THE EFFECT OF MAN-MADE PLATFORMS ON OSPREY REPRODUCTION AT LOON LAKE, SASKATCHEWAN

Since 1975 we have banded 277 nestling Ospreys at 138 successful nests near Loon Lake, Saskatchewan. There were 137 failed nesting attempts, in total yielding a production of 277 young from 275 attempts (1.0 young per active nest). Since 1986, over half (37 of 64) of successful nests have been on man-made platforms. Pairs on platforms had a success rate of 62.9% and raised 2.1 young per successful nest, compared with a success rate of 45.9% and 2.0 young per successful nest in osprey-built nests in trees. Alpha-numeric color bands have been added since 1988 to all nestlings and to 22 adults, including five males. Only one of the trapped adults had been banded as a nestling at Loon Lake; most others are presumed to have immigrated from elsewhere. There have been eight retrappings of six adults in subsequent years. From 299 Loon Lake Ospreys and 14 from seven other Saskatchewan lakes, 12 recoveries to date include 2 from Colombia and 1 each from Ecuador, Panama, Costa Rica, Vera Cruz, Louisiana and New Mexico.