End of blue ducks?

Press, 25 February 1986, Page 19

End of blue ducks?

By

OLIVER RIDDELL

Another of New Zealand’s native birds, an evolutionary curiosity, may be far down the road to extinction. This is the blue duck (whio of the Maori) which was once widespread but these days is restricted to a few steep, upper river valleys in the back country.

Clearance of land to leave rivers and lakes devoid of cover on the banks, modification of river flow, damming and channelling, have all forced the blue duck to retreat from the low country waters where once they were common.

They have also retreated from the impact of introduced ground predators such as cats, the development of farmland, and increased silting of rivers and eutrophication of lakes. They have coped better than many rare and endangered species but they are still in trouble. A big effort is now under way by the Wildlife Service to identify the rivers on which blue duck still occur, and what numbers are present In the North Island they are known to occur on rivers draining the Kaimai, Raukumara, Huiarau and Kawhenua Ranges, and from the central volcanoes. There have been other sightings in the Kaimanawa, Kaweka and Ruahine Ranges. Such a distribution might imply that the bird is widespread and perhaps numerous, says Dr Murray Williams of the Wildlife Service, an authority on ducks and game birds. But closer inspection reveals that this is not the case. Many sightings may be of one or a few birds, and the distribution is becoming discontiguous — a classic symptom of a species in decline.

The whereabouts of blue duck in the South Island is known in only general terms. They are in the Richmond and Spencer Ranges, along the western flank of the Southern Alps, in Fiordland, and have a tiny remnant in iCatlins Bush in South-East Otago. They have never been known in Stewart Island or the Chatham Islands. But their distribution and numbers in the South Island are not known, and may be very few. They are difficult to count. As a general rule of thumb there is likely to be a pair of blue duck every kilometre of river on which they occur. Once their distribution catchment by catchment has been pieced together, a crude estimate can be made, but Dr Williams says even then there is a danger of over-estimating. On many rivers, blue duck occur only in the headwaters, and further apart than on the slower lower sections. Blue duck are very difficult to count Long isolation has created some unique bird species for New Zealand. Some, such as the moa and huia, are extinct; others, such as the kakepo and black robin, are almost extinct; and others, such as the kiwi, and takahe, are under threat The blue duck fits into this third category.

New Zealand’s blue duck has no close relatives anywhere in the duck world. Scientific opinion is that the blue duck evolved at a vtry early stage in the evolution or ducks. Its subse-

quent isolation in New Zealan meant that it became well separated from the base stock which evolved into such a great diversity of duck forms worldwide.

There is evidence for its antiquity in some aspects of its behaviour and some of its anatomical features.

For example, the protein composition of its feathers is unique and unlike those of all other dabbling ducks. The blue duck lacks a wing speculum (the irridescent coloured patch on the inner wing feathers), and has black edging on the innermost secondary wing feathers — both unique features in the duck species.

Most ducks have elaborate courtship displays; that of the blue duck is very simple. Some of its uniqueness of behaviour is shaped by the habitat in which it lives. Rivers with strong currents are a difficult habitat in which to live, feed and rear young.

Dr Williams says the biggest threat to the future of the blue duck is its discontinous distribution. If birds from one catchment can no longer disperse to and top up the population resident in another catchment, numbers in both are likely to decline over time. The isolation induces decline, for the effect of poor breeding years cannot be compensated for by a good year somewhere else.

To ensure the bird’s future in hill country valleys may well require a constant programme of moving birds around as once they would have done naturally, and establishing them in areas such at Mt Egmont where the quality habitat remans but there are no birds any more, he says.