Takahe and the wapiti issue

Forest and Bird, Volume 14, Issue 3, 1 August 1982, Page 2

Takahe and the wapiti issue

By

ana

J. A. Mills,

R. B. Lavers,

M. C. Crawley*

OVER the past 2 years there has been considerable debate about whether wapiti should be removed from Fiordland National Park. The debate has led to differing interpretations of the National Parks Act, and pertinent questions have been asked about the philosophy of preservation of species and ecosystems and the rights of individuals using national park areas. These are important matters and it is right that they should be raised, questioned, and debated. Unfortunately, many statements have included bold generalisations about the ecology of Fiordland and its flora and fauna that cannot be sustained on the evidence available. Of particular concern to the Wildlife. Service is the inaccurate information that has been presented about the takahe. This article sets out the facts about the takahe and its habitat requirements and discusses the threat posed by mammalian competitors (red deer and wapiti) and predators (stoats) to the survival of the species.

FOR THE PAST 10 years research on takahe has been carried out by scientists of the Wildlife Service, Botany Division (D:S.1-R:) and. the Botany Department of the University of Otago. In addition, the impact of deer on the vegetation of northern Fiordland has been assessed by the Forest Service. The information collected has gone a long way towards explaining why takahe have declined and has enabled Wildlife Service scientists to prepare a comprehensive management plan for the species. Causes of takahe decline Takahe are at present restricted to an area of 650 sq km within that part of Fiordland National Park comprising the Murchison Mountains and an area to the north in the south-western section of the Wapiti Block. In the early 1950s the bird had a much wider distribution, being present also in small areas in the adjacent Kepler Mountains. Nowhere else in Fiordland are there large areas of takahe habitat. The takahe population in Fiordland has declined by almost 40 percent since 1972,

and now only 120 birds remain. Several factors have contributed to this decline, including severe modification of the vegetation by deer, preying by stoats, and breeding failures caused by inclement weather at hatching time. Of these factors the modification of the vegetation by deer and (in the Wapiti Block) by red deer and wapiti has been the most serious. Effect of deer on takahe Deer have affected both the summer grassland and_ the winter forest habitat of takahe. In the forest important food plants for takahe, such "as Uncinta and Chionochloa conspicua, have been either eliminated or severely depleted through heavy browsing and grazing by deer. The diet of deer in the tussock grasslands is quite varied, but there are distinct

preferences. Grasses and small herbs make up the bulk of the diet. When deer colonise an area the palatable small herbs are eaten first and when they become eaten out grasses and tussocks feature more in the diet. When deer numbers are high they compete with takahe for food. In concentrating their feeding on tussocks the deer show distinct preferences for certain tussock species; their order of preference coincides almost exactly with the ranking of species from the most nutritious to the least nutritious. Unfortunately, takahe show the same preferences as deer for tussocks high in nutrients. Deer concentrate their feeding in the sites where the most nutritious tussocks grow and repeated browsing of the same plants severely weakens and can kill the tussocks. The important point is that there does not have to be widespread destruction of the habitat to affect takahe — just the elimination or weakening of the most nutritious plants. Takahe are very susceptible to a change in the quality of their food because they have a very inefficient digestive sys-

tem which extracts only a small proportion of the nutrients from the food ingested. To obtain an adequate nutrient intake the bird spends over 90 percent of the day feeding and chooses the most nutritious individual plants. If there is a drop in the quality of food, the bird cannot compensate by feeding more. Similarly, it is not possible to feed faster. Research overseas on grouse has indicated that above an optimum food intake the digestion of nutrients actually decreases. The effect that changes in nutrients has is best illustrated by the striking increase in breeding success of takahe during tussock flowering years. When the tussocks flower (at about 3- to 4-year intervals, on average) there is an increase in the nutrient con-

tent of the succulent basal portion of the tussock tiller, the part the takahe eats. In the 1950s takahe were found in the Kepler Mountains, the Murchison Mountains, and the Wapiti Block. At the time that takahe disappeared from the Kepler Mountains deer had reached their greatest concentrations in the Te Anau-Manapouri_ catchment. Similarly, the spread and build-up of deer numbers in the Murchison Mountains coincided with the decline in takahe numbers. There was a lag between the arrival of deer and the decline of takahe, because it took time for the most nutritious plants to be eliminated. The surveys by the Forest Service (Protection Forestry

Report 92) showed that the degree of modification of the grassland was related to two factors: the ratio of forest to grassland and the ratio of palatable to non-palatable species of tussocks. This has been an important factor in the survival of takahe in an area. Takahe disappeared very quickly from areas where the ratio of grassland to forested areas was low. Such areas include parts of the Kepler Mountains, areas west of the main divide, and the Wapiti Block. Takahe managed to survive better in the Murchison Mountains Special Area _because not only was the grassland to forest ratio more equitable, but this area contained a higher proportion of alpine grasslands of palatable

species, which lessened the impact of deer. In recent years the grassland has shown improvement commensurate with the reduction in deer numbers brought about by heavy deer control. This is an encouraging sign, but the main problem at present is the relatively poor condition of the forest, the winter habitat of takahe. In parts of the bird’s range there has been a very slow recovery of the forest understorey. This produces two important consequences: First, there is a lack of variety of food plants for takahe and, second, because the understorey of the forest is depleted, the soils are prone to freezing, which prevents the birds from unearthing fern rhizomes, a staple diet in winter. Stoats Several correspondents to newspapers have argued that stoats have been a major cause of;..the-: decline: «of }takahe: Though both stoats and wekas have been observed as predators of takahe, and have obviously contributed to the

takahe decline, their preying has not been the major factor in that decline. Stoat numbers fluctuate markedly from year to year. High stoat numbers result from the _ periodic seeding of the beech trees, which initiates high mouse numbers. An abundance of mice causes better survival and breeding of stoats. When mouse numbers are low stoat numbers are also generally low. Over the past 10 years there have been two _ beechseeding years. There was a decline in takahe numbers in 1976 and 1977 at a time when stoats were plentiful, but we are not sure that the decline was dine to High stoat numbers, because the decline occurred in only one area while stoats were plentiful throughout Fiordland. As well as there being natural fluctuations in stoat numbers, we have some evidence that stoat numbers in the Murchison Mountains may have been kept at an artificially high level in the late 1960s through to 1972 because of the presence of deer

carcasses left during control operations, which stoats could have fed on. Generally, however, the number of stoats in the Murchison Mountains has declined markedly since 1973. . Management of takahe in Fiordland Though the takahe population is at a very low ebb at present, we believe that with correct management procedures, based on an extensive knowledge of the bird’s habitat requirements, the decline in numbers can be averted. Deer control is an important aspect of management, and the efforts of the Forest Service in reducing deer numbers in the Murchison Mountains havé led to a spectacular improvement of the summer grassland habitat. Unfortunately, there has not yet been a similar response in the winter forest habitat. A major thrust of some experimental management trials is to simulate the conditions which produce tussock-seeding years and thereby increase chick survival. This involves the use of fertilisers on two favoured species of food tussocks. The results of this experiment are encouraging, since over the last 2 years chicks have been produced in territories which normally have been unproductive. Stoat trapping has eliminated stoats from some localised areas and soon will be extended to other parts of the Murchison Mountains. Other management options include: relocating pairs in parts of their former range; maximising hatching success by swapping eggs to make sure that as many pairs of takahe as possible are incubating at least one fertile egg; and removing eggs and chicks for artificial rearing before returning them to the wild as yearling birds.

For many years the Wildlife Service has maintained a captive group of birds and attempts have been made to breed them. This is a safeguard against the possible loss of the wild population. However, with limited breeding success of the captive population so far, the major effort in conserving this species must still be undertaken in Fiordland. Need to retain all takahe habitat For reasons given above it is essential that all available takahe habitat in Fiordland be retained and managed for the conservation of takahe. The amount of ideal takahe habitat is limited and is predominantly in and around the Murchison Mountains, including a small area to the south in the Kepler Mountains and in parts of the Wapiti Block. Soon after the rediscovery of takahe in 1948 a 250-square mile area incorporating the Murchison Mountains was gazetted a Special Area with restricted access. It seems a large area, but in fact only 30 square miles contains adequate amounts of the required food plants on suitable terrain. Furthermore, not even all of the 30 square miles is entirely suitable for takahe, because the nutritional quality of the food plants in many areas is inadequate to support successful breeding. The largest area of takahe habitat outside the Murchison Mountains exists in the Wapiti Block. A recent survey of this area revealed that 39 percent of the above tree-line area is potentially suitable as takahe fiabitat; -~fakahe ‘were: once well represented in areas of the Wapiti Block, but now only a few pairs remain. The areas of potentially suitable takahe habitat in the Wapiti Block will be used for future takahe liberations, provided that the habitat quality is enhanced by

deer-wapiti control to reduce the browsing pressure. Removal of wapiti supported The Wildlife Service supports the removal of wapiti because the reduction of browsing pressure will preserve and enhance the habitat needed for takahe. The New Zealand Deerstalkers Association made representations to Parliament to have the Wapiti Block set aside as an area to be managed for wapiti. The management practices required would be in conflict with the management of the area for takahe and so naturally the Wildlife Service must oppose this proposal. It must be emphasised, however, that the Wildlife Service has no intention of increasing the size of the Special Area to incorporate the Wapiti Block. Some correspondents to newspapers and some editors have expressed the view that takahe should be moved from Fiordland and wapiti retained. Where is the sense of priorities? Takahe is an endemic, critically endangered species and the wapiti is introduced and not endangered in its country of

origin. The relocation of a species like deer, which is able to tolerate a wide range of habitat types, is a relatively safe procedure, but for species with very specific habitat requirements (that is, the most endangered species) there is always an element of uncertainty as to whether the animal will adapt to the new environment or not. The plan to shift kakapo and takahe to predator-free islands has nothing to do with administrative or research convenience; it is an attempt to safeguard the species from extinction and is undertaken alongside efforts to preserve the species in its natural habitat. The takahe is an_ integral part of the alpine tussock grassland ecosystem in Fiordland. It makes its own unique contribution to the functioning of that system by its method of feeding, which actually promotes tillering or new growth of tussock shoots. We believe that it has the potential to survive in its present habitat and that the major thrust of conserving the species should aim at maintaining it in Fiordland. «

*The three authors of this article are scientists in the Wildlife Service, Department of Internal Affairs.