Over 50% of world's migratory birds are declining. It's a bad sign for Earth

A global review has found that more than half of migratory bird species are declining across major flyways. Researchers say the losses demand urgent cross-border conservation to protect ecosystems and essential services.

In Short

• Nearly 300 migratory bird species are already listed as globally threatened
• Habitat loss and climate change are major drivers across migration routes
• Birds face added risks from pesticides, disease and infrastructure collisions

More than half of the world's migratory bird species are in decline, according to the most comprehensive global review of migratory birds ever conducted, raising fresh concerns about the accelerating biodiversity crisis and the growing threats posed by habitat destruction, climate change and human activity.

The landmark study, led by researchers from Georgetown University, the Smithsonian's National Zoo and Conservation Biology Institute, and an international team of ornithologists, has been published in Nature Reviews Biodiversity.

Drawing on decades of scientific research, global biodiversity databases, international monitoring programmes and conservation agreements, the review estimates that around 51% of migratory bird species are declining across every major flyway on Earth.

Nearly 300 migratory species are already classified as globally threatened, while many birds that were once abundant are also experiencing steep population losses.

Researchers say the findings points to the urgent need for coordinated international conservation efforts.

"The scale of migratory bird declines is both alarming and sobering," said Peter P Marra, Dean of Georgetown University's Earth Commons Institute and co-lead author of the study.

"What we're seeing is the predictable consequence of decades of environmental degradation. Yet these declines are not inevitable," Marra said, adding that the review not only documents the crisis but also identifies practical, science-based solutions to reverse the trend.

Migratory birds undertake extraordinary journeys across continents and oceans each year, relying on interconnected breeding grounds, stopover sites and wintering habitats spread across multiple countries.

This dependence on diverse ecosystems makes them particularly vulnerable to habitat loss and environmental changes occurring anywhere along their migration routes.

Beyond their ecological importance, migratory birds provide vital ecosystem services by controlling insect populations, dispersing seeds, pollinating plants and supporting food webs.

They also play a significant role in connecting people with nature, with millions of birdwatchers and citizen scientists contributing observations through platforms such as eBird, which have become invaluable tools for tracking bird populations.

The review identifies several major drivers behind the declines, including habitat destruction, climate change, invasive species, pesticide use, disease, and collisions with buildings, power lines and other infrastructure.

Scientists are increasingly relying on satellite tracking, GPS tags, artificial intelligence-powered acoustic monitoring and advanced population models to better understand migration routes and identify where conservation efforts can have the greatest impact.

According to Nathan W. Cooper, co-lead author from the Smithsonian's National Zoo and Conservation Biology Institute, previous research largely focused on declining migratory birds in North America and Europe.

"Until now, we did not have a good assessment about how birds are doing across all of the global terrestrial and marine flyways," he said.

The researchers argue that reversing the decline will require conservation strategies that extend beyond national borders. Their proposed framework calls for expanding scientific monitoring, protecting critical habitats, reducing human-caused threats and strengthening international cooperation by integrating ecological research with social and economic policies.

The study also highlights examples where targeted conservation has worked. Coordinated efforts over past decades have successfully helped recover several species of waterfowl, cranes, shorebirds and raptors that were once on the brink of extinction.

The researchers believe those successes can be replicated globally if governments, conservation organisations and local communities work together.

"We know conservation works," Marra said. "The challenge now is bringing together the partnerships, resources, political will and public commitment needed to implement those solutions at the scale migratory birds require."

The authors warn that without urgent action, continued declines among migratory birds could have far-reaching consequences for ecosystems worldwide, threatening not only biodiversity but also the ecological services upon which both wildlife and people depend.

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