Every year, humpback whales travel thousands of miles from the polar regions to the tropics for a variety of reasons, including to give birth to their young. When they live and feed in the higher latitudes, they build up blubber by consuming lots of krill, their typical food. As they migrate toward the equator, they subsist on that fat, defecating plumes of nutrients, fertilizing tropical waters and fueling the growth of microorganisms that other marine animals feed on. In short, the iconic marine mammals act as giant, globe-trotting factories that distribute nutrients.
Similarly, thousands of species, including billions of animals, make migratory journeys every year over land, in the oceans and in the air. They cross countries and continents, and some travel thousands of miles to feed, breed or hibernate. They play an important role by transporting nutrients, hunting pests or pollinating flowers, including crops. “Migratory species are an integral part of the ecosystems in which they occur,” said Amy Fraenkel, executive secretary of the Convention on Migratory Species, an international body that aims to conserve and protect these animals. “And what makes them unique is the fact that they move, which means they can provide a number of specialized services.”
Now a new State of the World’s Migratory Species Report, published by the Convention on Migratory Species, reveals the shocking and terrible plight of our planet’s animal pilgrims. Of the thousands of migratory creatures that inhabit the Earth, the body lists 1,189 in need of international protection. That includes 962 species of birds, 94 species of land mammals, 64 species of aquatic mammals, 58 species of fish, 10 species of reptiles and one insect, the monarch butterfly. The report was prepared for the convention by conservation scientists from the United Nations Environment Program’s World Conservation Monitoring Center.
Overall, more than one in five species listed by the Convention are considered at risk of extinction based on an assessment by the International Union for the Conservation of Nature (IUCN), a global organization that maintains a ‘red list’ of species who are in difficulties. The IUCN uses a slightly different definition of migratory species than the Convention on Migratory Species. The IUCN defines migratory species as those that must travel from one habitat to another at different times of the year to sustain themselves – think humpback whales, red knots or monarch butterflies. The framework of the Convention on Migratory Species is more human-centric. “The definition we use under the convention has to do with whether species routinely and regularly cross national boundaries,” Fraenkel explains.
Forty-four percent of species listed by the Convention on Migratory Species are in declining populations, and the organization points out that the list is not comprehensive. Nearly 400 migratory bird species that the IUCN considers endangered or near-threatened are currently not listed by the convention.
The risks are not the same for different creatures. While birds have the largest number of species on the list, migratory fish are in the greatest decline. Nearly 97 percent of the fish mentioned are in danger of disappearing.
Benjamin M. Van Doren, a biologist at the University of Illinois Urbana-Champaign who was not involved in the report but whose research focuses on migratory birds, was shocked by this fact. “The area that concerned me the most, or surprised me the most, given that I was focusing on birds, was that fish are so endangered,” he says. North America alone has lost about a third of its bird population since 1970. “But compared to birds, the report showed that migratory fish are in even greater trouble. I’m sure this wouldn’t come as a surprise to a fish biologist, but for me it was a real eye-opener.”
Both migratory fish and birds provide enormous benefits to the various ecosystems they travel to. When salmon migrate upstream to spawn, they serve as food for terrestrial animals, such as bears. Both the salmon carcasses strewn near the waterways and the bear feces provide a fertile contribution to the forest. And various migratory birds that fly around the planet eat and excrete seeds during their journey, causing plants to grow where they would not otherwise grow.
One of the reasons that migratory birds become extinct is that traveling involves many dangers. Many migratory animals regularly travel thousands of kilometers, Fraenkel explains. Along the way, they face unpredictable weather, changing climates, habitat loss, shortages of food sources, predation, disease and other dangers. They depend on at least two ecosystems to sustain their lifestyle – and in many cases on a few temporary stopovers. And if any of these places can no longer support them, or if they can’t physically get there, their entire population could die off, sending ripples through entire ecosystems.
Van Doren gives a striking example. “The Delaware Bay in the eastern United States is a critical stopover point for many migratory birds, especially the red knot, an example of an endangered migratory species,” he says. “And if the horseshoe crab eggs they feed on are not available at the right time and in the right quantities, they will not reach the Arctic in time to reproduce successfully, and their population could collapse.”
Fraenkel says countries’ policies often create obstacles to their habitats surviving, thriving and maintaining their habitat. Fraenkel mentions elephants, which are often described as “ecosystem engineers.” As they feed on young trees and shrubs, they thin out the new shoots that compete for water, space and sun. The saplings that survive have a huge advantage: they grow bigger and stronger and store more carbon in their trunks. If elephants cross from a country where they are safer to a country where poachers kill them, the forest on both sides of the border will suffer.
“Most of the threats to the species come from human activities,” Fraenkel said of the report’s findings. “The reason why [the Convention on Migratory Species] exists is to bring countries together to agree on key priorities for shared species.”
The report shows that humans are the main cause of the decline of the species on their list. Hunting and overfishing, both intentional and bycatch, can be harmful. People build roads, fences and train tracks, and cut down forests. They use pesticides, dump plastic waste and cause a lot of noise and light pollution.
A single road can disrupt the migration path of land animals, which has been used for centuries. A dam can make it impossible for fish to make their annual spawning trips. A wind farm that is in the path of migratory birds can decimate flocks over the years. Overall, the degradation and fragmentation of the creatures’ native habitats and pathways serves as a massive disruption to their movement. Three out of four species listed are affected by degrading and fragmented habitats.
Fraenkel points out that people can solve many of these problems. When building roads and tracks, humans can create viaducts and underpasses that serve as so-called wildlife corridors. The passages connect two sides of a forest or mountain range, allowing the species to move as they did decades ago. Windmill farms can be built away from the flight paths of birds and bats. As a city expands, more parks and green spaces can be created so that birds maintain their stopover sites. And some species may simply need stronger protection, consistent across neighboring countries. “These organisms make important contributions to all the places they spend their time,” says Van Doren, so their decline will inevitably impact more than one ecosystem, including in entirely different parts of the world.
Fraenkel cites some success stories from the recent past to demonstrate that recovery is possible. By the 1990s, the saiga antelope in Central Asia had declined by 95 percent, from 1.5 million to just 50,000. Traditionally, Saigas were hunted for food and their horns, but they also could no longer migrate when necessary because human-built obstacles disrupted their paths. That caused an overgrowth of grasses that saigas no longer grazed, changing the entire landscape. A concerted international effort led to the revival of the steppe and their migration routes, including the removal of fences that blocked the routes. Local communities also reduced hunting, allowing the animals to recover, at least in parts of their range, such as Kazakhstan. According to the IUCN, their population will rise again to around 1.3 million in 2022.
When whaling was made illegal, many of these marine mammals were on the brink of extinction.
Migratory species benefit ecosystems that support human and planetary health. If people want to enjoy functioning forests, rivers, mountains, steppes and oceans, they have to figure out how to keep these animals alive, Fraenkel notes. “A forest without species is not exactly a functioning forest,” she says.