Reproductive success of ospreys at Lake Almanor, California during 1975-1980 was compared with results of previous surveys from 1969-1971. Nest site data were analyzed to determine factors important in nest site selection, and to determine the value of artificial platforms constructed during 1974-1978. Results showed that the number of known pairs increased, and reproduction increased from an average of 0.93 young fledged per occupied nest in 1969-1971 to 1.35 in 1975-1980. We suspect that the increase has resulted from a decrease in pesticide levels following the banning of DDT in 1972. Nest site analysis showed that osprey select tall, large diameter snags, or live trees with broken or dead tops. Platform occupancy for nesting averaged 32% of the available platform-years, indicating that platforms are a worthwhile management tool.
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