NATIVE BIRD MANAGEMENT

Forest and Bird, Volume 17, Issue 4, 1 November 1986, Page 7

NATIVE BIRD MANAGEMENT

Dr

Murray Williams.

The following is a personal view of the future management of our vulnerable and endancered native birds by Wildlife Ser-

vice scientist

ticle raises more questions than it answers, giving readers pause to think who have always accepted that prevailing management practices are correct.

A: greater New Zealand emerged from the last ice age, about 15,000 years ago, it did so in concert with a rising sea level. Greater New Zealand, with its now three main islands then as one, shrank, its extensive lowlands were drowned and its old coastline disappeared eventually under some 180-200m of water. Just as the land connections between North, South and Stewart Islands were sundered, so were those between the hinterland and the near coast hills. These hills became islands, now termed landbridge islands — Kapiti, D’Urville, Great Barrier and Hauraki Gulf islands may be viewed as remnants of that Greater New Zealand. These islands carried with them, at separation, all the floral and faunal heritage of the mainland. But viewed some 10-15 millennia later, each island now has its own special character, its own, and in many cases unique flora, and an assemblage of native birds that may also be different from that of its near neighbours.

Obvious pattern

When the native forest-inhabiting bird faunas of New Zealand’s many landbridge islands are compared (see Box 1), an obvious pattern emerges. The large islands contain more native species than do the small islands, and the particular assemblage of native bird species on any island is directly related to the island's size. Simply, this is because large islands contain larger tracts of forest and a greater diversity of habitats within those forests. Thus, a greater number of species can live there side by side and each can exist in abundance. On the other hand, small islands

have few different habitat types and their bird populations are smaller; small islands characteristically contain only birds like fantail, silvereye and grey warbler, species which have small territories, are good at moving from one isolated habitat to another, and are capable of exploiting a wide variety of habitats. These relationships between an island’s size and the number and identity of bird species living there are but some of the findings of a branch of ecology called island biogeography. Throughout the world, the faunas of many groups of islands are being subjected to analyses by students of this discipline seeking to identify new relationships. This pursuit is not a flight of scientific fancy but has special relevance to the conservation of bird and other animal species in mainland reserves. Isolated patches of forest on the mainland, surrounded by a sea of grass farmland, are essentially islands, with some species of forest-inhabiting birds no more able to cross the sea of grass than they are to cross the water to landbridge islands. Thus, it is agreed, a study of landbridge island faunas, and the processes that affect them, can provide guidance for the conservation of species restricted to mainland forest "islands."

Perhaps the simplest and most obvious extrapolation from these island studies is that if a species has failed to survive the 10-15 millennia of isolation on a landbridge island of a particular size, then it is equally unlikely to survive long term in a similar sized isolated forest block on the mainland. The

corollary to this, of course, is that if a species — stitchbird, for example — failed to survive on Mercury Island (22 km?), but did so on Little Barrier Island (30 km2), then any mainland reserve for it has to be in the order of 30 km? to ensure its long term survival.

Ignores vital point

This simplistic extrapolation, while correct in general terms, ignores at least one vital point: that the modification of each island's avifauna after it separated from the mainland, took place under pressures which did not include a suite of mammalian predators or herbivores, nor other human-in-duced changes. The kokako, for example, failed to survive on Little Barrier Island, disappearing from there without being faced by deer, goats and possums, now known to compete with it for food in Pureora Forest, and without the attention of cats, mustelids and rats which have plundered their nests in Pureora. The number of kokako able to live on Little Barrier Island was simply too few to allow the bird to sur-

vive the natural vicissitudes of these 10-15 millennia. Today the combined effects of humans and their introduced animals maintain bird populations in mainland forests at lower densities than occurs on landbridge islands. And mainland forest patches also tend to contain fewer native bird species than islands of similar size. The conclusion is that for long term survival on the mainland, a species like the kokako is going to need an area of forest bigger than island biogeographic studies predict. For North Island kokako, there are no such areas left. The purpose of this short venture into the world of island biogeography is to illustrate that even in the absence of detailed biological studies on our forest-inhabiting birds, there are explanations as to why some species and not others are presently in the endangered category, and what sort of reserve size is needed to sustain them, long term, on the mainland. Island biogeography gives us some very clear messages. @ it is the highly endemic species, the truly unique New Zealanders, that are the ones most affected by forest fragmentation e itis the highly endemic species that need to exist in minimum numbers over very large areas in order to survive long term. Island biogeographic studies help identify the minimum area required, and hence the minimum numbers. e as forest fragmentation continues, those species now in the threatened category will also become endangered — yellowhead and whitehead, kaka, rifleman and robin, brown and great spotted kiwi are just some of the likely candidates. It is the inevitability that more uniquely New Zealand birds will fall into the endangered category, and the realisation that present conservation resources (manpower and finance) are so stretched as to be unable to cope with the endangered species we already have, that calls for some radical and clear thinking. With the advent of a Department of Conservation and the expectation that accompanies it, perhaps this is an appropriate time to review conservation objectives, priorities and operations. What follows are but some of the topics which I believe are germane to that review.

Endangered vs threatened — where to concentrate the effort

Gee efforts are directed almost exclusively at the highly endangered species kakapo and takahe, black robin and black stilt, kokako and little spotted kiwi. But the monocular concern with these species is allowing others to enter the selfsame category. Some can do so literally overnight, as little spotted kiwi did when the expectation that they occurred in Westland proved incorrect. The present distribution of North Island brown kiwi, great spotted kiwi, yellowhead, rock wren, weka, brown teal and blue duck (in the North Island) provide evidence for justifiable concern. Should we wait until they too become truly endangered before taking direct action? If the answer to that question is "‘no"’,

does it mean that work on some already endangered species should stop? It would be a courageous decision indeed to abandon a species, but it is one that ought not to be shirked if considered necessary. The belief that the battle to save the kakapo and the black robin is already lost and should be abandoned in favour of species offering better chances of success is not without its supporters.

Islands or mainland

actors which caused the decline or extinction of species on the mainland may stilll be present and it was logical to prevent total extinctions by establishing remnant populations on largely unmodified islands. But should our conservation horizons not now be extended? Should not our

long term aim be to re-establish those species (like stitchbird, saddleback and little spotted kiwi) back on the mainland? What would this involve? When should this be attempted -- now, next century or never? Island biogeographic studies suggest another reason why the mainland ought now to receive greater emphasis. The number of species resident on an island is limited by the island’s size. One simply cannot go on adding species after species to an island and expect them all to survive, even in the short-term.

Species or Sub-species

he islands of New Zealand have spawned a number of quite unique island races of mainland species (e.g. fernbirds, snipe, tit, robin, wren). Where do

An analysis of New Zealand forest bird species on landbridge islands was conducted by Rod East and the late Gordon Williams and published in the New Zealand Journal of Ecology (1984). Their principal findings are listed below.

AREA (km2) Figure 1: Occurrence of indigenous forest-dwelling birds on offshore islands of different size. For each species, symbols indicating absence are shown only for those islands larger than the smallest occupied as a resident breeder. Conclusions e As island size declines, species loss occurs sequentially in a predictable manner e Apart from the falcon, species restricted to one or both of the largest islands or the mainland (eg brown kiwi) are partially or completely flightless and are endemic e Species absent from islands of 15-30 km? are dependent on indigenous forests and belong to endemic families e Other species dependent on indigenous forests occur less frequently as island size declines below 10 km?, and are absent from islands of less than 1 km2 e Birds occurring on small islands are not dependent on indigenous forest There is a disproportionate loss of species showing a high level of endemism and dependence on indigenous forest as the size of the island declines from above 100 km? to below 1 km?.

they lie in the continuum of conservation interest? A commitment, indeed a very large one, has been made to black robin on the Chathams; if a similar problem occurs elsewhere should the same response be made? These island sub-species pose a special problem. Their transfer beyond their existing islands is likely to be especially controversial, even though such an action would reduce their vulnerability. The avifauna of The Snares is a case in point; sooner or later (and most likely sooner) rats will make it ashore and the delightful tits and fernbirds would fall easy prey.

Fighting with or against nature

A" appraisal of conservation priorities and activities should consider the natural events taking place. I make this point because efforts to save black stilt make me uneasy. The black stilt dilemma is that it is being genetically swamped by a recent colonist of New Zealand the pied stilt. Why are we fighting against a ‘natural process’, one that has occurred here, and all over the world, many times? Is this not one of the ways by which new species evolve? If we continue the fight for the black stilt, should we not also consider doing it for grey duck before it too is genetically swamped by mallard?

Self-sustaining or managed populations

n the scramble to at least get some populations of endangered species established on islands, birds have been released there and left to their own devices. Thankfully in almost every instance it has worked. This approach may be fine for the best of our landbridge islands, but is unlikely to be

successful on other islands and the mainland. A more active managerial role will be required. Kokako epitomise the need for constant management. There are no forests left in the North Island in which kokako are likely to survive long-term, and without human help. Yet in even small areas like Mapara Forest (1300 ha) a constant campaign of predator control and control of browsing mammals, and the planting of food plants for the birds could be enough to ensure their presence well into the next century.

Conservation of endangered species on the mainland is almost certainly going to require constant management; the ‘gamekeeper’ approach to wildlife conservation is surely an idea whose time has arrived in New Zealand.

Single species v communities

he emphasis is on single species! Those concerned with the conservation of New Zealand's wildlife have yet to embrace the philosophy so widely espoused by botanists, that of seeking the reservation of whole communities. Yet our forests were once home to unique assemblages of birds. Would it not be worth the effort to seek to conserve the best assemblages still remaining? Perhaps the best example I can offer is that of the avian community in wetland margins. Today, bittern, fernbird, marsh crake, spotless crake, pukeko and banded rail still occur in scattered locations but where are they still all together? There are, of course, numerous other topics which should be included in any review of the sort I am advocating. The question of resources is clearly central to the whole debate. What we should not overlook is that wildlife is an intensely saleable commodity, both in New Zealand and worldwide. The wider community, including the business community has yet to be exposed to a marketing approach akin to that for the Americas Cup challenge why not? The practical work in species conservation is still mainly handled by a small dedicated group within the Wildlife Service but there is clearly a need for a wider community involvement. If the ‘gamekeeper’ approach is adopted, who better than the Royal Forest & Bird Protection Society to promote the debate to redefine our conservation objectives and priorities? 34

2 8 1 1 By { 2 1 2 3 0 3 3 1 1 8 h L 1 3 3 h { X 1 3 3 8 little spotted kiwi RESIDENT BREEDER weka ABSENT OR NON BREEDING NZ falcon VISITOR kokako stitchbird brown creeper long-tailed cuckoo whitehead & yellowhead robin rifleman saddleback kaka shining cuckoo tui yellow crowned parakeet tomtit NZ pigeon bellbird red Crowned parakeet morepork grey warbler silvereye fantail 0.5 1.0 5 10 50 100 250