The Remarkable Journey of the Arctic Tern
The Arctic tern (Sterna paradisaea) undertakes the longest annual migration of any animal on Earth. Each year, these slender seabirds travel from their breeding grounds in the Arctic to the Antarctic and back again, experiencing two summers and more daylight than any other creature on the planet. For decades, scientists estimated this round trip to be roughly 40,000 kilometres, but recent tracking studies have revealed that the true distance is far greater.
In 2010, a team of researchers fitted tiny geolocators, weighing just 1.4 grams, to terns breeding in Greenland and Iceland. The devices recorded light levels, allowing scientists to calculate the birds' approximate position throughout the year. The results were astonishing: the terns covered an average of around 70,000 kilometres annually, with some individuals travelling more than 80,000 kilometres. Over a lifespan that can exceed thirty years, a single tern may fly a distance equivalent to three return trips to the Moon.
Rather than following a direct route, the terns take a meandering path. After leaving the Arctic, many birds pause for about a month in the rich waters of the North Atlantic to feed before continuing southward. Interestingly, the tracking data showed that the birds do not fly straight down the Atlantic. Instead, they follow a zigzagging course that takes advantage of prevailing wind systems, conserving energy despite adding considerable distance to the journey.
The terns' diet consists mainly of small fish and marine invertebrates, which they catch by plunge-diving into the sea. Their migration is timed so that they exploit the most productive feeding areas at the optimal moment. By spending the northern summer in the Arctic and the southern summer in the Antarctic, the terns enjoy near-constant daylight, which maximises their feeding opportunities. This extraordinary lifestyle, however, depends on the stability of ocean ecosystems that are increasingly threatened by climate change and overfishing, making the future of this remarkable migrant uncertain.
In 2010, a team of researchers fitted tiny geolocators, weighing just 1.4 grams, to terns breeding in Greenland and Iceland. The devices recorded light levels, allowing scientists to calculate the birds' approximate position throughout the year. The results were astonishing: the terns covered an average of around 70,000 kilometres annually, with some individuals travelling more than 80,000 kilometres. Over a lifespan that can exceed thirty years, a single tern may fly a distance equivalent to three return trips to the Moon.
Rather than following a direct route, the terns take a meandering path. After leaving the Arctic, many birds pause for about a month in the rich waters of the North Atlantic to feed before continuing southward. Interestingly, the tracking data showed that the birds do not fly straight down the Atlantic. Instead, they follow a zigzagging course that takes advantage of prevailing wind systems, conserving energy despite adding considerable distance to the journey.
The terns' diet consists mainly of small fish and marine invertebrates, which they catch by plunge-diving into the sea. Their migration is timed so that they exploit the most productive feeding areas at the optimal moment. By spending the northern summer in the Arctic and the southern summer in the Antarctic, the terns enjoy near-constant daylight, which maximises their feeding opportunities. This extraordinary lifestyle, however, depends on the stability of ocean ecosystems that are increasingly threatened by climate change and overfishing, making the future of this remarkable migrant uncertain.