The great migrations of the world are dwindling.
The mule deer is stumbling upon new oil wells along its ancient route, and watching helplessly as the greenery it once chased retreats ahead of it, and the icy Wyoming winter sets in.
Wildebeest, hemmed in by roads, railways, gas pipelines, farms and housing, are halting what is arguably the world’s most dramatic migration.
Birds, insects and the monarch butterfly are similarly finding themselves buffeted by new winds, stalled by a shifting Spring, or simply marooned, without the forests or host plants they had travelled all that way to meet.
The results are dramatic and far-reaching.
Forest fires in Africa. And dying baby giraffes.
Changes in bird diets in the Arctic, and desperate new flight schedules.
A sad silence in California, where once there was the hum of millions of winged things.
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The United Nations 2024 State of the World’s Migratory Species report found that nearly half of the world’s migratory species are on the decline, with migrations shrinking too.
Even as human activity disrupts these ancient ways of life, efforts are underway to help. A multinational initiative is working to clear at least parts of the Egyptian vulture’s massive arc (40 countries and three continents) of wind farms, power lines, poachers and poisoned bait.
A reserve in Mexico seeks to offer safe haven to the monarch butterfly. (Read the stories alongside for more on this and other such efforts.)
Meanwhile, we are still learning how little we know.
It was only last year that a comprehensive aerial survey of war-torn South Sudan revealed that the largest land-mammal migration on the planet isn’t the sea of movement formed by wildebeest in the Serengeti-Mara region of Kenya-Tanzania but rather what is now being called the Great Nile Migration, which involves gazelle, buck, antelope and a range of other species, amounting to six million animals, galloping from the Boma Badingilo Jonglei landscape in southeast South Sudan to the Gambella National Park in Ethiopia.
The Great Nile Migration still isn’t the largest on Earth by volume.
That tag, for now, goes to the 10 billion tonnes of zooplankton that swim to the surface of our oceans every night to feed, in what is called a diel vertical migration.
There is so much we don’t know. Read on for a bit more, on what we do.
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THE TRAIL GOES COLD FOR WILDEBEEST
Some wildebeest don’t migrate any more.
Forced to stay put, their absence has caused wildfires, altered landscapes, even resulted in a higher incidence of giraffe-calf death.
As tourism numbers rise and economies grow, roads, railways, oil and gas pipelines, housing, and fences to protect agriculture and livestock are blocking historical routes.
This has forced most of Africa’s scattered wildebeest herds to alter, shrink or give up their migrations.
“There used to be dozens of long-distance migrations of this species all over the continent until the turn of the century,” says Derek Lee, principal scientist with the US-based research and conservation group Wild Nature Institute. “Only three populations continue to migrate.”
Those three are the 1.5 million wildebeest that make up the Great Migration across the Serengeti-Mara in Kenya-Tanzania (alongside a few hundred thousand gazelles and zebras), the Tarangire migration in Tanzania, and Kafue in Zambia.
Even these face challenges from developments along their path, often for tourism.
As for the rest, wildebeest sicken without their habitual movement. Gene pools shrink as clusters become isolated; habitats come under intensifying strain, as they draw vast stores of food and water from a fixed swathe of land.
These aren’t the only consequences.
Wildebeest are nature’s lawnmowers, consuming tonnes of grass per herd, in a single day. Without them, wildfires see a rise in incidence and intensity. Meanwhile, the soil suffers, without the tonnes of nourishing excrement.
The migrating hordes essentially controlled parts of the carbon cycle.
“Nothing can replace the complex ecosystem effects these hordes had because only wildebeest move in such great numbers. African ecosystems are being degraded by the loss of their movement,” Lee says.
The lack of wildebeest movement is even impacting the survival rates of certain young animals.
A 2016 paper published in the journal Ecology and Evolution, lead-authored by Lee, showed that the seasonal presence of wildebeest in giraffe territory in Tarangire essentially provided more prey for predators, giving giraffe calves a better chance of survival. The study indicates that, as the thundering hordes go missing from these landscapes, baby giraffes could be paying the price.
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AN OBSTACLE RACE FOR MULE DEER
Continents away, in the US, another large herbivore is having its routes disrupted.
Every winter, as the mule deer races south down its usual paths, it is finding gas fields in its way.
Forced to find new routes, its carefully timed exodus is delayed. The result: It often cannot keep up with the “green wave” of retreating vegetation. It must now spend months struggling to survive in the long, icy winters of Wyoming.
The deer still try to make it, every year, and are typically delayed, a 14-year study by researchers at University of Wyoming found.
“This study makes clear that when development continues to erode the value of corridors, it could have long-term effects… But it points to conservation solutions as well,” co-author Matthew Kauffman of University of Wyoming said, in a statement. “Once migration corridors have been mapped, development can be planned to minimize disruptions to migrating herds whether in Wyoming, the American West, or wherever landscapes are rapidly changing.”
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AT A CROSSROADS IN THE SKY
The Egyptian vulture is hard to miss.
Its bare-skinned face is the yellow of chicken feet. It wears a spikey mane, and poufy feathers halfway down its legs. A beak shaped like a talon helps its scrape the meat off dead animals.
It is small, particularly for a raptor, growing to about 2 ft in height, with a wingspan of about 5 ft. But it’s a bird that uses those wings dramatically.
The Egyptian vulture’s migratory route arcs across 40 countries on three continents: Europe, where it breeds, and Africa and Asia, where it winters and rears its young.
That arc is ending prematurely and abruptly, for a number of individuals, as they crash into new power lines and wind farms thrown up across their migratory routes.
Older threats persist too, such as poisoned bait laid out by farmers in Europe, aimed at predators attacking their cattle. And, in Africa, the poaching and sale of this threatened species at exorbitant rates, for use in local medicine.
The result: Egyptian vulture numbers are falling fast.
There has been a 80% decline in the Balkan Peninsula, with number of adult pairs going from 600 in the 1980s to 60 pairs in 2019. There are only about 4,000 individuals overall left in Europe, according to the Zurich-based Vulture Conservation Foundation.
Over the past two decades, there has been a concerted effort to safeguard their three migratory pathways: the Central Asian flyway from Uzbekistan and Kazakhstan to the open scrublands and deserts of Rajasthan and Gujarat; the Western European flyway from France, Spain and Portugal to Western Africa via Gibraltar; and the Eastern Mediterranean flyway from Turkey and the Balkans to the Middle-East and East Africa, says José Tavares, director of the Vulture Conservation Foundation.
With funding from the European Union, an alliance of 20 NGOs from 14 countries launched the initiative Egyptian Vulture New LIFE in 2017, and have been working to identify hazardous practices and developments, as a first step towards easing such threats. Meanwhile, increased tagging is helping identify the exact locations and causes of death in individual cases.
“A risk-sensitivity map is being created, which overlays the existing network of electrical lines with the density of birds and their flight paths. Simple steps such as windmill companies taking migratory routes into account and taking on the extra cost of insulating their wires can help,” Tavares says. “Other migratory birds that use the same routes, such as buzzards, eagles and storks, stand to benefit too.”
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A TERN FOR THE WORSE
Spring in the Arctic is a time of cinematic change.
Ice gives way to green grass and bright flowers. Insects, butterflies and spiders come out of hibernation. Polar bears emerge to mate and feast (on frolicking seals).
Birds fly in, in the tens of millions, some from the literal ends of the earth.
The Arctic tern travels all the way from Antarctica, to feed and breed near the North Pole.
The thing about Spring here is, it is also very brief, typically just eight to 10 weeks long.
For millions of years, this was enough. The little tern, and a range of other birds, bred, hatched and then cared for their young for the necessary six weeks or so, before they could start to fend for themselves.
Now, that is changing. With ambient temperatures rising and sea-ice extent shrinking, snowmelt is setting in as much as two weeks earlier than it did in 1985.
The Arctic tern is arriving to find the party already underway; its chicks are hatching at a period in the new spring cycle when the glut of food sources such as mosquitoes and flies is already dwindling.
Some species have begun trying to adjust.
A 2018 study found that barnacle geese now arrive up to 13 days earlier than their usual timeframe in April. Tagging revealed that they are skipping rest stops along their 3,000-km journey from the North Sea to the Russian Arctic, to make the most of their Spring feeding grounds.
The little Arctic tern, 15 inches tall with a wingspan of 30, is travelling so far (about 35,000 km) that it cannot accurately assess conditions at its destination or adjust to account for them. “Only from closer by, let’s say 1,000 km, when birds are approaching their breeding grounds, can they start to make adjustments in response to how a Spring is progressing,” says Thomas K Lameris, assistant professor of migration ecology at Groningen University in the Netherlands.
Even for the barnacle geese, meanwhile, it isn’t all good news. They may arrive in time for early snowmelt, but their egg-laying cycles changed much less. So their chicks too miss the seasonal food peak of nutritious grass, says Lameris. Chicks of shorebirds such as red knots may also now miss that window when crane flies and larger species of mosquito are really abundant.
“In such years, they eat different insects, which shows high flexibility and is rather a good sign,” says Lameris. “But that might not always result in the best diet, and could affect their growth.”
In the end, adaptation might be the only option though, he adds, “even if the new choices aren’t always the best ones.”
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FORESTS LOSE THEIR WINGS
Like most insects, butterflies are not terribly good fliers. They often rely on wind currents to help them to their destinations. As rising temperatures affect forests, vegetation and Earth’s massive wind systems, the monarch butterfly is finding itself caught in the crosshairs.
It isn’t the only one, but it is a good bellwether of what is unfolding in the world of migratory insects, because few species have been studied so extensively, for so long. The wealth of data gathered on these lepidopterans since the 1950s is giving researchers unique insight into how hard these butterflies have been hit.
There was a time when they arrived in California in such large numbers, one could hear them congregate. As millions of the winged things settled in, after a 1,000-km journey from the Rocky Mountains, it was said they made a sound like that of a rippling stream or a summer rain.
They don’t make this sound any more. There simply aren’t enough of them.
The numbers that arrive in California now stand at 5% of what they were in the 1980s, according to a 2024 report by the Xerces Society for Invertebrate Conservation in Oregon.
The dip has been similar in the eastern population, which flies 4,000 km from the Rocky Mountains to the fir forests of central Mexico, says Emma Pelton, senior conservation biologist at the Xerces Society.
These butterflies once covered a staggering 45 acres of these forests, in 1995-96. (Monarchs are so small and numerous that their population is calculated by the area they occupy.) By 2003-04, that area had fallen to 27.5 acres. In 2024-25, they occupied just 4.42 acres.
“Forest loss in Mexico had been one of the major causes of the decline,” says Leslie Ries, an ecologist at Georgetown University and head of the North American Butterfly Monitoring Network. Herbicides for genetically modified crops made things worse in the early 1990s, she adds, by killing off the native milkweed that is the larval host plant for the monarch butterfly. “The most likely culprits impacting them now are insecticides and climate,” she adds.
Efforts are being made to stem the loss. A 56-hectare Monarch Butterfly Biosphere Reserve was notified by Mexico in 1980, and declared a UNESCO World Heritage Site in 2008.
In California, a number of state parks serve as protected areas too.
Across the US, organisations distribute monitoring kits and citizen scientists set up monarch waystations, complete with milkweed plants. These may help, but they cannot, of course, replace the forest networks that supported this species over tens of thousands of years.
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MEKONG GIANT CATFISH: A BATTLE IN THE DEPTHS
The Mekong giant catfish is a toothless bottom-feeder. This is not the admonition it sounds like.
The iconic species can live to the age of 60, grow to 10 ft long and weigh up to 300 kg. As for the bottom-feeder detail, they play a vital role in keeping the river and riverbed healthy, by munching on algae and detritus.
For a giant, the species is rather elusive, though. It is known to swim hundreds of km along the Mekong River, between its feeding and spawning sites, but is rarely sighted.
All this makes tracking, monitoring and conservation difficult. Meanwhile, dams and overfishing are altering its massive riverine ecosystems, causing its numbers to plummet.
Mekong giant catfish were once found all along the 4,900-km length of the river, which winds from China, through Laos, Thailand, Cambodia and Vietnam, before flowing into the South China Sea. Farming and constructing, as well as dams and industrial-scale fishing, now keep the large fish from moving freely, affecting feeding and spawning cycles.
Man-made fish passes help smaller species continue, somewhat, with their lives. Sadly, studies indicate that this behemoth is too large to use these.
As a result of all these factors, the Mekong giant catfish was declared critically endangered by IUCN (the International Union for Conservation of Nature) in 2003.
“To reach their spawning grounds, these fish need a free-flowing Mekong, free of obstructions,” says Kathy Hughes, biodiversity lead with the NGO Wetlands International. “The best mitigation is prior planning. Barriers such as dams should be planned and located to not impact the migration of this species.”
Conservationists are now working to help raise their numbers. Initiatives such as the Wonders of the Mekong Project, funded by USAID (the US Agency for International Development), has a captive-breeding-and-release programme, and is working to tag the fish in the wild.
It is worth noting that the Mekong is also home to species such as the giant barb and giant freshwater stingray, who face the same obstacles as its giant catfish.
With more individuals being tagged and released, perhaps data will help conservationists and researchers figure out how to do more.
