Seasonal changes in home range size and habitat selection by kakapo (Strigops habroptilus) on Maud Island

Abstract

Kakapo (Strigops habroptilus) are a critically endangered parrot endemic to New Zealand. They are large, flightless, nocturnal and exclusively herbivorous. Kakapo were once widespread throughout the North, South and Stewart Islands, and they inhabited a wide range of vegetation types, although it is thought that they favoured the wet west coast forests. Kakapo are thought to be extinct from their natural range and all known birds have been transferred to predator free off-shore islands, such as Maud Island, where they are intensively managed by the Department of Conservation's National Kakapo Team (NKT). The purpose of this thesis was to investigate kakapo home range size and habitat selection on Maud Island, a highly modified island with both native and exotic habitats. Understanding the role that exotic habitats play in kakapo habitat selection will help the NKT to make informed decisions about the suitability of other modified islands for kakapo and provide insight into how to manage exotic habitats for kakapo.

Kakapo were radio tracked at night in each of four seasons between December 2000 and October 2001. For each bird in each season home ranges were computed. Home range size varied from 1.8 to 145.0 hectares using the minimum convex polygon method. Home ranges were smallest in winter.

Habitat selection was determined by overlaying the kakapo locations and home ranges onto a vegetation map of the island using ArcView GIS. Each season selection ratios were calculated for each vegetation community. Pine plantation (Pinus radiata) was selected for in summer, possibly because pines are high in turpine, like rimu (Dacrydium cupressium) on which the majority of kakapo were raised. The treeland community dominated by five-finger (Pseudopanax arbereus) was selected for in the autumn, and kakapo may have been feeding on ripe fivefinger berries. Pasture communities were seldom used in any season. Dense pole stands of Manuka (Leptospemum scoparium) were also avoided by kakapo.

Rate of movement by kakapo was also investigated. The average distance moved by kakapo between successive fixes on the same night was 50m/hr (n=150 movements and 15 birds). No significant relationship was found between the rate of movement while foraging and the vegetation community occupied.

Recommendations for improving the habitat on Maud Island for kakapo are given. It is suggested that future research should focus on identifying the specific features of the vegetation communities that kakapo select for and against, and in particular why pine is a favoured food for kakapo.