Cliffs rise to a parapet 100 m high on the north-west coast of Mana Island, which gently slopes to the south-east like a great raft pitching in a turbulent sea. For centuries, offshore islands like this have been arks for endemic species plagued on the New Zealand mainland by the steady advance of pastoralism and invading hordes of rodents, cats and mustelids.

But Mana was not spared these ravages. It was cultivated by Maori as early as 1400, occupied by Ngati Toa in the 18th century, then cleared and farmed intensively for 154 years by Europeans producing some of the first wool ever exported from New Zealand. When restoration work started 23 years ago, the original vegetation was confined almost entirely to the cliffs and one small catchment.

But despite its harrowing history, three rare species clung to salvation on Mana—the goldstripe gecko, Cook Strait giant weta, and McGregor’s skink. Today, after concerted conservation efforts including the eradication of mice and planting half a million trees, the island is home to dozens of species threatened elsewhere in the country.

Few ecosystems are so peculiarly active after dark. After the DOC rangers retire for the evening, after the lights click out and the generator utters its final death rattle, Mana sparks into life. Imperceptible to the feeble night-vision of humans, a host of critters eschew the blinding light of day for the shroud of night, clattering about in the canopy of regenerating kohekohe, tawa and karaka, rummaging among the boulders on the shore or wading in the fertile ooze of Mana’s Waikoko wetland.

Their activities illuminated only by moonlight and the amber loom of sodium streetlights in Plimmerton seven kilometres to the east, they rely on acute senses and an array of adaptations that make nocturnal perambulations possible.

Some island dwellers, cold-blooded reptiles such as the extremely rare McGregor’s skink, have become extraordinarily efficient so they can hunt at night even in temperatures that would paralyse their diurnal cousins who go about their business only when fuelled by the warmth of the sun. Most lizards enter a torpid state in cold conditions, but Kelly Hare, a herpetologist at Otago University, has found that New Zealand skinks and geckos are among the most “fuel-efficient” in the world. Nocturnal species in particular are active in temperatures significantly below what their physiology is optimised for, pushing the limits of their range to occupy a unique ecological niche.

For other critters, such as the Cook Strait giant weta, the absence of predators has removed constraints on physical dimensions, a phenomenon called island gigantism, allowing them to dramatically grow in size over generations. This is typical of many island ecosystems and the biological logic behind of some of the giants that once inhabited New Zealand, such as moa and Haast’s eagle.