Conservation assessment of the Chatham Island Oystercatcher Haematopus chathamensis

The Chatham Island Oystercatcher is found only on the Chatham Islands, 860 km east of New Zealand, and birds breed on the coasts of four islands: Chatham, Pitt, Rangatira and Mangere. The majority of birds are found on 154 km of coast, and territories can range from 100 m to 1 km of coastline, depending on the local density of pairs. Habitat varies from rocky, boulder or sandy coasts or a mixture of these types, often including access to intertidal rock platforms or stream mouths. Breeding adults are generally sedentary and defend territories throughout the year, but juveniles migrate more extensively around the four islands, before setting up territories of their own at 2–6 years of age. Adult longevity can be >30 years.

There may have been as few as 50 birds alive in 1970, mainly centred on the Rangatira and Mangere island nature reserves. More definitive surveys in 1987 and 1998 found 110 and 144 birds respectively. Low numbers were a result of hunting, habitat destruction and introduction of predators since the arrival of Moriori 500 years ago and Europeans 200 years ago. Feral cats cause most loss of nests (76%), although sea wash can account for 50% of egg losses in stormy years. Vulnerability to sea wash has been exacerbated by introduced marram grass which has created less favourable nesting habitat and forced birds to nest closer to the high tide mark. Other losses of eggs and chicks include predation by introduced weka, skua, gulls, trampling by sheep, crushing by vehicles and disturbance by people and dogs.

Intensive management over seven seasons (1998–2004) on 16 km of northern Chatham Island coast was a combination of intensive predator control throughout the breeding season, shifting of nests away from high tide and exclusion of farm animals. Productivity increased from an average of 0.35 to 1.04 chicks per pair per year, and the resulting influx of young birds more than doubled the population to 316 birds by 2004. However, by 2010, after a period of less intensive management, the total population had levelled off at around 309 birds.

A management plan and Department of Conservation recovery group guides management of Chatham Island Oystercatcher. After the success of the management in northern Chatham Island it was planned to rotate efforts around different parts of the species’ range. However, lack of resources has meant that efforts have been less intensive, and therefore less effective.