Tracking showed a zig-zag route between Greenland and Antarctica each year. Over a roughly 30-year life, that's about three return trips to the Moon.
Source: Egevang et al., Tracking of Arctic terns Sterna paradisaea reveals longest animal migration, PNAS (2010). doi.org/10.1073/pnas.0909493107
Image: Charles J. Sharp, CC BY-SA 4.0, via Wikimedia Commons
