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154 Notornis, 2014, Vol. 61: 154-161 0029-4470 © The Ornithological Society of New Zealand Inc. Assessing minimum population size of Kermadec parakeets (Cyanoramphus novaezelandiae cyanurus) on Macauley Island, Kermadec Islands TERRY C. GREENE* IAN M. WESTBROOKE DEREK BROWN PETER J. DILKS Science and Technical, Department of Conservation, Private Bag 4715, Christchurch 8140, New Zealand JOHN W. BARKLA Department of Conservation, PO Box 5244, Dunedin 9058, New Zealand RICHARD GRIFFITHS Department of Conservation, PO Box 32026, Devonport 0744, New Zealand Abstract The minimum population size of Kermadec parakeets (Cyanoramphus novaezelandiae cyanurus) is reported for Macauley Island in the southern Kermadec Islands group. To minimise population impacts of any accidental parakeet deaths the confirmed presence of a minimum population of 3,000 parakeets was required prior to the attempted eradication of Pacific rats (Rattus exulans) from Macauley Island. Eight pre-defined vegetation strata were identified and 4 count methods ranging from simple counts to distance sampling were assigned to each strata depending on sampling conditions. As the resultant point estimate of 3,484 parakeets during the 29 June to 1 July 2006 survey period was greater than the minimum threshold the rat eradication was able to proceed. The potential impacts of changes in the vegetation on the population dynamics of Kermadec parakeets and recommendations for future monitoring of this species on Macauley Island are discussed. Greene, T.C.; Westbrooke, I.M; Brown, D.; Dilks, P.J.; Barkla, J.W.; Griffiths, R. 2014. Assessing minimum population size of Kermadec parakeets (Cyanoramphus novaezelandiae cyanurus) on Macauley Island, Kermadec Islands. Notornis 61 (3): 154-161. Keywords Kermadec Islands; parakeets; sampling design; abundance INTRODUCTION are young (< 2 million years) with consequent low The Kermadec Islands rise from the Kermadec sub- levels of floral and faunal endemism (Veitch et al. oceanic ridge midway between New Zealand and 2004). Tonga. They are comprised of a chain of widely The introduction of goats (Capra hircus), rats scattered active and extinct volcanic cones between (Rattus spp.) and cats (Felis catus) to the Kermadec latitudes 29°S and 32°S (Veitch et al. 2004; Greene et Islands over the previous 2 centuries has had a al. 2014). Only 6 islands exceed 5 ha in area and all profound detrimental impact on the birds of this isolated island archipelago (Veitch et al. 2004). Received 22 April 2014; accepted 31 August 2014 Following the successful removal of goats from *Correspondence: [email protected] Macauley Island by 1970 and from Raoul Island by Population size of Kermadec parakeets 155 Fig. 1. Location and significant geographic features of Mac- auley Island. 1985, the eradication of cats, Norway rats (Rattus Management Act 1991) to eradicate Pacific rats in norvegicus) and Pacific rats (Rattus exulans) from Raoul July 2006. Consent was granted subject to several Island and Pacific rats from Macauley Island was conditions (M. Ambrose, pers. comm.). The most scheduled for the winter months of 2002. However, significant of these in terms of risk to the project concerns about the risk posed to Kermadec parakeets was the requirement that a minimum population of (Cyanoramphus novaezelandiae cyanurus) by aerially 3,000 parakeets be confirmed inhabiting Macauley spread rat-baits containing the second generation Island before rat eradication could proceed. At the anticoagulant brodifacoum (20 ppm) resulted in the time the Macauley Island population of Kermadec postponement of rat eradication on Macauley Island parakeets was the most significant in the Kermadec to allow time for a more formal risk assessment. group and this condition was therefore imposed to Accordingly, Macauley Island was visited for 4 minimise the long-term population impacts of any days in July 2002 where the risk of rat eradication mortality on this species. to the parakeets was assessed and determined to Historical population estimates for Kermadec be minimal (Greene et al. 2004). The New Zealand parakeets inhabiting Macauley Island vary Department of Conservation subsequently reapplied markedly. Estimates range from a minimum of for resource consent (required by the NZ Resource >1,000 birds in 1966 (Taylor 1985) to 17,000-20,000 156 Greene et al. in September 1988. This was followed within 2 and second, to establish a baseline population months by an almost immediate decline to 5-10% of estimate and sampling methodologies suitable for the preceding estimate (Veitch et al. 2004). Seasonal future monitoring programmes. drought, food shortages, and successional changes Previous visits to Macauley Island strongly in the plant communities on Macauley Island suggested that Kermadec parakeet distribution and over the last 40 years have all been identified as density was largely determined by the predominant potential significant drivers of these highly variable vegetation communities (Greene et al. 2004). High population estimates (Taylor 1985; Greene et al. 2004; densities of parakeets were noted in areas of Scaevola Veitch et al. 2004; Greene et al. 2014). Additionally, gracilis, Cyperus insularis, within the few remaining the absence of a consistent and robust sampling remnant stands of ngaio (Myoporum rapense subsp. design and survey methodology has also hampered kermadecense) and vegetation adjacent to coastal the accuracy and precision of population estimates cliffs. Parakeets occured at much lower densities in (G. Taylor, pers. comm.; Greene et al. 2004). areas dominated by the fern Hypolepis dicksonioides During 2002, parakeet numbers on Macauley (Greene et al. 2004; Greene et al. 2014). In addition, Island were estimated using distance sampling the time limits imposed for the visit to Macauley methods (Greene et al. 2004). However, the Island (<7 days) and the difficulties of moving about short duration of the visit (4 days) and the need the island suggested that a simple randomised or to complete other priority tasks required that systematic sampling design imposed equally over sampling effort was low and biased toward areas of all habitats would be an inefficient means of rapidly greatest floristic diversity and high parakeet density assessing the abundance of parakeets. Intensive easily accessible to observers. Thus, the calculated sampling of habitats with low densities of parakeets population estimate of between 8,000 and 10,000 was likely to waste time when the principle objective parakeets was probably a significant overestimate was to simply determine whether or not a minimum (Greene et al. 2004). A more robust sampling design population of 3,000 parakeets was present. was clearly required to detect with confidence A more efficient alternative was to concentrate the presence of sufficient parakeets to allow the on those habitats, or strata, known to hold higher Macauley Island rat eradication to proceed. In this densities of parakeets and that were relatively study we report on the objectives, sampling design easy to survey. That is, those habitats with highest and survey methodologies used to determine the densities of parakeets and the greatest ease of minimum population size for Kermadec parakeets access were sampled first and most intensively on Macauley Island. using the most appropriate standardised sampling methodology to maximise abundance estimates METHODS as quickly as possible. The most important pre- Study site requisite for this type of stratified sampling Macauley Island (30° 13’S, 178° 33’W) is the 306 approach is prior knowledge of the location and ha remnant of an extinct basaltic volcano (Fig. extent of the various habitats. These habitats 1). The island is bounded on all sides by vertical can then be allocated as accurately as possible coastal cliffs and comprised of a sloping plateau to sampling strata so that sampling effort can be which climbs from relatively low eastern cliffs apportioned prior to fieldwork thereby avoiding about Windy Point to Mt. Haszard (238 m) in the sampling inefficiencies and resultant problems northwest. The plateau is dissected by numerous associated with data interpretation. Seven sampling erosion gullies, some of which have developed into strata were defined a priori using a combination of vertical sided ravines where they exit through the satellite imagery (panchromatic and multispectral coastal cliffs. Vegetation is dominated by tall and imagery obtained from Digital Globe 2005), recent dense Hypolepis dicksonioides fernland and Cyperus oblique aerial photographs (RNZAF 2006) and insularis (Sykes 1977 as Cyperus ustulatus) sedgeland. observations of parakeet distribution derived from More detailed examinations of the geology, climate our previous visit in 2002 (Fig. 2; Greene et al. and vegetation of Macauley Island can be found in 2004). Each of these strata (Table 1) was sampled Veitch et al. (2004), Greene et al. (2004), Barkla et al. in priority order (high to low parakeet density, (2008), Greene et al. 2014 and de Lange (in press). accessibility and sampling intensity). A further stratum comprising extensive patches of Solanum Sampling methods nodiflorum was defined on the island immediately Selection of sampling methods was dictated by 2 following our arrival once this habitat and its objectives. First, there was a need to provide a robust significance was identified. point estimate with acceptably narrow confidence intervals (i.e., CV ≤ 25%; Greene et al. 2004) of the Count methodologies minimum