THE RESCUE OF THE CHATHAM ISLAND BLACK ROBIN
Chris Coleborn
(Adapted from an article in the RAOU Newsletter 1989 by Don Merton)

With European colonisation the Chatham Island Black Robin, indigenous only to the Chatham Island group 850 km east of the New Zealand mainland, disappeared very early from nearly all the islands of this group. Its disappearance was caused by the introduction of rats and feral animals such as cats, and by land clearing which caused the loss of suitable habitat etc. Wonderfully however, a remnant Black Robin population of about 25 persisted from the 1880’s until the 1970’s, in less than 5ha of scrub forest on top of a 200m sheer-sided rock-stack - Little Mangere Island!

Sadly, by 1980 only 5 Chatham Island Black Robins existed. In the 1970’s the woody vegetation atop Little Mangere degenerated rapidly. A bird count in 1973 revealed only 18 robins. The population plummeted further, so that in 1976 only 7 individual birds existed - two females and five males. Frantic efforts were commenced to try to rescue the bird, including a revegetation programme, and the transfer of the 7 individuals to about 5ha of habitat to Mangere Island, but the population continued to decrease.

Black Robins tend to be long-lived and to have a low reproductive rate: usually only two eggs are laid per clutch. Thus the species lacks the ability to recover quickly. Black Robins are capable of re-nesting however, and this created a potential for greater reproductivity. In 1979, with the robin on the sharp edge of extinction, Don Merton, senior conservation officer with the NZ Department of Conservation, proposed cross-fostering as a means of capitalising upon this potential.

By September 1980 only five birds, two females and three males existed. There was however only one effective breeding pair, a female called Old Blue and her mate Old Yellow - so called because of the colour of their leg bands. It was decided that a daring programme of recovery, including cross-fostering, which involved the fostering of eggs and young to other species, would be implemented to rescue the species, even though the outlook was so very grim for the survival of the species.

In 1983 plans were made to set up the little population on South East Island (210ha), where there was much more suitable woodland habitat available (more than 100ha). For the first time in over a century the species would have sufficient space to increase and expand beyond the small 5ha it had been confined to for so long.

Much study and work was involved, including the close observation of the habits of the robin and potential foster parents, the development of techniques to facilitate safe handling of tiny fragile robin eggs and nestlings. The birds considered for fostering were the Chatham Island Warbler and the Chatham Island Tomtit. Study and experiment revealed that the robins, warblers and tomtits all proved to be generally tolerant of the necessary activity around their nests for the fostering programme. All birds could be induced to incubate for almost twice their normal incubation periods and further study showed that the foster birds would accept eggs and nestlings of the robin. The birds were even tolerant of poorly sited or insecure nests being secured with string or being moved a few metres in stages to more sheltered or accessible positions.

There were set backs in the programme. Although warblers were able to hatch and care for robin eggs and nestlings they proved incapable of raising robin nestlings beyond ten days of age. In 1981 there was the major and exciting discovery however, that tits were capable of hatching and fostering robin chicks through to independence. This was the break through for which all looked and worked. Though a discovery of major significance there was a further problem.

Tits did not occur on Mangere Island and so eggs for fostering had to be conveyed 15km by sea to South East Island. A portable incubator and brooder were developed to facilitate transfer of eggs and nestlings between the two islands. Transport depended upon a few local fishermen. The transfers took 2-5 hours to accomplish. One of the things that showed the care and forethought that went into the planning, was that during the cross-fostering programme, approximately 40 robin eggs, 10 nestlings and 25 independent birds were transferred between the two islands - without loss.

The programme was implemented, and about 30 pairs of tomtits that were breeding on South East Island were managed each spring to ensure a continuity of secure foster nests was available throughout the robin breeding season. More advanced pairs of tits were induced to re-nest, and those nests selected for fostering transferred into nest boxes where their contents could be more easily manipulated and where they were secure from interference from other birds and adverse weather. Because the number of Chatham Island Black Robins were so low survival of every egg and chick was important. Plastic mesh with holes just large enough for tits to pass through was placed over nest entrances to exclude White-faced Storm Petrels, Broad-billed Prions and European Starlings, which breed on the island in immense numbers, who would have been only too glad to use the boxes if given the opportunity to do so.

Breeding robins were closely watched and nests not built 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 to ensure the option existed to unite and return broods of similar age to robin nests before fledging.

Behaviour of tit foster parents was closely watched so that any problem was 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 this skill and often the newly hatched young perish in the process. Such inexperienced males were subsequently "taught" to feed young nestlings through placing week-old tit nestlings in their nests for a few days.

Although nest boxes and screens provided eggs and young with a very high level of security from outside influences, nestlings remained vulnerable to attack from nest parasites.

This problem was overcome through provision of fresh nests fumigated and dusted with pyrethrum powder.

At 15 days of age nestlings were sexed and individually colour-banded, and those in tit nests returned to robin nests where they were often united with a brood of similar age. Fostered young were returned to robin nests before, or at fledging, to avoid imprinting problems that occurred when young were raised entirely by tits. Mal-imprinting has proved an obstacle in some cross-fostering programmes so that the development of a means of overcoming it was of some significance. This would seem to be the first time that cross-fostering has been used in the management of an endangered passerine living in the wild.

Finally in 1983, with a slight increase in the numbers of robins, it was possible to transfer two pairs of robins to South East Island, and thus save the need to transport eggs and birds between islands.

The Black Robin conservation programme involved a party of from two to four people in the field for approximately four months each spring and summer since its inception in 1980, and proved a relatively inexpensive yet highly successful undertaking. Its success can be attributed to detail and very high level of commitment by a small dedicated team - with the blessing of divine providence.

Mention must be made of the wonderful little mother robin, Old Blue and her mate Old Yellow. At the beginning of the rescue programme in the late 1970’s and the early 1980’s, the Black Robin population had been critically reduced to the low, low level of only one or two effective breeding pairs. Without doubt the most important character in this rescue drama was Old Blue. This remarkable bird started her 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 she was one of only two surviving females and together with the last five males was transferred to nearby Mangere Island. Old Blue’s productive life began when she mated with Old Yellow at the incredible age of nine years at which time she was the only productive female remaining of the species! This fine old lady of the Black Robins, bred with her mate each year until here death in late 1983 or early 1984 - and unquestionably saved their species from extinction. All surviving Black Robins are descended from a this single pair. She deserves to be remembered as truly the mother of her race.

Despite all Black Robins descending from this single pair, there is no indication of "interbreeding depression" or "random drift" - genetic conditions which may jeopardise the survival of small isolated animal populations. Productivity and fertility (90%), hatchability (83-88%), and survival of young (65-90% to one year of age), are surprisingly high for what must be one of the most intensely inbred wild animal populations anywhere.

Following the 1988/89 breeding season 98 robins existed and the population in now believed to be sufficiently strong to continue its historic recovery unaided.

Because the robin is incapable of co-existing with introduced cats and rats, the species can never be reinstated on the main Chatham Island where these introduced animals exist, and where eradication is not feasible. On the other hand Pitt Island (6,270ha), the second largest island in the group is rat-free, and plans are already underway to eradicate it feral cat population. The NZ Department of Conservation intended to start this ambitious project in 1990. This will be one of the necessary requirements to the long term survival of the Black Robin - and many other Chatham Island species.

Though Don Merton does not make the following observations himself, this heart-warming story of a wonderful little bird and the remarkable circumstances that saved it from extinction, is surely an example of the Lord blessing the sincere efforts of men who cared for His creation with success. It is a moving story that speaks of the providence of God - His sovereign supervision and controlling care of all His creatures and their lives.

This recovery and rescue of the Chatham Island Black Robin is also an encouragement to us that when there is thoughtful dedication and care, species that are in danger of extinction may be recovered, often at little cost.



This article was published in The Christian Bird Observer’s Magazine, October 1996