Distribution and Behavioural Ecology of the Sulphur-Crested Cockatoo (Cacatua Galerita L.) in New Zealand

Abstract

1. Sulphur-crested cockatoos (Cacatua galerita) have colonised several sites in the North Island and on Banks Peninsula in the South Island of New Zealand. Galah (C. roseicapilla) have established in the South Auckland Region of the North Island. Original colonies are thought to have established from escaped cage birds, but the origin of populations of C. galerita that have appeared over more recent years is uncertain. 2. The distribution of C. galerita in Australia and New Zealand was modelled against environmental factors using multiple logistic regression to determine which characteristics of its environment are important in defining their distribution. 3. While C. galerita distribution in New Zealand falls within the range of ambient temperature experienced by this species in Australia, models of distribution produced from multiple logistic regression revealed temperature was not the only characteristic important in defining distribution. Instead distribution was best defined by a combination of temperature, availability of cultivated land and in New Zealand the presence of open woodland vegetation. 4. Observed daily and seasonal differences in the movement, time-activity budget, habitat use and diet of cockatoos in a population stronghold (Turakina Valley, Manawatu-Wanganui Region) were used to provide insight into the relationship between the environmental factors characteristic of C. galerita distribution and the range of this species. 5. Distribution of C. galerita was strongly influenced by the availability of crop seed mostly maize (Zea maize). In winter groups of C. galerita from large area (probably hundreds of square kilometres) congregated into a large flock, roosting in a reserve immediately adjacent to fields of maize, their main food source at this time. By congregating in this area they reduced the amount of time needed to forage for food especially time spent flying (the most energetically costly behaviour). 6. Despite greater energetic demands in winter, C. galerita in the Turakina Valley decreased the proportion of time spent feeding, instead increasing time spent resting. This was attributed to feeding on a very abundant food (maize), and lower energy demands resulting from reduced time spent flying (possible because of maize) and in feather maintenance and social behaviours. 7. Native podocarp forest remnants provided most of the non-food resource requirements of C. galerita, such as day-time refuges and nest and nocturnal roost sites. Most of their food was obtained from introduced vegetation available on the adjacent farmland, particularly cereal crops, grasses and exotic conifers. In contrast, sympatric populations of tui (Prosthemadera novaeseelandiae), bellbirds (Anthornis melanura and New Zealand pigeons (Hemiphaga novaeseelandiae) were more arboreal and preferentially foraged in native forest and exotic angiosperm tree species. 8. Freshly fallen leaves and green branches (greenfall) were collected from 100 plots in a podocarp-broadleaf forest in the Turakina Valley. Greenfall was categorised as "unexplained" or "cockatoo-caused". Leaves and branches (0-600mm) from 41 species or species groups were represented in the greenfall. Ten of these species also contributed to cockatoo-caused greenfall, including all four podocarp species and all of the epiphytic angiosperms present in the reserve. 9. Annual inputs of cockatoo-caused greenfall were compared with total foliar litter-fall measured in similar podocarp-broadleaf forests in the Orongorongo Valley, lower North Island. Although cockatoo-caused greenfall contributed only 0.08% of avenge litterfall, their impact was substantially greater for particular species, including > 5% of literfall recorded for Dacrydium cupressinum. 10. Defoliation of native tree and epiphyte species by C. galerita is considered to have potential consequences for forest dynamics, resulting in an increase in understorey vegetation, and could cause reductions in populations of some species (particularly D. cupressinum and rarer epiphytes).