Sandwich terns and the miracle of migration
During a recent trip to the island of Anglesey in North Wales we were pleased to encounter a breeding colony of Sandwich terns at the Cemlyn Nature Reserve. Adult birds were rearing their chicks on little islands in a lagoon behind the beach, occasionally breaking off from parental duties to go fishing. It was such a pleasure to witness – cute little chicks exploring the islands of their birth while their parents looked on caringly or whizzed around in the skies above us, their beaks loaded down with lunch as they returned from fishing expeditions. And all around us, a cacophony of sound as the birds called out noisily to one another.

A Sandwich tern carries home a spot of lunch for its chick
Despite the blustery wind, our morning spent at Cemlyn Bay was idyllic, just the sort of thing that brings joy to a birdwatcher’s heart. But such joys are transitory. In only a few weeks from now the birds we so admired will be at the other end of the world. We’ve all heard of migration, the process by which countless species of bird move from one geographical location to another in search of food or a suitable place to raise their young, but I think we underestimate the enormity of the undertaking.
Soon the Sandwich terns of Cemlyn Bay will be heading off to the coast of west Africa. The most intrepid amongst them will make it all the way to South Africa, a journey of around 10,000km (a little over 6,000 miles). And a few months later they’ll head back again, doing the journey in reverse!



Sandwich terns nesting on an island in the lagoon behind the beach at Cemlyn Bay, Anglesey
So, in just a few short months these guys will fly around 20,000km, and in between those epic journeys they’ll spend a lot of time cruising over coastal waters on fishing expeditions. Their average lifespan of 12 years means that Sandwich terns can clock up over 250,000km (150,000 miles) in the course of their lives. What an extraordinary achievement for a creature weighing in at around 250 grams (9 ounces), and with a wingspan of roughly 100cm (39 inches).
Remember, also, that the UK plays host to four other species of tern during the summer months. One of these, the Arctic tern, breeds close to the Arctic circle, but spends northern hemisphere winters on the edge of Antarctica. Depending on the exact starting and finishing points, and the circuitous route taken in between, it is reckoned that one of these birds may fly between 71,000km and 95,000km (44,000 to 59,000 miles) over a period of 12 months. And Arctic terns are famously long-lived, with a lifespan of up to 30 years. During the course of their lifetime the oldest birds may therefore fly a distance equivalent to taking three round-trips to the moon. Eat your hearts out, NASA and SpaceX!


Left: Sandwich tern Right: Arctic tern, the world’s champion migrator in terms of distance covered (to the moon and back, 3 times!)
I find the numbers quoted above almost impossible to comprehend. Small birds, huge distances! The annual travels of Sandwich terns, Arctic terns and all their cousins leave me in no doubt that bird migration is a miracle worthy of our absolute respect. Way to go, guys.







