Breeding biology, life history and spatial ecology of the endangered swift parrot

Abstract

Anthropogenic habitat change can have serious effects on the viability of animal populations, but some species are more vulnerable than others. However, basic ecological information is often unavailable to inform management of some species because they present major challenges for detailed field research. I studied the breeding biology of the poorly understood, endangered swift parrot Lathamus discolor. Swift parrots are vulnerable to anthropogenic change because their life history traits (tree cavity nesting, migration and predator naivety) expose them to a wide range of threats. This makes them an excellent model for investigating how complex conservation issues impact poorly known species. Using intensive field survey techniques, I monitored swift parrot nests across their entire potential Tasmanian breeding range. I found that swift parrots have specific habitat preferences. In particular, they only used a limited subset of the tree cavities available to them for nesting. Suitable cavities were uncommon at the landscape scale, and common survey techniques used to assess their availability are prone to error. Swift parrots had low breeding site fidelity, and nest cavities were rarely reoccupied between years. Facultative/irruptive movements between rich, ephemeral patches of food explained this result, and breeding areas were occupied or abandoned depending on local conditions. Facultative movements enabled swift parrots to maintain consistent breeding investment and nestling quality irrespective of where breeding occurred. However, the benefits of moving between rich patches became maladaptive when they settled in areas occupied by introduced sugar gliders Petaurus breviceps. Sugar gliders were major predators of adult female swift parrots and their eggs. Sugar gliders were introduced to the Tasmanian mainland in the 19th century but remain absent from several offshore islands where swift parrots breed. When food availability lured swift parrots into sugar glider infested areas, rather than to predator free islands, the predation penalty was severe. These conditions may create an ecological trap, where habitat selection cues (i.e. food availability) become maladaptive. However facultative movements and variable food availability may allow swift parrots to temporarily escape ecological traps when food availability shifts. This variability complicates swift parrot population dynamics over space and time. I propose that in forests degraded by anthropogenic habitat loss and sugar gliders, swift parrot populations are limited by more complex processes than sedentary or philopatric species. Detailed life history data are critical for accurately diagnosing decline and identifying management approaches for threatened, difficult to study species. The conservation problems faced by swift parrots highlight the necessity of detailed field research for understanding the complex, unexpected and synergistic interactions that may affect our less known difficult-to-study endangered species.