The drab but unusual sandwich tern

I LIVE ON the coast, where the typical sound of spring isn’t the song of the blackbird or the mistle thrush.

The harbinger of spring here is a seabird, the sandwich tern; its noisy call is usually heard a day of two after St Patrick’s Day. This year, however, the terns did not arrive until April 14, a full three weeks later than usual. Despite the pronouncements on global warming, spring is very late this year.

The bird owes its name to John Latham, an 18th-century English medical doctor and naturalist. Known as the “father of Australian ornithology,” he examined, and named, many bird specimens sent to England from Australia in the wake of Captain Cook’s expedition of 1768. But he also examined local birds and, in 1775, was sent the carcass of a tern near Sandwich in Kent. He named the bird after the village.

Terns are related to gulls. More delicate in appearance, terns have forked tails and are sometimes referred to as “sea swallows”, appropriate because, like swallows, terns spend most of their time on the wing. To keep body weight to a minimum, their legs and feet are tiny.

The terns in our part of the world are pale grey and white all over, with jet black skullcaps. We have five species here and it can be difficult to tell them apart. The sandwich is easy to identify, because it is the biggest. Our other terns manage a dash of red or yellow on the bill or legs - they are glamorous in a restrained way but the sandwich is a drab puritan, black, grey and white all over.

The name is an imitation of the bird’s call. Unusually for seabirds, terns are noisy, even when fishing out at sea. The sandwich’s grating hoarse cry is most distinctive, but why it makes so much noise is a bit of a mystery. Terns spend most of their time quartering the waters offshore, their eyes peeled for their favourite prey, sand eel and sprat. Their constant calling may alert other terns to the presence of food but this makes little ecological sense. If you want to plunge-dive on fish, you don’t want others scaring away your meal. A calling parent might be alerting its youngsters to the presence of fish and teaching them hunting skills, but terns are equally noisy in the spring when they are no longer in family groups. Nor are they calling to their mates. Although terns are monogamous, they separate for the winter, not meeting again until they return to the nest for breeding season.

Once it has spotted a shoal, a tern hovers briefly. Then it plunges, seizing a fish and lifting it clear of the water. The fish is swallowed or carried back to the young in the nest. This technique, apparently, is difficult to master and young sandwich terns take a long time to learn the skills. They are fed by their parents for about four months after leaving the nest, an unusually long period for a relatively small bird. They don’t start to breed until they are three or four-years-old, by which time they will have perfected their hunting skills. The family flies to the west coast of Africa for winter, but inexperienced first-year birds stay and don’t return until they are two.

Terns are among the world’s greatest migrants. The most mobile creature on Earth is the Arctic tern, which spends almost all of its life in daylight, frequenting the southern oceans during our winter and the northern regions during the summer. They travel 35,000km per year. Sandwich terns don’t travel as far but their journeys are still impressive.

Like all terns, the sandwich is choosy when it comes to nesting. Although they fish all along the east coast, they travel north as far as Carlingford and Strangford Loughs to nest. There are colonies in Wexford but none elsewhere on the south coast. Whole colonies can desert if disturbed by people or foxes or for no apparent reason. They often nest with black-headed gulls, even though gulls eat tern eggs and chicks. The more aggressive gulls can see off larger predators such as grey crows, stoats and rats and so help to protect the terns. Perhaps it’s a case of “my enemy’s enemy is my friend.”

Unusually for a seabird, baby sandwich terns sometimes gather into crèches. The parents seek out, and feed, their chicks among the throng. According to the BTO/IWC Atlas of Breeding Birds, we had 4,400 breeding pairs in Ireland in 1985-87, a 50% increase on the numbers recorded in 1969-70. Terns are sensitive and need careful protection as their history in the Netherlands reveals. There were between 25,000 and 40,000 pairs of sandwich terns there up to the mid-1950s but, by 1965, pesticide poisoning reduced this to 650.