Black fronted terns are found on the braided rivers of the South Island from Marlborough to Southland. They also nest on the shingle riverbed of the Eglinton River in Fiordland. They are endemic species, it means they live only in New Zealand. Generally, terns are sea birds, but the threatened black-fronted tern lives and breeds inland, only visiting the coast in autumn and winter to feed. Black-fronted tern feed on the wing over main channels, catching insects in the air, or swooping down on fish and insects at the water's surface. They sometimes hunt insects and lizards on surrounding farmland. In the case of the Eglinton Valley they feed over open meadows which are the remains of past farming in the valley.Black-fronted terns nest in loose colonies on open shingle, often on islands. Their eggs and chicks are well camouflaged. Unlike many other river birds, young tern must remain near the nest, relying on parents to bring them food. To defend their eggs and chicks from intruders, parent birds dart at them, calling loudly while swooping past. Terns often desert their nests if people or predators disturb them. There are only about 5,000 black-fronted terns remaining within New Zealand. At present they are declining in numbers nationally because of loss of suitable habitat and high levels of predation.In the Eglinton Valley a predator control programme has been operating for over ten years, initially aimed at reducing the numbers of stoats, more recently rats have also been targeted. Though not specifically designed to benefit the river nesting birds, the control programme appears to have made a difference. While the black fronted tern is experiencing a steady decline in numbers nationally, here in the Eglinton the numbers have showed an increase since predator control work was established. The most significant threat however to the tern in the Eglinton Valley is the encroachment by lupins of the nesting habitat. These pretty flowering nitrogen fixing plants were probably first introduced by residents at the time of the road construction but are now threatening to completely take over the shingle river beds and river margins of the Eglinton.
References
http://www.birdlife.org/datazone/species/index.html?action=SpcHTMDetails.asp&sid=3289&m=0