Rare birds made good use of mating season

Press, 9 March 1984, Page 17

Rare birds made good use of mating season

With the notable exception of the Campbell Island flightless duck (only four were found during January and a major rescue operation is being mounted in July) it has been an excellent breeding season and summer for New Zealand’s rare and endangered birds.

What had been considered the world’s rarest bird, the Chatham Island black robin, has more than doubled its numbers from nine to 20 and the Wildlife Service considers that the robin’s crisis is past. Eleven chicks survived to the independent fledgling stage this summer, there are now 11 males and nine females. Since the last five birds were transferred from the devastated Little Mangere Island six years ago, the black robin has staged a notable fight back.

There are now eight birds on Mangere Island, to which the five were transferred and that is just about the limit for the island. But 12 birds have been transferred to South East Island and on its lOOha of good bush habitat their numbers can continue to grow.

Principal Wildlife Officer (endangered fauna) Don Merton says “the crisis is over” and an extra sign of hope is that most of the fledgling chicks this summer were produced by the two youngest pairs

of the four robin pairs. “We are now breeding up a young and vigorous stock for the future,” he says. “In 1984-85 we will probably do about the same as this year, but by 1985-86 there could be six young breeding pairs and the population could double again.”

Mr Merton attributes the success to the cross-fostering and eggmanipulation programme during the last three seasons and the hours of devoted attention — much of it by volunteers. The black robins themselves have been found to be excellent mothers, better than the Chatham Island tit used this season and much better than the Chatham Island warbler tried in other years. Mr Merton thinks the poor mothering qualities shown in previous years was by older birds. “After being down to one breeding pair for several seasons, we are now on the way to recovery,” Mr Merton says, “and the remarkable thing is that even though we had brother mating with sister the black robins show no signs of inbreeding. “There have been no egg or chick losses from any genetic weakness that has emerged; losses have been because of petrels crashing into the nests.” But one sad feature of the

summer has been the failure of “Old Blue” to produce a fertile egg. This remarkable bird is at least 13 years old and, when all the others were dying off, seemed to set herself the single-handed task of ensuring that the species survived. It has, but she is now too old to do any more. While on South East Island, the Wildlife Service officers gained permission to transfer the rare and endangered Chatham Island pigeon from its last refuge on the south of the main Chatham Island on to South East Island. Later, more pigeons will be transferred to a

rejuvenating reserve on Pitt Island. There are only 50 left. Two pigeon pairs have been “gently” liberated on South East Island, which means they were not just taken there and left but were introduced to it gradually. South East Island has been clear of stock for 23 years and has many more of the species the pigeon likes to eat, and the birds are doing well.

But Mr Merton says the pigeons are quite capable of flying back to the main island, and he hopes they will like the food enough to stay on

South East Island. The world’s largest (and most unusual) parrot — the kakapo — is going through its weird mating ritual of “booming” on Stewart Island even though only 10 males and three females are known to be still there. No nests have been found, but the females are expected to breed. Meanwhile, the balance of more than 20 birds taken from one end of the country to the other to find refuge on Little Barrier Island are not “booming” this season. Mr Merton said they were not really expected to “boom.” It happens only occasionally and the birds were expected to need a couple of years in their new environment before they began. They have put on weight and are in excellent condition. A famous bird which has been facing an increasingly doubtful future — the takahe — is also having a bumper season. Thirty chicks survived to leave the nest this summer in the Murchison Mountains behind Lake Te Anau, the greatest number for many years. Another six have been bred in captivity.

Mr Merton attributes the success to the good climatic conditions for breeding, and nest manipulation of eggs, so that birds with two fertile

eggs contributed one to breeding pairs that did not have a fertile egg. That way, nearly all the fertile eggs could be batched and raised as only children by the breeding pairs.

Wildlife Service scientist Jim Mills said he was “elated” with the success of the season after the disappointments of some previous seasons.

But attention is turning to the Campbell Island flightless duck. The expedition to Dent Island off the coast of Campbell Island in July is the earliest the Wildlife Service can organise it.

One male duck has been taken to the Mount Bruce Wildlife sanctuary for blood tests and so that avicultural techniques can be devised to be applied to the remaining ducks on Dent Island. The blood tests are to establish whether it is a separate sub species or just a refugee washed south-east from the Auckland Islands, where what may be another sub-species of flightless duck is found.

If the birds on Dent Island are found to be identical with those on Auckland Island, then some of the pressure to save them will be lifted.

—Oliver Riddell