Browsing by Author "Berkelman, James"

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    Habitat Requirements and Foraging Ecology of the Madagascar Fish-Eagle
    Berkelman, James (Virginia Tech, 1997-05-06)
    With a population estimate of 99 pairs, the Madagascar fish-eagle (Haliaeetus vociferoides) is one of the rarest birds of prey in the world. I investigated the ecological requirements of the Madagascar fish-eagle in 1994 and 1995 to help determine management action to prevent its extinction. I investigated fish-eagle foraging ecology in 1996 to determine its prey preference and whether fish abundance and availability affect fish-eagle foraging rates and foraging success. Madagascar fish-eagle nest and perch trees were taller, broader, had more unobstructed branches, and had a greater arc of accessibility than unused trees. Perch trees also were deciduous more often and had a narrower growth form than unused trees. Nest sites had more shoreline perch trees than unused sites. Lakes occupied by fish-eagles were deeper and clearer, and had more shoreline perch trees, more fish, a greater total fish weight, and more fish species than unoccupied lakes. I developed logistic regression models to predict the probability of Madagascar fish-eagle use based on the measured habitat variables. Nest and perch tree models included tree height. The nest site model included number of shoreline perches. Lake models included number of shoreline perches and either number of fish, total fish weight, or number of fish species. These models can be used to predict fish-eagle habitat use with > 70% accuracy. Introduced tilapia, Oreochromis spp. and Tilapia spp., made up the majority of both the gill net (66.3%) and fish-eagle catch (64.7%) in similar proportion, which suggests that the fish-eagle is an opportunistic predator. Replacement of native fish species by exotics, thus, probably has not been detrimental to the island's fish-eagle population. Male fish-eagle foraging success was positively correlated with number of fish, total fish weight, and number of fish species, which suggests that declines in the fish population could adversely affect the fish-eagle population. The results of this study indicate that Madagascar fish-eagles require bodies of water with large shoreline trees and an ample fish population. I recommend greater protection of aquatic habitats, monitoring and management of freshwater fish populations, and education of local people in sustainable tree harvesting practices.
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    Nesting and Perching Habitat Use of the Madagascar Fish-Eagle
    Berkelman, James; Fraser, James D.; Watson, Richard T. (Raptor Research Foundation, 2002)
    We documented Madagascar Fish-Eagle (Haliaeetus vociferoides) nest and perch use on lakes and rivers and compared parameters of used trees to unused reference trees. Nest and perch trees were broader and taller, had more unobstructed branches, and were less obstructed by adjacent trees compared to reference trees. Perch trees also were more often deciduous than reference trees. Nest sites had more shoreline perch trees than reference sites. Logistic regression models with tree height as the independent variable distinguished nest and perch trees front randomly selected reference trees. Models with number of perch trees along a 1.25 ba (50 in width) shoreline section distinguished nest sites from reference sites. These models suggest that the presence of trees greater than or equal to15 in tall within 50 in of the shoreline is a good predictor of Madagascar Fish-Eagle habitat use.