[2] The cliffs are subject to very strong prevailing westerly winds and the scrubby vegetation that grows there is low and stunted by the 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).

Most of the forest is regenerating after years of burn-offs and farming, but some areas of original bush remain, with 30 m (98 ft) trees.

The full original name for the island is Te Waewae-Kapiti-o-Tara-rāua-ko-Rangitāne, meaning "the boundary of Tara and Rangitāne" and referring to it as a place where the rohe (territories) of Ngāi Tara (now known as Muaūpoko) and Rangitāne (descendents of Whātonga) iwi adjoined each other.

[8] In 2010 the Māori Language Commission acknowledged that, while the ordinary word kapiti does not have a macron, iwi of the Kāpiti region have evidence from history and local pronunciation that the place name is a variant form of āpiti, and that Kāpiti (with a macron) is correct.

[4] Around the year 1150, Māori navigator Whātonga of the waka Kurahaupō divided the country into two sections: land from the southern tip of Kapiti Island north was given to his son Tautoki and his ancestors, who became Rangitāne iwi, and from the southern tip south was given to his son Tara and ancestors (Ngāi Tara, now known as Muaūpoko).

[2] Te Rauparaha of Ngāti Toa saw the advantage of settling on Kapiti Island, after noticing how Western ships frequented the Cook Strait area, who would be good trading partners.

[2] In 1821, amid pressure from tribes in the Waikato, Te Rauparaha led a migration of Ngāti Toa from Kawhia Harbour to the Cook Strait, and went on to settle on the Kapiti Coast and Waikanae in 1822, securing it and the island from Muaūpoko in 1823.

In the Battle of Waiorua (1824) the Ngāti Toa destroyed a force of 2,000 mainland warriors who had landed at the northern end of Kapiti in an attempt to capture the island.

[citation needed] Te Rauparaha encouraged European ships to visit Kapiti, which by 1830 became a centre for the New Zealand flax trade.

[14][16] Between 1874 and the 1890s, the Māori Land Court partitioned the island into blocks, primarily owned by Western Maori MP Wiremu Parata and his family members.

[18] By 1895, the government had begun considering making Kapiti Island into a wildlife reserve, due to the losses in native flora and fauna caused by introduced predators and deforestation across mainland New Zealand.

[14] Parata and his family members protested these plans, and in 1896 stated that they had no intention of selling the land to the government – by this time, Kapiti Island was the only part of the Ngāti Toa rohe still in Māori ownership.

[18][23] Ranger Peter Winston Daniel, who between 1980 and 1987 coordinated the programme which eradicated the pests, was recognised in the 1990 New Year Honours.

[25][26] In 2003 the anonymous Biodiversity Action Group claimed to have released 11 possums on the island, but no evidence of such were found.

[30] Rat eradication has led to increases in red-fronted parakeets, North Island robins, bellbirds, and saddlebacks.

It provides predator-free nesting habitat to little blue penguins, red-billed gulls, white-fronted terns and reef herons.

[39] A stoat, an introduced mustelid responsible for decimating the bird life in New Zealand, was seen on the island in December 2010, and by August the next year the Department of Conservation had removed three of them.

The eastern section is 1,825 ha (4,510 acres) and extends from Kapiti Island to the Waikanae Estuary Scientific Reserve.

The western section of the reserve is an area of 342 ha (850 acres) to the west of Kapiti Island, and is known for its pāua and rock lobsters.

[43] Other marine life around Kapiti Island includes the common dolphin, New Zealand fur seal, orca, and the eagle ray.

[5] There is a weather station at Rangatira Bay that measures rainfall, wet and dry-bulb temperatures, wind speed and direction, cloud cover, and visibility.

[16] Kapiti's tawa forest is often covered by a cloud cap which causes increased precipitation and soil moisture in the area, and decreased temperature and sunlight.

[45][2]: 42  A submarine canyon called the Kapiti Seavalley runs parallel to the island, approximately seven kilometres to the west.

After the island became a nature reserve, the Whare housed caretakers and conservationists, including Richard Henry.

After a building specially made for caretakers was constructed in the early 20th century, the Whare was used to house guests of the island instead.

This track allows visitors to see trypots previously used for rendering whale blubber, and the historic Whare.

The Trig Track is 2 km (1.2 mi) one way, and ascends to near the summit, taking approximately 2 hours to complete.

The Okupe Valley Loop Track is 4.8 km (3.0 mi) and takes approximately 90 minutes, going to cliffs on the west of Kapiti Island.

[5] A film for television Island of Spirits, was made by Alistair Te Ariki Campbell in 1973, exploring the history of the island from the time of it being a base for Māori chief Te Rauparaha, to being the site of whaling stations and then its transition to a bird sanctuary.