Effect of changes in water level on numbers of black stilts (Himantopus novaezelandiae) using deltas of Lake Benmore

The black stilt (Himantopus novaezelandiae) is a critically endangered wadi ng bird that inhabits rivers, wetlands and lake deltas in the Upper Waitaki Basin, South Island, New Zealand. Changes in numbers of black stilts using the Ahuriri and Tekapo/Ohau Deltas of Lake Benmore, during temporary drawd owns in 1982, 1992, and 1994, were investigated. Numbers of black stilts on the deltas increased during all drawdowns for which data are available, ev en though the drawdowns varied in magnitude and duration, and occurred at d ifferent times of year. Habitat conditions, food supplies, and foraging beh aviour at these deltas were measured during the 1994 drawdown, when highly suitable physical habitat, and abundant aquatic invertebrate food supplies for black stilts, were exposed. Invertebrate biomass comprised mainly larva l Chironomidae, Oligochaeta, and Gastropoda (Lymnaea spp.). Feeding rates o f black stilts on the exposed deltas were high in comparison with feeding r ates at other sites in the Upper Waitaki Basin. Manage ment implications of these results are discussed.