Arctic tern

Tiny light-sensing tags showed Arctic terns flying about 70,900 km (44,000 miles) a year between Greenland and Antarctic waters, almost double the distance people had assumed. Individual birds covered anywhere from 59,500 to 81,600 km.

Based on 11 tracked birds in a 2010 study.

Context

Before small geolocator tags existed, scientists knew Arctic terns bred in the far north and wintered near Antarctica, but not the route. The 2010 study fitted tags weighing about a gram to birds at a Greenland colony and recovered them a year later. The tags recorded light levels, from which daily positions could be estimated, though with an uncertainty of a few hundred kilometres.

The data revealed that terns do not fly a straight line. They travel down the Atlantic in a long S-shaped route that follows prevailing winds and areas rich in food, and some spend weeks in the middle Atlantic on the way south. The roughly 70,900 km average is therefore far longer than the straight-line distance between the two ends of the trip.

Because the birds can live for 30 years or more, a single tern may cover a distance equal to several round trips to the Moon over its lifetime, though that figure is an extrapolation rather than a measurement. The result comes from a small sample of 11 birds from one colony, so other populations may travel somewhat different distances.