Postnatal Development Of Steller'S Sea Eagles Sexing And Aging Techniques

To evaluate the impact of varying feeding conditions on reproductive success of Steller's Sea Eagle Haliaeetus pelagicus, I studied development of 71 eaglets during seven breeding seasons. Significant differences between the sexes in body development are manifested at 45-50 days. According to discriminant analysis of a complex of eaglet morphometric characteristics, females comprised 45.07% of the nestlings studied. Rate of development and the number of eaglets produced were significantly correlated with hatching date. Eaglets hatched out early grew significantly slower than those hatched later. The number of eaglets per brood (soon after hatch), correlated negatively with the time of egg laying. Females hatched significantly earlier than males in nests with two eaglets of different sexes. Older siblings were usually dominant over younger ones during the first month after hatching due to difference in size. The rate of growth of younger siblings decreased significantly (P = 0.05) in comparison with older siblings in conditions of low food supply. Worsening feeding conditions are probably caused by changes in the hydrologic regime of water bodies upon which eagles nest, and explains the relation between water regime and growth rate of eaglets. Growth rate decreases when water level fluctuates far enough from an average optimal value. Declines in food supply related to water level may aggravate age-related differences in size, promote fratricide and lead to decreased breeding success. In years with average water level breeding success was significantly higher.