A NEW ZEALAND bird that clawed its way back from the brink of extinction
is thriving—despite being astonishingly inbred.

The population of the Chatham Island black robin, Petroica traversi,
had plunged to five in 1980 when conservation managers launched a daring rescue
programme. They removed robin eggs and put them into the nests of tomtits. The
tits accepted the eggs as their own, and went on to raise the chicks. This way,
the conservationists were able to raise up to three clutches from a single pair
each season, rather than just one.

Today, there are 200 robins on two islands in the Chatham Island group, 850
kilometres off New Zealand’s east coast. Because they are all descended from a
single pair of birds, Don Merton of the New Zealand Department of Conservation
decided to find out just how similar the birds are.

Merton commissioned David Lambert of Massey University in Palmerston North to
produce DNA fingerprints from blood samples taken from the birds. The tests
revealed that, for the genetic sequences on which the fingerprints were based,
the robins appeared genetically identical—apart from the differences
between males and females (Molecular Ecology, vol 6, p 21).

Lambert now plans to study genes in a region called the major
histocompatibility complex (MHC), which help control immune responses.
Scientists believe that low diversity in the MHC makes animals susceptible to
disease—and some have blamed this for the health problems that seem to
afflict another inbred species, the cheetah.

But the robins are prospering. Just over 70 per cent of their young survive
to fledgling stage, compared with only 42 per cent for their mainland cousin the
bush robin, Petroica australis australis. This is mostly due to the
fact that the islands where the black robins live are free of stoats, cats and
rats. But there are no signs that the robins are suffering because of their
genetic impoverishment.

Merton says that these findings should bring hope to conservationists who
fear that low genetic diversity will ultimately doom some endangered species to
extinction. Inbreeding, he points out, has benefits as well as costs. In the
case of the black robins, which survived as a tiny population on the exposed
islands for at least 100 years, the inbreeding probably ensured that all the
birds carry genes that help them survive in a harsh environment.

HOPES are rising for a large and flightless New Zealand parrot that is
one of the world’s most endangered species. Four kakapo chicks have hatched on
Codfish Island—one of three small islands that hold the entire population.
This makes 1997 the most successful breeding season since 1981, and boosts the
bird’s numbers to 54. No other chicks have hatched since 1992.

The kakapo used to live throughout New Zealand. But introduced animals,
principally cats and stoats brought in by European settlers, nearly wiped it
out. From the 1980s, biologists with the New Zealand Department of Conservation
moved the surviving birds to Codfish, Little Barrier and Maud Islands, where
there are no cats or stoats.

This year’s successful breeding on Codfish Island is linked to a “mast”
fruiting of the rimu tree, a species of conifer that produces fleshy fruit
rather than cones. In a mast year, the trees produce huge quantities of fruit.
Female kakapos, which care for their chicks alone, need rimu fruit in their food
in order to come into peak breeding condition. They also regurgitate the fruit
for their chicks.

Mast fruiting usually occurs every three to five years. But on Codfish Island
the last mast year was 1981. Three times since then, the rimu crop appeared to
be heading for a mast year but then failed.

The four chicks were hatched by three females. One appeared to neglect her
chick, so it was transferred to a fourth female. The females are now being fed
nuts, apples and sunflower seeds. The same diet was also fed to other birds in
the hope it would make them breed. “Even though the rimu rather than the diet
triggered the breeding, the diet is essential to making sure the chicks
survive,” says Paul Jansen, who manages the kakapo recovery programme.

Given that natural mast years are few and far between, Jansen and his
colleagues are working on ways to mimic the nutritional content of rimu fruit
and incorporate it into the parrots’ diet.

They are also exploring the possibility of injecting the trees with
gibberellins, plant hormones that trigger fruiting. As a last resort, the
researchers may also try injecting adult kakapos with sex hormones to bring them
into breeding condition.

AT THE first sign of clear weather this month, New Zealand’s rat
exterminators will take to the air in their most ambitious campaign yet to rid
one of its offshore islands of foreign rodents. The target is Kapiti Island, off
the North Island coast, where rats threaten several native species.

With an area of 1965 hectares, Kapiti is eight times the size of any of New
Zealand’s other islands which have been successfully cleared of rats. And the
island has to contend with not one but two species—the Norway rat,
Rattus norvegicus, and the smaller Polynesian rat or kiore, Rattus
exulans. Both species compete with native animals for food and eat their
eggs and chicks.

As soon as the skies clear, a helicopter chartered by the Department of
Conservation in Wellington will spend two days scattering 26 tonnes of
rodenticide over the island. With the help of the Global Positioning System
network of satellites, the pilot will be able to ensure that the island is
evenly covered with the poison, says Raewyn Empson of the DoC.

The DoC decided on aerial poisoning rather than working on the ground because
it will be faster to cover the difficult terrain. The conservationists also had
to allow for the difficulty of dealing with two species of rat. In past
campaigns, where bait was left at fixed “bait stations”, the bigger Norway rats
kept the Polynesian rats away from it. Dropping poisoned bait from the air is
more likely to succeed because most rats will have access to bait at the same
time.

A number of threatened species will benefit from the removal of the rats,
including birds such as the saddleback, the stitchbird and the kaka, several
species of lizard and a variety of invertebrates. If the campaign succeeds, the
DoC will consider reintroducing two of the country’s rarest species, the
tuatara, the sole survivor of an ancient group of reptiles, and the kakapo, a
flightless parrot on the brink of extinction.

Empson admits that the rats might not be the only casualties. One unintended
victim could be the flightless weka, which is an omnivore and might eat the
bait. Some wekas have been moved to the mainland, and others have been placed in
protective enclosures on the island. Any deaths should be offset by the
improvements following the rats’ removal, says Empson.

So far, the biggest campaign against the Norway rat was last year’s attempt
on Langara Island, one of the Queen Charlotte group in British Columbia, which
covers an area of 3200 hectares. New Zealander Roly Taylor, who advised the
Canadians, says the campaign “appears to have succeeded but we don’t want to
make any claim until we know exactly”. Taylor says clearing Kapiti’s rats is
probably more of a challenge because there are two species of rat and the
terrain is more difficult. It will be at least two years before the DoC is
confident that the operation has succeeded.