Kapiti: Choral island

Setting aside the small matter of having to travel halfway round the world to get there from the UK, there are few nature reserves as easily accessible as Kapiti Island. That said, you need a keen sense of direction to track it down. The location given in a tourist guidebook I picked up in Wellington was enough to make my head spin: "The island is five kilometres off the west coast of southern North Island."

It's not nearly that complicated. About an hour's drive north of the capital you come to the pleasant seaside town of Paraparaumu, notable for its fine beach and magnificent golf links, which is consistently rated among the top 100 in the world. It was from a vantage point on the course that I had my first, unexpected view of the island, lying dark and empty out to sea, running for about 10km along the western horizon, demanding to be explored.

Kapiti was singled out for special treatment as long ago as 1897, when the word "environmentalism" probably didn't exist. The island had been originally settled by the Maoris. It was discovered by Captain James Cook on his approach to the turbulent stretch of water that separates New Zealand's North and South Islands (and has borne his name, the Cook Strait, ever since). In the 19th century, whalers and stock farmers settled on Kapiti, raising the population at one point to around 2,000, but neither group could sustain a proper living there. The Maoris – squeezed into a reservation at the north end of the island – eventually left too. By the 1890s Kapiti's only permanent residents were the animals and rodents introduced by man.

Left to their own devices, these semi-feral cats and dogs and non-native possums and stoats not only damaged the flora and fauna, but also preyed on Kapiti's rare birdlife. It was nearly 100 years before the government finally managed to clear the place of rats, the last of these predatory pests, at which point the birds were finally left in peace. In the process what is now regarded as the jewel in the crown of New Zealand's conservation movement was created.

The boat trip from Paraparaumu takes barely 20 minutes, but numbers on board the two vessels that run back and forth to the two landing points are strictly controlled. A maximum of 50 visitors per day are allowed permits to land at Rangataua, halfway along the eastern shore. A further 18 tourists are allowed to visit the north end. Shelter on shore is sparse: it pays to study the weather forecast before booking your slot. If conditions turn out fine, the reward for your modest investment (NZ$9/£3.30) is unforgettable.

The first thing you experience is the birdsong. Not an isolated call here and trill there, but a joyous, full-throated thousand-voice choir, with unfamiliar, virtuoso soloists spanning the full range from bass to soprano, echoing through the dense woodland.

Parrots and parakeets talk and squawk, flashing their vivid plumage. In an otherwise neat, trim corner of New Zealand, you are entering a patch of primordial rainforest.

Marked trails lead from the shore towards the island's central spine, converging near the summit of Tuteremoana, the highest point. Whichever path you chose, it's a lung-bursting trek of an hour, two hours, perhaps even three, up above the treeline to open grassland.

Gradually, the musical accompaniment subsides and the experience changes from aural to visual. Along the way there are sad relics of man's failed attempts to bring this wild place to heel: blubber pots, used by the whalers to process their meat, are scattered about, neglected and decaying.

Kapiti Island, unsuitable for man, has a new breed of colonisers now. Clear of the foliage, gulls and gannets, terns and shearwaters hover, swoop and dive, flying without fear or caution, secure in the knowledge that the predators have left. With an experienced guide to point you in the right direction, you might see evidence of the elusive little spotted kiwi, now extinct on the mainland, or a miniature blue penguin keeping tight to the shore.

The panoramic view at the 521-metre summit reveals steep cliffs along the west dropping dramatically to the sea, while the everyday bustle of the mainland coast in the other direction seems close enough to touch, yet manifestly belongs to another world.

For a permit to visit Kapiti Island, apply to the New Zealand Department of Conservation (00 64 4384 7770; e-mailkapiti.island@doc.govt.nz

Two companies operate launches from Paraparaumu Beach to the island: Kapiti Marine Charter (00 64 4 297 2585; www.kapitimarinecharter.co.nz) and Kapiti Tours (00 64 4 237 7965; www.kapititours.co.nz)