Why do birds migrate?

It’s primarily about finding food. Migrating long distances can use up a huge amount of energy – the bar-tailed godwit flies 11,500 kilometres (7,145 miles) from Alaska to New Zealand every year, without stopping to rest or eat! But the alternative is to starve through the whole of an Alaskan winter. Mammals in cold climates hibernate through harsh winters but for certain birds, long migrations are actually a cheaper strategy.