Snipe and the sword of Damocles

Forest and Bird, Volume 18, Issue 1, 1 February 1987, Page 22

Snipe and the sword of Damocles

By Colin Miskelly*

Fe New Zealand birds are as unfamiliar to the public as our native snipe. Con fined to isolated southern islands, snipe are usually overlooked by researchers and film crews, who focus their attention on !arger and more conspicuous neighbours such as penguins, albatrosses and sealions. Yet these ‘living fossils’, far removed from other snipe species, are one of our most interesting endemic birds. Their present distribution symbolises the vulnerability of New Zealand's ecosystems to modification by man and his camp-followers. New Zealand snipe belong to a large family which includes godwits, curlews, sandpipers and woodcocks. Most members of the family breed in the Northern Hemisphere, although many migrate to southern latitudes during the non-breeding season. The New Zealand snipe is the only species of the group that breeds in the Australasian region. It is thought to be a relict stock of a formerly widely distributed form, from which both modern snipe and woodcock arose. New Zealand snipe are considered the most primitive of the snipe-like birds.

Fearlessness is downfall

Shorter in leg and tail than other snipe spe-

cies, New Zealand snipe look more like small woodcock than true snipe. Each island group holds a separate subspecies, the forms differing in size and plumage. The Chatham Island snipe is smallest, being about the size of a starling, while the others are thrush-sized. They are all attractively marked with buff, russet and dark brown. The sexes are similar, but females are larger. New Zealand snipe are confiding, usually flying only when pressed, and are easily caught with a handnet. During the day they are typically found among dense growth on the forest floor, or among tussock. Snipe are most active at night, when they venture into more exposed habitats to probe for worms and insects. Some incubating birds are so tame that they remain sitting while their eggs are inspected. This fearlessness, and their low reproductive rate explain why snipe disappear so quickly following introductions of rats, cats and wekas.

Formerly widespread

Subfossil remains indicate that New Zealand snipe occurred throughout the three main islands and the Chatham Islands, as

well as on The Snares, Auckland and Antipodes Islands. Mainland snipes were presumably wiped out by kiore and kuri following Polynesian colonisation, as the only historical record is of a bird caught on Little Barrier Island in 1870 (before cats became established). The Stewart Island snipe survived on offshore islands well into the 20th century, where it was observed by some of our early naturalists, including Guthrie-Smith, Edgar Stead, and Lance Richdale. The populations on Jacky Lees and Herekopare Islands, off Halfmoon Bay, disappeared during the 1920s following the introduction of wekas by muttonbirders. Several writers of the time commented on the vulnerability of snipe to introduced vermin. The prophetic words of Guthrie-Smith: "though always hangs overhead the sword of Damocles; should rats obtain a footing, farewell to Snipe, Robin, Bush Wren and Saddleback, none of which species are able to adapt themselves to novel conditions’’, were horribly realised when ship rats reached Big South Cape Island. Rat numbers reached plague proportions in 1963,

and no snipe have been reported on Big South Cape since September 1964. Chatham Island snipe were confined to the southern islands of the group by 1870, when collections were first made. They disappeared from Mangere Island during the 1890s following the establishment of rabbits and cats. Burning and grazing on South East Island reduced the only remaining population to very low numbers. There has been considerable regeneration on South East following the removal of stock in 1961, and snipe are now common there. Cats and rabbits had died out on Mangere when it was purchased by the Crown, with the assistance of the Royal Forest & Bird Protection Society, as a flora and fauna reserve in 1966. Mangere has only four hectares of forest, although extensive planting of akeake and flax should increase the regeneration rate of former pasture on the rest of the island. Twenty three snipe were reintroduced to Mangere from South East Island by the Wildlife Service in November 1980, soon after stock were removed. This introduction coincided with a heavy infestation of grass grubs, and snipe rapidly spread over the whole island, even

colonising neighbouring Little Mangere Island. Now the exotic grassland on Mangere is so rank and impenetrable that snipe are largely confined to the robin bush. Even the remote southern populations of snipe have not escaped the effects of introduced predators. The Auckland Island snipe had disappeared from the main island of the group by 1840. Cats and pigs were established on the island then, and still occur, along with goats and mice. Auckland Island snipe are found in good numbers on unmodified Adams and Disappointment Islands, and on Ewing Island in Port Ross. On nearby Enderby Island, snipe are uncommon because cattle and rabbits have modified the habitat. The only introduced mammal on the isolated, tussock-covered Antipodes Islands is the house mouse. Although mice have probably affected insect and plant species, snipe still abound on the main island and several of the offshore stacks. This ability to survive in the presence of mice is important for the long-term. If pigs and cats could be removed from Auckland Island, and pigs, cats and wekas from Pitt Island (also rat-free) in the Chatham group, then

these large islands may prove suitable for re-establishment of snipe. (There have been several recent reports of snipe on Pitt Island.)

One unmodified population

The only subspecies of New Zealand snipe that has escaped any major habitat modification or introduction of exotic mammals is the Snares Island snipe. The Snares are a small group of two islands and a number of stacks that lie about 100 km south of Stewart Island. Administered by the Department of Lands & Survey, they were designated a National Reserve in 1983 in recognition of their international importance as an unmodified ecosystem, and as breeding grounds for vast numbers of seabirds and seals. Although only 330 hectares in area, The Snares are home to over three million pairs of muttonbirds, which have burrows under the central olearia forest and surrounding tussock grasslands. Snares crested penguins march inland from the few places that they can clamber ashore, following muddy highways to their noisy colonies under the forest. Buller’s mollymawks sit

on mud-pillar nests near the clifftops, their weird calls echoing across the bays, while black and white Cape Pigeons cackle from cliff ledge nest sites below. Inquisitive fernbirds and black tits forage for insects from the top of the island to the tideline, and the indomitable skuas dive, screaming, at anyone who approaches their nests or chicks. Fur seals breed among rock tumbles below the granite cliffs, and huge Hooker's sealions lumber into the forest to lie in wait for unwary naturalists. Noisy enough during the day, the wildlife can be deafening after sunset. The braying of penguins is overwhelmed by the shrieks and moans of muttonbirds and the softer cackles and croonings of prions and diving petrels. Mottled petrels indulge in aerial chases over the clifftops, giving vent to hysterical giggles or long drawn-out wails. Smaller animals are also more active at night — weta scavenge at seabird carcasses, while large, flightless weevils and beetles feed on the large-leaved punui. Leeches, up to 10cm long, come out of hiding to feed on muttonbirds, penguins, mollymawks, sealions, or even the occasional snipe researcher. Snipe occur over the two main islands and the largest offshore stack, with a total population of about 1000 birds. Densely vegetated areas are preferred; few snipe are found in the interior of the island, where the activities of the muttonbirds keep the forest floor bare.

High densities, low productivity

In favourable habitats on The Snares, snipe occur at densities of 2.5 pairs/ha, far higher densities than recorded for Northern Hemisphere snipe. Mortality rates are much lower than those for relatives in North America and Europe. Annual mortality for Wilson's Snipe in Canada is around 50 percent, with a longevity record of 12 years. Far less banding has occurred in New Zealand, but we already have one bird known to be over 14 years old, and The Snares population has an estimated annual mortality of 22 percent. High mortality in Northern Hemisphere snipes is due to a combination of preda-

tion, shooting, and the stress of migration. Natural predators are virtually absent for New Zealand snipe, although skuas and harriers occasionally catch adults that stray from cover during the day, and I have one record of a red-billed gull consuming a snipe chick on The Snares. Compared with their relatives, New Zealand snipe have smaller clutches and slower growth rates, possibly because there is less food for them as the result of the inhospitable climate in the southern seas and high snipe densities. Nests are depressions under overhanging vegetation, or in the centre of grass or sedge clumps, and are lined with grass, leaves or fern fronds. On The Snares nests are usually situated under solid wood or fern stems, to give protection from crashlanding muttonbirds. Both sexes of New Zealand snipe incubate, and the adults each care for one of the chicks independently. Only females incubate in other snipe species, but care of young is usually shared. Snipe chicks have disproportionately large legs and feet at hatching, and are capable of following their parents away from the nest soon after they are dry. Chicks are fed by the parent birds until their bills are long enough for efficient probing. They can become independent when about eight weeks old, though some remain with their parents for longer periods.

One feeding method

Snipe get all their food by probing in soft soils, so occur most abundantly in moist areas. A wide variety of prey is taken, but important items include earthworms, amphipods, adult and larval beetles, and fly larvae. They are vigorous feeders, probing almost continuously during feeding periods, and moving rapidly between feeding areas. I have counted 344 probe holes in an area 30 x 30 cm. Favoured feeding sites include among dense mats of low vegetation and the bases of tussocks. Adult snipe hold food items in the tip of the bill when feeding young, and the same method of food transfer is used during courtship feeding.

Only male snipe defend territories, which are about 0.4 ha in area on The Snares. The territories are only defended against other males that call within them; birds that do not call can feed unchallenged alongside the territory owner. This system appears to ensure that other males cannot mate with the female, but the food resource withir the territory is not defended. The birds cease defending territory when the eggs hatch, and the territory is taken over by one or more territorial males, which are mainly one-year-olds. These birds occasionally breed, so a territory may be used sequentially in one season by two different pairs. The original territory owner usually regains his territory by the following breeding season. Mates are also generally retained from year to year. Management attempts with New Zealand snipe have met with mixed success. Following the rat invasion of Big South Cape Island, two snipe were caught during Au-gust-September 1964. Unfortunately these birds perished when rough weather delayed attempts to move them to another island. Snipe require a constant supply of live food, as they feed almost continously. Methods of keeping snipe in captivity were perfected before the successful transfer to Mangere Island in 1970, but food collection requires a huge investment of time and energy. Attempts by the Wildlife Service to raise Chatham Island snipe from eggs have not been successful to date. These experiments with the relatively accessible Chatham Island snipe population should continue, and will prove invaluable if rats or other vermin colonise any of the snipe’s more distant retreats, where we won't have the time necessary to perfect management techniques. We must understand the ecological requirements and life history of any species before forming a successful management plan. Much of the data collected during the present study of New Zealand snipe will prove invaluable for attempts at captivebreeding or island transfers. Important information already obtained includes habitat and dietary preferences, how to

distinguish the sexes, age of first breeding, and chick growth rates. Continuing research should reveal factors that limit population density and those that contribute to breeding success.

Populations at risk

AS a species, the New Zealand snipe is presently found in four island groups, on at least 15 islands and stacks; yet each of the distinctive subspecies is vulnerable to extinction should rats, cats, wekas or other vermin become established on their island retreats. Four populations have been eliminated in the last 120 years (although the population on Mangere Island has been reestablished). The animal that presents the greatest threat to remaining snipe populations is the ship rat. The biggest worry is the possibility of a large rat-infested vessel being wrecked on any of the islands. Of particular concern are the squid boats currently working south of New Zealand. The threat of rat invasion from small coastal fishing vessels mooring close offshore is well publicised for The Snares, but is of equal concern for populations on the Chatham Islands. Ensuring that these boats remain rat-free requires the co-operation of their operators, including maintenance of bait stations and precautions to prevent rats getting aboard before departure for the fishing grounds. The third possible means by which rodents could reach snipe islands is among expeditions stores. All the islands supporting snipe are administered by the Department of Lands & Survey, and landing permits include strict controls to prevent the introduction of alien plants and animals. It is the responsibility of the expedition leader to ensure that the permit conditions are satisfied.

The Future

The first objective of any management policy concerning snipe should be to ensure their survival as members of the unmodified ecosystems to which they belong. However, the small and vulnerable population of Snares Island snipe could disappear

very rapidly if alien predators ever become established on The Snares. Efforts should be made to establish further populations of this snipe on suitable islands off Stewart Island. It is easier to catch snipe before rats or other predators get a chance. The only introduced mammal that snipe are known to be able to maintain a healthy population alongside is the house mouse. This greatly reduces the number of islands that are suitable for snipe transfer, as even those islands supporting kiore populations must be excluded. Weka eradication schemes may allow reintroduction of snipe to some islands where they were known or

thought to occur, e.g. Jacky Lee and Solander Islands. Keeping snipe in captivity may be a safeguard against colonisation of snipe islands by predators, especially if there is a time lapse between the establishment of the predator, its discovery, and the commencement of rescue operations. Captive rearing is also the only feasible way that members of the public could observe these fascinating relicts of our prehistoric biota. #& Colin Miskelly is carrying out research towards a PhD, based at_ University of Canterbury, and has been studying snipe on The Snares and Chatham Islands for the past four years. Colin has been an active member of the Ornithological Society for over ten years, and has carried out fieldwork throughout New Zealand and its offshore and outlying islands. His work is funded by the Department of Lands & Survey, with assistance from the Forest & Bird Society.

au , to the . Maori, Lepidium oleraceum is well-known by the name Cook's scurvy grass, but few people have the chance to see plants in the wild these days. Even in cultivation scurvy grass is uncommon, perhaps because the plants have a rather weedy appearance and, although their leaves are edible, they have a strong odour and flavour. Scurvy grass received its common name in 1769 on Captain James Cook's first visit, when it was eaten as a green vegetable to prevent scurvy. Actually it is not a grass but a relative of cresses, in the cabbage-radish family (Cruciferae). At Tolaga Bay Cook’s crew gathered ‘‘as much Sellery [Apium spp.] and Scurvy grass as loaded the Boat", and also took quantities around the shores and islands of Queen Charlotte Sound on each visit. Today, scurvy grass is almost confined to islands; Dr David Given (DSIR) (1981) regards it as a threatened species, with a ‘‘vulnerable"’ status. At least some of the major decline in scurvy grass on the mainland occurred last century. Botanist Thomas Kirk (1899) noted that it was "‘restricted to small islands in the north [and] has become very rare. The plant is everywhere destroyed by cattle and sheep’. Thomas Cheeseman (1906) also blamed cattle and sheep for its extinction in several places where Captain Cook had recorded it. In 1982, Hugh Wilson stated that around Stewart Island, where scurvy grass was formerly common, it was now very local and confined to islands free of introduced mammals. In September 1984, the re-discovery of scurvy grass in one site on Mana Island showed that it still retains a tenuous hold near Wellington. More than 80 years ago it was on the mainland nearby, at Titahi Bay, Ohau Bay, Ocean Beach (between Ohiro Bay and Sinclair Head) and Cape Turakirae (Buchanan 1873, Aston 1909, Zotov et al. 1938). Michael Meads (DSIR) had found it on Mana Island in 1975, but early in 1984 an intensive botanical survey of the island failed to find it at his recorded site. Its present habitat is on the opposite side of Mana to Meads's site, in a shallow soil pocket on a rock which is also a gull roost. When found, the six or so scurvy grass plants were spattered with bird droppings. Mana Island had both sheep and cattle until quite recently, but the site where scurvy grass occurs would have been inaccessible to livestock. Similarly, on Stephens Island scurvy grass remains on steep cliffs out of reach of the island’s sheep and cattle. Because there are plenty of places on the mainland’s coasts which have always been stock free it seems overly simplistic to place all the blame on cattle and sheep for the losses of scurvy grass. Perhaps wider-rang-ing browsers such as rabbits, hares, or possums have contributed to mainland extinctions of the plant? These mammals were never on farmed islands which retain scurvy grass, such as Mana and Stephens. Dr Given (1981) suggested that the white butterfly might have been partly responsible — certainly its larvae have totally defoliated some of my pot-grown specimens — but scurvy grass was probably rare on the mainland before 1930 when white butterflies established in New Zealand. Many

other garden pests of Cruciferous vegetables attack Cook's scurvy grass in cultivation, including diamond-backed moth, leaf miners, aphids, garden snails and the parasitic white fungus, A/bugo. They are likely to occur on inshore islands at least, particularly inhabited ones, so that the presence of scurvy grass on Mana and Stephens Islands, and islands close to cities such as New Plymouth and Dunedin, is in apparent defiance of browsing invertebrates and parasitic fungi.

Nitrogen-rich soils, probably with a high PH (low acidity) level, are characteristic of at least some places with scurvy grass. Brian Bell of the Wildlife Service knows it in the Chathams group but only on small islands with many roosting and burrowing seabirds, and Dr Ian Atkinson of DSIR reports it around gull roosts on islands off Northland’s coast. In the late 1950s, Dr

Mary Gillham (1960) found that scurvy grass was one of several native and introduced species which thrive around seabird colonies. Others include the native iceplant (Disphyma australe), sea celery (Apjum spp.) and shore groundsel (Senecio lautus), plants which are still common and widespread around our coasts but which seldom, if ever, achieve the luxuriance of plants of the same species on guano-en-riched sites. Some other species which Dr Gillham found growing well on soils around bird roosts on islands are rather local on the mainland’s coasts, and in some places have certainly declined. Crassula moschata, Einadia (Chenopodium) allanii, Asplenium obtusatum and, of course, Cook’s scurvy grass, are some of these. After propagating a plant of scurvy grass from a small twig from Mana Island, | attempted to reproduce its natural situation by growing the rooted cutting in a mixture comprising one half sandy loam with additional gravel, and one half poultry manure. The scurvy grass grew into a muchbranched sub-shrub which flowered and fruited just over a year later. More plants have been grown from this plant from cuttings and seed, the latter being used to obtain some genetic diversity in cultivated stock. Transplanting of these plants to other locations on Mana Island now awaits action on the island’s management plan. In cultivation, rapidly growing scurvy grass plants are more resistant to garden pests than those which are pot-bound or in poor soil. This suggests another reason why scurvy-grass grows where the soil is made very fertile by seabirds. Because of human disturbance and predators on the mainland, seabirds now tend to use islands for roosting and nesting. As a result, the soil of mainland sites which previously supported scurvy grass is likely to have become less fertile and therefore unable to promote rapid growth which would have allowed scurvy grass to survive browsers and parasites. Whatever the reason, or combination of reasons, for the national decline in Cook's scurvy grass, it is clear that islands, including suitably managed islands like Mana Island, will be important in conserving wild populations of the species. # References Aston, B.C. 1909. Unrecorded habitats for New Zealand plants. Trans. Roy. Soc. N.Z. 42: 26-28. Buchanan, J. 1873. Notes on the Flora of the Province of Wellington. Trans. Roy. Soc. N.Z. 6: 210-235. Cheeseman, T.F. 1906. Manual of the New Zealand flora. Govt. Printer, Wellington. Gillham, Mary E. 1960a. Plant communities of the Mokohinau Islands. Trans. Roy. Soc. N.Z. 88: 79-94. — 1960b. Vegetation of tern and gannet colonies in northern New Zealand. Ibid. 211-234. — 1960c. Vegetation of New Zealand shag colonies. Ibid: 363-380. Given, D.G. 1981. Rare and endangered plants of New Zealand. Reed. Kirk, T. 1899. Student's flora of New Zealand and the outlying islands. Govt. Printer, Wellington. Wilson, H.D. 1982. Field guide: Stewart Island plants. Field Guide Publications, Christchurch. Zotov, V.D. and N.L. Elder, A.D. Beddie, G.O.K. Sainsbury, E.A. Hodgson. 1938. An outline of the vegetation and flora of the Tararua Mountains. Trans. Roy. Soc. N.Z. 68: 259-324.