How Birds Migrate: Navigation Across Continents

Every spring and autumn, billions of birds travel between breeding grounds and wintering areas. Some fly just a few hundred kilometres, while others cross oceans and continents. Migration is one of the most remarkable feats in the animal world, and scientists are still working out all of its secrets.

Key takeaways

• Birds migrate to follow food and suitable breeding conditions.
• Navigation uses several cues, including the Sun, stars, landmarks and Earth's magnetic field.
• Some migratory behaviour is inherited, and some is learned from other birds.
• Different species use different routes, called flyways.
• Habitat loss, light pollution and collisions threaten migrants.

Why birds migrate

In many regions, food becomes scarce in winter. Insects disappear and plants stop producing seeds, while in summer the long days of northern areas provide plenty of food for raising chicks. Migrating lets birds take advantage of the best conditions in each season. The distance varies a lot: some birds shift only to lower altitudes, while the Arctic tern makes one of the longest known migrations, travelling between the Arctic and Antarctic regions.

How birds find their way

Birds appear to combine multiple navigation tools. Many species use the position of the Sun during the day and patterns of stars at night. Birds can also sense Earth's magnetic field, and research suggests that certain light-sensitive molecules in their eyes may be involved, although the exact mechanism is still being studied. Landmarks such as coastlines and rivers help, and some birds may use smell. Combining these cues gives them a flexible "map and compass" system.

Instinct and learning

Young birds of many species that migrate at night, such as warblers, set off alone and still find their winter home, which shows that a good deal of the behaviour is inherited. Others, such as geese and cranes, travel in family groups and learn routes and stopover sites from experienced adults. This is why conservation programmes sometimes use ultralight aircraft or other methods to teach young birds a new route.

Flyways and stopovers

Migratory routes often follow broad corridors called flyways. Along the way, birds rely on stopover sites such as wetlands, estuaries and forests, where they rest and refuel. A bird may nearly double its body weight before a long flight. If a key stopover habitat is lost, the whole journey can be affected.

Timing and weather

Birds respond to day length, temperature and wind conditions. Many time their departures for favourable tailwinds. Radar images can show large pulses of birds taking off at dusk on good nights, and scientists use this data to track migration patterns.

Threats and what helps

Migrants face habitat loss, collisions with buildings and wires, hunting in some regions, and bright lights at night that can disorient them. Simple steps can help, such as reducing unnecessary night lighting during peak migration, making windows more visible to birds, and protecting wetlands and other stopover habitats.

Record-breaking journeys

Some migrations are astonishing. The Arctic tern breeds in the Arctic and spends the northern winter around Antarctica, and tracking devices have shown that individuals can travel tens of thousands of kilometres in a year, one of the longest migrations known. The bar-tailed godwit makes a nonstop flight of more than ten thousand kilometres from Alaska to New Zealand and Australia, flying for about a week without feeding. Common swifts can remain airborne for months, eating, drinking and even sleeping on the wing, while the tiny rufous hummingbird travels thousands of kilometres between Alaska and Mexico.

How scientists track migrants

For more than a century, researchers have fitted birds with lightweight leg rings, which give information when a ring is found again. Modern tools are far more detailed. Light-level geolocators record the timing of sunrise and sunset to estimate location, and small satellite or GPS tags can transmit positions in real time on larger birds. Weather radar shows pulses of birds taking off at dusk, and microphones record flight calls overnight. Citizen scientists also contribute through projects where people log their sightings, creating huge datasets of bird movements.

Climate change and timing

Migration is closely tied to the seasons, and changes in climate are shifting its timing. In many places spring is arriving earlier, and some species are returning sooner. A risk is a mismatch between arrival and food supply: if insects that feed chicks peak earlier than birds arrive, breeding success can fall. Some species are also shifting their ranges toward cooler areas, and others are changing routes or wintering closer to breeding grounds.

Helping migrating birds

Individuals can help in practical ways. Switching off unnecessary lights at night during migration seasons reduces disorientation and collisions, and many cities run lights-out programmes. Marking windows with decals or patterns helps birds see glass, and keeping cats indoors protects birds that stop in gardens. Planting native shrubs and trees provides food and shelter, and leaving a source of fresh water helps tired travellers. Supporting wetlands and other habitat protection safeguards stopover sites.

Partial migrants and irruptions

Not all migration is a neat north-south trip. In partial migrants, some individuals migrate while others stay put. Blackcaps from central Europe have developed a new wintering route to Britain, partly helped by garden feeding. Irruptions are irregular movements when food runs short in one area, and birds such as waxwings and crossbills may appear far outside their usual range in some years.

Frequently asked questions

Do all birds migrate?

No. Many species are residents and stay in the same area all year, and some only move short distances.

How high do migrating birds fly?

It depends on the species and weather. Many fly at a few hundred to a few thousand metres, and a few cross very high mountains.

Do birds fly in a V shape to save energy?

Studies of some large birds suggest that flying in formation can reduce effort for followers, though not every species does it.

Do all birds of a species migrate together?

Not always. Some species migrate in flocks, while others travel alone or in loose groups, and many species migrate by night. Within a species, different populations may migrate different distances or not at all.

How do birds know when to leave?

Cues include changes in day length, temperature, food supply and an internal annual clock that prepares their bodies, for example by building fat and restlessness. The exact timing on a given night depends on weather, especially favourable winds.

What is the longest non-stop flight recorded?

The bar-tailed godwit is recorded as making nonstop flights of more than eleven thousand kilometres from Alaska to the southern Pacific, lasting around a week without stopping to eat or drink.

Sources and further reading

• Bird migration (Wikipedia)
• Cornell Lab of Ornithology: All About Birds