THE MYSTERY OF THE VANISHING WEKA

Forest and Bird, Volume 22, Issue 1, 1 February 1991, Page 14

THE MYSTERY OF THE VANISHING WEKA

by

Ann Graeme

ARLY SETTLERS called it the woodhen, and spoke affectionately of its amusing antics and annoying habits. Last century weka were numerous and very tame, and could readily be encouraged into homes and camps. Their curiosity was engaging, but less endearing was their habit of stealing bright objects like watches and jewellery! The weka is one of our most personable endemic birds, and quite a tough customer. Flightless it may be, but its strong legs and stout beak make it a formidable fighter and predator. Weka eat almost anything. In forests they scratch for insects, worms and fallen fruit amongst the leaf litter. In farmland they

eat seeds, foliage, fruit, grass grubs and wire worms, making up for the maize and tomatoes they enjoy. Weka scavenge dead animals, catch rats and mice and sometimes take baby birds. On the coast they skewer sandhoppers, shellfish and storm-cast food. Weka can learn to like new foods. During the possum eradication programme on Kapiti Island, weka added possum carcases to their diet. Early Maori introduced weka to Codfish Islands as a source of live food. There, the weka learnt so efficiently to kill the burrowing Cooks petrels, that the weka themselves had to be eradicated. They live in many habitats: alpine tussock grassland, forest and shrubland, swamp, sand dunes and rocky coast, and settled farm land with gorse and hedgerows for cover. Weka would seem to have a lot going for them, and last century they were abundant throughout the North and South Islands. Yet today, the North Island weka, Gallirallus australis greyi, has almost disappeared. Scant records show the following picture: Early 19th — Weka occurred throughout the century North Island. Late 19th — Declining but still abundant in century many areas. 1920s — Reduced to Northland and Poverty Bay and perhaps the King Country. 1924 — Northland population plummeted, only isolated populations remained.

1950s — Northland population extinct. 1970s — Weka introduced to Kawau Island. 1986 — Major decline in Poverty Bay, population split into two, at Gisborne and Motu. 1990 — Gisborne and Motu populations recovering, Kawau Island weka decline severely.

Why did the Weka decline?

Nobody knows for sure, but there are a number of theories. Some put it down to loss of habitat and competition for food from introduced animals, particularly possums. These factors have had a disastrous effect on many native species, but the versatile weka might have been expected to cope. After all, another native rail, the pukeko, thrives in our cultural landscape. A critical food shortage at some time of the year may be a factor. Early settlers spoke of weka migrations masses of thin, scabby weka moving across country, often in time of drought.

Introduced predators

Around the turn of the century, waves of invading predators swept through the North Island, and may be associated with the dramatic decline of many species. However, weka can defend themselves much better

Weka Sub-species

HERE ARE FOUR SUB-SPECIES of weka: the North Island weka, the Western weka of Nelson, Marlborough and the West Coast, the Buff weka of Canterbury and the Stewart Island weka. The Buff weka narrowly escaped extinction. In 1905 it was introduced to the Chatham Islands, where it flourishes to this day, but back in its home range in Canterbury it died out in 1924. In 1962 Buff wekas from the Chatham Islands were taken back to Arthur’s Pass National Park, but did not survive.

than most of our native birds. They can kill rats and mice, and rout cats, stoats or weasels in defence of their eggs and chicks. Despite this, predation must always be a problem for a ground-nesting bird.

Disease

It is widely held that introduced poultry disease caused the sudden decline in weka numbers. This may account for the population collapses this century, and the abrupt appearances and disappearances of local populations last century. These declines could also be attributed to starvation, perhaps linked to drought. No hard evidence or diagnosis exists. Many attempts have been made to reestablish weka in the North Island. Most of these releases failed. An important factor may have been the remarkable homing instinct of the adult weka. A weka taken from Gisborne to Hawkes Bay walked 130 km home. Captured Gisborne weka were banded and released in the Waitakere Ranges, west of Auckland. Three weeks later, one of these banded birds was killed on the road at Taneatua, more than 300 km south of Auckland, and on course for Gisborne! Weka taken from Maud Island swam a kilometre back to the island, and some of those deported from Codfish Island to Stewart Island, survived the stormy seas and tide rip and swam the three kilometres back! Such powerful homing instincts may have

sabotaged the crude re-introductions of wild captured, adult birds. A more sophisticated release succeeded at Rawhiti, in the Bay of Islands. Robertson liberated weka in the summers of 1966 to 1971, and accustomed the wild birds to their new surroundings by penning them for six weeks at the release site. More than 20 years later, the Rawhiti weka are established and extending their range. At present, the North Island weka occurs as a natural population in Poverty Bay, and as introduced populations at Rawhiti, Kawau Island, Mokoia Island (Lake Rotorua) and Arid Island. In 1986, in its stronghold in Poverty Bay, the wekas suffered a massive decline, and as much as 90 percent of the population disappeared. The population now appears to be increasing, but research is urgently needed to replace the speculation. Will the North Island weka, like so many of our endemic birds, dwindle to endangered status, or even to extinction?

Return of the Weka

Forest and Bird has researched the North Island weka and consider it has potential for careful re-establishment in selected habitats. First, we are initiating a captive breeding programme to produce a pool of young adults suitable for establishing a new population. This will avoid taking excessive numbers of wild birds from an already stressed population, and young, non-terri-torial birds will be more suitable to liberate

in new habitat. This summer Forest and Bird members and Department of Conservation officers will conduct weka surveys to establish population levels, before capturing weka pairs for breeding. Pairs will be distributed to approved breeders. While the captive weka population is building up potential release sites will be evaluated and the ecology of weka studied further. If the project succeeds the weka may return to enliven the forests of its former haunts. #

Weka breeders wanted

EMBERS INTERESTED in bird rearing may wish to take part in the Captive Rearing Programme. Participants must have a suitable aviary and obtain from DoC a permit to hold protected wildlife in captivity. Further details are available from conservation officers Ann and Basil Graeme, 53 Princess Road, Tauranga (075) 65593.