Why do animals migrate?

Why do animals migrate?

Before understanding why animals migrate, let’s start at the beginning and ask ourselves “What is migration?”. It is not easy to define migration, because there are many variables to take into account. In short, migration can be defined as the periodic movement of a population (or part of it) between specific areas where favorable environmental conditions vary depending on the time of year.
The animals most famously known for migrating are birds, but migration is actually widespread throughout much of the animal kingdom, especially among mammals. Migration generally takes place in large groups, but it can also occur individually. It may happen every day or every year, lasting weeks or months, and it is regulated in different ways depending on the organism.

Migration is generally an adaptive response to seasonal or geographic changes that lead to variations in available resources. By migrating, an animal moves from an environment that has become hostile to one that offers a better chance of survival. This is due to factors that vary depending on the species.

The main biological purposes of migration are two:

1) Greater availability of resources: one example can be seen in Africa, with the great migration of wildebeest, zebras, and gazelles. We talk about the Great Migration in Tanzania in this article, in case you would like to take a look! It is a spectacular migration in which, every year, millions of these animals migrate north during the dry season because of the decreasing availability of water. These species move in search of water sources, and then return south during the rainy season, which replenishes African water basins.
2) More favorable climates: many animals migrate toward optimal habitats to complete their life cycle, as in the case of sea turtles, or to avoid seasonal changes in their area of origin that would compromise their survival. This is the case for migratory birds that overwinter elsewhere.
Other possible advantages of migration include, for example, avoiding predators.

It is also interesting to know that the same species may migrate for different purposes. For example, did you know that herrings (yes, herrings migrate too!) move between breeding, feeding, and overwintering areas?

In the vast world of migration, some common behaviors can be recognized among all animals:
1) Periodicity: migration occurs in a consistently similar way. In general, it is synchronized with environmental changes and takes place from a specific area, where resources are declining, to another one.
2) Directionality: there are precise routes, generally linear, followed by the individual during migration.
3) Suppression of stimuli: some animals suppress certain behavioral responses that would “distract” them from migration.
4) Energy reserves: these long journeys are very demanding in terms of energy. Sometimes animals run out of strength and die before reaching their destination. For this reason, it is essential that they prepare for the journey with certain adaptations, for example by eating more than usual (hyperphagia) and training their muscles.

How do animals find their way when they migrate?

Orientation methods can be innate or learned. Migratory animals navigate in many different ways and generally use several orientation methods at the same time. They may rely on cognitive maps, landmarks, stars, the polarization of sunlight, and the Earth’s magnetic field (as we saw in the lesson on animal orientation).

Some use smell, such as sockeye salmon. These animals are anadromous: they are born in a river, move to the sea where they spend most of their lives, and then return to their river of origin to reproduce and die. During their journey back up the rivers, twelve of their genes are expressed, giving them a much greater ability than normal to distinguish odors. This allows them to recognize the smell of the river where they were born and to which they are headed. As soon as they reach their destination, the expression of these genes decreases, and consequently so does the fishes’ sense of smell.