientation and Navigation at Night

Abstract

Animals that move around after dusk face many challenges but none as great as the need to be able to orient and navigate in low light levels. Bats are most famous for their adaptation to the nocturnal niche and have developed one of the most sophisticated biological sonar systems known. This echolocation allows them to capture small insects on the wing, sometimes in dense forests with high accuracy. Indeed in tests it is impossible to distinguish between a bat that uses echolocation to detect objects and one that uses vision. Despite the fact that echolocating bats produce some of the loudest sounds known to man, echolocation is only of very short range however. Being wide ranging animals capable of flight, bats often move beyond the useful limits of echolocation and must call on a variety of sensory cues to be able to find there way round in the dark, to return to a home roost or to migrate from breeding to wintering grounds. It turns out that “blind as a bat” is a misnomer in every sense of the word. Not only is vision important to these animals but a number of other senses are called upon to allow them to return home after a night of foraging for insects. It is not just bats that face this challenge. Many songbirds migrate at night to allow them to use more favourable atmospheric conditions and to avoid predators. In this chapter I will discuss the theory and the evidence of how animals such as bats and songbirds perceive the world around them at night for the purpose of finding their way home, whether it be a journey of 20 km to return to a home roost after a night of hunting insects or a migratory journey of 1000s of km across continents. This task is achieved using sensory systems in ways that humans can only imagine, and nowhere is the term “Umwelt” more appropriate.