Foraging behaviours of translocated takahē (Porphyrio hochstetteri) at two contrasting sites, New Zealand

摘要

The South Island takahē (Porphyrio hochstetteri) is an endangered ground-dwelling species, endemic to New Zealand. To prevent the species’ extinction, individuals were translocated to protected sites, such as off-shore pest-free islands and pest-fenced, mainland sites. The takahē may be one of the most researched bird species in New Zealand, but there are very few studies on its behavioural habits and ecology at these protected offshore island and mainland sites. This study was an investigation of translocated takahē foraging behaviour at two very different sites, Motutapu Island (Hauraki Gulf, Auckland) and Maungatautari mainland site (Waikato region), with two translocated takahē populations (18 vs 6 takahē respectively). In total, 24 takahē were observed at the time of this study. The aims of this research were to determine: (1) how takahē foraging behaviour differed between pasture and other habitats on Motutapu Island and at Maungatautari, (2) how other habitat elements (incl. vegetation cover, water, roads, tracks) affected foraging behaviour, and (3) if habitat restoration may assist takahē establishment. This study was conducted in reference to future successional habitat changes on Motutapu Island, as it is subject to active re-vegetation of native trees and shrubs. Similarly, Maungatautari is not actively maintaining the pastoral grassland sites between forest edge and the pest-proof fence. Therefore, without management, natural forest successions of these sites are likely to decrease food availability for takahē in the future. Plant species eaten by takahē were identified during field observations. Foraging behaviour was categorised into three main behaviours: (1) cutting for grass-blades, (2) tillering for grass meristems (leaf base, leaf blade discarded) and (3) stripping (grass seeds). A multinomial regression analysis, with confidence intervals of 95% level confidence, determined the odds of a takahē behaviour occurring according to various habitat variables. Foraging behaviours were found to differ according to the percentages of vegetation cover. On Motutapu Island, the main findings were that takahē favoured tillering grass meristems at sites where a high percentage of shrubland was available rather than at sites with high tree cover (vegetation >6 m) or with a high percentage of open grassland. In contrast, stripping seeds was favoured at sites with high tree cover and/or at restoration planting sites. Qualitative behavioural data from Maungatautari showed that takahē foraged primarily on pastoral grassland species, obtained primarily between the fence and the forest. Nesting and breeding observations were also made during incubation and chick-rearing. Only one chick reached juvenile-adult stage at Motutapu Island, compared to two chicks at Maungatautari. I identified nest material and nest cover plant species used by takahē (native and exotics- sedges/flax/shrubs/native long grass) during the breeding season and present a plant list based on qualitative fieldwork. Extensive pastoral grasslands on Motutapu Island are now being restored into forested areas, but wetland and native grassland restoration should be another priority for takahē habitat management. Similarly, the Maungatautari Ecological Island Trust (MEIT) may have to control the natural succession of the forest at the edge of the pest-proof fence. Overall, adding native species in pastoral grassland takahē territories at Motutapu Island and Maungautari will be necessary for the future well-being of these translocated takahē. This study has shown that analysing takahē foraging behaviours can help conservation management to improve habitat restoration and subsequent breeding success.