Habitat selection and breeding ecology of the endangered Chatham Island oystercatcher (Haematopus chathamensis)

Abstract

The Chatham Island oystercatcher (Haematopus chathamensis) is an endangered shorebird endemic to the Chatham Islands, New Zealand. In the late 1980s the population was estimated at less than 110 individuals and was feared to be declining. The objectives of this study were to collect information on breeding ecology and to determine habitat selection at the general and territorial scales to assist conservation management. Research on Chatham Island oystercatcher (CIO) breeding biology and habitat use was conducted for three seasons between 1994 and 1997 on Chatham Island. Breeding effort was high, with 98% of pairs attempting to breed (n = 42 pair-seasons). Productivity averaged 0.44 fledglings/pair/season. Flooding was the main cause of egg loss (48%). Offspring were evicted (or dispersed) from their natal territories about 33 days after fledging. Over-winter habitat is probably not a critically limiting factor based on the high survivorship rates of first-year CIOs. Chatham Island oystercatchers used coastline, rather than the lagoon shoreline, almost exclusively. Intertidal rock platforms and wide sandy beaches were selected in much greater proportions than available. Paddocks were used extensively for foraging by some pairs.