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Feral goat control in New Zealand
Biological Conservation 54 (1990) 335-348
Feral Goat Control in New Zealand J o h n P. Parkes Forest Research Institute, PO Box 31 011, Christchurch,New Zealand (Received 16 September 1989; revised version received30 January 1990; accepted 7 February 1990)
ABSTRACT About 150feral goat herds occupy about 16% of New Zealand. They are pests because of their effects on indigenous biota. Since 1936, government agencies have attempted to eradicate or control many herds. Common flaws in control campaigns include confusing ends (protection of resources) with means (killing goats), no measures of effectiveness, and lack of sustained action where eradication is impossible. One of four strategic options may be adopted: no action--giving a stable but undesirable outcome; eradication-giving a stable and desirable outcome; annual sustained control-- giving a stable and desirable outcome but only if inherently fickle government effort is sustained; and occasional sustained control--giving unstable outcomes with or without the desired results depending on the goals and hunting frequency. Control tactics used are hunting on foot with or without dogs, hunting from helicopters, poisoning natural foliage, and fencing.
INTRODUCTION Goats Capra hircus were first liberated in New Zealand by Captain Cook in 1773 and 1777 (Beaglehole, 1961). This was a naval tradition usually intended to provide food for shipwrecked mariners, and it continued into the 20th century, e.g. on the subantarctic islands from 1865 to 1909 (Rudge, 1976). Early whalers, sealers and other mariners also liberated goats in New Zealand (Straubel, 1954; Jane & Pracy, 1974). Descendants were soon joined by escapees from domestic herds, and about 150 feral herds now occupy more-or-less discrete areas totalling about 4.3 million ha (16%) of mainland 335 BioL Conserv. 0006-3207/90/$03-50 © 1990ElsevierSciencePublishers Ltd, England. Printed in Great Britain
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New Zealand and seven offshore islands (Parkes, in press). Most herds are on state-owned land in indigenous vegetation reserved for conservation. Feral goats are regarded as pests because of their impact on indigenous biota (Oliver, 1910; Thomson, 1922). Government agencies have conducted regular campaigns against them since 1936; since 1987 this has been done by the Department of Conservation (DoC). Damage caused by goats varies from subtle to catastrophic. In grassland/shrub habitats where goats can reach most plants, a dynamic equilibrium between goats and vegetation is quickly reached and the habitat remains in grassland/shrub. In forest habitats where goats cannot reach all plants, changes may be long-term and potentially catastrophic; forest may be destroyed and replaced by grassland/shrub (or bare ground) if goats or other ungulates prevent regeneration of canopy trees (Nugent & Challies, 1988). Goats may also threaten the survival of some indigenous species of plants and animals, especially those with limited distributions. Insular endemics such as Hebe breviracemosa and Homalanthus polyandrus on Raoul Island (Sykes, 1969; Parkes, 1984a) and Tecomanthe speciosa, Elingamitajohnsonii, Myrsine oliveri, Alectryon grandis and Pennantia baylisiana on Great Island (Williams & Given, 1981) were all nearly exterminated by goats--two species to a single plant each. Both these islands are now free of goats. Animals threatened by goats include competitors for food, e.g. the vulnerable kokako Callaeas cinerea wilsoni (Leathwick et al., 1983), and species whose habitat they destroy, e.g. the frog Leiopelma hochstetteri (Ogle, 1980). This paper discusses some of the lessons learnt, and illustrates crucial problems of policy, strategy, tactics and logistics encountered in feral goat control in New Zealand.
ERRORS IN PEST M A N A G E M E N T Three types or errors occur among goat control campaigns: confusing means (killing the goats) with ends (protecting resources), using inappropriate strategies to attain goals, and using inefficient tactics to kill the goats.
Goals of goat management The ultimate goal of any pest control is to halt or minimise damage to a resource. Managers must identify the resource and know how it is being damaged so that they can set precise goals and not vague concepts such as 'wise land use' or 'protection of flora and fauna'. These phrases leave unanswered what is wise, what land, which flora, and which fauna? They are
Feral goat control in New Zealand
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'theologies' (Caughley, 1989), not amenable to scientific or managerial solutions. The most c o m m o n flaw in New Zealand goat control has been to confuse goals (protection of the indigenous biota) with means (control of goats). For example, the National Parks Act requires managers to eradicate, as far as possible, all introduced plants and animals from parks. Eradication is not possible for most introduced species (for a variety of technical, financial, or political reasons) so the goal is usually expressed by the slogan 'as few as possible'. This goal appeals to some managers and conservation groups because it is always achieved. As many pests as possible are killed with the resources available, but managers are not obliged to decide whether the real goal--protection of the indigenous biota--has been achieved. More subtle flaws are often included in pest control goals. For example, the desire to 'retain an area as representative of some forest type' is often advanced in management plans. If the forests contain goats that cannot be eradicated, the area can only be representative of a forest type influenced by goats; in which case the influence of goats and their density should be specified.
Strategies to control goats One of four strategies can be adopted by managers of goat herds: no action; eradication; annual control in perpetuity; or occasional control in perpetuity. No action DoC may choose to do nothing to kill goats and accept the outcome. Extrapolating from the minimum costs of successful control, it would cost at least NZ$15.6 million per annum (all NZ$ are in 1988 values and NZ$1 = US$0"59 or £0-38) to keep densities low enough to prevent undue damage (Parkes, 1990). DoC cannot afford this cost (about 15% of its entire budget). It currently spends only about $1.5 million per annum on goat control, and must set priorities and control goats in the most important conservation areas. On most other land infested with feral goats the department can only encourage recreational hunters, who may or may not hunt with sufficient intensity to achieve the department's goals. Eradication The permanent removal of goats from an area may be attempted for two reasons. Resource protection may require eradication. Elsewhere, this may not be necessary but it may be cheaper than control in perpetuity. Successful eradication depends on the ability to put all individuals at risk, to kill goats faster than they can replace losses, on the likelihood of recolonisation, and on the conviction by those responsible that the task is possible.
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John P. Parkes TABLE 1 New Zealand Islands from which Feral Goats have been Eradicated
Island
Area (ha)
Liberated
Eradicated
Raoul Kapiti Great (Three Kings) Macauley Maud Ocean South East Cuvier Whale Mokoia Burgess Herekopare Ernest Nukutaunga East Rurima
2938 2023 350 323 309 300 219 195 140 133 60 25 25 13 8 4
Before 1836 c. 1830 1889 Before 1836 ? 1865 Before 1900 1890s ? 1987 9 1975 ~ 9 ? ?
1936-84 1928 1949 1966-70 c. 1972 1942 1914-16 1959-6 ! 1977 1989 1973 1976 1980s 1972 c. 1960 ?
Feral goats have been eradicated from 16 offshore islands around New Zealand (Table 1). However, on North and South Islands, recolonisation into cleared areas remains likely, and zero density with a sustained harvest of immigrants best describes 'successful' eradication campaigns in these areas.
Raoul Island. Raoul Island (2938 ha) is a Nature Reserve in the Kermadec group. It is the least modified of the four islands (Macauley, Lord Howe, Norfolk, and Raoul) at about 30 ° S in the south-west Pacific. It has 18 taxa of endemic plants (Sykes, 1977). Goats were liberated before 1836 (Straubel, 1954), and the destruction of the vegetation was noted by 1908 (Oliver 1910). As well as the potential loss of endemic plants, goats may also affect the regeneration of canopy trees (e.g. Metrosideros kermadecensis) by browsing seedlings and the epicormic shoots that are important for regeneration after cyclones (Parkes, 1984a). Oliver (1910), Merton (1968) and Sykes (1969, 1977) advocated that the herd be eradicated, and this has been attempted since 1936 (Fig. 1). Until 1971, goats were shot by staffofthe Island's meteorological station and by a hunting expedition in 1956. However, the' first serious attempts were not made until 1972, when annual hunting expeditions began. The last five goats were shot in 1984. The total cost of the campaign since 1972 has been about $1 million, or $339/ha. Most goats were killed by hunters with dogs, but latterly a few were shot from helicopters or killed in snares set on ledges. Raoul Island is an example of successful but inefficient eradication. In
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retrospect, it would have been better to have reinforced early expeditions to eradicate the herd quickly. The long campaign allowed the forest understorey to regenerate. This made access and visibility more difficult and provided more food per capita for the goats, which doubled their breeding rate from 0.96 kids/female/year in 1972 (Rudge & Clark, 1978) to 1.70 kids/female/year in the 1980s (Parkes, 1984b). The turning point came in the early 1980s when managers were convinced that eradication was possible. Greater effort was then spent hunting more elusive survivors as well as those more easily hunted. As a final check, the island was searched in 1986 by a team led by the leader of an earlier expedition who had doubted that eradication was possible.
Great Barrier lsland. The control of goats in the northern forests of Great Barrier Island is an example of an efficient but as yet unsuccessful attempt at eradication. The island (28 500 ha) is on the outer edge of the Hauraki Gulf offNorth Island. Forests on the northern end of the island have outstanding wildlife value (Ogle, 1980) and contain several endangered species of animals (e.g. kokako and Hochstetter's frog) and plants (e.g. Nestegis apetala and Fuchsia procumbens) threatened by feral goats. These forests consist of about 3230 ha of conservation reserve, bordered to the south by about 800 ha of forested private and Maori tribal land. The goats here are isolated by farmland from other herds on the Island, so reinvasion risks are low. In 1984, it was decided to 'do something about the goats'. Eradication was technically possible but politically awkward as the Maori landowners were concerned that hunters would also kill feral pigs which they valued as a food resource. They restricted access to their land. Nonetheless, the reserve land was hunted in 1986/87. Six hunters, each with two dogs, killed 930 goats in 372 hunter-days (K. Broome, pers. comm.). This cost $18/ha, and reduced the goats in the reserve to almost zero, thereby achieving most of the protection goals. However, the herd was not eradicated because goats can recolonise the reserve from adjacent Maori forests. In 1988 and 1989, for example, 29 and 4 goats, respectively were shot along the boundary of the reserve, despite an unknown number being shot by Maori on their land during 1989. The positive aspect of this campaign was that, unlike that on Raoul Island, maximum effort was expended in the first operation so that the herd was quickly reduced to very low densities. The flaw was that action began before the optimum plan for eradication was negotiated. Annual sustained control This strategy requires managers to choose some density of goats at which damage is acceptable and then reduce the herd to that density, and shoot
Feral goat control in New Zealand
341
subsequent annual increments. The strategy requires that managers have knowledge of the relationships between goats and the vegetation and other animals. Most mainland New Zealand goat herds are also regularly hunted by sportsmen. However, despite an annual harvest of about 60 000 (Nugent, 1989), this is not usually enough to allow palatable plants to regenerate (Parkes, 1990). Mt Egmont National Park. Mt Egmont National Park in North Island covers 33000ha of forest and alpine vegetation around the volcanoes Taranaki, Pouakai, and the Kaitake Range. Goats colonised the park in about 1910 and by the early 1920s were damaging vegetation (Thomson, 1922). Annual goat control began in 1924, and at least 35 600 goats were shot by Park rangers and private bounty hunters until 1960. Since 1961, control has been by government-employed hunters using dogs, who have killed a further 52 000 goats. The annual effort has increased from about 0.3 hunter-years in the early 1960s to about 4-0 hunter-years in the 1980s, the usual pattern in New Zealand goat control campaigns. This is, in my opinion, the wrong way to conduct a long-term campaign. Hunting is most efficient early in the campaign when the goats' rate of increase is lowest and the animals are unwary and easy to find in depleted forest understorey. The annual kill has declined from about 3000 in the early 1960s to about 1000 since 1984. The declining kill rates (Fig. 2), used as an index of density, indicate that the herd was reduced to about one-sixth of its 1961 size. This decline has resulted in a general improvement in the forest understorey (Clarkson, 1986), reflected by the high proportion of browse-susceptible, preferred plants in the goats' diet (Mitchell et aL, 1987). Goat density reached an equilibrium with hunting effort in 1981 since when the goats killed per hunter-day has not changed significantly (r2= 0-0006). The mean annual kill since 1981 has been 1207 goats. An exponential rate of increase of 0.395 was calculated based on a fecundity rate of 0.5 (Parkes, unpublished data) and mortality rates of 0.105 observed in other feral herds in New Zealand (Rudge & Smit, 1970). The present herd may, therefore, contain about 3000 goats to sustain the observed kill rates. If control ceased, the herd might double every 21 months until limited by food supply. This campaign also illustrates another common flaw in sustained control strategies--fluctuating effort. Budgets increased during the early 1980s and hunting effort doubled, but this has not been sustained since 1987 (Fig. 2). Therefore, the extra effort was wasted as the plant-goat-predator system regained its previous equilibrium.
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The harvest, effort, and time needed to eradicate the herd can be estimated (assuming all goats are at risk, logistic growth rates, and that the observed rate of increase approaches the intrinsic rate of increase). For example, we could eradicate the herd in 5 years if 1500, 1500, 1000, 100 and 25 goats were killed in successive years. It would take at least 4 hunter-years per year to attain the first two or three of these harvests, at a cost of $233 000/year. The cost of shooting the last few survivors cannot be estimated, but would be substantial. It has cost $3.18 million since 1961 (at 1988 costs of $160/hunter/ day), and will cost $160 000 ($4.8/ha) per year to maintain present densities, so it is worth considering eradication. However, as a prerequisite domestic goats would need to be prevented from escaping from adjacent farms, a minor problem in this area (L. Stanley, pers. comm.). Occasional sustained control The final strategic control option is to kill as many goats as possible in one
Feral goat control #1 New Zealand
343
intensive campaign, then monitor the protection values as they respond. Control is repeated only when damage again becomes intolerable. This strategy also requires detailed knowledge of goat population dynamics and how goats interact with the vegetation. Palatable plants always accessible to goats are unlikely to benefit from this strategy, and canopy plants will benefit only if their seedlings can grow through the browse tier before the goat population recovers. Most occasional control campaigns are not deliberate attempts to use this option, but are results of changing priorities or vagaries of government funding. G&borne Water Reserve. Gisborne city draws its water from the Puninga
catchment, about 2000 ha of indigenous forest and regenerating scrub on abandoned farmland. Goats have been in the area since at least 1950. They were hunted four times between 1965 and 1977. Hunting was annual between 1977 and 1986, and then it ceased (Table 2). Goats were fenced from a 8.4 x 8.4m plot in 1965. In 1981, the structure and composition of the herbaceous ground cover and the saplings present were measured in the exclosure and compared with that on two adjacent, unfenced plots on similar sites. The methods used are described by Allen et al. (1984). Despite the operations between 1965 and 1981, differences inside and outside the fence were still marked. Outside, more ground was covered by the unpalatable grasses Microlaena avenacea and Uncinia uncinata. Such goat-induced swards have also been described in other New Zealand forests TABLE 2 Number of Goats Killed and Success Rate in 13 Campaigns from 1965 to 1986, Gisborne Water Reserve Year 1965 1966 1973 1977 1978 1979 1981 1982 1983 1984 1985 1986
No. o f goats killed 2983 160 1092 599 342 208 1 062 189 1065 70 59 77
Kills~hunter-day 7"5 1"1 2"4 5"4 34.2 6"9 9-7 2"7 5"4 1"3 0"8 1"9
344
John P. Parkes TABLE 3
Sampling Counts on 30 2.25-m 3 Plots in an Area From which Goats were Excluded, and on Two Areas where they were not Excluded. Gisborne Water Reserve, 1981
Species
Exclosure
No. o f saplings Control 1 Control 2
Coprosma australis (highly palatable) a Geniostoma rupestre (palatable) Coprosma tenu(]'olium (palatable) Macropiper e.w'elsum (palatable) Pseudopana.v crassi['olius (palatable) Brachyglottis repanda (not palatable) Knightia e.xcelsa (not palatable) C.vathodes.[ascicularis (not palatable) Neom)'rtus pedunculatus (not palatable) Beilschmiedia tawa (not palatable)
49
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(Moore & Cranwell, 1934). Inside, more ground was covered by litter and moss. Palatable saplings were common inside the fence, but the few saplings outside were all of unpalatable species (Table 3). I conclude that either not enough goats were killed to allow regeneration, or the campaigns were too infrequent to allow plants to grow through the browse tier, or both--at least up to 1981.
TACTICS A N D COSTS OF GOAT CONTROL
The method most favoured for controlling goats in New Zealand has been by shooting on foot with or without dogs. Shooting from helicopters, poisoning natural foliage, and fencing are used less often.
Feral goat control in New Zealand
345
Shooting on foot Government has employed hunters to shoot goats (and other ungulate pests) since 1930. During the 1980s, up to 50 hunters have been employed to hunt goats in about 15 major operational areas, for an annual kill of up to 40000. Several hunting methods are used, depending on the terrain and vegetation. Forested areas are usually first hunted without dogs as naive goats are easily found and shot. Goats living in more open grassland or scrub are also best hunted without dogs as they are visible from a distance, tend to be in larger groups, and are more easily stalked without dogs. Hunting with dogs is commonly used during the latter stages of campaigns in forested areas when the goats have become wary. Some dogs are trained to stay close to their master and point when they scent goats. Others, usually two or three per hunter, are trained to chase and kill, or bail and bark to attract the hunter. The tendency of dogs to disperse goats is more than balanced by their ability to locate the groups. Costs of hunting on foot vary with the method of payment and difficulty of access, but are usually about $160/hunter/day. This includes wages, allowances for food and dogs, access, and track and hut maintenance. Goats in mainland New Zealand forests have been reduced to low densities for between $3.14 and $5.00/ha/year.
Aerial shooting The use of helicopters as shooting platforms was developed in New Zealand to kill and recover red deer for the German venison market (Challies, 1974) and to control Himalayan thar Hernitragusjemlahicus(Tustin, 1980). Tallies of 100 goats per flying hour have been achieved in unforested country using turbo-powered machines. Costs vary from about $350/flying hour for the smaller piston helicopters up to about $800/flying hour for turbo machines, plus wages and ammunition.
Poisoning foliage Goats have been successfully poisoned with c o m p o u n d 1080 (sodium monofluoroacetate) in a gel or grease smeared on the leaves of palatable foliage (Parkes, 1983). This works well where goats have eaten most preferred plants, but is less successful where preferred foods are readily available. It cannot be used where non-target animals may be at risk. Costs are about the same as for ground shooting. In two trials in forests of the R a u k u m a r a Range, 1500 ha were treated with poison and 1500 ha were
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John P. Parkes
hunted for about $7/ha and 90% + kill in both methods. A later poisoning over 6000ha cost about $3/ha for an 85% kill (Parkes, unpublished data). Exclusion Fencing is often mooted to stop goats dispersing (e.g. on Arapawa Island (Dingwall & Rudge, 1984)). Fences may be useful as a tactical technique either to create short-term manageable units during control (e.g. in Hawaii (Baker & Reeser, 1972)), or to limit recolonisation during sustained control. However, as some goats will always get past even well-maintained fences, they are of limited strategic use in eradication campaigns.
DISCUSSION Feral goats concern those who wish to protect New Zealand's distinctive flora and fauna. Many conservationists advocate eradication of pests, either specifically as for Himalayan that (Anon., 1989) or for rabbits (see Gibb, 1967), or generally for all introduced biota as in the National Park Act. This goal is sensible only if it is technically possible with the resources available. It is not technically possible to eradicate all feral goat herds in New Zealand because of the continuing certainty of domestic escapes. Therefore, a general policy to eradicate all herds is futile. Such a goal ensures that effort is not targeted where it is most needed or most effective. Managers need to ask why goats are pests, how much control is needed to minimise or eliminate their impact, and which areas should be given priority. Only then can they choose which strategy and tactics best suit the particular problem. Caughley (1989) argued that, other things being equal, management of plant-herbivore systems that leads to stable ecosystems is preferable to that which leads to unstable systems. Of the four strategies for goat management discussed, the first (with no action) and second (with no goats) are most likely to result in stable ecosystems, although managers may disapprove of the first option. The third strategy requires sustained, constant and sufficient effort by government agencies. The history of goat control in New Zealand has shown that this is rarely achieved, and many campaigns evolve into the inherently unstable fourth strategy. The problems of unsustained or inconstant effort can be overcome by dividing the budget for goat control into two parts. One can be spent on sustaining control in highest priority areas. This fund needs to be constant, not increased or decreased at departmental whim. The second can be spent on attempts at eradication, and can be increased or decreased as resources vary.
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A C K N O W L E D G E M ENTS I thank G. Nugent, J. D. Coleman, J. A. Gibb and J. Orwin for comments on early drafts o f this paper. I also thank the m a n y government officers who provided information on goat control campaigns. This study was partly funded by the New Zealand Department of Conservation.
REFERENCES Allen, R. B., Payton, I. J. & Knowlton, J. E. (1984). Effects of ungulates on structure and species composition in the Urewera forests as shown by exciosures. N Z J. EcoL, 7, 119-30. Anon. (1989). Himalayan thar. Conservation News, 51, 3. Baker, J. K. & Reeser, D. W. (1972). Goat management problems in Hawaii Volcanoes National Park: A history, analysis and management plan. Nat. Resour. Rep., No. 2, US National Park Service. Beaglehole, J. C. (1961). The Discovery of New Zealand Oxford University Press, London. Caughley, G. (1989). Control of wild animals. In The Future of New Zealands Wild Animals, ed. A. E. Newton. New Zealand Deerstalkers' Association, pp. 101-3. Challies, C. N. (1974). Use of helicopters in the New Zealand commercial venison industry. E. Afr. Agr. For. Jl, 39, 376-80. Clarkson, B. D. (1986). Vegetation of Egmont National Park. Natn. Parks Sci. Ser., No. 5. Dingwall, P. R. & Rudge, M. R. (1984). Biological and ecological values of Arapawa Island Scenic Reserve. Dep. Lands & Surv. Inf. Ser., No. 13. Gibb, J. A. (1967). What is efficient rabbit destruction? TGMLI Rev., 12, 9-14. Jane, G. T. & Pracy, L. T. (1974). Observations on two animal exclosures in Haurangi forest over a period of twenty years (1951-1971). N Z J. For., 19, 102-13. Leathwick, J. R., Hay, J. R. & Fitzgerald, A. E. (1983). The influence of browsing by introduced mammals on the decline of North Island kokako. N Z J. EcoL, 6, 55-70. Merton, D. V. (1968). Narrative of the Kermadec Islands expedition 10/10/66-29/1/67. Notornis, 15, 3-22. Mitchell, R. J., Fordham, R. A. & John, A. (1987). The annual diet of feral goats (Capra hircus L.) in lowland rimu-rata-kamahi forest on eastern Mount Taranaki (Mt Egmont). N Z J. Zool., 14, 179-92. Moore, L. B. & Cranwell, L. M. (1934). Induced dominance of Microlaena avenacea (Raoul) Hook. f., in a New Zealand rain-forest area. Rec. Auck. Inst. Mus., 1, 219-38. Nugent, G. (1989). Hunting in New Zealand in 1988: Survey results. Forest Research Institute Report (unpublished), Christchurch. Nugent, G. & Challies, C. N. (1988). Diet and food preferences of white-tailed deer in north-eastern Stewart Island. N Z J. Ecol., 11, 61-71.
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Ogle, C. C. (1980). Wildlife and wildlife habitat of Great Barrier Island. N Z Wildl. Ser. Fauna Surv. Unit Rep., No. 24. Oliver, W. R. B. (1910). The vegetation of the Kermadec Islands. Trans. Proc. N Z Inst., 42, 118-75. Parkes, J. P. (1983). Control of feral goats by poisoning with Compound 1080 on natural vegetation baits and by shooting. N Z J. For. Sci., 13, 266-74. Parkes, J. P. (1984a). Feral goats on Raoul Island, II. Diet and notes on the flora. N Z J. Ecol., 7, 95-101. Parkes, J. P. (1984b). Feral goats on Raoul Island, I. Effect of control methods on their density, distribution and productivity. N Z J. Ecol., 7, 85-94. Parkes, J. P. (1990). Procedures for ranking and monitoring feral goat (Capra hircus) control operations. Forest Research Institute Report (unpublished), Christchurch. Parkes, J. P. (in press). Eradication of feral goats on islands and habitat islands. J. Roy. Soc. NZ. Rudge, M. R. (1976). Feral goats in New Zealand. In The Value of Feral Farm Mammals in New Zealand, ed. A. H. Whitaker & M. R. Rudge. Dep. Lands & Surv. Inf. Ser., No. 1, 15-21. Rudge, M. R. & Clark, J. M. (1978). The feral goats of Raoul Island, and some effects of hunting on their body size and population density. N Z J. Zool., 5, 581-9. Rudge, M. R. & Smit, T. J. (1970). Expected rate of increase of hunted populations of feral goats (Capra hircus L.) in New Zealand. N Z J. Sci., 13, 256-9. Straubel, C. R. (1954). The Whaling Journal of Captain IV. B. Rhodes. Whitcombe & Tombs Ltd. Christchurch. Sykes, W. R. (1969). The eft~ct of goats on vegetation of the Kermadec Islands. Proc. N Z Ecol. Soc., 16, 13-16. Sykes, W. R. (1977). Kermadec Islands flora: an annotated checklist. DSIR Res. Bull., 219, 297-99. Thomson, G. M. (1922). The Naturalisation of Animals and Plants in New Zealand. Cambridge University Press, Cambridge. Tustin, K. (1980). Recent changes in Himalayan thar populations and their effect on recreational hunting. N Z Wildl., 8, 40-8. Williams, G. R. & Given, D. R. (1981). The RedData Book of New Zealand. Nature Conservation Council, Wellington.
Feral Goat Control in New Zealand J o h n P. Parkes Forest Research Institute, PO Box 31 011, Christchurch,New Zealand (Received 16 September 1989; revised version received30 January 1990; accepted 7 February 1990)
ABSTRACT About 150feral goat herds occupy about 16% of New Zealand. They are pests because of their effects on indigenous biota. Since 1936, government agencies have attempted to eradicate or control many herds. Common flaws in control campaigns include confusing ends (protection of resources) with means (killing goats), no measures of effectiveness, and lack of sustained action where eradication is impossible. One of four strategic options may be adopted: no action--giving a stable but undesirable outcome; eradication-giving a stable and desirable outcome; annual sustained control-- giving a stable and desirable outcome but only if inherently fickle government effort is sustained; and occasional sustained control--giving unstable outcomes with or without the desired results depending on the goals and hunting frequency. Control tactics used are hunting on foot with or without dogs, hunting from helicopters, poisoning natural foliage, and fencing.
INTRODUCTION Goats Capra hircus were first liberated in New Zealand by Captain Cook in 1773 and 1777 (Beaglehole, 1961). This was a naval tradition usually intended to provide food for shipwrecked mariners, and it continued into the 20th century, e.g. on the subantarctic islands from 1865 to 1909 (Rudge, 1976). Early whalers, sealers and other mariners also liberated goats in New Zealand (Straubel, 1954; Jane & Pracy, 1974). Descendants were soon joined by escapees from domestic herds, and about 150 feral herds now occupy more-or-less discrete areas totalling about 4.3 million ha (16%) of mainland 335 BioL Conserv. 0006-3207/90/$03-50 © 1990ElsevierSciencePublishers Ltd, England. Printed in Great Britain
336
John P. Parkes
New Zealand and seven offshore islands (Parkes, in press). Most herds are on state-owned land in indigenous vegetation reserved for conservation. Feral goats are regarded as pests because of their impact on indigenous biota (Oliver, 1910; Thomson, 1922). Government agencies have conducted regular campaigns against them since 1936; since 1987 this has been done by the Department of Conservation (DoC). Damage caused by goats varies from subtle to catastrophic. In grassland/shrub habitats where goats can reach most plants, a dynamic equilibrium between goats and vegetation is quickly reached and the habitat remains in grassland/shrub. In forest habitats where goats cannot reach all plants, changes may be long-term and potentially catastrophic; forest may be destroyed and replaced by grassland/shrub (or bare ground) if goats or other ungulates prevent regeneration of canopy trees (Nugent & Challies, 1988). Goats may also threaten the survival of some indigenous species of plants and animals, especially those with limited distributions. Insular endemics such as Hebe breviracemosa and Homalanthus polyandrus on Raoul Island (Sykes, 1969; Parkes, 1984a) and Tecomanthe speciosa, Elingamitajohnsonii, Myrsine oliveri, Alectryon grandis and Pennantia baylisiana on Great Island (Williams & Given, 1981) were all nearly exterminated by goats--two species to a single plant each. Both these islands are now free of goats. Animals threatened by goats include competitors for food, e.g. the vulnerable kokako Callaeas cinerea wilsoni (Leathwick et al., 1983), and species whose habitat they destroy, e.g. the frog Leiopelma hochstetteri (Ogle, 1980). This paper discusses some of the lessons learnt, and illustrates crucial problems of policy, strategy, tactics and logistics encountered in feral goat control in New Zealand.
ERRORS IN PEST M A N A G E M E N T Three types or errors occur among goat control campaigns: confusing means (killing the goats) with ends (protecting resources), using inappropriate strategies to attain goals, and using inefficient tactics to kill the goats.
Goals of goat management The ultimate goal of any pest control is to halt or minimise damage to a resource. Managers must identify the resource and know how it is being damaged so that they can set precise goals and not vague concepts such as 'wise land use' or 'protection of flora and fauna'. These phrases leave unanswered what is wise, what land, which flora, and which fauna? They are
Feral goat control in New Zealand
337
'theologies' (Caughley, 1989), not amenable to scientific or managerial solutions. The most c o m m o n flaw in New Zealand goat control has been to confuse goals (protection of the indigenous biota) with means (control of goats). For example, the National Parks Act requires managers to eradicate, as far as possible, all introduced plants and animals from parks. Eradication is not possible for most introduced species (for a variety of technical, financial, or political reasons) so the goal is usually expressed by the slogan 'as few as possible'. This goal appeals to some managers and conservation groups because it is always achieved. As many pests as possible are killed with the resources available, but managers are not obliged to decide whether the real goal--protection of the indigenous biota--has been achieved. More subtle flaws are often included in pest control goals. For example, the desire to 'retain an area as representative of some forest type' is often advanced in management plans. If the forests contain goats that cannot be eradicated, the area can only be representative of a forest type influenced by goats; in which case the influence of goats and their density should be specified.
Strategies to control goats One of four strategies can be adopted by managers of goat herds: no action; eradication; annual control in perpetuity; or occasional control in perpetuity. No action DoC may choose to do nothing to kill goats and accept the outcome. Extrapolating from the minimum costs of successful control, it would cost at least NZ$15.6 million per annum (all NZ$ are in 1988 values and NZ$1 = US$0"59 or £0-38) to keep densities low enough to prevent undue damage (Parkes, 1990). DoC cannot afford this cost (about 15% of its entire budget). It currently spends only about $1.5 million per annum on goat control, and must set priorities and control goats in the most important conservation areas. On most other land infested with feral goats the department can only encourage recreational hunters, who may or may not hunt with sufficient intensity to achieve the department's goals. Eradication The permanent removal of goats from an area may be attempted for two reasons. Resource protection may require eradication. Elsewhere, this may not be necessary but it may be cheaper than control in perpetuity. Successful eradication depends on the ability to put all individuals at risk, to kill goats faster than they can replace losses, on the likelihood of recolonisation, and on the conviction by those responsible that the task is possible.
338
John P. Parkes TABLE 1 New Zealand Islands from which Feral Goats have been Eradicated
Island
Area (ha)
Liberated
Eradicated
Raoul Kapiti Great (Three Kings) Macauley Maud Ocean South East Cuvier Whale Mokoia Burgess Herekopare Ernest Nukutaunga East Rurima
2938 2023 350 323 309 300 219 195 140 133 60 25 25 13 8 4
Before 1836 c. 1830 1889 Before 1836 ? 1865 Before 1900 1890s ? 1987 9 1975 ~ 9 ? ?
1936-84 1928 1949 1966-70 c. 1972 1942 1914-16 1959-6 ! 1977 1989 1973 1976 1980s 1972 c. 1960 ?
Feral goats have been eradicated from 16 offshore islands around New Zealand (Table 1). However, on North and South Islands, recolonisation into cleared areas remains likely, and zero density with a sustained harvest of immigrants best describes 'successful' eradication campaigns in these areas.
Raoul Island. Raoul Island (2938 ha) is a Nature Reserve in the Kermadec group. It is the least modified of the four islands (Macauley, Lord Howe, Norfolk, and Raoul) at about 30 ° S in the south-west Pacific. It has 18 taxa of endemic plants (Sykes, 1977). Goats were liberated before 1836 (Straubel, 1954), and the destruction of the vegetation was noted by 1908 (Oliver 1910). As well as the potential loss of endemic plants, goats may also affect the regeneration of canopy trees (e.g. Metrosideros kermadecensis) by browsing seedlings and the epicormic shoots that are important for regeneration after cyclones (Parkes, 1984a). Oliver (1910), Merton (1968) and Sykes (1969, 1977) advocated that the herd be eradicated, and this has been attempted since 1936 (Fig. 1). Until 1971, goats were shot by staffofthe Island's meteorological station and by a hunting expedition in 1956. However, the' first serious attempts were not made until 1972, when annual hunting expeditions began. The last five goats were shot in 1984. The total cost of the campaign since 1972 has been about $1 million, or $339/ha. Most goats were killed by hunters with dogs, but latterly a few were shot from helicopters or killed in snares set on ledges. Raoul Island is an example of successful but inefficient eradication. In
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340
John P. Parkes
retrospect, it would have been better to have reinforced early expeditions to eradicate the herd quickly. The long campaign allowed the forest understorey to regenerate. This made access and visibility more difficult and provided more food per capita for the goats, which doubled their breeding rate from 0.96 kids/female/year in 1972 (Rudge & Clark, 1978) to 1.70 kids/female/year in the 1980s (Parkes, 1984b). The turning point came in the early 1980s when managers were convinced that eradication was possible. Greater effort was then spent hunting more elusive survivors as well as those more easily hunted. As a final check, the island was searched in 1986 by a team led by the leader of an earlier expedition who had doubted that eradication was possible.
Great Barrier lsland. The control of goats in the northern forests of Great Barrier Island is an example of an efficient but as yet unsuccessful attempt at eradication. The island (28 500 ha) is on the outer edge of the Hauraki Gulf offNorth Island. Forests on the northern end of the island have outstanding wildlife value (Ogle, 1980) and contain several endangered species of animals (e.g. kokako and Hochstetter's frog) and plants (e.g. Nestegis apetala and Fuchsia procumbens) threatened by feral goats. These forests consist of about 3230 ha of conservation reserve, bordered to the south by about 800 ha of forested private and Maori tribal land. The goats here are isolated by farmland from other herds on the Island, so reinvasion risks are low. In 1984, it was decided to 'do something about the goats'. Eradication was technically possible but politically awkward as the Maori landowners were concerned that hunters would also kill feral pigs which they valued as a food resource. They restricted access to their land. Nonetheless, the reserve land was hunted in 1986/87. Six hunters, each with two dogs, killed 930 goats in 372 hunter-days (K. Broome, pers. comm.). This cost $18/ha, and reduced the goats in the reserve to almost zero, thereby achieving most of the protection goals. However, the herd was not eradicated because goats can recolonise the reserve from adjacent Maori forests. In 1988 and 1989, for example, 29 and 4 goats, respectively were shot along the boundary of the reserve, despite an unknown number being shot by Maori on their land during 1989. The positive aspect of this campaign was that, unlike that on Raoul Island, maximum effort was expended in the first operation so that the herd was quickly reduced to very low densities. The flaw was that action began before the optimum plan for eradication was negotiated. Annual sustained control This strategy requires managers to choose some density of goats at which damage is acceptable and then reduce the herd to that density, and shoot
Feral goat control in New Zealand
341
subsequent annual increments. The strategy requires that managers have knowledge of the relationships between goats and the vegetation and other animals. Most mainland New Zealand goat herds are also regularly hunted by sportsmen. However, despite an annual harvest of about 60 000 (Nugent, 1989), this is not usually enough to allow palatable plants to regenerate (Parkes, 1990). Mt Egmont National Park. Mt Egmont National Park in North Island covers 33000ha of forest and alpine vegetation around the volcanoes Taranaki, Pouakai, and the Kaitake Range. Goats colonised the park in about 1910 and by the early 1920s were damaging vegetation (Thomson, 1922). Annual goat control began in 1924, and at least 35 600 goats were shot by Park rangers and private bounty hunters until 1960. Since 1961, control has been by government-employed hunters using dogs, who have killed a further 52 000 goats. The annual effort has increased from about 0.3 hunter-years in the early 1960s to about 4-0 hunter-years in the 1980s, the usual pattern in New Zealand goat control campaigns. This is, in my opinion, the wrong way to conduct a long-term campaign. Hunting is most efficient early in the campaign when the goats' rate of increase is lowest and the animals are unwary and easy to find in depleted forest understorey. The annual kill has declined from about 3000 in the early 1960s to about 1000 since 1984. The declining kill rates (Fig. 2), used as an index of density, indicate that the herd was reduced to about one-sixth of its 1961 size. This decline has resulted in a general improvement in the forest understorey (Clarkson, 1986), reflected by the high proportion of browse-susceptible, preferred plants in the goats' diet (Mitchell et aL, 1987). Goat density reached an equilibrium with hunting effort in 1981 since when the goats killed per hunter-day has not changed significantly (r2= 0-0006). The mean annual kill since 1981 has been 1207 goats. An exponential rate of increase of 0.395 was calculated based on a fecundity rate of 0.5 (Parkes, unpublished data) and mortality rates of 0.105 observed in other feral herds in New Zealand (Rudge & Smit, 1970). The present herd may, therefore, contain about 3000 goats to sustain the observed kill rates. If control ceased, the herd might double every 21 months until limited by food supply. This campaign also illustrates another common flaw in sustained control strategies--fluctuating effort. Budgets increased during the early 1980s and hunting effort doubled, but this has not been sustained since 1987 (Fig. 2). Therefore, the extra effort was wasted as the plant-goat-predator system regained its previous equilibrium.
342
John P. Parkes
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The harvest, effort, and time needed to eradicate the herd can be estimated (assuming all goats are at risk, logistic growth rates, and that the observed rate of increase approaches the intrinsic rate of increase). For example, we could eradicate the herd in 5 years if 1500, 1500, 1000, 100 and 25 goats were killed in successive years. It would take at least 4 hunter-years per year to attain the first two or three of these harvests, at a cost of $233 000/year. The cost of shooting the last few survivors cannot be estimated, but would be substantial. It has cost $3.18 million since 1961 (at 1988 costs of $160/hunter/ day), and will cost $160 000 ($4.8/ha) per year to maintain present densities, so it is worth considering eradication. However, as a prerequisite domestic goats would need to be prevented from escaping from adjacent farms, a minor problem in this area (L. Stanley, pers. comm.). Occasional sustained control The final strategic control option is to kill as many goats as possible in one
Feral goat control #1 New Zealand
343
intensive campaign, then monitor the protection values as they respond. Control is repeated only when damage again becomes intolerable. This strategy also requires detailed knowledge of goat population dynamics and how goats interact with the vegetation. Palatable plants always accessible to goats are unlikely to benefit from this strategy, and canopy plants will benefit only if their seedlings can grow through the browse tier before the goat population recovers. Most occasional control campaigns are not deliberate attempts to use this option, but are results of changing priorities or vagaries of government funding. G&borne Water Reserve. Gisborne city draws its water from the Puninga
catchment, about 2000 ha of indigenous forest and regenerating scrub on abandoned farmland. Goats have been in the area since at least 1950. They were hunted four times between 1965 and 1977. Hunting was annual between 1977 and 1986, and then it ceased (Table 2). Goats were fenced from a 8.4 x 8.4m plot in 1965. In 1981, the structure and composition of the herbaceous ground cover and the saplings present were measured in the exclosure and compared with that on two adjacent, unfenced plots on similar sites. The methods used are described by Allen et al. (1984). Despite the operations between 1965 and 1981, differences inside and outside the fence were still marked. Outside, more ground was covered by the unpalatable grasses Microlaena avenacea and Uncinia uncinata. Such goat-induced swards have also been described in other New Zealand forests TABLE 2 Number of Goats Killed and Success Rate in 13 Campaigns from 1965 to 1986, Gisborne Water Reserve Year 1965 1966 1973 1977 1978 1979 1981 1982 1983 1984 1985 1986
No. o f goats killed 2983 160 1092 599 342 208 1 062 189 1065 70 59 77
Kills~hunter-day 7"5 1"1 2"4 5"4 34.2 6"9 9-7 2"7 5"4 1"3 0"8 1"9
344
John P. Parkes TABLE 3
Sampling Counts on 30 2.25-m 3 Plots in an Area From which Goats were Excluded, and on Two Areas where they were not Excluded. Gisborne Water Reserve, 1981
Species
Exclosure
No. o f saplings Control 1 Control 2
Coprosma australis (highly palatable) a Geniostoma rupestre (palatable) Coprosma tenu(]'olium (palatable) Macropiper e.w'elsum (palatable) Pseudopana.v crassi['olius (palatable) Brachyglottis repanda (not palatable) Knightia e.xcelsa (not palatable) C.vathodes.[ascicularis (not palatable) Neom)'rtus pedunculatus (not palatable) Beilschmiedia tawa (not palatable)
49
0
0
13
0
0
1
0
0
2
0
0
1
0
0
1
0
0
1
0
0
3
0
0
0
0
4
0
0
2
a The broad palatability to goats of the plant species recorded is indicated.
(Moore & Cranwell, 1934). Inside, more ground was covered by litter and moss. Palatable saplings were common inside the fence, but the few saplings outside were all of unpalatable species (Table 3). I conclude that either not enough goats were killed to allow regeneration, or the campaigns were too infrequent to allow plants to grow through the browse tier, or both--at least up to 1981.
TACTICS A N D COSTS OF GOAT CONTROL
The method most favoured for controlling goats in New Zealand has been by shooting on foot with or without dogs. Shooting from helicopters, poisoning natural foliage, and fencing are used less often.
Feral goat control in New Zealand
345
Shooting on foot Government has employed hunters to shoot goats (and other ungulate pests) since 1930. During the 1980s, up to 50 hunters have been employed to hunt goats in about 15 major operational areas, for an annual kill of up to 40000. Several hunting methods are used, depending on the terrain and vegetation. Forested areas are usually first hunted without dogs as naive goats are easily found and shot. Goats living in more open grassland or scrub are also best hunted without dogs as they are visible from a distance, tend to be in larger groups, and are more easily stalked without dogs. Hunting with dogs is commonly used during the latter stages of campaigns in forested areas when the goats have become wary. Some dogs are trained to stay close to their master and point when they scent goats. Others, usually two or three per hunter, are trained to chase and kill, or bail and bark to attract the hunter. The tendency of dogs to disperse goats is more than balanced by their ability to locate the groups. Costs of hunting on foot vary with the method of payment and difficulty of access, but are usually about $160/hunter/day. This includes wages, allowances for food and dogs, access, and track and hut maintenance. Goats in mainland New Zealand forests have been reduced to low densities for between $3.14 and $5.00/ha/year.
Aerial shooting The use of helicopters as shooting platforms was developed in New Zealand to kill and recover red deer for the German venison market (Challies, 1974) and to control Himalayan thar Hernitragusjemlahicus(Tustin, 1980). Tallies of 100 goats per flying hour have been achieved in unforested country using turbo-powered machines. Costs vary from about $350/flying hour for the smaller piston helicopters up to about $800/flying hour for turbo machines, plus wages and ammunition.
Poisoning foliage Goats have been successfully poisoned with c o m p o u n d 1080 (sodium monofluoroacetate) in a gel or grease smeared on the leaves of palatable foliage (Parkes, 1983). This works well where goats have eaten most preferred plants, but is less successful where preferred foods are readily available. It cannot be used where non-target animals may be at risk. Costs are about the same as for ground shooting. In two trials in forests of the R a u k u m a r a Range, 1500 ha were treated with poison and 1500 ha were
346
John P. Parkes
hunted for about $7/ha and 90% + kill in both methods. A later poisoning over 6000ha cost about $3/ha for an 85% kill (Parkes, unpublished data). Exclusion Fencing is often mooted to stop goats dispersing (e.g. on Arapawa Island (Dingwall & Rudge, 1984)). Fences may be useful as a tactical technique either to create short-term manageable units during control (e.g. in Hawaii (Baker & Reeser, 1972)), or to limit recolonisation during sustained control. However, as some goats will always get past even well-maintained fences, they are of limited strategic use in eradication campaigns.
DISCUSSION Feral goats concern those who wish to protect New Zealand's distinctive flora and fauna. Many conservationists advocate eradication of pests, either specifically as for Himalayan that (Anon., 1989) or for rabbits (see Gibb, 1967), or generally for all introduced biota as in the National Park Act. This goal is sensible only if it is technically possible with the resources available. It is not technically possible to eradicate all feral goat herds in New Zealand because of the continuing certainty of domestic escapes. Therefore, a general policy to eradicate all herds is futile. Such a goal ensures that effort is not targeted where it is most needed or most effective. Managers need to ask why goats are pests, how much control is needed to minimise or eliminate their impact, and which areas should be given priority. Only then can they choose which strategy and tactics best suit the particular problem. Caughley (1989) argued that, other things being equal, management of plant-herbivore systems that leads to stable ecosystems is preferable to that which leads to unstable systems. Of the four strategies for goat management discussed, the first (with no action) and second (with no goats) are most likely to result in stable ecosystems, although managers may disapprove of the first option. The third strategy requires sustained, constant and sufficient effort by government agencies. The history of goat control in New Zealand has shown that this is rarely achieved, and many campaigns evolve into the inherently unstable fourth strategy. The problems of unsustained or inconstant effort can be overcome by dividing the budget for goat control into two parts. One can be spent on sustaining control in highest priority areas. This fund needs to be constant, not increased or decreased at departmental whim. The second can be spent on attempts at eradication, and can be increased or decreased as resources vary.
Feral goat control in New Zealand
347
A C K N O W L E D G E M ENTS I thank G. Nugent, J. D. Coleman, J. A. Gibb and J. Orwin for comments on early drafts o f this paper. I also thank the m a n y government officers who provided information on goat control campaigns. This study was partly funded by the New Zealand Department of Conservation.
REFERENCES Allen, R. B., Payton, I. J. & Knowlton, J. E. (1984). Effects of ungulates on structure and species composition in the Urewera forests as shown by exciosures. N Z J. EcoL, 7, 119-30. Anon. (1989). Himalayan thar. Conservation News, 51, 3. Baker, J. K. & Reeser, D. W. (1972). Goat management problems in Hawaii Volcanoes National Park: A history, analysis and management plan. Nat. Resour. Rep., No. 2, US National Park Service. Beaglehole, J. C. (1961). The Discovery of New Zealand Oxford University Press, London. Caughley, G. (1989). Control of wild animals. In The Future of New Zealands Wild Animals, ed. A. E. Newton. New Zealand Deerstalkers' Association, pp. 101-3. Challies, C. N. (1974). Use of helicopters in the New Zealand commercial venison industry. E. Afr. Agr. For. Jl, 39, 376-80. Clarkson, B. D. (1986). Vegetation of Egmont National Park. Natn. Parks Sci. Ser., No. 5. Dingwall, P. R. & Rudge, M. R. (1984). Biological and ecological values of Arapawa Island Scenic Reserve. Dep. Lands & Surv. Inf. Ser., No. 13. Gibb, J. A. (1967). What is efficient rabbit destruction? TGMLI Rev., 12, 9-14. Jane, G. T. & Pracy, L. T. (1974). Observations on two animal exclosures in Haurangi forest over a period of twenty years (1951-1971). N Z J. For., 19, 102-13. Leathwick, J. R., Hay, J. R. & Fitzgerald, A. E. (1983). The influence of browsing by introduced mammals on the decline of North Island kokako. N Z J. EcoL, 6, 55-70. Merton, D. V. (1968). Narrative of the Kermadec Islands expedition 10/10/66-29/1/67. Notornis, 15, 3-22. Mitchell, R. J., Fordham, R. A. & John, A. (1987). The annual diet of feral goats (Capra hircus L.) in lowland rimu-rata-kamahi forest on eastern Mount Taranaki (Mt Egmont). N Z J. Zool., 14, 179-92. Moore, L. B. & Cranwell, L. M. (1934). Induced dominance of Microlaena avenacea (Raoul) Hook. f., in a New Zealand rain-forest area. Rec. Auck. Inst. Mus., 1, 219-38. Nugent, G. (1989). Hunting in New Zealand in 1988: Survey results. Forest Research Institute Report (unpublished), Christchurch. Nugent, G. & Challies, C. N. (1988). Diet and food preferences of white-tailed deer in north-eastern Stewart Island. N Z J. Ecol., 11, 61-71.
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Ogle, C. C. (1980). Wildlife and wildlife habitat of Great Barrier Island. N Z Wildl. Ser. Fauna Surv. Unit Rep., No. 24. Oliver, W. R. B. (1910). The vegetation of the Kermadec Islands. Trans. Proc. N Z Inst., 42, 118-75. Parkes, J. P. (1983). Control of feral goats by poisoning with Compound 1080 on natural vegetation baits and by shooting. N Z J. For. Sci., 13, 266-74. Parkes, J. P. (1984a). Feral goats on Raoul Island, II. Diet and notes on the flora. N Z J. Ecol., 7, 95-101. Parkes, J. P. (1984b). Feral goats on Raoul Island, I. Effect of control methods on their density, distribution and productivity. N Z J. Ecol., 7, 85-94. Parkes, J. P. (1990). Procedures for ranking and monitoring feral goat (Capra hircus) control operations. Forest Research Institute Report (unpublished), Christchurch. Parkes, J. P. (in press). Eradication of feral goats on islands and habitat islands. J. Roy. Soc. NZ. Rudge, M. R. (1976). Feral goats in New Zealand. In The Value of Feral Farm Mammals in New Zealand, ed. A. H. Whitaker & M. R. Rudge. Dep. Lands & Surv. Inf. Ser., No. 1, 15-21. Rudge, M. R. & Clark, J. M. (1978). The feral goats of Raoul Island, and some effects of hunting on their body size and population density. N Z J. Zool., 5, 581-9. Rudge, M. R. & Smit, T. J. (1970). Expected rate of increase of hunted populations of feral goats (Capra hircus L.) in New Zealand. N Z J. Sci., 13, 256-9. Straubel, C. R. (1954). The Whaling Journal of Captain IV. B. Rhodes. Whitcombe & Tombs Ltd. Christchurch. Sykes, W. R. (1969). The eft~ct of goats on vegetation of the Kermadec Islands. Proc. N Z Ecol. Soc., 16, 13-16. Sykes, W. R. (1977). Kermadec Islands flora: an annotated checklist. DSIR Res. Bull., 219, 297-99. Thomson, G. M. (1922). The Naturalisation of Animals and Plants in New Zealand. Cambridge University Press, Cambridge. Tustin, K. (1980). Recent changes in Himalayan thar populations and their effect on recreational hunting. N Z Wildl., 8, 40-8. Williams, G. R. & Given, D. R. (1981). The RedData Book of New Zealand. Nature Conservation Council, Wellington.