1997

Large Animal Migrations

Prior to the invention of agriculture and the establishment of cities, humans were a nomadic species, moving with the seasons to follow food and water resources. Similarly, other members of the animal kingdom have established seasonal migratory patterns (moving from one habitat to another), many of which continue today. Bird migrations are perhaps the best known and involve the largest number of (non-insect) individual animal migrations, but significant populations of fish and aquatic mammals (like salmon, sardines, whales, and dolphins), land mammals (like zebras, wildebeest, springbok, and oryx), and even reptiles and crustaceans also embark on seasonal migrations that can span great distances.

The drive to migrate appears to be triggered by a variety of both environmental and instinctual or inherited cues. Environmentally, seasonal changes in the weather and the ensuing changes in the availability of food or water are of course immediately compelling reasons to seek a different place to be. However, in some migrating species, there appears to be a sort of inherited map of some kind, perhaps keying in on specific orientations relative to the Sun’s path across the sky, or to the Earth’s magnetic field, or to specific ocean currents, that seemingly must be somehow reinforced through natural selection. Human encroachment and habitat destruction can thus wreak havoc on the instinctual plans of many migrating species. This was a primary motivation for the United Nations’ establishment in 1997 of the Convention on the Conservation of Migratory Species of Wild Animals, designed to help protect the cross-national habitats through which migratory animals pass.

Some biologists have attempted to define the typical characteristics of a large animal migration in order to better understand its origin and to better predict how to help conservationists protect this critical animal behavior. These characteristics include prolonged linear movements to a new habitat; special advance preparations or arrival behaviors like overfeeding; special or stored allocations of energy; and the ability to avoid distractions and focus on getting to the new destination. How information on the path and destination is transmitted from generation to generation (sometimes during the migration itself) is not fully understood by biologists, nor is it clear how the group comes to the initial consensus that, indeed, it’s time to go.

Zebras are an example of a large animal species that makes substantial seasonal migrations.