Migratory species under pressure: Nearly every second species is declining worldwide

Migratory species are among the most fascinating phenomena in nature. Every year, birds, fish and mammals often travel thousands of kilometers between breeding grounds, feeding areas and wintering sites. Yet it is precisely this mobility that makes them especially vulnerable: they depend on intact habitats along their entire migration route.

The UN report State of the World’s Migratory Species – Interim Report (2026) uses current data to show how these species are faring worldwide. The conclusion is clear: The situation continues to deteriorate.

The focus is on species listed as migratory under the Convention on the Conservation of Migratory Species of Wild Animals (CMS), also known as the Bonn Convention. These roughly 1,200 species—from migratory birds to whales, sharks and insects to bats—regularly cross national borders and therefore depend on international protection to a special degree. This does not refer exclusively to classic migratory species in the strict sense (e.g. anadromous or catadromous fish), but also to species that use large-scale, often transboundary habitats and move between important sub-habitats.

The key finding: an alarming trend

The core message of the report can be summarized in the following figures:

• 24% of migratory species are considered globally threatened (nearly one in four migratory animal species) —an increase from 22% in 2024
• 49% of species show declining populations—so nearly every second migratory species is becoming rarer (previously: 44%)
• Of 386 newly assessed species, 26 were moved into a higher threat category, while only seven species improved

This confirms the trend identified in the first report—and it is continuing to intensify. Particularly critical is the fact that many populations are not just declining, but shrinking ever faster. At the same time, it is becoming clear that part of this trend is only now becoming visible because new data are correcting earlier assessments. Species long considered “stable” are increasingly being recognized as declining.

Sharp declines in migratory birds, migratory fish and sharks

The current State of the World’s Migratory Species report shows particularly dramatic developments in several groups of species—especially migratory birds, freshwater fish, as well as sharks and rays.

Migratory birds under pressure

Wading birds in particular are heavily affected: of the 26 species whose threat status worsened, 18 are migratory shorebirds, including, for example:

• The curlew sandpiper (Calidris ferruginea) has likely lost 30 to 49% of its population
• The white-rumped sandpiper (C. fuscicollis) lost 40 to 49%
• The buff-breasted sandpiper (C. subruficollis), a long-distance migrant with a migration distance of up to 30,000 km, was uplisted to Vulnerable
• The Siberian sand plover (Charadrius mongolus) is estimated to have lost 50 to 62% and is now considered Endangered
• The marbled godwit (Limosa fedoa) and the Hudsonian godwit (L. haemastica) were uplisted to Vulnerable

For one species, however, all hope comes too late: the slender-billed curlew (Numenius tenuirostris) is now considered extinct—with no confirmed record since 1995. Its disappearance is seen as a stark warning that population declines must be addressed early.

The situation is also serious for birds of prey: more than 53% of species show declining populations worldwide. Vultures and eagles are particularly affected. The steppe eagle (Aquila nipalensis), for example, is endangered—threatened by habitat loss, illegal killings and collisions with energy infrastructure.

Another example is the great bustard (Otis tarda), the heaviest flying bird in the world. In 2023, it was uplisted from Vulnerable to Endangered—mainly because of intensive agriculture, infrastructure and disturbance.

Migratory fish, sharks and rays in crisis

Migratory freshwater fish are among the most threatened animal groups of all. According to the Living Planet Index, their populations declined by an average of 81% worldwide between 1970 and 2020—in Latin America and the Caribbean the decline even reaches 91%, and in Europe 75%. The main causes of this development are dams and river regulation, the loss of connectivity in river systems, and overfishing.

Sharks and rays are no better off: their populations have declined by around 50% since 1970. Sawfishes (Pristidae), hammerhead sharks and devil rays are particularly affected. The narrow sawfish (Anoxypristis cuspidata) was recently placed in the highest threat category (Critically Endangered) after an estimated decline of more than 80%. A substantial loss of range is suspected as the cause, driven by overfishing (including bycatch) and habitat destruction.

Other threatened migratory species

Other migratory species are also coming under increasing pressure:

• The African penguin (Spheniscus demersus) is now considered Critically Endangered—mainly because of overfishing and climate-driven changes to its food base
• The Humboldt penguin (Spheniscus humboldti) and the Peruvian pelican (Pelecanus thagus) were heavily impacted by outbreaks of avian influenza (H5N1)
• The Amazon river dolphin (Inia geoffrensis), the Tucuxi (Sotalia fluviatilis) and the Arrau turtle (Podocnemis expansa) are suffering from increasing dam construction and the loss of river dynamics in the Amazon region

The causes: What is driving the decline?

The causes of the decline of migratory species are diverse. Classic threats continue to operate, but are increasingly being amplified by new risks. Migratory species are especially vulnerable because they are exposed to different dangers along their entire route. Several pressures often act at the same time and reinforce one another.

The main drivers include:

• Habitat loss and fragmentation
  The destruction and fragmentation of habitats remain the central cause of species decline.
  – Shorebirds are losing important stopover and wintering areas worldwide—such as the tidal flats of the Yellow Sea
  – Mammals such as the Mongolian gazelle (Procapra gutturosa) are losing their freedom of movement because of roads, fences and rising traffic—their mobility declined markedly between 2002 and 2021
• Infrastructure as a barrier
  Roads, railways, pipelines and fences cut through migration corridors and interrupt movement patterns that are thousands of years old.
  The Saiga antelope (Saiga tatarica) provides one example: after a railway line was built in Kazakhstan, the antelopes stopped their cross-border migrations and thus lost access to important winter habitats in Uzbekistan.
  Such barriers can isolate entire populations—with long-term consequences for their survival.
• Overexploitation of the oceans
  For many marine species, overfishing remains the greatest threat:
  – Sharks and rays are targeted by fisheries or die as bycatch
  – Sea turtles are also severely affected—despite local recovery trends
  The report emphasizes that bycatch remains the most severe pressure on sea turtles and has improved little since 2011.
• Climate change as an amplifier
  Climate change is altering key ecological processes:
  – shifts in breeding times
  – changes in food availability
  – more frequent extreme weather events
  Long-distance migrants are particularly affected, such as migratory birds that depend on agriculturally shaped habitats.
• Disease and new risks
  New threats are also increasingly emerging:
  – Since 2021, highly pathogenic avian influenza H5N1 has caused mass mortality worldwide
  – Numerous species are affected—from penguins in South America to cranes in Asia
  – Marine mammals have also already been infected on a larger scale
  Species with long lifespans and low reproductive rates are especially sensitive to such additional losses.

The decline of migratory species cannot be traced back to a single cause. Rather, it results from an interaction of global changes that affect entire migration corridors. Successful conservation must therefore start exactly there: connected, international—and along the entire route.

The winners: Where protection works

As alarming as the overall situation is, the UN report State of the World’s Migratory Species also shows this: Targeted conservation works. Several examples demonstrate that even severely threatened species can recover:

• The Saiga antelope has recovered significantly after massive population losses caused by disease outbreaks in the 2010s. It was downlisted from Critically Endangered to Near Threatened. Stronger measures against poaching, the protection of key habitats and close cooperation with local communities in Kazakhstan were decisive.
• The scimitar-horned oryx (Oryx dammah), once extinct in the wild, is an example of successful reintroduction: following release projects in Chad, the species was classified as Endangered. Today, around 575 animals live in the wild again.
• The Mediterranean monk seal (Monachus monachus) is also showing a positive development. Thanks to targeted conservation measures and a slow expansion of its range, it was downlisted from Endangered to Vulnerable. Even so, the situation remains fragile—worldwide there are still fewer than 1,000 individuals.
• A similar pattern can be seen in many sea turtles: numerous populations are now stable or increasing again. This development is the result of decades of conservation efforts, such as nesting-site protection, catch restrictions and international agreements.

These examples make one thing clear: if threats are reduced in a targeted way and habitats are protected, even severely depleted populations can recover.

What needs to happen now

The report makes it clear: without substantially stronger conservation measures, the negative trend will continue. Although knowledge about migratory species has improved considerably in recent years—for example through new tracking technologies and international initiatives to map migration movements—there is still a major deficit when it comes to actual protection.

More than 9,000 Key Biodiversity Areas of central importance for migratory species have now been identified worldwide. Nevertheless, only a little more than half of these areas are actually covered by protected areas. In some regions, especially in Asia, the share is significantly lower. For numerous highly threatened species, even less than a quarter of their most important habitats are effectively protected. This means that many crucial breeding, stopover and feeding areas remain unsecured.

One problem is that migration does not take place in individual, isolated habitats. Migratory species depend on a network of interconnected areas that often stretches across thousands of kilometers and several countries. New tracking data show how sensitive these systems are: even single obstacles such as roads, fences or energy infrastructure can interrupt movements and isolate populations from one another. Protecting individual areas therefore falls short if the connections between them are lost.

At the same time, many of the known threats persist or are even increasing. Overfishing and bycatch continue to endanger numerous marine species, while pesticides, plastic pollution and light pollution create additional pressures. Climate change intensifies these developments by altering habitats and shifting ecological processes.

Against this backdrop, the report’s authors call for much more determined action. In future, conservation measures must be conceived more strongly along entire migration corridors, not just in isolated spots. Equally crucial is closer international cooperation, because migratory species do not stop at political borders. Their protection can only succeed if states coordinate their actions along the entire route.

Migratory species connect ecosystems across continents. Their decline is therefore not just the loss of individual species, but a sign of profound changes to our natural foundations of life. It is correspondingly urgent to expand existing conservation approaches before more of these global connections are lost.

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Source

• UNEP-WCMC (2026): State of the World’s Migratory Species – Interim Report (2026)
  https://www.cms.int/sites/default/files/publication/swms_interim-report_2026_e_0.pdf