Assessment of Chatham Island as a location for liberation of black stilts

At the high water level that we encountered, Te Whanga Lagoon and its immediate environs are largely unsuited to black stilts. Nevertheless, the area of shallow-water foraging habitat that does exist at this water level would be sufficient to maintain a population of them. At low water levels, large areas of shallows would be available to black stilts. Suitable nesting sites are generally small and scattered away from the main lagoon. The lagoon edge would be unsuitable for nesting because it is susceptible to flooding by wind-generated water level fluctuations. Biomass of aquatic invertebrates in the shallows at high water level are relatively low compared to biomass in shallows in the Mackenzie Basin but would be adequate for black stilts. The types of prey species present would be easily caught and eaten by them. The type and quantity of food supplies at low water levels is unknown. The inland waters on Chatham Island are generally brown, saline, alkaline, and high in dissolved oxygen. They are warmer in winter than waters of the Mackenzie Basin. The warmer conditions are likely to result in higher winter food production in Chatham Island shallow waters than in shallow waters of the Upper Waitaki Basin. Twenty seven pied stilts were seen on Chatham Island. This was probably the entire population, or close to it. Although pied stilts may regularly move to and from mainland New Zealand, the presence of two juveniles indicates that they also breed on the island. The small population size, and high adult to juvenile ratio suggest that breeding success is low. Pied stilt feeding and searching rates were similar to feeding and searching rates of black stilts in winter. This similarity provides further support for the conclusion that food supplies on Chatham Island would be adequate for black stilts. Wekas appear to be present in high numbers everywhere. Cats, rats and pos-sums are present but their density and distribution are unknown. Kahu (Circus approximans) are present but at much lower density than in the Macken-zie Basin. The potential effects on black stilts of these predators, particularly wekas, may be just as serious as the present effects of predators in the Mac-kenzie Basin. There is good potential to enhance the habitat for black stilts by creating better nesting areas and by erecting barriers to exclude predators from the eastern spit area, or around individual ponds.