Fish do it, so do reptiles and insects. Mammals – including humans – do it too. The way some birds do it will blow your mind. We’re talking migration. Why do some animals travel around the globe and how do they find their way? And what happens when the habitat they need along the way disappears?
Just keep swimming
It’s hard to know where to begin when it comes to writing about animal migrations: there are so many extreme journeys to choose from. Perhaps I’ll start with whales, some of the best-known migrators. For example, Humpback whales spend their summers in Antarctic waters gorging on krill, but as it starts to turn cold, they migrate north to breed, off the coasts of Central and South America, Australia, New Zealand and Southern Africa. The longest humpback migration we know about was 18,840 km.
Leatherback turtles swim massive distances – up to 11000km – in search of jellyfish to eat. The turtles travel in the open ocean, where there aren’t a whole lot of landmarks. But amazingly, they manage to follow a consistent compass direction across thousands of kilometres. How do they do it? We don’t know for sure but they are probably using either the sun or the earth’s magnetic field. Turtles are also famous for being able to find their way back to the very same beach, decades later, where they hatched. We think turtles can memorise the magnetic coordinates of this beach so they can find it again, no matter how far they’ve travelled in the intervening years.
Not content just to swim during their migration, freshwater eels will also wriggle across the ground if that’s what it takes to get where they’re going. Eels begin their lives out in the deep ocean, but migrate to freshwater rivers and lakes, often thousands of kilometres away. A female eel may spend 50 years living in the upper reaches of a river, but when the time is right, she will journey back to the sea, lay up to 20 million eggs and then die.
Of course there are famous land migrations too. The spectacle of millions of brilliantly-coloured red crabs migrating from forest to the coast on Christmas Island is a major tourist attraction. Similarly, the mass movement of more than a million Wildebeest and 20,000 zebras through Tanzania and Kenya draws nearly as many tourists. This journey crosses about 800 km and like most migrations, is highly predictable. Caribou, also known as reindeer, may move in herds of more than a hundred thousand and travel nearly 5000 km in a year.
Some migrations are less obvious but no less impressive. Globe skimmer dragonflies fly 18,000 km back and forth across the Indian Ocean – from India to East Africa via the Maldives and Seychelles. This is the longest migration of any insect. Further than the well-known monarch butterfly migration across North America.
Around the world in 46 days
But when it comes to long-distance migration, birds come in at number one – step aside Phileas Fogg. In their lifetime, grey-headed albatrosses may fly not just once, but twice around the entire globe. And they don’t need 80 days to do it: one bird circumnavigated the globe in just 46 days. And a bird doesn’t need wings the size of an albatross to cover big distances. A tiny bird called a Blackpoll warbler, weighing about the same as a box of matches, flies non-stop from northeastern Canada to South America in just three days.
Alpine Swifts leave their Swiss breeding grounds every winter to travel to the warmer shores of West Africa. Extraordinarily, the latest tracking data suggests these animals don’t stop flying for six months. They feed as they go and must also sleep during their 200 days of non-stop flying. An Arctic tern weighs the same as a smallish apple and in a lifetime, can fly up to the equivalent of three round trips to the moon. In just one year, an Arctic tern can fly 80,000 km from the Arctic to breeding grounds in the Southern Ocean. That is a world record.
Another incredible bird journey is undertaken by Bar-tailed godwits – they fly the 11,000 km from Alaska to New Zealand in eight days, without any stops for rest or refueling. And Bar-headed geese follow an unbelievably high-altitude migration path from sea level in India, up over the Himalayas to their breeding grounds in central Asia. The geese fly up to 60 km/hour for seven or eight hours up to 7000 m above sea level – that’s setting a new bar for high-intensity aerobic exercise.
It’s a small world after all
Why do animals migrate? Because the earth’s geography and seasons mean at different times of the year, there will be plenty of food in some places but not others. Animals migrate so they can find the food they need, and to have opportunities and good conditions for mating and raising their young. For the animals that do it, we can assume migration is essential.
But the sad truth is that for many of these animals, migration is getting more and more difficult. Of course climate change is one huge issue.
Just as important is the fact these migrations cross international and political boundaries. There’s almost no point protecting one part of a migrating animal’s habitat if somewhere else along the route, their breeding or feeding grounds are destroyed. This is particularly true for shorebirds. Birds migrating via the East Asian-Australasian Flyway follow a migration path shared by four billion people in 22 countries on four continents. Coordinating the protection of these species is a mammoth undertaking, dependent on levels of international cooperation we rarely see.
And that’s why zoologist Milly Formby is taking to the sky in a microlight aircraft flying from Australia to Siberia. She’s following the migration path of the tiny Red-necked stint, a bird that weighs the same as a Tim Tam biscuit but flies 25,000 km every year.
Milly wants us all to know that unless we start protecting their habitat, many migrating shorebirds are going to face extinction, and soon. Please help Milly to raise awareness about what we stand to lose! Not just these extraordinary birds but the habitats they – and we – depend on.
Fascinating (& scary) stuff, thank you. As was Kingsolver’s book on the monarchs.
Thanks, as always, for reading. Yes the monarch story is incredible. For a wonderful story about the discovery of the dragonfly migration I can highly recommend this TED talk: Dragonflies that fly across oceans
That’s pretty amazing. I thought I had good knowledge on the migrators of the globe, but I obviously don’t – dragonflies!
The dragonfly story (see the TED talk I linked to above) is amazing. Particularly because of the way the researchers had to go about understanding what was going on. There aren’t any trackers small enough to go on a dragonfly!