Graduate Thesis Or Dissertation
 

Production, nest site selection, and food habits of ospreys on Deschutes National Forest, Oregon

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/2801pk43h

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  • A study of population trends, nest site selection, and food habits of ospreys (Pandion haliaetus carolinensis) nesting on the Bend District of the Deschutes National Forest, Oregon, was conducted during 1970 and 1971. Intensive observations were made of 95 nesting attempts of ospreys. Energy demands of the population were estimated with the aid of a simulation model employing data from the study. A total of 99 young was fledged from 95 active nests during the two breeding seasons. Average production of fledglings per active nest was approximately one. The population appeared to be stable during the study. Ponderosa pines (Pinus ponderosa) were used exclusively by ospreys nesting over land. The average nest tree in the forest was 36.6 m tall and had a dbh of 109 cm. All nest trees had a dead, somewhat flattened, basket-shaped top typical of old-growth ponderosa pines. Nests located over water on Crane Prairie Reservoir were generally built on snags averaging 9 m in height with a dbh of 53 cm, Collectively, ospreys captured 43 percent tui chubs (Gila bicolor) and 57 percent salmonids. Ospreys caught approximately 0.6 more fish per hour of observation during the early morning and early evening hours than during the middle of the day. Average daily consumption of fish estimated for different age classes of ospreys were: adults, 286 g; nestlings, 127 g; fledglings. 254 g; and juveniles, 280 g. The impact of osprey predation on the sport fishery at Crane Prairie Reservoir was judged to be negligible. Forest management practices should be modified to prevent logging activities within 400 m of active osprey nests from April to September. Also, potential nest sites should be preserved when possible, and timber harvesting should be prohibited within 45.7 m of lakes and streams that attract foraging ospreys.
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