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 wading 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 drawdowns in 1982, 1992, and 1994, were investigated. Numbers of black stilts on the deltas increased during all drawdowns for which data are available, even though the drawdowns varied in magnitude and duration, and occurred at different times of year. Habitat conditions, food supplies, and foraging behaviour 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 larval Chiro-nomidae, Oligochaeta, and Gastropoda (Lymnaea spp.). Feeding rates of black stilts on the exposed deltas were high in comparison with feeding rates at other sites in the Upper Waitaki Basin. Management implications of these results are discussed.