The immense journey of the Arctic Tern
Among migrants, the Arctic Tern holds the world record for the longest and most prodigious journeys undertaken by any life form on this planet.
Terns are small, elegant and graceful seabirds. As its name tells us, the Arctic Tern is associated with the region around the North Pole in that it nests there. However, it is not confined to the far north; it breeds in the sub-arctic too and as far south as Ireland with the most notable concentrations located on our western seaboard, Co Down and Co Wexford.
In their Arctic breeding grounds these terns experience near-perpetual daylight during the long polar summer. When the summer breeding season finishes the birds head south to better feeding grounds before the Arctic region is gripped in the chilly embrace of winter. And the journey south is a prodigious one: the birds fly the entire length of the north and south Atlantic Oceans to winter in the Antarctic.
By the time the Arctic Terns reach the Antarctic summer has arrived there and the birds experience good feeding and near-perpetual daylight during that long polar summer.
The distance between the North Pole and the South Pole as the crow flies is 20,014km. The terns feed along the way as they migrate and weather may cause them to be blown off course or force them to make detours. Allowing for such incidents and the return journey it is very likely that the average individual covers well in excess of 40,000 kilometres each year.
The average Arctic Tern weighs no more than your average garden Blackbird, less than 120 gramme, yet evidence from radar studies and from geolocators fitted to birds' bodies shows that their modest amount of wing muscle is capable of carrying them on their 40,000km return journey from pole to pole. Isn't that amazing?
Even more amazing is the fact that Arctic Terns can live to the ripe old age of 30 years or more. If you do the sums to calculate how far they might fly in a lifetime and factor in all the flying they do each regular day hunting for food and wandering about the answer runs into millions of kilometres.
While it is believed that juveniles learn the migration routes by following their parents and from other adults it takes several years for a young bird to become an expert migrator along the global Atlantic flyways.