1 Introduction

Donnie Zehr Mar 09, 25

Many animals perform extended migrations. Most famous are the annual migrations of millions of birds that, in autumn, leave regions with adverse winter conditions to overwinter in more favorable parts of the Earth. The record holder in distance is the Arctic tern, Sterna paradisea, a sea bird breeding in the Arctic regions that spends the winters at the edge of the Antarctic Continent, thus staying in eternal summer, avoiding coldness and darkness. But many other birds migrate as well, covering several thousand kilometers every year; among them are, e.g., water birds, raptors, swifts and small songbirds such as swallows, warbler and others. They spend the summer in the northern temperate zones and move to lower latitudes, some of them crossing the equator for wintering. Whales cover long distances between their Arctic or Antarctic feeding grounds and areas with warmer water where they give birth to their calves. But also terrestrial mammals, like many hoofed animals, perform long distance migrations to follow the annual change in vegetation, e.g., the caribous in northern Canada or zebras, gnus and antelopes in eastern Africa. Some animals migrate between nesting and feeding grounds, e.g., marine turtles. Many fishes migrate; some of them, like eels and salmons, only at the beginning and end of their life. Even some insects migrate: the monarch butterfly, Danaus plexipus, is a prominent example.

Most of these migrations involve specific routes and defined end points. Eels and salmons, as well as marine turtles are known to leave their feeding sites after years to return to the places where they were born to lay their eggs. Banded birds were found to return to the same breeding site year after year, and many of them seem to spend the non-breeding season in the same wintering grounds every year.

Birds are also known to return after passive displacement from unfamiliar sites. Homing pigeons, Columba livia domestica, bred from the Mediterranean rock dove, were domesticated and used to transport messages already since antiquity. But other bird species, too, were found to be able to compensate for displacements; that is, they can directly head toward a specific goal. The same appears to be true for numerous other animals, with the distances involved correlated with the size of their home range.

Yet, the ability to navigate is not only required for extended migrations and displacements like those mentioned above, but also during their everyday movements within their home range animals profit greatly from good orientation, because it is advantageous to optimize routes—this saves energy and helps to avoid predation.

To answer the question what factors animals use to navigate, it is important to understand how they proceed when they want to reach a specific goal. Birds are by far the best-studied group—homing pigeons are available ad libitum and can be easily used for orientation experiments. When they are released at a distant site, they leave this site heading in directions close to the home direction. With migratory birds, their innate tendency to seasonally move in their migratory directions provides a reliable, solid baseline for cage experiments. Hence much of our present knowledge on animal navigation comes from studies with birds, but many of the processes and procedures identified in birds seem to have parallels in other animals.