How Do Birds Know Where to Migrate? Navigation Explained

An inborn program for young birds

Many young birds make their first migration alone, without adults to follow. Cuckoos in Europe, for example, leave weeks after their foster parents and still reach central Africa. This works because the basic direction and length of the journey are inherited.

Caged birds show this clearly. When it is time to migrate, they become restless at night, a behavior scientists call Zugunruhe (German for “migratory restlessness”), and they hop in the direction their wild relatives would fly. Young birds raised in captivity even change direction at the right time of year, as if following a built-in route map.

The program is not perfect. Blackcaps from central Europe once wintered almost entirely around the Mediterranean, but since the 1960s a growing number fly northwest to Britain and Ireland instead, a new route that is passed on from parents to young.

The sun compass

Birds that migrate by day, such as hawks, swallows and pigeons, use the sun’s position as a compass. Because the sun moves across the sky, a bird has to allow for the time of day, and it does this with its internal clock. The German biologist Gustav Kramer showed in the 1950s that caged starlings oriented using the sun, and that changing the angle of the sunlight with mirrors changed the direction they chose.

Birds can also read the pattern of polarized light in the sky, which remains visible when the sun is hidden behind clouds or just below the horizon. Many night migrants seem to calibrate their other compasses at sunset, using the glow and polarized light where the sun went down.

The star compass

Most small songbirds migrate at night, when the air is calmer and predators fewer. In planetarium experiments in the 1960s and 1970s, American ornithologist Stephen Emlen showed that young indigo buntings learn the point in the night sky around which the stars rotate. In the Northern Hemisphere that point is close to the Pole Star, so it marks north.

Birds raised under a planetarium sky that turned around a different star chose a direction based on that false center. The lesson is that the star compass is learned during the nestling period, not inherited star by star.

The magnetic compass

Birds can sense the Earth’s magnetic field. In the early 1970s, Wolfgang and Roswitha Wiltschko showed that caged European robins changed their preferred direction when the magnetic field around them was altered. Bird magnetic compasses do not work like a human compass needle; they detect the angle at which the field lines dip toward the ground, which tells the bird whether it is heading toward the pole or the equator.

Scientists think part of this sense sits in the eye. Light-sensitive proteins called cryptochromes, found in the retina, form short-lived chemical pairs whose behavior is affected by the magnetic field, and this may let a bird perceive the field as a visual pattern. Birds may also use the strength and angle of the field like a coordinate system, a kind of magnetic map that tells them roughly where they are. How magnetite particles and nerves in the beak area may contribute is still being researched.

Landmarks, smell and maps

Experienced birds use what they see. Many daytime migrants follow coastlines, river valleys and mountain ridges, and birds gather at narrow crossings such as Gibraltar and the Bosporus. Near home, familiar landmarks guide them to the exact barn, cliff or wood where they nested.

Smell matters too, at least for some species. Studies of homing pigeons in Italy and Germany found that birds whose sense of smell was blocked often failed to home from unfamiliar places. Seabirds such as shearwaters and petrels also appear to use smell over the open ocean. Pigeon homing is explained in more detail in How do homing pigeons find home? and the bird itself in our rock pigeon profile.

A classic experiment by Dutch scientist Albert Perdeck in the 1950s showed the difference between young and old birds. Thousands of starlings caught in the Netherlands during autumn migration were released in Switzerland. Adults corrected their course and still reached their usual winter area in Britain and northern France, while young birds kept flying in the inherited direction and ended up in Spain and southern France.

Different birds, different strategies

The Arctic tern, which makes the longest migration of all, shows how precise this can be: after a round trip of up to 90,000 km (56,000 mi), it returns to the same small colony and often the same partner. Read more in Which bird has the longest migration? Barn swallows likewise return to the same farms and often the same nest after wintering in Africa or South America.

Myths and open questions

Myth: birds simply follow the leader. Geese, cranes and swans do travel in family groups and learn routes from their parents, but many songbirds and young cuckoos migrate alone and still find their way.

Myth: birds rely on one sense. Birds combine several cues and cross-check them. If clouds hide the stars, they can switch to the magnetic compass, and they recalibrate one compass against another.

Open question: scientists still debate exactly how birds know their position on a map, which is harder than knowing a direction. Magnetic, smell-based and visual maps may all play a part, and different species may rely on different mixes. Why birds migrate in the first place is covered in Why do birds migrate?