Arctic tern

The arctic tern (Sterna paradisaea) is the world record holder for migration. It spends its entire life in the summer, flying from the high northern latitudes to the high southern ones, and back, every year. It therefore enjoys more hours of daylight than any other bird or animal on the planet.

Males and females are very similar in appearance, being about 38 centimetres (15 inches) long, with long tail streamers that are prominent when the birds hang in the wind prior to diving into the sea for food. The upperparts and wings are silvery-grey and the underparts lighter in shade. The top of the head and the nape of the neck are black and the legs and bill bright red. It is certainly one of the more elegant seabirds to be seen in the UK.

Arctic terns have a number of preferred breeding grounds in the UK, including the Farne Islands and the coastal dunes of Northumberland. They arrive in May after a three month long migration from Antarctica, 11,000 miles away, and form a colony of around 1,500 birds. This coincides with an abundance of small fish, particularly sand eels, being available in the coastal waters.

The male bird performs a courtship dance that includes the presentation of a fish to the female. If she accepts the gift, mating will take place. The nest is simply a depression scraped in the sand, either at the top of the beach or among the dunes. Two eggs are laid, which both birds take turns to incubate. The chicks hatch after about 23 days and are fed on sand eels by their parents.

The chicks start exploring their neighbourhood after about a week, but are vulnerable to predators and will hide among the dunes not far from their parents, who continue to feed them even after they are capable of flying, which is at around four weeks.

The breeding colony in Northumberland is protected from human encroachment, but nothing can stop summer storms from creating havoc on occasion, which can lead to serious degrees of loss among young birds.

The colony has to continue to feed as much as possible in preparation for the migration south, which happens towards the end of July, an event that is awaited eagerly by birdwatchers. An unseen signal is given and all the birds rise up and fly off together, leaving the beach empty of arctic terns for another year.

Populations of arctic terns are very dependent on food supplies, and when these decline so does the ability of young birds to survive the long journey south. This vulnerability has led to the arctic tern being placed on the amber list of threatened species, as maintained by the RSPB (Royal Society for the Protection of Birds).

© John Welford