For , scientists have scratched their heads over one of the most basic mysteries of the natural world: Where do birds go?

appear and disappear with the seasons every year. Early naturalists offered explanations for the disappearances that today seem fantastical: Birds , one theory went. Others suggested they or even .

The truth, that these small animals were traveling thousands of miles across the planet, must once have seemed just as improbable.

Then, in the early 1800s, dramatic evidence emerged supporting the theory of migration. White storks began appearing in Germany with African arrows embedded in their bodies. These birds became known as .” They provided compelling evidence that birds disappearing from Europe were traveling all the way to Africa and back.

When storks began showing up with African arrows in their backs, early ornithologists made an important discovery: Birds migrate.

Almost two centuries later, scientists are still asking the same question, but our ability to answer it has been transformed.

For most of ornithological history, scientists understood migration through brief glimpses of a bird, a specimen collected somewhere else, or the rare instance of a banded bird recovered hundreds or thousands of miles from where it had been marked. From these fragments of intelligence, scientists reconstructed journeys that took place largely beyond their view.

Today, it’s possible to see the journeys themselves, almost in real time.

A century of following birds

Bird banding was used to attempt a systematic approach to connect these fragments of information. Since the early 1900s, researchers have on birds and hoped someone, somewhere, would encounter them again.

Of . That generally told scientists just two things: where a bird was banded and where it was encountered again. Everything between them remained invisible.

Carefully attaching a band to a bird’s leg allowed scientists to see where that bird ended up, but it couldn’t show its entire journey.

Over the past quarter-century or so, the tools used to determine where birds go have changed dramatically.

Tracking devices can now be carried by increasingly smaller birds, and communicating with land-based receivers or satellites orbiting the earth. Testing in feathers and other tissues can reveal where a bird originated. can distinguish populations.

At the same time, the extraordinary has created another revolution.

Millions of observations by bird-watchers submitted to , an online database to record the birds they see, across a continent throughout the year in ways early ornithologists could scarcely have imagined.

Collectively, these methods open an extraordinary new window into migratory birds and one of nature’s most remarkable behaviors: migration.

Burrowing owls breed in the Western U.S., raising their young in burrows often taken over from ground squirrels or prairie dogs. In winter, they migrate to Southwestern states, Mexico or Central America.

Discovering unknown migrations

More than are migratory. Yet scientists have known surprisingly little about where specific populations go.

A species like the may breed across thousands of miles of North America, with different breeding populations migrating to entirely different places for the winter. Birds breeding in one part of the continent may travel one route and encounter one set of environmental conditions, while members of the same species experience a completely different set of conditions along another route.

The yellow-billed cuckoo has three main flyways but many other routes between the U.S. and South America.

These connections between where a bird breeds and where it spends the winter is called . They are critical for understanding everything from the consequences of climate change on birds to how avian pathogens and diseases spread, to a species’ basic ecology.

We are and who have spent almost 15 years along with a team of contributors compiling this rapidly expanding knowledge on bird movement into . The atlas, being published on Nov. 3, 2026, by Princeton University Press, covers the latest information on seasonal movements for nearly 600 species and combines a century of bird-banding data with eBird observations, tracking studies, stable isotope testing, genetics and other sources of information.

What emerges is a picture of migratory birds that is both more complicated and more remarkable than the simple arrows pointing between breeding and wintering ranges on a map.

Consider the . These birds breed over a wide range of the eastern two-thirds of the U.S. but migrate to a relatively small wintering area in the of northern Argentina, Paraguay and southern Bolivia.

The peregrine falcon travels as far north as Alaska in summer, then some individuals return as far south as South America.

In contrast, that breed in Alaska migrate almost directly south, dispersing across the Americas to wintering grounds that extend as far as southern South America.

Discoveries like these are accumulating rapidly. Collectively, they amount to a renaissance in our understanding of animal movement never before imagined.

Living masterpieces

The more clearly scientists can follow individual birds and populations across the planet, the more extraordinary these species can seem.

Migratory birds such as the and cross oceans, deserts and mountain ranges. Some, like the . Others, like the American redstart, return year after year to and locations.

In winter, large flocks of sandhill cranes can be found in places like Bosque del Apache, N.M., and Anahuac National Wildlife Refuge, Texas.

They navigate landscapes and respond to winds, weather, food and environmental conditions across enormous geographic scales.

The Atlas of North America’s Migratory Birds’ combines illustrations and maps to show where bird populations go when they migrate.

We see these species and their migrations as among evolution’s great living masterpieces. That’s why we combined science with natural history and artist extraordinary illustrations of the birds themselves. The maps allow us to see where birds travel, and the art brings the species to life.

Together, they make visible something that humans could only imagine for most of our history.

A map for conservation

North America has during the past half-century, and many migratory species continue to decline.

To understand why a population is declining and help save it, researchers need to understand the species’ entire annual cycle: its critical stopover habitats, wintering grounds and threats along its migration routes.

For much of the history of ornithology, scientists studied birds primarily during their breeding season. That made practical sense. – singing, defending territories, building nests and raising young.

Male buff-breasted sandpipers perform a courtship dance on the Arctic tundra to attract their mates.

But a migratory bird may spend only a few months of its life in its breeding grounds. Conditions such as weather, food availability and habitat quality encountered during migration can .

Drought thousands of miles away can affect a bird’s condition months later. depart and . Declining horseshoe crab populations in Delaware Bay have reduced food availability for migrating , contributing to .

Rusty blackbirds favor wetlands. The males have feathers with rusty edges in winter, but they turn glossy black during breeding season.

The power of people

All of this knowledge has accumulated because people value birds and have devoted enormous time and effort to understanding them.

For more than a century, thousands of bird-banders have woken up before the crack of dawn to set traps, carefully place bands on birds’ legs and release them, often knowing the chances of ever learning what happened to those individuals were exceedingly small.

More recently, tracking technology has allowed researchers to . Those tracks exist because scientists, students, technicians and others have spent countless hours attaching and recovering tags, and contributing and sharing their data.

In this animation, Cornell’s Bird Lab traced the routes of 15 species using tracking signals. From tiny sensors to networks of humans with binoculars, efforts to understand migrations are helping to show where cruicial habitat can be preserved.

Today, millions of bird-watchers contribute observations that, thanks to advances in data science, allow us to across an entire continent.

We have spent much of our careers , and we know the challenges facing migratory species are formidable. But we also have hope for these creatures’ survival. Scientists today know more about where migratory birds go, how populations are connected and what they encounter along the way than at any previous point in history. That knowledge is helping to identify where conservation efforts can make a difference for the future.

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