In the “Ecosystem restoration on Mainland New Zealand”
The Chathams are oceanic islands not recently connected to the New Zealand mainland. Unlike islands such as Cuvier, levels of endemism are high in the Chathams. Most of the trees and shrubs are endemic (13 species); two thirds of the 15 extant indigenous landbird species are endemic (some at the species level); and 20% of the insect fauna is also endemic (references in Towns et al. in press).
The arrival of people, perhaps 400 years ago, exacted a terrible toll. Twenty one species of landbirds disappeared and two thirds of these were endemic (most to species level).
On Mangere Island (113 ha) up to 22 species of birds have died out since people arrived; seven species are now totally extinct in the island group. The losses were the result of habitat destruction, predation and harvesting. Sheep, goats, and rabbits were introduced and the island became largely denuded of forest vegetation except for 5 ha of fragmented scrub and forest. In the late 19th century commercial bird collectors were active in the Chathams, and cats were introduced to Mangere Island to control the rabbits. By 1950 the cats had eliminated all rabbits, at least two species of seabirds and most forest birds. The cats then died out (Tennyson and Millener 1994). One of the species lost from Mangere Island was the black robin.
Mangere Island was purchased as a wildlife refuge in 1966, and the last introduced mammals (sheep) were removed in 1968. This paved the way for one of the most ambitious conservation programmes undertaken anywhere (Butler and Merton 1992).
By 1975 the entire black robin population was nine birds in degrading habitat on Little Mangere Island. Unfortunately, the remaining forest on Mangere Island only provided sufficient habitat for about six birds, so 80,000 flax and shrubs were planted on the island between 1974 and 1979. The plantings now form the nuclei for expanding areas of coastal scrub (Butler and Merton 1992).
In 1976-77 the entire population of black robin, then only seven birds (two breeding pairs), was transferred from Little Mangere to Mangere Island in a last ditch effort to halt their decline. The desperate, successful measures to induce these birds to breed, including the use of cross fostering under Chatham Islands tit, are lessons in dedication. Suffice to say two breeding pairs from Little Mangere Island have since expanded to about 200 birds on Mangere and nearby South East Island. In addition, other rare species benefited from the habitat restoration. For example, Chatham Island snipe were successfully reintroduced in 1970, 99 years after the last recorded sighting on the island, and Chatham Island tits were re-established by 1992 (Butler and Merton 1992).
The restoration programme on Mangere Island is most unusual: forest-dwelling species were reintroduced to an island from which almost all forest had been removed and where much of the original bird fauna was extinct.
The efforts on Cuvier and Mangere Island have only been possible because public access could be restricted. This was necessary to reduce risks of reinvasion by pests, protect fragile habitats and provide security for species management projects such as the breeding areas for black robins. On Cuvier and Mangere Islands the objective was to protect and enhance sites either previously or presently inhabited by rare species. These high levels of protection were assisted by the land being in Crown ownership. But there are also initiatives possible on islands where the risks to threatened species are not as great and where high levels of community involvement and access can be encouraged. One such example is Tiritiri Matangi Island.