There are two key reasons why animals migrate, for food or for sex. Here are five mind-blowing migration events from the natural world.





Monarch Butterfly (Danaus plexippus)

Migration of the monarch butterfly. Zhan et al. 2011

To: Mexico





From: North America





When: Autumn





Distance: ~5,000km





Every autumn, when the temperatures drop, the monarch butterfly leave their summer breeding grounds in North America and head south to warmer territory where they spend the winter in the mountainous region of central Mexico. Once there, the monarchs group together by the millions on the branches of oyamel fir trees (Abies religiosa). It can take up to 5 generations of monarchs to make the trip up to North America in the spring, and these butterflies will complete their life cycles in 5–7 weeks each. However, when autumn rolls around again, a special generation of monarchs that can live up to eight months, utilise the air currents to fly all the way back to Mexico! An absurd feat for such a fragile-looking insect.





Humpback whale (Megaptera)

Drawing of a humpback whale from the Biodiversity Heritage Library

To: Pacific Ocean





From: Southern or the Atlantic Ocean





When: Autumn





Distance: greater than 5,000km





Humpback whales make particularly long migrations every year between their polar feeding and breeding grounds. In the autumn, the humpback whales leave their feeding grounds in colder waters and travel to their breeding grounds in the warm protected waters of the tropics, this migration can take 6–8 weeks. Northern and southern hemisphere populations had been thought to be two distinct populations that rarely mixed. This is because the northern hemisphere populations travel towards their breeding grounds in tropical waters when the southern hemisphere populations are traveling towards the south pole to feed, and vice versa. However, there is evidence of culturally transmitted song exchange between humpback whales from northern and southern hemisphere populations!





Northern Wheatear (Oenanthe oenanthe)

Image of a male Northern Wheatear by Zeynel Cebeci

To: Northern Hemisphere (central Asia, Europe, Greenland, Alaska)





From: Africa





When: Autumn





Distance: 15,000km





Over 4,000 species of birds migrate and the Northern Wheatear is one of them! This gorgeous little songbird is 6 inches tall and no heavier than 3g, makes one of the longest migrations of any small bird in the world, flying over oceans and deserts! They winter in Sub-Saharan Africa and then in spring migrate to the Northern hemisphere to breed. It’s ludicrous to think of an animal so small travelling over 15,000km in distance, but the Northern Wheatear finds a way!





American Bison (Bison bison)

To: Great Plains (south)





From: Great Plains (north)





When: Autumn





Distance: ~650km





In the past, herds of up to 4,000 American bison would make an annual migration from the north of the Great Plains in North America to the south of the Great Plains. In the winter grass, the bison’s main food source, is more abundant in the south. This migration no longer occurs in the Great Plains because between 1870–1875 bison were hunted for their hides to the point where the population was reduced to 1,000 bison! Thanks to conservation efforts ~4,000 bison live in Yellowstone National Park. This pales in comparison to the millions that used to roam the Great Plains but a fantastic achievement nonetheless. One day I wish to see these majestic animals roam the wilderness of Yellowstone.





Atlantic Salmon (Salmo salar)









To: Freshwater rivers in the Northern hemisphere





From: Atlantic Ocean





When: October–November





Distance: 1,000’s km (varies depending on which river they are travelling too)





The Atlantic Salmon is an anadromous species, which means they grow up in the Atlantic Ocean and once mature, migrate ‘up’ freshwater rivers to spawn in the ancestral river they were spawned from! This phenomenon is known as the salmon run and is a major event for many species such as bald eagles and grizzly bears. Unlike the Pacific salmon species who die after one spawning event, the Atlantic salmon can have several spawning events, although most only have two spawning events. This migration is treacherous, if they survive the Atlantic Ocean they must navigate the dangers of swimming upstream where you are easy pickings for predators, then if they actually make it to the spawning grounds, they have to do it all again and survive the journey back to the Atlantic!

Hope you enjoyed learning about these migration events. Which is your favourite one? Are there any migration events you think should be on the list?





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Further Reading

1. Manning, A and Stamp Dawkins, M. An Introduction to Animal Behaviour 6th Edition. Cambridge University Press, 2012.

2. Zhan, S et al. 2011. The monarch butterfly genome yields insights into long-distance migration. Cell, 147(5), pp.1171-1185.

3. Rekdahl, M.L et al. 2018. Culturally transmitted song exchange between humpback whales (Megaptera novaeangliae) in the southeast Atlantic and southwest Indian Ocean basins. Royal Society open science, 5(11), p.172305.