Story: Gulls, terns and skuas
Page 5 – White-fronted, sooty, Antarctic and Arctic terns
The white-fronted tern or tara (Sterna striata) is the most common tern living along New Zealand coasts, and on the Chatham and Auckland islands. Their name refers to the narrow white band between their black cap and bill. Their body and sharply forked tail are white, and their wings are pale grey. They are 42 centimetres long and weigh about 160 grams.
A flock of white-fronted terns diving into the sea can be a sign that kahawai fish are close by. The birds feed on small fish, such as pilchards and smelt, which the kahawai chase to the surface.
White-fronted terns bred only in New Zealand until 1979, when they also began breeding on islands in Bass Strait, between Tasmania and Australia. In autumn, large numbers of young terns and some adults fly to Australia, returning in spring for the breeding season. They nest from October to January in large colonies on beaches, shingle banks or rock stacks. They lay one or two spotted, pale green-blue to light brown eggs. The young fly at 29–35 days. They can live to 26 years.
The New Zealand population was reckoned at 12,000 to 15,000 pairs in 1997, much lower than a 1984 estimate. Detailed counts in Northland show that their numbers are dwindling. Threats include stoats, hedgehogs, rats, dogs and beach vehicles. A reduction of kahawai stocks may also be contributing to their decline.
The sooty tern (Onchyoprion fuscatus) is also called the wideawake tern because of its noisy call. They nest on the Kermadec Islands, and are rarely seen on the mainland. They differ in appearance from mainland terns in that their backs are brownish black. They have a large white triangular forehead patch, and white underparts and sides of the neck. They grow to 45 centimetres long and weigh 210 grams. Their primary foods are squid, small fish and crustaceans.
Sooty terns nest in a scrape on sand and lay one cream egg between October and December. The young fledge at 30 days old. They live for up to 33 years.
With a population of around 25 million living in the world’s tropical latitudes, the sooty is the most abundant tern globally and in the New Zealand region. In 1990 it was estimated that the country was home to 22,000 breeding pairs.
The Antarctic tern is the southernmost of the New Zealand terns. The subspecies Sterna vittata bethunei breed on islands between Stewart and Macquarie islands.
These birds are 36 centimetres long and weigh 140 grams. They have a grey body and wings, a white rump and a white, sharply forked tail. During the breeding season their black cap extends down to the bill, which becomes bright red. They feed close to shore on small fish and crustaceans.
Breeding occurs between September and March. They nest in small colonies on the ground or on ledges, where they lay one or two buff-olive eggs. The young leave the nest at 27–32 days. They live to 14 years.
New Zealand has fewer than 1,000 breeding pairs. Their main predators are skuas and black-backed gulls, and on some islands feral cats also threaten eggs and chicks.
The Arctic tern (Sterna paradisaea) is smaller than its Antarctic cousins, measuring 34 centimetres and weighing 110 grams. Their plumage is similar, but Arctic terns are in non-breeding plumage when Antarctic terns are breeding.
As world travellers, Arctic terns have few rivals. After breeding in the Arctic they may fly as far as 17,500 kilometres to the Antarctic before returning. Since some birds live up to 12 years, they might travel the equivalent of the distance from the earth to the moon in their lifetime. They are rare visitors to New Zealand.