The marvels and mysteries of migration.

By June 9, 2021Editorial

Caption: Lone springbok in Namibia’s dry Hoanib River. Although the species remains prolific, the spectacular annual migrations are long gone. © Christin Winter/Shutterstock.
 

We all migrate all the time. It’s what living things do to survive, to reach the resources we need. So, a daily commute to an office is as much a migration as a mundane food gathering trip to a nearby supermarket. But these are trivial human examples compared with the ongoing tragedy of desperate people attempting to migrate from the savagery of war-torn, economically destroyed regions of the world into areas perceived to offer something better.

Like people, creatures in Nature migrate in response to changing circumstances, and some of the more intriguing and worrying examples show how species are on the move due to anthropogenic warming of the global climate. Scientists have long anticipated this phenomenon, but they have been astounded by the speed at which it is happening.

2017 National Geographic article revealed that of some 4,000 species around the world, about half are on the move. Land species are moving more than ten miles a decade, and marine ones four times faster. Among the more extreme migrants are the Atlantic cod and Europe’s purple emperor butterfly that has staggeringly moved their distribution limits over 125 miles in ten years.

And plants do it too when needs must. Of course, they cannot just lift their roots and move on, but they do move, with seed dispersal being the most obvious strategy. Again, global warming is accelerating the pace. A study of 171 forest species in Western Europe shows that most of them shift their favored locations to higher, cooler spots. For the first time, research can show the “fingerprints of climate change” in the distribution of plants by altitude, and not only unsupportive ecosystems—comparative distribution studies have shown upward shifts of 95 feet per decade. Short-lived species with faster reproduction cycles—herbs, ferns, and mosses, for example—are the sprinters of the plant world, while large, slow-growing trees are not as nimble.

As I sit here writing, I am watching everyday migrations in my garden through my study window. A shimmering avian jewel has just arrived, a male southern double-collared sunbird alighting on the fiery-red inflorescence of an aloe. His comparatively drab mate has joined him momentarily to probe the nectar-rich resource. They do this daily, as does a feeding party of Cape White-eyes. Soon they are gone, off to my neighbor’s garden no doubt to explore the bounty there, and a dozen or so African honeybees move in to collect pollen.

Migrations happen in the truly micro-world just as they surely do amongst the greatest creatures of the land and the sea. Witness the vertical migration of zooplankton whose daily routine is to rise up the water column at night and retreat into the dark depths with sunrise. The triggers for doing so are not entirely understood, but as Sara Mynott wrote in Saltwater Science, “This process, known as diel vertical migration, is carried out all over the world by marine and freshwater plankton alike. The reason for this has long been attributed to the trade-off between obtaining tasty morsels in the surface ocean and avoiding becoming a tasty morsel for predators while they’re there.”

At the other extreme, we have Leatherback turtles that travel as many as 10,000 miles or more each year searching for their jellyfish food source. Japan’s loggerhead turtles aren’t far behind. They migrate almost 8,000 miles from their natal beaches to feed in the waters of Mexico’s Baja California, only returning to breed and nest once they have reached sexual maturity.

Birds, of course, are the real champion migrators, some winging across continents and oceans every year to reach their breeding and feeding grounds. Near the top of the list must be the Arctic tern that annually moves between the Arctic Circle and Antarctica—a round-trip journey of about 19,000 miles.

When we think of migrations, however, the minds of most of us are more likely to flash to images of wildlife and places such as East Africa and the annual, more or less clockwise movement of wildebeest around the Serengeti-Mara system. Or, alternatively, we reflect on the truly great migrations of the past. For example, we once had the movement of millions of bison across the prairies of North America. While on the other side of the planet were the trekbokke, hordes of springbok that once migrated across the expanse of the Great Karoo. Fences, disease, and hunting almost put an end to those events, but not quite. Bison still move seasonally in as much as they can within the boundaries of conservation areas, and springbok still disperse in some places across the South African, Namibian, and Botswana borders. But these are pale shadows of the spectacles that once were.

Imagine what it must have been like to witness the ground-shaking sight and sound of horizon-to-horizon bison thundering across the plains. The bison, or buffalo, is the biggest and heaviest land mammal in North America. In the 1500s, there were some 30-60 million of them from the Canadian hinterland, down through the US and into northern Mexico. From the 1700s, hunting, cattle-borne disease, and agriculture started to take their toll, and by the 1840s, bison had ceased to roam West of the Rocky Mountains—wholesale slaughter for their hides and bones had reduced them to a few remnant populations. In less than 200 hundred years, a keystone species vital to the Great Plains ecosystem was ecologically extinct.

Likewise, southern Africa’s springbok migrations must have been spectacular events to experience. Early settlers’ eyewitness accounts spoke of these graceful, high-leaping antelope moving across the open veld in such numbers that they would literally take days to pass through towns and villages. In his book Karoo, Lawrence Green related farmer Gert van der Merwe’s account of the great springbok migration. It is retold here in Africa Geographic. Of course, hunters took huge advantage of the mobile larder, and thousands and thousands of springboks were shot, but this made little impression on their numbers, so prolific were they. To the early farmers trying to eke out a living in the semi-arid conditions of South Africa’s vast central plateau, these voracious antelope moved through the land like locusts, devouring everything in sight and leaving precious little for domesticated livestock. The consequence, of course, was removal. Again fences, persecution, hunting, and disease took their toll, and the last great migration was recorded in 1896. Ironically, this beautiful antelope that settlers tried so hard to eliminate is today the proud symbol of South Africa’s national rugby team.

Sometimes, however, there are migration events that are hard to explain. Like me, I am sure that thousands, probably millions, of people around the world have been following with fascination the extraordinary, unfolding story of a small group of Asian elephants that left their home and, for the past 14 months, have been traipsing across China. En route, they have passed through villages, towns, and cities to get to…well, no one knows. Quite what their motivation has been and where they will end up seems to be anybody’s guess at this stage.

Some commentators, quite reasonably, have suggested that access to resources has prompted the migration, but that doesn’t quite add up. After all, the elephant’s home is in China’s Xishuangbanna National Nature Reserve, a UNESCO World Heritage Site, and not exactly devoid of resources. Xishuangbanna lies in a wedge of land in southern Yunnan Province near the border with Myanmar to the West, Laos to the south, and northern Vietnam to the east. The region holds the largest tract of old-growth tropical forest in all of China, an ecosystem of significant plant and animal biodiversity. About 90 percent of the country’s remaining 300-odd Asian elephants live in this primary forest.

The Asian elephant is listed as “Endangered” on the IUCN Red Data List. Some 40,000–50,000 remain, and while this may sound a fair number, it should be seen in the context of the species’ population having fallen by some 50 percent over the past three generations. The elephants of Yunan are an outlier population of the Indian subspecies (Elephas maximus indicus) and remain essential to the genetic diversity of the Asian elephant as a whole.

Something must have perturbed a group of 17 elephants in the heritage site, as in March 2020, they left the sanctuary and set off northwards, reaching Pu’er City in November, where one of the females gave birth. They settled in the region for five months before heading northeast on April 16. By May 17, they had reached the town of Eshan in Yuxi City and walked the streets for some hours before continuing their journey. By then, not only had the odyssey captured all of China but the world as well.

On June 2, the wandering herd entered the Jinning district of Kunming, Yunnan’s capital and a city of nearly seven million people. Then a few days later, they changed direction and started heading in a southwesterly direction. Now they are resting up in a forest, and the world waits with bated breath for their next move.

So far, the elephants have traveled some 300 miles. Their story is astonishing in itself, but almost more interesting has been the reaction of the Chinese people and of officialdom. China is roundly criticized on so many social, conservation, and environmental fronts. Still, it has been extraordinary to watch how everyone has gone to enormous lengths to protect both the elephants and the communities they have passed through. Some 14 drones are being used to track the herd, while 510 people and 110 vehicles have been employed to block roads and highways and guide the elephants to safety. Compassion and respect for fellow creatures come to mind—not a standard Chinese trope in Western minds.

I am sure there have been many other strange and wonderful tales of inexplicable animal migrations. The one that has stayed with me since early childhood has been the story of Huberta, the hippo. For some reason that will forever remain a mystery, in November 1928, she decided to strike out from her home in the St Lucia Estuary in South Africa’s KwaZulu-Natal Province. Hippos, of course, make daily commutes from rivers, dams, and lakes to visit their nocturnal grazing grounds, but Huberta’s journey was something apart. Over the next three years, she became a celebrity as she traveled southwards for about a thousand miles. People turned out to watch her progress through towns and villages, and she was regularly featured in newspapers and over the radio. Eventually, in March 1931, she arrived in the Eastern Cape city of East London, but a month later, the peripatetic Huberta was dead. Despite being declared royal game and thus protected, a cretinous gang of farmers shot her. They were arrested and fined £25, but the deed had been done, and an incredible saga had come to an end. Well, not quite. Postmortem examination revealed that Huberta was, in fact, Hubert. His remains were sent to a taxidermist in London, and a year later, he returned preserved for posterity, and 20,000 people turned out to celebrate.

Perhaps, though, the thread that binds all these stories together is the importance of migration in the health of ecosystems around the world. At the very least, we need to make sure that natural corridors, migration pathways, and ancient and new routes that may channel millions of animals, or perhaps just a single individual with a bee in its bonnet, remain open.