Contemporary Status of the White-Bellied Sea Eagle in Australia: A Tale of Many Scales

Abstract

Considered to have a declining world population, concern has been expressed in recent years over the conservation status of the White-Bellied Sea-Eagle (Haliaeetus leucogaster) within Australia. Although widespread, regionally it is thought to be declining in response to human induced disturbance. We used mitochondrial control region sequence data and the Australian Bird Atlas data to investigate the current genetic and spatial distribution of the species at the continental level and within and between specified regional units. At ecological timescales the Atlas Data was used to identify the extent and pattern of change in range and density of the species between three Atlas Periods (1901-1976, 1977-1981, and 1998- 2001) using a new standardized frequency measure, the Occupancy Index (OI). Sequence data were obtained from 128 individuals describing 15 haplotypes. Overall, genetic diversity was low and although there were regional differences, AMOVA results failed to provide any significant level of genetic subdivision. We suggest that the population expanded from a bottleneck approximately 160,000 years ago during the late Pleistocene, and spread throughout the continent through a contiguous range expansion. At the continental scale, there was no significant difference in the spatial extent of occupancy between Atlas Periods. However, there were considerable changes in frequency and range extent between defined regions, and there were distinct differences in the pattern of change in OI between coastal and inland areas over time. The over-riding factor associated with distributional shifts and frequency changes was apparently El Nino driven climatic fluctuation. It is clear from the combined analyses that there are signatures of both historical and contemporary processes effecting the current distribution, and that the high level of genetic exchange between regions bodes well for the long-term survivorship of the species within Australia. This study reinforces the importance of multiscale analyses both temporally and geographically