Hope yet for black robins

Forest and Bird, Volume 14, Issue 6, 1 May 1983, Page 15

Hope yet for black robins

Contributed by the

Wildlife Service

THE BLACK ROBIN population on the Chatham Islands has dropped to 11, one fewer than last year. But though the news is not good, Wildlife Service officer Mr Don Merton remains "quietly optimistic" for the birds’ future.

MR MERTON, who recently returned from the Chathams, 800 km east of the mainland, admits: ‘‘The season was disappointing. It just wasn’t a good breeding year."’ He attributes the season’s lack of progress to unusual weather-a dry winter followed by a wet, cold, and windy spring and early summer. ‘‘The birds are closely attuned to environmental and climatic conditions. One can’t

draw conclusions from _previous seasons; their breeding success and behaviour have been different each time.’’ Two died last winter Not unexpectedly, two black robins died last winter; so the season started with 10 birds, including only two good breeding pairs. Another pair, both yearlings, did not breed. This is normal. Much time was wasted waiting for eggs, says Mr Merton. ‘‘They generally lay 8 to 12 days after the nests are completed. This year the birds waited about a month.’’ But even then the result was nothing to write home about: there were only four normal two-egg clutches where nine had been expected. Three single infertile eggs were also laid, an indication perhaps of overcrowding within the tiny remnant habitat on Mangere Island.

Four eggs hatched, but only two chicks survived past the nestling stage. And then a tragedy occurred. **A valuable 2-year-old female disappeared during a wet, cold spell, of which we had many,’’ says Mr Merton. The bird had laid two clutches this season and was about to lay her third. A thorough search of the island failed to find any trace of her.

Spectacular results In the past two breeding seasons the Wildlife Service’s cross-fostering programme on Mangere has brought spectacular results. When it was started, in 1980-81, five black robins existed, including only two males and one productive pair, which made it perhaps the world’s rarest and most endangered species of bird. The programme included transferring black robins’ first clutches to the nests of foster parents (Chatham Island warblers and Chatham Island tomtits) for incubation and rearing. Thus the Wildlife Service induced the robins to renest and in the first year boosted the population to eight. Last season started with seven birds. Six young fledged and five survived to bring the population to an encouraging 12. It has been suggested that this season’s poor results were due to the Wildlife Service pushing the black robins too hard by producing additional eggs. ‘*This is a natural reaction,"’ says Mr Merton ‘‘but we have thought it through carefully and don’t believe it is valid. Many bird populations failed to breed successfully this season and a number apparently failed to nest at all. Furthermore, the young robin pair which have never bred before behaved in the same way as the other birds this season. They can’t possibly have been overstressed."’ Old»: Green. (previously known as Old Blue) is now at least 12 years old and still going strong. She is the mother of seven of the surviving 11 robins and raised one chick this: "years. «Phere: © is. "every chance she will be around next season, too.

Second population But the most significant development this season must surely be that permission was granted by the Department of Lands and Survey to establish a second population of black robins on South East Island, another. of. the Chatham group. One pair of black robins was moved to the island in January and it is hoped that another two birds will be transferred there later this year. South East is larger than Mangere, with considerably more habitat (about 100 ha compared with Mangere’s 4.2 ha.) It has a northerly aspect, and prevailing southerly and south-westerly gales are broken by huge bluffs. Unlike Mangere’s habitat, which loses the sun in the early afternoon, that of South East gets sun all day. ‘"‘This must have psychological and physiological benefits for the birds. They just love the sun, often basking in it for long periods when they are not busy nesting or raising chicks,’’ says Mr Merton. The range of plant species and communities is greater on the new island. ‘‘On South East the robins can choose exactly what they want instead of being confined to a tiny bush remnant’’. Gourmet’s delight The new island is also a gourmet’s delight for black robins..; ‘There: 18.a- greater range of insects available, including three species of weta (one of which does not appear to be present in the bush on Mangere). Wetas are a favourite food for the robins. ‘‘The wetas live in sea bird burrows, of which there are tens of thousands on the island. At dusk the _ insects come out and hop and forage in the litter on the forest floor. *‘On a calm evening you can

hear them-pitter-patter-everywhere. When we released the robin pair on South East in January they spent much time sunning themselves. But at dusk they would descend to the forest floor and feed on the nocturnal insects until it was almost dark."’ There was concern the robins might disperse on such a large island. But they have remained almost exactly where the Wildlife Service officers have put them and radiated out from those points. ‘*We were also worried that the tomtits (which do not live on Mangere) might bully the robins or vice versa. For a start the tomtits, especially those with dependent young, did try to drive the robins away. But the robins learnt not to be afraid. ‘Soon the two_ species, which belong to the same genus, were taking no notice of one another."’ Mr Merton says the crossfostering programme will continue next season, though funds are strictly limited. Last season this cost about $15,000 (excluding Wildlife Service officers’ wages). ‘*Transport is the most costly item. Five Wildlife Service officers and several (unpaid) volunteers were involved this season. Much of the cost has been met by donations from the public and especially from the Royal Forest and Bird Protection Society and World Wildlife... Fand -CN2Z,.)3.-10r which we are most grateful,"’ says Mr Merton. _ "All going well, we will have three good breeding pairs of robins next season. That’s the most we will have had since the historic decline on Little Mangere 10 years ago, when the tiny forest habitat died off, and with it the robins. ‘‘Next year is just as likely to be a bumper one. We sincerely hope so."’ .