(JULY 23, 2026) WASHINGTON, D.C. — More than half of the world's migratory bird species are declining according to a major new review led by researchers from Georgetown University, the Smithsonian’s National Zoo and Conservation Biology Institute, and a global collaboration of ornithologists.
Published in Nature Reviews Biodiversity , the paper provides the most comprehensive global assessment of migratory bird population status, threats, and conservation approaches, and presents a new framework for reversing population declines. The review synthesizes decades of research, international monitoring efforts, global biodiversity databases, and conservation agreements to identify what scientists know, where major knowledge gaps remain, and what actions are needed to reverse declines before more species become threatened with extinction.
The findings point to a broader challenge facing global biodiversity conservation. Because migratory animals, including birds, move across continents, oceans, and political boundaries throughout their annual cycles, they depend on interconnected networks of breeding grounds, migration stopover sites, and non-breeding habitats. As a result, they face a complex and often overlapping set of threats throughout their lives, making them among the most difficult groups of animals to conserve.
The authors estimate that approximately 51% of migratory bird species are declining globally across every major flyway on Earth. While nearly 300 migratory species are already considered globally threatened, many once-common and widespread birds are also experiencing substantial population losses, underscoring the scale of the biodiversity crisis.
"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. This review goes beyond documenting the crisis by identifying the major threats, highlighting the critical knowledge gaps, and providing a science-based framework for reversing declines before more species are pushed toward extinction."
Migratory birds are among the most visible and widespread components of global biodiversity. They help regulate insect populations, disperse seeds and pollinate plants, and support food webs across ecosystems and continents. They are also one of the primary ways people connect with nature, with millions of birdwatchers and community scientists around the world contributing observations to global databases that have become essential for understanding bird populations and informing conservation action.
Yet understanding exactly where and why populations are declining, and which of the world’s 11,000 bird species should be considered migratory, remains a challenge. Scientists are increasingly using advances in tracking technology, community science initiatives such as eBird, AI-enabled acoustic monitoring, and population modeling to identify migration routes, understand how populations are connected across seasons, and uncover the drivers of decline, including habitat loss, climate change, invasive species, collisions with buildings and infrastructure, disease, and pesticide use. The authors argue that reversing declines will require conservation strategies that address these threats across entire migratory lifecycles and international flyways rather than in isolation.
"Previous analyses have brought global attention to the fact that North American and European migratory birds are declining at alarming rates," said Nathan W. Cooper of Smithsonian’s National Zoo and Conservation Biology Institute and co-lead author of the study. “But, until now, we did not have a good assessment about how birds are doing across all of the global terrestrial and marine flyways.”
The review outlines a framework for reversing declines that includes expanding monitoring and scientific understanding, strengthening conservation social science, protecting critical habitats, reducing major threats, and increasing international cooperation. It calls for integrating ecological and social sciences to develop conservation solutions that are effective locally and scalable across countries, cultures, economies, and governance systems.
One example of this approach is Road to Recovery , a science-based initiative co-founded by Marra and now housed at Georgetown University. The initiative coordinates a hemispheric response to identify the factors limiting populations and implement targeted conservation actions before species become threatened by combining advances in science and technology with the human dimensions of species conservation.
The researchers stress that despite the concerning trends, species-focused conservation initiatives have a proven record of success. Past efforts have helped recover waterfowl, cranes, shorebirds, and raptors once on the brink of extinction. The challenge, they argue, is scaling those successes to match the geographic scope and complexity of migratory birds.
"These declines are not inevitable," Marra said. "We know conservation works. This review shows that we have the scientific knowledge needed to reverse many of these declines. The challenge now is bringing together the partnerships, resources, and political and public commitment to implement those solutions at the scale migratory birds require."
Nature Reviews Biodiversity
Literature review
Animals
Status, threats and conservation of Earth’s migratory birds
23-Jul-2026
The authors declare no competing interests.