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Migrating Birds
In autumn you can see large flocks of birds flying from Russia to warmer countries. In spring, they come back to us. Migration is a periodic seasonal 1___________(move) of birds.
The main routes connect Europe and Africa, Europe and South-Eastern Asia and so on. How do we know about these routes? 2____________(science) study birds. They catch birds, place small rings(bands) with numbers on the birds’ legs and let them fly away. The rings tell about the route.
Some birds fly very 3___________(quick) and they can feed on the wing. They migrate in the daytime.
Swimming birds can fly both during the day and night, in complete 4__________(dark).
How long can birds fly for without a stop? The tiny hummingbird(колибри) weighs only about as much as a small coin. But it has 5___________(power) wings.
It flies 1,000 km across the Gulf of Mexico to the southern coast of the USA in 24 hours without a stop! You may think it 6__________(possible), but other small birds can fly non-stop for up to 90 hours!