Restoring

Forest and Bird, Issue 293, 1 August 1999, Page 38

Restoring

SIMON HEPPELTHWAITE

finds the South Island’s shingle riverbeds

‘undervalued, under-represented and under threat’.

he braided river habitat and surOP sundin wetlands of the Upper Waitaki River catchment is disappearing fast, and its unusual wildlife is in consequent decline. Here, as in similar habitat throughout the South Island, the homes of some of New Zealand’s rarest birds (and animals) are under threat. This is a place drowned and dewatered by hydro development, and often drained for farmland. It is also extensively invaded by weeds, predators, exotic fish, and people. The Department of Conservation’s Project River Recovery is about piecing together the fabric of this degraded landscape to restore the rich tapestry which forms the braided river habitat. The complexity and scale of this dynamic landscape is daunting. Sinuous strands

of icy water, loosely woven into braids across vast shingle riverbeds, issue forth from glacially carved valleys. The rivers flow across the largest inter-montane basin in New Zealand, and their shifting boundaries are dotted with ponds and wetlands. Among the broad, barren beds of rounded riverstones are the last feeding and breeding grounds of the critically endangered black stilt, one of the world’s rarest wading birds. Threatened black-fronted tern and wrybill also nest here, although they migrate to coastal areas for the winter. During spring and summer these braided rivers are home to 26 species of water birds. Wrybill, in particular, have adapted to this environment by becoming the only bird in the world to have a bill which curves to the right. This allows them to more easily catch

insects on the underside of river stones. All of these species, however, have requirements so specific to this habitat that extracting them to the sanctuary of predator-free offshore islands is not an option. Nor can they be isolated from the surrounding farmland or the pressures of recreational pursuits such as angling and off-road driving. The challenge to reverse the decline in numbers of black stilt, combined with the loss of other braided river species, led to the concept of Project River Recovery conducted by the Department of Conservation in the Mackenzie Basin, near Aoraki/Mount Cook. Its goal is to retain the habitat and native ecological communities of the Upper Waitaki River catchment and stabilize or increase the populations of native animals under threat. Since its establishment in 1991 it has made significant gains, setting the pattern for future river recovery here, and elsewhere on the South Island’s shingle riverbeds, which are found from Marlborough to Otago. ‘The tools we have developed for the restoration of rivers in the Upper Waitaki catchment could be applied to other restoration projects, says Kerry Brown, manager of Project River Recovery. "The project will continue to focus on the key tasks of weed control, predator research and wetland enhancement. Through weed control we can retain habitat, but we need to know more about predators to achieve cost-effective predator control. Our assessment of constructed wetlands with preda-tor-proof fences is very encouraging. ™™" xotic weeds such as crack willow, gorse, =® broom, lupins and wilding (weed) "mma trees seriously degrade the value of the riverbeds by covering feeding and breeding grounds. As they stabilize the normally shifting river channels, these weeds limit the positive effects of freshes and floods which once regularly eroded islands and channels and flushed the habitat clean. The weeds also attract rabbits: predators following them

find nesting birds, eggs and chicks easy prey. Weed control has so far resulted in more than 11,000 hectares of riverbed being maintained or restored as prime feeding and breeding grounds for birds. Targeted use of chemical herbicides has produced the best results on lupins, gorse and broom. On the productive deltas where the Tekapo and Ahuriri rivers flow into Lake Benmore, large areas of crack willow, which were smothering the riverbeds, have been mechanically removed and burnt. Lupin and willow control is controversial. Many locals regard the plants as attractive additions to the landscape. There were also fears that both spraying and willow removal would degrade trout stocks. Stringent ecological monitoring of herbicide applications found no_ negative impacts on introduced trout, native fish, insects, birds or water quality. To accommodate the concerns of the community, Project River Recovery reduced the spray area while staff of the Fish and Game Council surveyed trout numbers. They identified a long-term decline in all size classes of trout which began before willow removal occurred. The decline also occurred in areas not affected by willow, or other weed control, which suggests a natural process is the cause. Herbicide application provides safe, cost-effective management for Russell lupin. More than $100,000 was spent investigating biological control without discovering any other viable options. Measuring the benefits of weed control has not been easy or cheap. Aerial photography of weed distribution is expensive. Superbly camouflaged chicks also make it difficult to measure increases in bird productivity. Monitoring breeding birds in the Tekapo and Ahuriri deltas shows black stilt, black-

fronted tern, and many other species nest in the restored habitat. Studies comparing foraging and nesting behaviour, between cleared, uncleared and willow free areas, conclude that willow removal is beneficial to birds. Predator control may also be required, however, to increase populations. Along with habitat loss, predation is a major threat to birds in braided rivers. ‘Project River Recovery now has the tools to provide quality habitat for these species to feed and breed, says Kerry Brown. "The challenge is to provide enough protection from predation and disturbance to allow their populations to grow. Initially there was little definitive evidence of population decline among many riverbed species. Project managers set out to determine the importance of predation and to identify the key predators; and to measure bird population trends. Over a five-year study, video cameras recorded the causes of death at 138 nests of black stilt, black-front-ed tern and banded dotterel. Cats, ferrets and hedgehogs caused 89 percent of predation. All except one raid occurred at night. Simply eliminating these predators is not an option, however, due to constant reinvasion from surrounding land. Research now aims to identify how much predator control is needed to enable threatened bird species to recover. (See box). Fences to control predators may be an alternative to trapping but they cannot be applied to braided rivers because of the unpredictable, changing courses of the river channels. The option of fencing adjacent wetlands was tested at seven sites by Mark Sanders, who was based at Canterbury University in 1993 and 1994 (prior to joining the project staff). He found that new or modified wetlands could provide large quantities of suitable prey species for wetland birds. uring the 1970s pioneering work _ on predator fencing was undertak"mi en at two high-country lagoons by Soin Canterbury Forest and Bird, along with the Wildlife Service and Ray Pierce. The fences and lagoons have since been enlarged and updated as part of Project River Recovery, and water levels are better controlled through stop log weirs. By gradually lowering the level of water, to create fresh shallows, the maximum feeding habitat is provided during the breeding season. The weeds, which sprout up in the freshly exposed areas, become food for microbes and insects when the ponds are refilled during winter. On a terrace above the Ohau River, the 11-hectare Ruataniwha Wetland was created and fenced in 1993. So far 98 hectares of

wetland and surrounding breeding areas have been predator fenced. Another 19 hectares of wetland have recently been created at two further sites, although they have yet to be fenced. A six-year study is currently underway to determine the relative conservation gains of wetlands with predator fences. Wetland enhancement and creation, along with predator fences and trapping, have already proved highly successful, with a variety of birds making immediate use of them. Some wetlands have been used as release sites for captive-reared black stilt. A colony of 80 black-fronted tern nesting in the new Ruataniwha Wetland was another notable success. The birds nesting in the fenced wetlands have a much higher breeding-survival rate — over 90 per cent. Birds nesting outside the fences typically have less than a 40 percent survival rate. Fenced wetlands also have the advantage of keeping out people, who are another major factor in disturbing the birds. There has long been conflict between some anglers and river birds, while the growth of 4WD use has dramatically increased interaction and conflict in the riverbeds. The spring fishing season clashes with the breeding season and disturbance from anglers, walkers, drivers and dogs can cause birds to abandon nests and chicks. Four-wheel-driving can crush eggs and chicks, and the wake from a jet boat can swamp nests. It is difficult for recreational users to see braided rivers as fragile nurseries for threatened species when they look like barren wastelands. To increase awareness of the needs of wildlife, an advocacy programme has been established to alert the public to the impacts of weed invasion, predation and disturbance. Signs, articles, pamphlets and press releases have been produced and riverbed access roads have been clearly marked to encourage the use of established tracks. A liaison officer was based at the Ohau-Tekapo delta last summer when adjoining campgrounds were full. A ‘braided river care code’ has been produced and efforts are directed at educating anglers to recognize bird disturbance, and respond appropriately. Project River Recovery is producing the hard facts about conservation and the techniques which could save our threatened braided rivers elsewhere in the South Island. SIMON HEPPELTHWAITE is community relations officer for the Department of Conservation at Twizel in the Mackenzie Country. His background is in ecotourism, education and ecological restoration.