The phenomenon of migratory birds is well known, particularly because they are clearly visible in the sky and hunters can take advantage of them to shoot certain species. On the other hand, much less people know that there are also migratory mammals. Which animals does this concern? Where and why do these mammals migrate?
The migration of some whales
We sometimes forget that the whale is a mammal and that it migrates, being able to cover impressive distances of up to 10,000 kilometers. The cause of these displacements is far from being clearly explained. Scientists have undertaken many studies, following them on their journey by drone or satellite. We can consider today that we are still only at the stage of hypotheses. The answer may be the sum of several factors.
The phenomenon is observed in both hemispheres of the planet and occurs differently depending on the species. It is mainly baleen whales that migrate. Toothed whales are nomadic or sedentary. Migration is sometimes done alone or in groups comprising many individuals.
The facts create the consensus: Migrating whales settle to feed in cold waters and migrate to warm waters to give birth. However, the explanation for migration to give birth in an environment that would be more favorable to babies does not hold up because thermoregulation in cold water is not insurmountable for young calves. Also, among the hypotheses explored, there is the idea that adults move above all to protect their offspring from predators.
The migration of some bats
While some bats choose to hibernate for the winter, others choose to migrate. Common Noctula, Bicoloured Serotine, Nathusius’s Pipistrelle or Leisler’s Noctule thus follow a North-East / South-West European axis. The study of their movements is done by following the trace of ringed subjects. A study carried out in September 2016 followed a Pipistrelle from Germany to Franche-Comté, nearly 662 km away.
Other migratory mammals
The migrations observed in most other mammals are linked to food issues. Herds move to escape drought or to continue feeding when available quantities are reduced.
This was the case with american bison, when they were still 50 to 70 million, before the Europeans settled down and exterminated them en masse to the point of making them almost disappear. They lived and moved then on the grassy plains of North America, from Mexico to Canada. Since they needed a large amount of grass in a very short period of time, they had to move regularly to maintain access to a sufficient amount of food. Today the problem is different because they mainly live in parks or farms.
At the reindeer, animal living in cold regions of Europe, Asia and America, not all species are migratory. Among those that are, let us quote the wood caribou which lives in the boreal forest, between Alaska and Newfoundland. It feeds on grasses, bushes, bark and lichens. Even if it is able to find its food under the snow, it moves to areas where it is easier to find food, traveling up to 2000 kilometers.
In hot areas of the Earth, let us quote the wildebeest. Herbivore living in herds in Africa, it has a sedentary lifestyle. But it does not hesitate to migrate when food becomes insufficient. The oryx and addax, two other African bovids, also move with the seasons. The Springbok, jumping antelope from southern Africa and the zebra can join these herds.
The tundra lemming is a rodent known for the importance of its migrations. It is done in an anarchic manner, in large groups wandering in all directions. It therefore happens that a very large number of these rodents perish from exhaustion, most often by drowning while crossing a watercourse, obviously not knowing how to assess the importance of the watercourse and therefore the feasibility of the crossing. .
Migration and nomadism among humans in prehistoric times
Let’s not forget the human being who is also a mammal! Regarding it, a distinction is made between nomadic pastoralism and migration. Nomadism is a way of life that places hunting, fishing and gathering at the center of human activities. The search for pasture is also a form of nomadism. During Prehistory, man was nomadic throughout the Paleolithic and Mesolithic. He spent his days looking for and preparing food. In the Neolithic, man invented agriculture: it was the beginning of a sedentary lifestyle, this way of life forcing him to settle in the same place for several months in a row. When we talk about prehistoric migrations, we are talking more about the displacement of populations that spread over several generations, each settling on the edge of the territories occupied by the previous ones.