Kapiti Island is a small but conspicuous island about 8 km (5 miles) off the west coast of the lower North Island of New Zealand. It is 10 kilometres long, running southwest/northeast, and roughly 2 kilometres wide, being more or less rectangular in shape, and has an area of 19.65 km² (7.6 sq miles).
The island is separated from the mainland by the Rauoterangi channel. The highest point on the island is Tuteremoana, 521 m. The seaward (west) side of the island is particularly rocky and has high cliffs, some hundreds of metres high, that drop straight into the sea. The cliffs are subject to very strong prevailing westerly winds and the scrubby vegetation that grows there is low and stunted by these harsh environmental conditions. A cross-section of the island would show almost a right-angled triangle, revealing its origins from lying on a fault line (part of the same ridge as the Tararua Range).
The island's vegetation is dominated by scrub and forest of kohekohe, tawa, and kanuka. Most of the forest is naturally regenerating after years of burn-offs and farming, but some areas of original bush with 30 m (100 ft) trees remain.
In the 1700s and 1800s Māori settled on the island. Te Rauparaha formed a base here, and his Ngāti Toa tribe regularly sailed in canoes on raiding journeys up to the Whanganui River and down to Marlborough.
The sea nearby was a nursery for whales, and during whaling times 2,000 people were based on the island. Oil was melted from the blubber and shipped to America for use in machinery, before petroleum was used. Although whales can be seen once every year during birthing season, there still are not as many as there used to be.
The conservation potential of the island was seen as early as 1870. It was reserved as a bird sanctuary in 1897 but it was not until 1987 that the New Zealand Department of Conservation took over the island. In the 1980s and 1990s efforts were made to return the island to a natural state; first sheep and possums were removed. In an action few thought possible for an island of its size, rats were eradicated in 1998.
In 2003 the anonymous Biodiversity Action Group claimed to have released 11 possums on the island. No evidence of the introduced possums has been found.