BLUE DUCK — Symbol of wild and untamed rivers

Forest and Bird, Volume 22, Issue 4, 1 November 1991, Page 22

BLUE DUCK — Symbol of wild

and untamed rivers

Forest and Bird's South Island Field Officer Mike Harding, has taken an active interest in blue duck carrying out his own research at Arthur’s Pass. Here he explains what is special about the blue duck, or whio, and describes the current threats facing the species.

|= "OR ANYONE who has tramped _. through the mountains of New Zealand, the whistle of the blue duck is one of the most characteristic sounds of the wilderness. The spectacle of a pair of blue ducks bobbing downstream with their fluffy chicks, expertly negotiating rapids and white water, is unique to unmodified mountain rivers. Even the most hardened back country traveller treasures the memory of these tame and confiding birds. Yet, despite its legal protection, the future

of the blue duck is by no means secure. Blue ducks are river specialists, a distinction they share with few other species of duck world-wide, notably the African black duck, Salvadori’s duck of Papua New Guinea and the torrent ducks of South America. None of these species are closely related. All have evolved separately to live in the difficult fast-water habitat a textbook case of convergent evolution. The blue duck is an ancient New Zealand species. It has very simple courtship dis-

plays and is territorial unusual features for a duck. Most revealing, however, are the distinctive proteins that make up its feathers. These are an important indication of its genetic uniqueness and ancient origins.

Species in decline

When Forster, a naturalist on COOK'S Endeavour, first described the blue duck, it was present throughout the mountains of the New Zealand mainland. It appears to

have been common in all forested river catchments, particularly in steep high altitude areas, and occasionally right to the coast as observed in Fiordland. Well known to the Maori, it was an important source of food on inland expeditions. They named it whio after the distinctive whistling call of the male bird. For the early European explorers it was a charming and friendly source of companionship and amusement. So tame in fact that it often ended up in the billy for the evening meal.

Charlie Douglas, the famous surveyor of South Westland, noted that ". . . its prevailing characteristic is stupidity to an amazing degree. This combined with what appears to be a fatal thirst for admiration is its ruin, and make it an easy prey to dogs and men, and nothing but the inaccessible places it frequents saves it from being exterminated." Blue ducks were a staple food of back country explorers such as Barrington who, on his epic exploration of the Red Hills in West Otago, ate blue ducks to help survive the rigours of this remote and unforgiving country. Early oral records show that blue ducks were widespread and abundant. Sadly, that is not the case today. Most birds are now confined to unmodified mountain rivers in the central North Island and western South Island. River diversions and hydro dams for irrigation or power generation have turned clear rushing waters into slow turbid streams, as in the headwaters of the Whanganui River. Forest removal and agricultural development have led to siltation of clean rivers and the loss of necessary riparian (streamside) vegetation. Populations of introduced trout compete with blue duck for in-stream invertebrate food sources. Introduced predators threaten accessible populations of the blue duck, whose ground nesting habits make it especially vulnerable. Its only natural predators were other birds such as the black-backed gull and maybe the native falcon or now extinct birds of prey. Concern has been mounting in recent years over the apparent contraction of blue

duck distribution. Trampers and hunters noted its disappearance from favoured back country haunts such as the Tararua Ranges. Sightings of birds, and systematic surveys of rivers, in the Arthur's Pass area show that blue ducks have disappeared from several river tributaries over the last 20 years. But detailed monitoring of small populations has so far failed to provide a conclusive answer to one of the mysteries of blue duck populations — where do all the young birds disperse? Most years there is a surplus of fledglings, but very few manage to either

squeeze in a new territory amongst existing pairs, displace an adult bird, or fill the gap left by a dead bird. However, numerous sightings of blue ducks on alpine tarns and of single male birds have suggested that young birds are more mobile than previously expected. This has been confirmed recently by sightings of colourbanded birds in rivers some distance from their home territory in both the North and South Islands. Blue duck show all the symptoms of a species in decline. Populations are scattered between the headwater tributaries of major rivers. Blue ducks are present in some streams but absent from adjacent, and apparently similar, streams. The lower modified reaches of rivers are usually unoccupied as though blue ducks are reluctant to disperse over land or across unfavourable habitat. While the total population is estimated to be about three

to four thousand adults, this is split into discreet sub-populations. The largest two in the North Island are the 40 pairs in each of the Motu and Whanganui catchments. Their small size and lack of interaction makes these populations increasingly vulnerable to habitat changes. In 1980, Wildlife Service (now DoC) scientist Murray Williams set out to solve the mysteries of the blue duck by studying their ecology on the Manganui-a-te-Ao River, a tributary of the Whanganui. The stimulus, Murray recalls, came from two people Janet Kear of England’s Wildfowl Trust and US waterfowl biologist Frank McKinney. They had carried out brief

studies of blue duck and recognised the need for further, more detailed, research. As well as their encouragement there was a conservation imperative. The National Government's subsidised loans for small hydro schemes had focussed attention on the Manganui-a-te-Ao. The entire river, the only remaining free-flowing tributary of the Whanganui rising in Tongariro National Park, was under threat. For over ten years, Murray colourbanded every resident bird and all juvenile birds that fledged in a ten kilometre stretch of the river, monitoring an increase from four to nine pairs. Initially limited to 20 field days each year, the research project is now one of the longest studies of any duck species in the world and certainly the most important study of a riverine duck. It has revealed some interesting results. Most significant is that inbreeding appears to be a natural feature of the blue duck population — a surprising discovery in light of the widely-held view that a broad genetic base is essential for the long term survival of a species. Colour banding of individuals by Murray, and genetic ‘fingerprinting’ by fellow DoC scientist Sue Triggs, has confirmed that there are successful brothersister pairings and even a grandmothergrandson pairing. In this study no duckling established a territory more than ten

kilometres from its natal area. Blue ducks have much in common with other relict New Zealand species. They are relatively long-lived, have a low reproductive rate and irregular breeding success, similar to our more critically endangered species. Fortunately, the blue duck is still what Murray calls a ‘second tier’ species. The blue duck joins a long list of native birds which are still reasonably widespread but are nowhere common. Birds like the kea, kaka, kiwi, falcon, robin and blue duck are still adjusting to extensive loss of habitat, introduced predators and competition from browsing mammals. At least

with these species, early attention may ensure that last-ditch rescue programmes, like those mounted for the black robin, black stilt and kakapo, may not be necessary.

Suited to fast water

Blue ducks are admirably suited to the fast water habitat. Their strong webbed feet can propel them across rushing white water the young chicks literally run across the top. They are superb divers and adept at foraging amongst the stones in riffles, and in the lee of large boulders. A curious-looking black flap on either side of the bill protects it from abrasion against rocks. So harsh is their rough rocky home that plastic leg bands can wear through completely in two years and the identification numbers stamped into the thick aluminium bands soon become illegible. Blue ducks rely on insect larvae for food. These invertebrates live on and under the stones of the river, occasionally drifting downstream, particularly in floods. Recent studies by Kevin Collier (DoC) and Clare Veltman and Ian Henderson (Massey University) indicate that large prey items, particularly caddis fly larvae, are preferred in North Island rivers. The frequent shiny dark fragments of insect exoskeleton in their conspicuous droppings testify to their

rich invertebrate diet. In the Southern Alps, where blue ducks are present in the subalpine zone, fruit from riparian shrubs forms an important part of their autumn diet. | have observed blue ducks amongst the streamside shrubs, gorging themselves on Coprosma berries and leaving thousands of undigested seeds splattered on the open riverbed. Year-round territoriality has probably evolved from the need for a pair to maintain their breeding partnership and to defend their nesting and feeding areas. Observations by blue duck researchers, including my own over several years in the Arthur’s Pass area, indicate that the main constraint on blue duck productivity is the availability of females. Female blue ducks have a lower survival rate than males, because of the energy demands of producing eggs and their vulnerability to predators during nesting. Males are more common. They often engage in spectacular fights, swiping at each other with the prominent spurs on their wings, when competing for the limited number of females.

Recovery plan

Work on blue duck is now coordinated by a national liaison group with representatives from DoC, Forest and Bird, Ducks Unlimited and universities, as well as independent researchers. The group’s working document, compiled after the first national blue duck meeting in 1987, has directed efforts over the last five years. A revised version of this Blue Duck Recovery Plan will guide blue duck work for the next decade, identifying research and monitoring priorities for blue duck conservation. The annual meetings of the group provide valuable forums for discussing the latest research results and for encouraging

regional conservation projects. Colourbanding of individual birds and monitoring of small populations is now occurring in most blue duck areas. Several studies of blue duck ecology are being carried out by Massey University and DoC researchers, including an important study of the effects of introduced trout on blue duck productivity. Birds have been transferred from the central North Island to Mt Taranaki where they have successfully established a new breeding population. Also, scientists are experimenting with radio transmitters in an attempt to solve

the great blue duck mystery Where do all the young birds go? Preliminary results show that some young males move right out of the catchment, returning again after a few months. An important part of this national conservation effort is captive breeding. ‘Op-

eration Whio’ aims to breed blue ducks in captivity for eventual release into the wild to supplement existing populations or establish new ones. Over 40 blue ducks, nearly all raised in captivity, are now held in aviaries around the country. The breeding effort is coordinated by Ducks Unlim-

ited, a national waterfowl organisation. The Mt Taranaki experiment has shown that it should be possible to re-establish blue duck in areas where they have become extinct. However, further research to determine the critical requirements of good blue duck habitat is essential, as the reasons for the decline in blue duck populations are still not clearly understood. A survey of blue duck habitat throughout the country by scientist Kevin Collier has shown that favourable rivers tend to have narrow channels, high gradients and stability, low summer water temperatures, large boulders, and intact native forest as riparian vegetation. With an improved understanding of blue duck ecology, and the guidance of a recovery plan, efforts to protect the species can be better directed. According to Murray Williams, the key to survival of the species lies in the protection of successful family lines. Some pairs are very productive, consistently raising at least two young per year on average. Other pairs rarely succeed in their breeding attempts. He found the recovery of the blue duck population on the Manganui-a-te-Ao was primarily due to the efforts of two pairs whose abundant offspring colonised the vacant territories up and down the river. In an effort to assist the Manganui-a-te-Ao blue duck population, white water rafters have voluntarily agreed to stop rafting down the river during the critical months of October and November, when newly born chicks are vulnerable to outside disturbance. Unfortunately, the major threat to the survival of the blue duck, and the historic cause of its decline, is still with us. Destruction or modification of blue duck habitat continues today and has taken on a whole new meaning with the creation of Electricorp — a State Owned Enterprise which believes it has a mandate to increase electricity consumption. With the growing demand for energy, pressure is mounting to increase hydro power generation from the country’s untamed rivers. The Government does not have an energy conservation policy and New Zealanders are facing a succession of battles throughout the country as wild rivers are eyed by electricity producers to supply more power. Increasing hydro power generation is not necessary if proper energy conservation and energy efficiency measures are implemented. The blue duck requires unmodified rivers. Its present distribution is testimony to this. While the intricate ecological requirements of the blue duck are still only partially understood, there is no doubt about its requirement for a pristine habitat. The blue duck is a symbol for the life-blood of the country our wild and scenic rivers. Its presence indicates healthy and unmodified river ecosystem, upon which many agricultural, industrial and urban uses downstream are dependent. If New Zealand loses the distinctive ‘whio. . . whio. . . ’ from its mountain streams then it has lost not only a national symbol of the back country, but will have sacrificed the quality and character of the country’s river systems. &