Mystery #1Tier 2migration / survival / food

Why do some birds fly halfway around the world and back every year?

Twice a year, the sky fills with birds on the move. Some tiny ones, no heavier than a bar of chocolate, set off on a journey of thousands of miles, cross whole oceans, and then turn round months later and fly all the way back. It would be far safer to stay put. So why on earth do they bother?

An Arctic tern gliding low over the sea with its long narrow wings spread wide, a bird that crosses the world twice a year — Photo: Charles J. Sharp · CC BY-SA 4.0 · via Wikimedia Commons

Your guess

What is your best guess: why would a bird put itself through such an enormous journey twice a year?

There's no single magic word to type, have a go in your own words, then reveal the answer to see how close you got.

Make a guess to unlock the hints and the answer.