Angels watch over at-risk flock

Eight endangered bird species have found a guardian angel on a remote island in the Chatham Islands - the Department of Conservation.

A generation after its predecessor the Wildlife Service began a successful programme to save the Chathams' black robin, DoC is now trying to rescue other birds threatened by lost bush habitat, predators such as possums and cats, and native species competing for space and resources.

It is replanting forests, killing the pests, and monitoring endangered species such as the northern royal albatross to make sure they compete successfully for nesting space.

Now on Rangatira or Southeast Island, south of Pitt Island, it is installing felt doors on the burrows of the endangered ranguru (Chatham petrel), with slits which are just big enough to let the ranguru through but too small for its main competitor, the native broad-billed prion.

Boxes built by children at tiny Pitt Island School have been placed over each of the 130 known ranguru burrows so that DoC staff can lift the lids to monitor the birds.

Young chicks rest safely behind these defences during the day, waiting for their parents to return at night with fish dinners caught in nutrient-rich subantarctic waters hundreds of kilometres to the south.

The parents have a keen sense of smell and can find their burrows, despite their artificial fortifications.

"These birds are so keen to get into their burrows that they will put up with this sort of thing on them," said Canterbury University ornithologist Paul Scofield.

It is too soon to be confident that the ranguru will multiply as a result.

So as extra insurance, DoC has recently transferred about 40 ranguru chicks to a patch of bush on Pitt Island enclosed with a cat-proof fence. (Possums and rats have never made it to Pitt.)

"We try and move them just before the chicks fledge," Mr Scofield said. "Chicks return to where they are born, but the only way they can recognise where they were born is what they see just after they leave the nest, so we have a nice protected piece of forest where we hope they will return."

Despite being farmed for 122 years from 1840, Rangatira has proved a last refuge for several other endangered birds, including the small coastal tuturuatu (shore plover).

DoC's Chathams area manager, Alison Davis, knew all 44 surviving pairs when she studied the tuturuatu on Rangatira in the 1980s.

Fossil evidence shows that the tuturuatu was once found all round the New Zealand coast. Almost miraculously, this tiny remnant population hung on at Rangatira.

Twenty years later, Ms Davis said there were still only about 120 individuals, and there was no room for more on Rangatira because the birds were fiercely territorial.

"They fly to Pitt but they don't last long because the cats get them."

So DoC has transferred eggs from Rangatira to the Mt Bruce wildlife centre in the Wairarapa, where they have been incubated and raised.

This month, some of these birds were released on Mangere Island, west of Pitt, and on an island off the North Island coast which cannot be identified at the landowner's request.

Fertile island

* More than a million seabirds breed today on Rangatira's 300ha, with an average of 1.5 burrows in every square metre of bush.

* Only Snare Island, off Stewart Island, and a handful of other isolated islands around the world now come close to this density.