CROWDSCIENCE:
Why do animals migrate?

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You may have heard about some of the animal kingdom’s epic migrations, such as humpback whales travelling from the poles to the equator, or hundreds of thousands of monarch butterflies arriving in Mexico every winter. Many animals make long, treacherous journeys year after year, so why do they go to all that effort?

Many birds, mammals, fish, reptiles, amphibians, crustaceans and insects migrate, and they usually do it to find food, a safe place to breed, or a suitable climate. For example, European swallows migrate south every winter to Africa or Asia where the climate is warmer, and food is more plentiful. Flying 320km a day, they use fat reserves to avoid starvation on their long journey. Another famous migration is that of wildebeest in the Serengeti, which follow the seasonal rains that nourish the grasses on which they graze.

But not all migrations are seasonal: Atlantic salmon spend most of their lives in the sea, and when it is time to reproduce, they travel thousands of kilometres to return to the exact river where they were born. A study published in 2021 found they can travel up to 2,940km to return to their birth river, all to ensure their offspring get the best start in life.

Although their feats of endurance are incredible, animals that migrate tend to be more vulnerable to climate change, deforestation and habitat fragmentation because they rely on multiple habitats, across countries or even continents, to survive or complete their life cycle. CA