Humans are driving migratory animals—sea turtles, chimpanzees, lions and penguins, among dozens of other species—towards extinction, according to the most comprehensive assessment of migratory species ever carried out.

The State of the World’s Migratory Species, a first of its kind report compiled by conservation scientists under the auspices of the U.N. Environment Programme’s World Conservation Monitoring Centre, found population decline, a precursor to extinction, in nearly half of the roughly 1,200 species listed under the Convention on Migratory Species (CMS), a 1979 treaty aimed at conserving species that move across international borders.

The report’s findings dovetail with those of another authoritative U.N. assessment, the 2019 Global Assessment Report on Biodiversity and Ecosystem Services, that found around 1 million of Earth’s 8 million species are at risk of extinction due to human activity. Since the 1970s, global biodiversity, the variation of life on Earth, has declined by a whopping 70 percent.

Migratory species face unique and heightened risks because they rely on connectivity among multiple ecosystems spanning national borders and because their predictable migration patterns make them vulnerable to poachers. The State of the World’s Migratory Species, released Monday, found that one in five species on the CMS list is threatened with extinction—and for listed fish, that number is a stark 97 percent. 

The report’s authors say the numbers could be even more dire because the CMS treaty, also known as the Bonn Convention, covers only about a quarter of the world’s known migratory species—mammals, birds, reptiles, fish and one insect (the monarch butterfly). To be listed on one of the treaty’s two appendices, the 133 state parties must agree on the listing, and the species must generally either be endangered or have an “unfavorable conservation status.” 

The report found that an additional 399 migratory species not covered by the treaty, including carp fish, ground sharks and petrels, also have declining populations and would benefit from CMS treaty protections. 

To compile the report, the authors reviewed scientific literature and performed novel analyses using data from sources including the IUCN Red List of Threatened Species, the Living Data Index, the World Database of Protected Areas and CMS technical reports. 

Among those analyses was an assessment of key locations where migrations take place. Pinpointing those areas was no easy task. Each year, billions of wild animals embark on journeys across Earth’s land, waters and sky. From troops of mountain gorillas knuckle-walking across central Africa’s rainforests, to monarch butterflies fluttering thousands of miles from North America to Mexico, and giant manta rays winging their way through the oceans, these species travel short and long distances seeking out favorable living conditions, food and places to breed. 

The researchers were able to identify 9,500 key locations for CMS species. A little over half of those areas lack protected status while other key locations have yet to be identified. 

Amy Fraenkel, executive secretary of CMS, called the report’s findings “startling” and pointed to the myriad of ways that humans and non-human parts of nature depend on migratory species. 

As they make their way around the planet, migratory species contribute to the complex web of life on Earth by distributing seeds and nutrients, pollinating plants and controlling other species’ populations. Their loss can change the entire ecology of the ecosystems they inhabit. They also provide human communities with sources of food and income, contribute to overall ecosystem health and provide spiritual and aesthetic value. 

Fruit bats, for instance, pollinate flowers and disperse seeds, helping cashew, passionfruit, fig and other fruit and nut trees reproduce. The Andean condor has cultural and spiritual significance for many Indigenous peoples and helps eliminate animal carrion, reducing the risk of disease. And a range of iconic animals like the African elephant and jaguar draw tourists hoping to catch a glimpse of their splendor, supporting local economies. 

The report, like other authoritative assessments on Earth’s biodiversity, is unequivocal about what is driving the mass loss of life: the activities of just one species—humans. 

Root Causes of Population Decline

Unsustainable human activities threaten migratory species in a myriad of ways. By far, the two greatest pressures come from habitat loss and overexploitation, report co-author Kelly Malsch said. 

Habitat loss, largely driven by land use change for agriculture, is degrading and fragmenting the ecosystems that are fundamental for migratory species survival, affecting three-fourths of all CMS species. Mountain gorillas, for example, have lost portions of their habitat to deforestation caused by the expansion of agriculture. 

Overexploitation from hunting, fishing and incidental catch (the unintentional taking during fishing operations) affects seven out of ten CMS species, like the gray-headed albatross, birds whose population decline is largely attributed to their incidental capture in longline fisheries. Those and other entrapments in nets and lines cause immense amounts of suffering, raising serious ethical and animal welfare issues. Many CMS listed animals have complex social networks and high levels of intelligence.

Also driving the loss of migratory species is pollution from pesticides, plastics, heavy metals, light and noise, as well as the construction of roads, fences, dams and other infrastructure that creates physical barriers. With the human population surpassing 8 billion people in 2022 and a growing global economy, nearly a quarter of Earth’s surface is now affected by artificial lights, which disorient migrating animals and can cause life-ending collisions with human infrastructure. 

Increasingly, all of these threats are amplified by human-induced climate change, which is itself a driver of migratory species loss. Rising temperatures, changes in precipitation, extreme weather, sea level rise and ocean acidification are outpacing species’ ability to adapt. 

Animals’ migratory journeys are calibrated to coincide with optimal conditions for feeding and breeding. Warmer temperatures have snarled that synchronicity, causing some species to “arrive too early, too late or not at all,” the report said. In the case of Great Barrier Reef green turtles, rising temperatures have been linked to changing sex-determination, with an increasing number of new hatchlings born female. And in African wild dogs, extreme heat has been linked to less foraging behavior and decreases in new pups. 

Impacts on migratory species from climate change are expected to worsen in the coming decades. Last week, the European Union’s Copernicus Climate Change Service determined that the Earth’s average global temperature over the last 12 months had breached the critical 1.5 degree celsius threshold, portending grim prospects for certain species like narwhals, known as the unicorn of the sea for the long tusk protruding from their heads. Narwhals are highly sensitive to warming oceans. They depend on Arctic habitats where they feast on fish underneath sea ice. Warmer seas will impact the species’ ability to find sources of food, while growing ship traffic through melting Arctic areas will increase anthropogenic noise, disorienting narwhals and further harming their ability to forage for food. 

Although the report features much devastation and bleak trends, the authors emphasize that further species declines and habitat destruction are not inevitable. 

“There is hope if we act now to protect, connect and restore species populations and their habitats,” said Malsch, the head of Nature Conserved at the U.N. Environment Programme World Conservation Monitoring Centre.

Malsch pointed to the case of the humpback whale as a success story. The giant of the sea travels thousands of miles across all of Earth’s oceans. Thanks to a moratorium on commercial whaling, its population has rebounded to an estimated 80,000 globally, though subpopulations of humpbacks in the Arabian sea remain endangered. 

The authors described a range of actions that can be taken to reverse the negative trends highlighted in the report: identifying additional key habitats, combating overexploitation, expanding conservation areas, restoring and maintaining connectivity between protected areas, and accounting for migratory species needs when building human infrastructure. Creation of protected areas, and their management, must respect the rights of Indigenous peoples and local communities, who have proven to be the best stewards of ecosystems, the report said. 

Enforcement of the legally-binding CMS treaty is largely limited to the naming and shaming of violators through the treaty’s review mechanism. The United States is not a party to the treaty, but has signed onto non-binding Memorandums of Understanding developed under the auspices of the CMS.