Black-fronted tern  (Sterna albostriata)

Classified as Endangered (EN) on the IUCN Red List 2006 (1).

This small, threatened bird is one of many tern species that live around the New Zealand coast, but is unique by being the only one that breeds exclusively inland. Terns belong to the same family as gulls, but are distinguishable by a forked tail, which has led to their other popular name of sea swallows (3). The black-fronted tern has a grey body and a noticeable black cap, under which a thin white line extends along the cheek. The wings are also grey, and contrast with its white rump when in flight. The bill and legs are vivid orange (4). Non-breeding adults moult, and therefore differ in appearance from breeding adults by having a grey head and a black patch around the nape of the neck. Juveniles have a greyish-brown head, a black-flecked crown, and a white throat (2).

Found only in New Zealand; it breeds on the South Island, and visits the North Island, where it used to breed (2).

The black-fronted tern breeds on shingle, stoney or sandy areas in fast-flowing braided rivers, and on the shores of lakes, with sparse vegetation (5). It searches for food over rivers, lakes and farm fields, and in winter can be found in coastal areas, roosting on tidal flats and islands (6), rarely venturing further than 10 km offshore (2).

From the middle of October to late November, the black-footed tern can be found on its inland breeding habitat. Here, they nest in colonies of up to 50 pairs, and typically lay two eggs in a simple scrape in the shingle. Like other New Zealand terns, both parents take turns to incubate the eggs, for a period of 21 to 23 days (2) (6), during which time they can exhibit very aggressive behaviour. They will dive at any intruders, screeching harshly, and often striking the intruder’s head with their feet. Whilst this is effective on sheep and hawks, unfortunately their fearless attacks do little to deter predators such as cats and dogs (5) (6). The chicks fledge at around 30 days old (3).

Whilst breeding, they will search for food in flocks, over rivers, lakes and farmland. Their tendency to follow farmers’ ploughs, catching insects and worms from the freshly dug earth, has earned them the names ploughboys or the ploughman’s friend (3). They fly over rivers and lakes, dipping down to feed on mayflies and stoneflies from the surface, and sometimes even diving into the water to take small fish. Once summer and breeding is over, they move to the coast, and again feed on worms from coastal farmland, but also on crustaceans from the ocean (6).

Numbers of the black-fronted tern have decreased dramatically in the last forty years; there used to be tens of thousands, and now there are about 5000 birds. Increased disturbance of breeding colonies is one of the main reasons of this decline, caused by greater numbers of people, animals and vehicles around rivers. Unfortunately, black-footed terns will swiftly abandon their eggs and young if their breeding site is disturbed, resulting in a very low number of chicks reaching maturity (5).

Their breeding habitat is threatened by the encroachment of exotic plants such as willows and lupins, which smother nest sites (3) (6), and also the development of hydroelectric plants, and extraction of gravel from river beds (7). Black-fronted terns also have to contend with a large number of introduced predators including feral cats, brown rats, hedgehogs, brush-tailed possums and ferrets (1).

There are a number of measures currently in place, to help halt the decline of this endangered tern. Project River Recovery, managed by New Zealand’s Department of Conservation, is a restoration programme for the wildlife and plants of the braided rivers and wetlands around Twizel, Tekapo and Omarama (8). As part of the project, the Mackenzie River Basin is receiving protection, and willows are being removed to restore the breeding habitat of black-fronted terns (7). Information signs have been erected close to large black-fronted tern colonies, which aim to educate the public about the best way to enjoy and use the river, while minimising the negative impacts on the birds (5).

The loss of any more braided rivers would have a significant effect on the black-fronted tern, and therefore it is important that any future plans for hydroelectric plants, or gravel removal, should be carefully examined to determine the impact they may have on the tern (7). The removal of exotic weeds from braided rivers would also be very beneficial to this species. Nest protection may be required, if research currently underway reveals that introduced predators are in fact having a significant impact on the breeding success of black-fronted terns (7)

View information on this species at the UNEP World Conservation Monitoring Centre.

For further information on this species, see Birdlife International:
http://www.birdlife.org/datazone/species/index.html?action=SpcHTMDetails.asp&sid=3289&m=0