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Each one looks after itself, but they keep in touch other using contact calls, and may gather at roosts along the way. Migrating flocks of small birds tend to be much more broadly scattered.

Some, such as geese and cranes, travel in their family groups inside larger flocks. This provides safety in numbers, since each individual is less likely to be attacked by a predator than if it were travelling alone. For penguins, which are flightless, swimming is the only option. They set off on their migration by swimming. Young auks, such as puffins and guillemots, often leave the nest before they can fly properly.

They are strong swimmers and their well-oiled feathers keep them afloat. But seabirds, such as gannets and shearwaters, often take a break on the sea to feed and rest. Landing would spell disaster, since they’d quickly become waterlogged and drown. Most birds try to cross the sea in a single flight. They’re also much less likely to bump into a predator after dark. The air is calmer and cooler then, so they lose less energy by flapping and less water through evaporation. Birds such as swifts and swallows that feed on flying insects also migrate by day, feeding as they go.īut many songbirds, including warblers, thrushes and starlings, migrate mostly at night. Many large birds migrate by day in order to make use of thermals. But birds’ lungs can take in more oxygen from the thin mountain air.

No mammal could survive long at this altitude. Mountains also force birds to fly higher.īar-headed geese in central Asia regularly cross the Himalayas – the world’s highest mountains – by reaching heights of 18,000 metres. With the wind blowing behind them (a tailwind), they fly up high to where it will whisk them along faster. When the wind is against them (a headwind), they stick closer to the ground, where ridges, trees and buildings slow the wind down. Most migrating birds usually fly at a height of between 200 and 1,500 metres above sea level.

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