Black robins claw back from brink

Just 15cm tall and limited to land masses in the Chatham Islands group, the Chatham Islands black robin remains on the endangered list.

In 1980, the robin had a population of five with just one female and things were not looking good. It was expected to be the first New Zealand bird to become extinct since the huia in 1907.

But conservationist Don Merton came up with the idea of crossing foster eggs to bring the bird back from the brink.

The eggs from the only breeding pair, affectionately named Old Blue and Old Yellow, were taken by Department of Conservation (DoC) staff and placed in the nests of warblers and tomtits.

The warblers turned out to be poor substitute parents, but the tomtits were a resounding success, with the birds tending and raising the young robin chicks.

DoC says shifting the eggs had the added effect of encouraging the female bird to lay more eggs than the usual two each year.

Current estimates put the black robin population at between 200 and 250 birds - all descended from Old Blue and Old Yellow. They are now flourishing in the Chathams area on Mangere and South East Islands.

However, an attempt to establish a new population on nearby Pitt Island did not go well, showing the birds will need a helping hand for some time yet.

The programme manager for fauna at the DoC Chatham Islands area office, Adam Bester, said 14 adult birds were moved to Pitt Island in September last year - the first time black robins had knowingly been on the island for 50 years.

They were transferred from nearby Rangatira (South East) Island to the Ellen Elizabeth Preece Conservation Covenant on Pitt Island - a 40ha area that was fenced to exclude predatory cats and weka.

But despite continued monitoring efforts, all the birds have disappeared.

"We want to try and get a little population going on Pitt," Mr Merton said. "But unfortunately the 14 leaped over the predator fence.

"The robins spend a lot of time on and around the forest floor. They are absolutely predator naive." DoC still considers Pitt can sustain a viable black robin population and there are plans to have another attempt next month when about 20 birds are to be moved.

DoC black robin recovery group leader Hilary Aikman said Pitt Island was targeted because there were few others to choose from. "If we do nothing, then the population just sits still. They are okay on South East and Mangere islands, but they can't expand. They've filled up all the available forest, so the population will just stay at a low number unless we provide new habitat somewhere."

The juvenile birds being produced in the current populations were now struggling to find their own territory to settle in. The biggest problem facing the relocation team was keeping the birds within the protected sanctuary.

Despite the earlier Pitt failure, total numbers of the birds are improving.

Mr Bester said surveys on South East and Mangere islands showed numbers were up on Mangere.

"It's looking up to between 200 and 250 birds. Hopefully, we can get a viable population based on Pitt as well, because that would change their threat classification ... They would be downlisted from endangered to a vulnerable species."

But predators are not the only threat to the Chatham Islands black robin, as research led by Massey University Professor David Lambert has found.

The scientists found the whole population had virtually identical DNA, and have carried out gene research on the birds.

"We have been looking at the genes in black robins that are responsible for their ability to resist bacteria and viruses. They are quite depleted in genetic variation in that way," Professor Lambert said.

"It is a source for concern, because should some new thing come along, it may be that they don't have the ability to withstand those pathogens."

A new bacteria or virus, he said, could wipe out the entire black robin population.

- NZPA