The Chatham Island Black Robin

Forest and Bird, Volume 21, Issue 3, 1 August 1990, Page 14

The Chatham Island Black Robin

How the world’s most endangered bird was saved from extinction

By 1980 only five Chatham Island black robins remained. The story of the daring bid to rescue the bird from extinction is as dramatic a conservation tale as any in the world. Here Don Merton, the chief architect of the plan, gives a full accou0000000 and brings readers up to date with the robins’ progress.

A Bic CHATHAM ISLAND BLACK ROBIN is endemic to that land apart — the windswept cluster of islands 850 km east of the South Island we refer to as the Chathams group. Once widespread on the islands, the robin together with many other native birds disappeared from the larger islands following European colonisation early last century. Forests and scrubland were cleared, and rats and cats introduced. Seven bird species were exterminated. Miraculously however, a remnant black robin population of about 20-30 birds persisted for the subsequent 90 years in 5-7 hectares of scrub forest on top of a 200 metre sheer-sided rock stack — Little Mangere Island. Little Mangere is rarely visited, so extremely difficult is it to climb. However, in 1938 the late Sir Charles Fleming, Alan Wutherspoon and Graeme Turbott scaled the cliffs and rediscovered the black robin there. In the 1970s the woody vegetation atop Little Mangere degenerated rapidly following the clearing of a helicopter landing pad. The robin population plummeted from 18 birds in 1973 to seven (two pairs and three males) in 1976, when the Wildlife Service relocated the survivors on nearby 130 ha-Mangere Island. Prior to this 120,000 trees had been planted on Mangere to provide additional habitat for

the robins and other native wildlife — a programme heavily sponsored by the Royal Forest and Bird Protection Society.

Teetered on the Brink

During the final three years on Little Mangere only one robin chick had survived to breeding age. Although chick survival improved following the transfer (5 chicks in 4 years) the skewed age-structure of the population meant that recruitment of young was offset by natural mortality of old birds. Unaided, no rapid recovery was possible and the species teetered on the brink of extinction; an urgent remedy was required. In common with some other New Zealand endemics, black robins tend to be long lived and to have a low reproductive rate: the normal clutch size is just two eggs and a successful nesting cycle takes more than three months. Thus, the species lacks the ability to recover quickly when its population is reduced. However, because black robins are capable of renesting, their potential productivity is greater. For this reason in 1979 when the species had declined to just five birds, I proposed cross-fostering as means of capitalising upon this potential — to boost productivity and so quickly restore the population to a viable level.

Five birds, including only one effective breeding pair (Old Blue and her mate Old Yellow) existed in September 1980. However, an intense management programme developed since then resulted in a spectacular recovery to about 116 birds by early 1990. This recovery can be attributed largely, if not entirely, to innovative management which included manipulating the behaviour of both black robins and Chatham Island tits living in the wild. This involved: e Manipulating robin nesting cycles, and fostering eggs and young to other species, so increasing production by over 100 percent. Improved nest security virtually eliminated accidental losses during incubation and nestling periods. e Establishing the major robin population on South East Island. This move has vastly increased the area of habitat available to the black robin, so that for the first time this century the species has sufficient space to increase and expand. (Little Mangere, where the species was confined for almost a century, and Mangere to which the depleted population of seven birds was transferred in 1976, each had about 5 ha of habitat, whereas South East Island has more than 100 ha). Survival, particularly of

juveniles and unattached birds, has improved markedly since their release in 1983 on South East Island. The result is that there is now a younger, more productive and successful breeding population.

How It Was Done

But to return to 1980.... W: HAD TO FIRST quickly determine the feasibility of this daring proposal in a species whose numbers were so incredibly low. We were also mindful of the immense logistic problems associated with living and working on a small, remote island for around four months each year. Summarised below are some immediate objectives we had to resolve in order to pioneer the cross-fostering programme which was to continue each spring and summer from 1980 to 1988:e obtain basic biological information for the black robin and three potential foster species; e determine the limits of tolerance within which the robin and three potential foster species would permit us to operate;

@ gauge reaction to manipulation of nest contents in donor and host species; © gauge reaction of host and donor species to alien and artificial eggs, and clutches of different size and colour to their own; e gauge reaction of host and donor species to reduced and increased clutch size; e gauge reaction of host and donor species to increased and reduced incubation periods; @ gauge reaction of host and donor species to nestlings of alien species, to nestlings of differing age, and of their introduction to nests at different times of the breeding cycle; e determine the time that embryos at various stages of development might safely remain out of incubation in the cool Chatham Islands climate; e determine what constitutes normal incubation, brooding and nestling feeding routines in host and donor species; e determine incubation, nestling and fledging periods of host and donor species; and e closely observe breeding robins and up to 40 pairs of potential foster parents in order to find their nests early in the nesting cycle, log their progress, and prepare some to receive robin eggs. We also had to develop ways of safely handling tiny fragile eggs and nestlings in and out of enclosed Chatham Island warbler

nests and more open robin and Chatham Island tomtit nests. Warblers, robins, and tomtits proved to be unusually tolerant at all stages of the nesting cycle. European dunnocks, however, were prone to desertion and so were unsuitable. Robin, warbler and tit could be induced to incubate for almost twice their normal incubation periods and would accept eggs and nestlings of other small passerines. Poorly sited or insecure nests of all three species could be secured with string, or in the case of the robin and tit nests, transferred into the safety of a nest-box. It was even possible to move nests a metre or two in stages to more sheltered or accessible positions. A poorly constructed or damaged nest could even be replaced with a fresh nest. Although warblers were able to hatch and care for robin eggs and nestlings, they proved incapable of raising robin nestlings beyond 10 days of age. It was thus a major breakthrough to discover in 1981 that tits were capable of hatching and fostering robin chicks through to independence. Tits, however, did not occur on Mangere Island and so eggs and nestlings for fostering had to be transported 15 km by sea to South East Island. A portable incubator and brooder were developed to help transfer eggs and nestlings between the two islands. No heli-

copter is based in the Chatham Islands so for transport we were entirely dependent upon the few local fishermen — without their help the programme could not have taken place. At 44 degrees south the Chatham Islands are within a zone of constant strong winds — the infamous "roaring 40s’ — so that any boat trip entailed days of planning to co-ordinate weather conditions, availability of a fishing boat and stage of development of eggs or nestlings. Transfers took 2-5 hours to accomplish. During the course of the cross-fostering programme approximately 40 robin eggs, 10 nestlings and 25 independent birds were transferred between the two islands — without loss.

Turning Point

In 1983 permission was granted to establish a robin population on 219 ha-South East Island where extensive areas of scrub and forest exist. Two pairs of robins were transferred to South East Island in 1983 and this event proved to be a turning point in the species recovery, for the major population is now found there. Furthermore, the need to transport eggs and birds between islands diminished. Throughout the course of the programme, techniques and procedures have been constantly reviewed and refined, so that those

used in the final years were very effective. The following is a summary of the management strategy used in the final years of the programme. About 30 pairs of tits breeding on South East Island were managed each spring so as to ensure a continuity of secure foster nests was available throughout the robin breeding season. More advanced pairs were induced to re-nest, and those nests selected for fostering transferred into nest-boxes. Here they were more easily manipulated, and were safe from interference from other birds and adverse weather — in a species whose numbers were So critically low, survival of every egg and chick was vital. Plastic mesh with holes just large enough for tits to pass through was placed over the entrances of the nest-boxes so as to exclude white-faced storm petrels, broad-billed prions and starlings, which breed on the island in immense numbers and which otherwise enter and destroy some nests. Management of each clutch was carefully planned before it was in fact laid. We closely watched breeding robins. Any that did not build their nests in nest-boxes were transferred into boxes during laying. First and often second clutches were removed and fostered to tits for incubation, but

third clutches were normally left with their natural parents. Where practicable the commencement of incubation in two or more "close" clutches was synchronised so as to ensure the option existed to unite and return broods of similar age to robin nests prior to fledging. As will be seen later this synchronisation in hatching times of clutches was a key element in avoiding the effects of mal-imprinting. Tit foster-parents were observed so that any behavioural problems were identified early. For instance, for the first 2-3 days following hatching, male tits and robins feed their young while females brood almost continuously. Inexperienced males must learn to respond to the female's cue to cease feeding her and start feeding the nestlings, and often the newly-hatched young perish in the process. Thus, it was necessary to have an alternative nest on hand to which such young could, if necessary, be transferred at short notice. Such inexperienced males were subsequently "taught" to feed young nestlings through our placing week-old tit nestlings in their nests for a few days. To facilitate this a continuity of "borrow-nests’’ was necessary. Although the eggs and young were well protected from the outside — from attacks by starlings for example — nestlings in particular

remained vulnerable to attack from within (from nest mites or fleas), and losses occasionally occurred. To overcome this problem we fumigated and dusted nests with pyrethrum powder.

When about 15 days old, nestlings were sexed and individually colour banded, and those in tit nests were returned to robin nests where they were often united with a brood of similar age. Although broods of 4-5 young do

not occur naturally, robins are able to raise this number if supplementary food is provided. The fostered young were returned to robin nests prior to, or at fledging, so as to avoid imprinting problems which occurred when young were raised entirely by tits. Malimprinting has proved an obstacle in some cross-fostering programmes so that our development of a means of overcoming it is of some significance and may have application elsewhere. Briefly then, the main elements of the programme were: to increase robin egg production by inducing breeding pairs to re-nest; to foster the additional robin eggs to Chatham Island tits for incubation and raising to near fledgling age; and to synchronise the time of hatching in fostered clutches so as to facilitate their return (as composite broods) to the few robin nests prior to fledgling in order to avoid mal-imprinting. From what we know, this was the first time that cross-fostering had been used in the management of an endangered passerine (perching bird) living in the wild. As a consequence of the programme, cross-fostering, and the manipulation of breeding behaviour, are already being used with success in the management of some other endangered species in New Zealand and elsewhere.

The black robin programme has been relatively inexpensive yet highly successful. Since 1980 a team of between two to four people have stayed in the field for approximately four months each spring and summer. The programme has created unprecedented interest from both within New Zealand and overseas. Its success can be attributed to the patience, perseverance, attention to detail and very high level of commitment by the small dedicated team — together with the obvious cooperation of the robins and tits, and of course more than a fair measure of good luck! Perhaps the most remarkable feature of the black robin story however, is the incredible endurance and resilience of the birds themselves — despite intense inbreeding over a very long period. For such a tiny population to survive entirely isolated for almost a century on the windswept summit of a rock stack in mid-ocean is no mean feat of endurance. I believe that no more than 30 birds could have existed at any time on Little Mangere and the population was at a critically low level — only one or two effective breeding pairs — during the late 1970s and early 1980s. All surviving robins are descended from a single pair, Old Blue and Old Yellow. Nonetheless, there is no indication of "inbreeding

depression" or "random drift’ — genetic conditions which may jeopardise the survival of small isolated animal populations. The new generation of robins show no indication of genetic degeneration. They are highly productive, and fertility (about 90 percent), hatchability (83-88 percent) and recruitment to the breeding population (75 percent of young reaching independence) are surprisingly high for what must be one of the most intensely inbred wild animal populations anywhere. Adult mortality is low (21.6 percent average over the last nine years).

Most Important Character

Without doubt the most important character in the black robin drama was Old Blue, a female so named for the colour of her leg band. Old Blue started life on Little Mangere Island in about 1970, and lived for at least 13 years — more than twice the life span of almost any other robin (females average 3-4 years). In 1976 Old Blue was one of two surviving females and together with the last five males was transferred to nearby Mangere Island. Old Blue's productive life began at the incredible age of about 9 years when she mated with Old Yellow at which time she was the only productive female! Old Blue and her mate then bred each year until her death in

late 1983 or early 1984 — and unquestionably saved their species from extinction. All surviving black robins are descended from this pair. The black robin is the only avian species living in the wild in which the identity and lineage of every individual is known and can be traced to a common ancestor.

The Future

Following the 1988/89 breeding season, 99 robins existed and since the population was believed to be sufficiently strong to continue its recovery unaided, we ceased manipulative management. Nevertheless, during the 1989/90 breeding season the population increased to around 116 birds, an increase of approximately 17 percent over the previous year! This was the proof everyone had been waiting for — that the robins could continue their historic recovery without our help. Although manipulative management has ceased, it is desirable to re-establish the species on a major island in the Chathams group. However, because the robin is incapable of co-existing with cats or rats, the species can never be reinstated on the main Chatham Island where feral cats and two species of rats are established and eradication is not feasible. On the other hand, Pitt Island (6,270 ha), the second largest island in the group, is

rat-free, and plans are already in train to eradicate its feral cat population. In a cooperative programme with Pitt Island residents the Department of Conservation intends to start this ambitious project as soon as possible for such is probably the only means by which the long term survival of the black robin and many other Chatham Island species might be assured. The black robin’s rescue has demonstrated that manipulative management of an endangered species living in the wild is practicable, and that even in the most extreme case (one remaining viable pair) recovery is possible.

Acknowledgements

The black robin could not have been saved without the extraordinary dedication and commitment of Wildlife Service — and more recently DoC — teams, which often included volunteers. Over the nine years of the intense management programme many departmental staff and volunteers have been involved. In particular I'd like to acknowledge the major contribution made by my colleagues Brian Bell, David Crouchley, Rod Morris, Allan Munn, Geordie Murman and Rick Thorpe, and of my wife Margaret for her crucial support throughout. Furthermore, success could not have been achieved without the support

and cooperation of the Chatham Islands community — in particular the Pitt Islanders who provided vital transport between the islands. John and Bridget Preece and Ken and Eva Lanauze of Pitt Island deserve special mention in this context, for their outstanding support and hospitality throughout the programme. The black robin rescue has been a classic team effort. 9 Postscript: A comprehensive account of the black robin history and rescue from imminent extinction is currently being written by Dave Butler (author of Quest for the Kakapo) and Don Merton. It is to be published as a book later this year.