Spatial scale and nest distribution of little penguins (Eudyptula minor)

摘要

The breeding habitats of all seabirds are not uniformly distributed spatially and temporally, but typically exist as discrete patches. Most species of seabirds breed in colonies that vary in size, and are generally located close to foraging areas. These colonies typically form patterns in the landscape and maintain some inter-connectivity that can be at the genetic and / or demographic levels.udInteractions between abiotic and biotic factors determine the extent and distribution of a population in a geographical area. Temporal factors such as the seasonal variation in the availability of food and breeding season phenologies also determine spatial and temporal species distributions. This study investigates the abiotic and biotic interactions that can operate in a hierarchical series of habitat spatial scales extending from the Meso (100s – 1000s km), Topo (100s m), Micro (10s m) to Nano (1+ m) scales.udThe spatial distribution of colonies and nests of a burrowing seabird, the little penguin (Eudyptula minor) found along the North West Coast of Tasmania are investigated. These colonies are recognised to be a component of the little penguin metapopulation that has been identified for south-east Australia. The metapopulation embraces the concepts of source-sink colonies and that of the role of habitat quality. The spatial distribution of little penguin colonies was investigated at different spatial scales, and the relationships between habitat, nest-site quality, microclimate and chick productivity are examined as the spatial scale decreased from landscape to individual nest-sites.udIn this thesis, I present data and analyses that examine:ud1) Spatial distributions of little penguin and burrows. Geographical Information Systems (GIS) were used to analyse the spatial patterns of colonies along the North-West Coast of Tasmania. Data collected using differential GPS were analysed in order to describe the distribution of nest-sites within and among colonies. The spatial analyses showed that colonies were not distributed randomly and that nest-sites were clustered within colonies.ud2) Environmental factors influencing nest distribution. A habitat model was used to statistically explain the presence or absence of burrows. The model was developed using the following terrain variables: elevation, slope, aspect (extracted from a high resolution 1 m × 1 m DEM); and calculated solar radiation and wetness index. The distance to the coast was also calculated for each presence and absence point included in the model.ud3) Microclimate of burrows. Temperature and relative humidity were measured in different burrow types (grass, sand, vines and artificial) over the main period of the breeding season to investigate the extent of microclimate variation within and among burrow types. The relationship between the burrow and external temperature was also examined among the burrow types. The frequency with which the burrow temperatures exceeded 27°C, the Upper Critical Temperature (UCT) at which penguin chicks may experience difficulty in thermoregulation, was also determined.ud4) Influence of burrow type on breeding success. The presence or absence of chicks as well as the number of chicks produced per burrow type was analysed during three breeding seasons using GLMM to investigate whether there was a difference in the productivity per burrow type.udThe use of spatial habitat scales in the analyses of a burrowing seabird and the examination of abiotic and biotic factors (and their interactions) has provided new insights into how little penguins interact with their environment at a range of spatial scales. The study has also developed a novel approach to investigating the relationships between the distribution of seabirds and their habitat.udNew findings have emerged in three areas of seabird ecology:ud(i) The spatial analyses of seabird colonies undertaken by GIS showed a dispersed pattern of distribution at both the meso- and coarse scales, yet within the colonies the nest-sites were clustered.ud(ii) A habitat model based on a range of terrain variables provided a statistically valid model to explain the presence, but not the absence, of burrows within colonies. This may be the result of the presence of suitable habitat that is underutilised by the penguins or that space is not a limiting factor, or other factors such as vegetation cover that may also be necessary to model habitat utilisation more accurately.ud(iii) Microclimate variations were not uniform among the burrow types, and some burrow types were more prone to exceed the UCT of 27°C in a way that could be potentially harmful to adult penguins and their chicks.ud(iv) Chick production during three years of this study was higher in artificial burrows compared to the natural burrows. The implications of the findings of this study are discussed in terms of conservation and management in peri-urban environments of little penguin colonies.