Black Robin Update

Forest and Bird, Volume 15, Issue 2, 1 May 1984, Page 9

Black Robin Update

Wildlife Service

Allan Munn

Society members will have a special interest in this black robin update article, and the effort to save this little bird from extinction. After all, the Society’s assistance in the purchase of Mangere Island in 1966 and the later supply of 120,000 Olearia traversii seedlings which were planted on the island to make a new safe habitat for the birds, was support help gladly given. The Wildlife Service in this most important rescue work is congratulated on the success that seems to attend the efforts after all these years. Editor.

Following the most successful breeding season ever recorded, the Wildlife Service believes the black robin ‘crisis’ has passed and the birds are well on the road to recovery. From a total population of five in 1980, including only one successful breeding pair, the population now stands at twenty.

The black robin’s 1983/84 breeding season marked the fourth year since the Wildlife Service’s cross-fostering programme began and was critical — another bad year like the previous breeding season would have put the programme back to where it was when we started. After the first two seasons which were largely experimental, and the disappointing 1982/83 season, it was with high hopes and an underlying optimism that we packed our supplies and headed for the Chathams in October. We left Wellington knowing that down in the Chathams we had several things in our favour: M@ The black robin/Chatham Island tit cross-fostering technique on South East Island had been perfected over the past three years. @ As a result of efforts in previous years we now had a much younger breeding stock. M@ |t was probable that the season would begin with three, possibly four, breeding pairs (in previous years there had been only one successful breeding pair and last year, although the season started with two pairs, one female died part-way through the period).

M@ The second black robin population on South East Island (c. 100 ha of habitat) had a far greater capacity for expansion than the remaining population on Mangere Island (4.2 ha of habitat) ... With these thoughts in mind we arrived at Mangere and South East Islands eager to find out just how many black robins had survived the winter, which birds had paired and what stage they were at with breeding. We found nine robins still alive. The pair that had been transferred to South East Island in January 1983, ‘Crunch’ and ‘Ngaio’, were active and before long ‘Ngaio’ was seen carrying a feather — a sure sign of nest building. We could find no sign, however, of the male of the second pair transferred to the island last June. ‘Margaret’, the female of the second pair was, therefore, without a mate and did not breed. On Mangere Island two pairs were preparing to breed. One pair were young birds that had not bred before and the other were the established pair — the male ‘Yellow’ and ‘Old Blue’, the latter now being at least 13 years old. Two lone females on the island took the total number of birds to nine. On the surface, it appeared we had not achieved much since 1980 when

there were only five birds, all on Mangere Island. We had, in fact, lost a little ground since October 1982 when the number of birds had climbed to ten. However, there was no time for pessimism and with Don Merton at the helm, we began the task of locating Chatham Island tit nests ready for the job of cross-fostering. We had no idea of the great breeding season which lay ahead. Our plan was to induce the black robins to lay three clutches of eggs by removing their first two clutches and placing them in the nests of Chatham Island tits. We would then leave the robins to raise their own third clutches. The season was an outstanding success and several ‘firsts’ were achieved: @ The first black robin hatched and reared by Chatham Island tits paired and bred successfully. @ Four three-egg clutches were recorded. No three-egg clutches have been known before and remarkably one female laid three 3-egg clutches. @ |t was the first time a one-year-old bird had been recorded breeding. Black robins do not normally breed until their second year but this season an 11-month-old female mated successfully with an older male. By the end of the season the robins had laid a total of 22 eggs. Of these, 17 hatched and 13 chicks fledged (i.e. left the nest). Of these fledglings, 11 survived to independence. The black robin population now stands at twenty. Had we not intervened in the nesting cycle, no more than 4-5 chicks could have been expected this season. There were no losses this season that could be attributed to genetic degeneration. The eggs and young lost were the results of

accidents — generally petrels crashing into foster nests at night. We now have 11 males and 9 females — eight birds on Mangere Island and twelve on South East Island. ‘Old Blue’ has been virtually the only successful breeder since 1979 and of the twenty robins alive, she is mother of six and grandmother of eleven. In spite of close in-breeding this year by her offspring, all young are vigorous and healthy and the fertility of the ‘new generation’ of robins has been faultless. With the establishment of a population on South East Island the robins for the first time in the last 100 years have enough space to expand and recover. The head count is now the highest ever recorded since actual numbers have been known. When the Wildlife Service began its research/conservation efforts on Little Mangere Island in 1970, the highest count was 18 birds. While the prospects for the robin’s survival and recovery have never appeared brighter, the bird’s future is not entirely assured. The black robin has persisted at a low population level for almost a century and ata critically low level for the past decade. This long

history of close inbreeding could cause genetic problems although this now seems unlikely. It is possible that some black robins will die during the winter as this period is a testing time for all birds. The Wildlife Service will continue its cross-fostering programme next season (OctoberJanuary) but believes the end of intensive management of the birds is in sight. With another good breeding season next year, who knows? And ‘Old Blue’? She’s been retired from breeding and transferred to South East Island where she has earned the respected title — ‘Grandmother’. yt