IT WAS long believed that arctic terns flew about 22,000 miles (35,200 km) on their journey from the Arctic region to Antarctica and back. Recent studies, however, revealed that the birds actually fly much farther.

Tiny instruments called geolocators were attached to a number of birds. About the weight of a paper clip, these amazing devices revealed that some terns flew an average of 56,000 miles (90,000 km) on the round-trip​—the longest animal migration known. One bird flew nearly 60,000 miles (96,000 km)! Why the revised estimates?

No matter where they began their migration, the arctic terns flew an indirect route. As shown in the illustration, a common Atlantic Ocean route took an S shape. The reason? The birds simply take advantage of prevailing wind systems.

During their lifetime of about 30 years, terns may travel well over 1.5 million miles (2.4 million km). That is equal to three or four round-trips to the moon! “This is a mind-boggling achievement for a bird of just over 100 grams [3.5 ounces],” said a researcher. What is more, because arctic terns experience the summers at both poles, they see “more daylight each year than any other creature,” states the book Life on Earth: A Natural History.