0
0
A young cuckoo never meets its parents. Its mother lays the egg in another bird’s nest and leaves. A small bird of a different kind feeds the chick until it is grown.
Then, weeks after its real parents have already left for Africa, the young cuckoo takes off alone. It flies at night. It crosses a sea and a desert. And it arrives in central Africa, in a place it has never seen, with nobody to follow.
So how do birds know where to migrate? Every northern autumn, far more people than usual type that question into a search bar, usually after watching a line of geese or cranes pass overhead. It is a fair thing to wonder. Billions of birds make trips like this each year, and many of them do it for the first time with no guide.
Scientists have been working on the answer for more than seventy years. They have most of it. And what they found is stranger than a built-in map. Birds do not hatch with a map at all.
How do birds know where to migrate? The short answer
A migrating bird hatches with two things already inside it: a direction and a timer. Fly this way. Keep going for about this long.
To hold that direction, it uses at least three compasses. One reads the sun. One reads the stars. One reads the magnetic field of the Earth itself.
What it does not have, on its first trip, is a map. A map is something a bird earns by making the journey. That one detail changes how the whole thing looks, and we will come back to it.
A caged bird that has never migrated still tries to leave
The best clue came from birds that never went anywhere.
Researchers raised young songbirds by hand, indoors, where they could not watch other birds leave. When autumn came, the birds changed. They stopped sleeping through the night. They hopped and fluttered in the dark, hour after hour, on the side of the cage that faced the way their kind normally flies.
German scientists gave this a name: Zugunruhe. It means migration restlessness. Nobody taught these birds anything. The season arrived, and something in them said go.
The restlessness even keeps time. Kinds of birds that fly a long way stay restless for many weeks. Kinds that fly a short way settle down sooner. The length of the trip seems to be written inside the bird as a length of unrest.
The direction is inherited too. In 1991 the German bird scientist Andreas Helbig bred two groups of blackcaps, a small European warbler. One group’s families fly southwest in autumn. The other group’s families fly southeast. He paired them up. Their chicks, raised by hand, tried to head roughly south, in between the two. The heading had been passed down from both parents, the way height is.
Three compasses in one small head
A direction is no use unless you can find it in the sky. Birds have more than one way.
The sun. Birds that fly by day can steer by where the sun is, and they correct for the time of day as it moves across the sky. Many night fliers also take a reading at sunset before they set off.
The stars. In the late 1960s, Stephen Emlen at Cornell University put indigo buntings inside a planetarium. Under the fake night sky they pointed the right way. When he turned the sky, they turned with it. Then came the surprise. Young buntings are not born knowing the stars. They learn them, by watching which point the whole sky seems to turn around. When Emlen raised chicks under a sky that turned around a different star, Betelgeuse, they grew up treating Betelgeuse as north.
This is one reason bright lights at night are hard on migrating birds. They steer by the dark. We wrote about that in our piece on a plan to beam sunlight down from space after sunset.
The magnetic field. In the 1960s in Frankfurt, a young researcher named Wolfgang Wiltschko put European robins in a cage wrapped with wire coils. With the coils he could turn the magnetic field around the birds. When he turned the field, the robins turned too.
Later work showed the bird’s compass is not like the one in your pocket. It does not point north. It reads the tilt of the field. Near the poles, the Earth’s magnetic field dives steeply into the ground. Near the equator it runs flat. A bird can sense that slope, so it can tell “toward the pole” from “toward the equator.”
The compass also seems to sit in the eye. It needs light to work, and it fails under red light. In 2021, a team from the universities of Oldenburg and Oxford reported in the journal Nature that a protein from the robin’s eye, called cryptochrome 4, reacts to magnetic fields. The robin’s version reacted more strongly than the same protein from chickens and pigeons, which do not migrate.
The researchers were careful about what that proves. They tested the protein on its own, in a lab, with fields stronger than the Earth’s. Nobody has yet watched it work inside a living bird’s eye. The best guess is a strong one. It is still a guess.
What a 97-million-year-old fossil adds
In 2025, scientists from the University of Cambridge and the Helmholtz-Zentrum Berlin, a research centre in Germany, published a study of some very odd fossils in the journal Communications Earth and Environment.
The fossils are tiny magnetic grains found in old mud from the floor of the North Atlantic. They are about 97 million years old. Scientists call them “giant,” but only because they are ten to twenty times bigger than the magnetic grains some bacteria make. You still could not see one without a powerful microscope. They come in shapes like spearheads, spindles, bullets and needles.
The team made the first 3D picture of the magnetism inside one. It swirls around a line through the middle, like a tiny tornado. That shape, they found, is well suited to sensing two things: the tilt of the Earth’s magnetic field and how strong it is. Those are the two readings an animal would need to work out roughly where it is.
So some animal was very likely steering by the planet’s magnetic field 97 million years ago. The honest part is what comes next. Nobody knows which animal. It lived in the sea, so it was not a bird. Eels are one suggestion, and Rich Harrison of Cambridge, who helped lead the work, says finding the maker is the next question.
What the fossil does show is how old the idea is. Finding your way by a force you cannot see is not a new trick. Life has been doing it since the age of the dinosaurs.
The part that is not built in: the map
Here is the detail that gets lost.
In the 1950s, a Dutch scientist named Albert Perdeck caught more than 11,000 starlings as they passed through the Netherlands in autumn. He put them on planes, flew them to Switzerland, and let them go. That put them hundreds of kilometres off their normal route.
The adult birds worked it out. They changed course and headed northwest, toward the places where they had spent earlier winters. The young birds, on their first trip, did not. They kept flying southwest, the same heading they had before, and many ended up in southern France and Spain. They held the right direction from the wrong starting point.
The young birds had a compass. The adults had a compass and a map. The only difference between them was that the adults had made the trip before.
A fair warning: in 2020 a group of researchers looked at those results again and raised a problem. Starlings travel in flocks. The young birds may simply have joined local starlings and gone where they went. So that famous test is less tidy than textbooks make it sound.
But the cuckoo has no flock. And first trips keep showing the same thing. In October 2022, a bar-tailed godwit only five months old, carrying a small satellite tag, flew from Alaska to Tasmania without landing. That is 13,560 kilometres in 11 days, the longest non-stop flight ever recorded for a bird. Young godwits usually set off weeks after the adults have gone, so it had no older bird to copy. The tracking showed it took a sharp turn late in the flight. Many godwits from Alaska spend the southern summer in New Zealand. This one came down in Tasmania instead.
A record flight, on a first try, and it may not even have landed where its kind usually does. That is what a compass without a map looks like. The bird is born with the pull and the heading. The map only comes from going.
The oldest note on bird migration
People noticed all this long before anyone built a planetarium.
About 2,600 years ago, a Hebrew writer living in the hills near Jerusalem watched the birds go over. He lived under one of the busiest bird flyways on Earth. Storks still cross that sky in huge flocks every spring. He wrote one line about it. The stork in the sky knows her appointed times, he said, and the dove, the crane and the swallow keep the time of their coming.
Notice what he picked out. Not the direction. The timing. That is the same thing the caged birds showed in the lab: the clock comes first. Something inside the bird knows when.
He was not really writing about birds, though. He was writing about people. His point was that people wander off too, and that, unlike the stork, we often do not turn around when it is time.
It is hard to read about Zugunruhe and not think of that. Most people know the feeling of being restless for somewhere they cannot name. The Welsh have a word for it, hiraeth. We tend to treat that feeling as a problem to fix or a mood to wait out. The old writer’s comparison suggests another way to see it. If a bird’s unrest is a signal that it is time to head home, maybe ours is too. He believed people have a home to return to as surely as the stork does, and that the home is God.
The bird does not understand its restlessness. It just does not ignore it.
What you can do this week
- Look up at dusk. In the north, September and October are the big weeks. In the south, birds are arriving for the southern summer. It costs nothing, and you do not need to know their names.
- Listen after dark. Many small birds migrate at night and call as they pass. On a quiet, clear night you can sometimes hear thin, short calls from overhead.
- Turn off outside lights you do not need. Night fliers steer by a dark sky, and bright lights pull them off course. One dark doorway helps.
- Put out water or a little food if you can. A bird on a long trip needs places to stop. We looked at what feeding birds really does for the person doing it, and the answer was not what the study expected.
Somewhere tonight, a bird that hatched a few months ago is flying over ground it has never seen. It has no map. It has a heading, a clock, and a restlessness it did not choose.
For a very long time, that has been enough to start with.
A good place to start:
The Beginner’s Guide to Feeling God’s Presence Every Day (Free)
A short video guide and PDF with a simple three-step rhythm for noticing God in ordinary moments, even on a busy day. Get the free guide. Free.
Discussion question
Which surprised you more: that birds are born knowing which way to fly, or that they are not born with a map? And do you think restlessness in people is something to fix or something to follow? Tell us in the comments.
Share this
A young cuckoo never meets its parents, then flies alone to Africa at night. Turns out birds hatch with a compass heading and a timer, but no map. The map comes from making the trip. https://bgodinspired.com/index.php/nature-and-creation/how-do-birds-know-where-to-migrate/
Scientists once raised baby birds under a fake night sky that turned around the wrong star. The birds grew up thinking that star was north. https://bgodinspired.com/index.php/nature-and-creation/how-do-birds-know-where-to-migrate/
Caged birds that have never migrated still get restless at night when the season comes, and they face the right way. There is a word for it: Zugunruhe. I keep thinking about this one. https://bgodinspired.com/index.php/nature-and-creation/how-do-birds-know-where-to-migrate/
Questions and answers
How do birds know where to migrate?
Birds know where to migrate through a mix of instinct and experience. A young migratory bird hatches with an inherited compass direction and an inner timer that tells it roughly how long to keep flying. It holds that direction using the sun, the stars and the Earth’s magnetic field. On later trips, birds add a learned map of places they have already been, which lets adults correct their course if they are blown or carried off route.
Do birds use the Earth’s magnetic field to navigate?
Yes. Experiments with European robins since the 1960s have shown that migratory birds change direction when the magnetic field around them is turned. A bird’s magnetic compass reads the tilt of the Earth’s magnetic field rather than pointing north, so it tells the bird which way leads toward the pole and which way leads toward the equator. The sense appears to sit in the eye and needs light to work. A 2021 study in Nature found that a protein from the robin’s eye, cryptochrome 4, reacts to magnetic fields in the lab, but this has not yet been confirmed inside a living bird.
Are birds born knowing their migration route?
Birds are born knowing a direction and a rough distance, not a full route. Hand-raised birds that have never migrated still try to fly the correct way at the correct time of year. Young common cuckoos, which are raised by other species and never meet their parents, reach Africa alone. But a detailed map is learned. In a well-known 1950s experiment, adult starlings moved from the Netherlands to Switzerland corrected their course, while young starlings on their first trip kept their old heading and ended up in the wrong place.
What is Zugunruhe?
Zugunruhe is a German word meaning migration restlessness. It describes the way caged migratory birds become restless at night during the season when they would normally migrate, hopping and fluttering toward the direction their species flies. Zugunruhe appears even in birds raised by hand that have never migrated, and it lasts longer in species that travel farther. Scientists use it as evidence that the urge to migrate, its timing and its direction are inherited.
How long have animals been using the Earth’s magnetic field to navigate?
For at least 97 million years, according to a 2025 study by researchers at the University of Cambridge and the Helmholtz-Zentrum Berlin, published in Communications Earth and Environment. The team made 3D images of the magnetism inside tiny magnetic fossils from North Atlantic seabed mud and found a structure suited to sensing both the tilt and the strength of the Earth’s magnetic field. The animal that made the fossils has not been identified. It lived in the sea, and eels have been suggested as one possibility.
