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Phelps III, James M. (Tad) – Factors affecting foraging and productivity of ospreys (Pandion halieatus) at Cascade Reservoir, Idaho. 1993.

ospreySix breeding male ospreys (Pandion halieatus) were radio-tracked to determine home ranges, foraging efficiency, and factors affecting foraging habitat selection. Ospreys were trapped with a modified bal-chatri trap placed over the nest, and breeding males were fitted with tail-mounted radio transmitters. Females were caught most easily and most often. Capture of males was more difficult and took longer. Nests were observed throughout the remainder of the nesting season in order to approximate hatching, fledging, and failure dates. Success of nests where trapping occurred was compared to that of nests where no trapping took place. Results indicated that trapping male ospreys at their nests increased the likelihood of nest failure, however, the exact cause of nest failure was unclear.

Habitat characteristics of foraging sites were compared to characteristics of randomly selected sites throughout the study area to determine important features of osprey foraging habitat. Results suggested that ospreys tend to forage adjacent to the shoreline, in shallow water where the bottom is often visible, and where bottom feeding fish such as brown bullheads (Ictalurus nebulosus) are abundant. Foraging sites also had less wave action than random sites. This information suggests that shoreline development at ecologically similar lades and reservoirs could have a greater than expected impact on breeding ospreys.

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