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How do birds migrate?

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Quick answer

Birds migrate by combining an inherited compass with learned routes. They use the sun, stars, and Earth's magnetic field to navigate, often flying thousands of kilometres. Before leaving, they eat heavily to store fat for fuel. Most travel at night or in flocks, resting at stopover sites to refuel.

Birds migrate by using innate compasses—the sun, stars, and Earth's magnetic field—to navigate between seasonal homes. They build fat reserves and may fly thousands of kilometres, often in flocks, to reach food or breeding grounds.

Step by step

  1. Day length changes in autumn or spring, triggering hormonal shifts in the bird's body.
  2. The bird eats more, building fat reserves that can double its weight.
  3. It orients using the sun, stars, or Earth's magnetic field as a compass.
  4. It follows a fixed route, often learned from parents or flock mates.
  5. It stops at familiar sites to rest and refuel before continuing.
  6. It reaches the wintering or breeding ground and repeats the journey the next season.

Key things to understand

  1. Migration is triggered by changing day length, which shifts hormone levels and restlessness.
  2. Birds lay down fat as fuel and may double their body weight before departure.
  3. They navigate using the sun's position by day and star patterns by night.
  4. Earth's magnetic field provides another compass, thought to be sensed by light-sensitive proteins in birds' eyes.
  5. Many species follow fixed routes, often along coastlines or mountain ranges, learning them over generations.

Labelled diagram

  1. Sun compass

    Birds track the sun's position, adjusting for time of day to keep a steady direction.

  2. Star compass

    At night, birds learn the rotation of star patterns around the pole star.

  3. Magnetic sense

    Special proteins in the eye detect Earth's magnetic field as a backup compass.

  4. Fat reserves

    Extra fat provides energy for long flights over oceans and deserts.

  5. Stopover sites

    Wetlands and forests along the route let birds rest and refuel.

How birds navigate during migration

Real-world examples

  • Arctic terns fly from the Arctic to the Antarctic and back each year, a round trip of about 70,000 kilometres.
  • Bar-tailed godwits make a non-stop flight over the Pacific Ocean from Alaska to New Zealand.
  • Barn swallows migrate from Europe to southern Africa, crossing the Sahara Desert.
  • Ruby-throated hummingbirds fly non-stop across the Gulf of Mexico, a journey of about 800 kilometres.

Common mistake

✗ Myth: Birds migrate only because they feel cold.

✓ Fact: Cold is not the main trigger; food scarcity is. Most birds leave when their insect or plant food disappears in winter, even if temperatures are still mild.

People also ask

How do birds navigate during migration?
Birds use a combination of compasses. They track the sun by day and stars by night, and they sense Earth's magnetic field through proteins in their eyes. They also use landmarks like coastlines and mountain ranges. Young birds inherit a rough direction but refine their routes with experience.
How far can birds migrate?
Distances vary widely. Arctic terns travel about 70,000 kilometres round trip each year, the longest known migration. Bar-tailed godwits fly over 11,000 kilometres non-stop. Even small songbirds may cover several thousand kilometres, often flying at night to avoid predators and heat.
Do birds sleep while migrating?
Some birds can sleep briefly during flight, shutting down one half of the brain at a time. Others take short naps at stopover sites. Long-distance migrants often fly for many hours without sleep, then rest deeply once they land to refuel.
How do birds know when to migrate?
Changing day length in autumn and spring triggers hormonal shifts in birds. This internal clock, set by the photoperiod, makes them restless and prompts them to fatten up and depart. Weather patterns like cold fronts also influence the exact timing.
Do all birds migrate?
No. Only about half of bird species migrate. Many tropical birds stay put year-round, and some partial migrants move only short distances. Migration is most common in birds breeding in temperate or Arctic regions where winter food disappears.
How do young birds find the way without experience?
Many young birds inherit a compass direction and a rough map. They use celestial cues and Earth's magnetic field to head the right way. Some species, like cuckoos, migrate alone, while others follow experienced adults in flocks.
What dangers do migrating birds face?
Storms can blow them off course, and predators wait at stopover sites. Collisions with buildings and communication towers kill millions each year. Habitat loss along migration routes reduces safe places to rest and refuel.

Part of the guide: Nature & Earth: Living Things and Rocks →