Which bird migrates the farthest each year?

The Arctic tern, which breeds in the Arctic summer and then flies to the Antarctic for the southern one - a bird weighing about 110 grams covering something like 70,000 kilometres a year once the wandering route is counted rather than the straight line. Over a life of thirty years that is comparable to three trips to the Moon and back.

It does not fly straight, and that is the clever part. Tracking with tiny geolocators showed the birds taking a great looping course down the Atlantic that follows the prevailing winds rather than the shortest path, and pausing mid-ocean to feed. Going the long way round is cheaper.

The consequence is that it sees more daylight than any animal on Earth, spending both polar summers in near-continuous sun. The bird was also the reason the migration was proved at all: a tern ringed in Britain in 1913 turned up in South Africa, at a time when the scale of bird migration was still genuinely disputed and some naturalists had believed swallows spent the winter in mud at the bottom of ponds.