Productivity of Osprey, Pandion haliaetus, Nesting on Natural and Artificial Structures in the Kawartha Lakes, Ontario, 1991-2001

Abstract

Ospreys (Pandion haliaetus) declined throughout the Great Lakes basin during the 1950s to 1970s due to usage of organochlorine pesticides. Following the banning of DDT in 1972, artificial elevated nest structures were erected in the Kawartha Lakes region of south-central Ontario to aid in their recovery. As the population grew, large stumps of flooded trees, < 1 m above the surface of the water became important nesting sites, despite their propensity to flood in turbulent weather conditions. We compared the productivity of Ospreys among nest substrates and longevity of the nests in this area from 1991 to 2001. Of 260 individual nesting attempts made over the 11 years, 57% used man-made structures, primarily either quadrupod nesting platforms or utility poles. Of nests on natural substrates, stump nests accounted for 37% of total nesting attempts; elevated tree nests were relatively uncommon (6%). Productivity of stump nests was significantly greater than that of artificial or tree nests (1.48 versus 1.16 and 0.73 chicks produced per occupied nest, respectively). Nevertheless, survivorship of stump nests was less than that of platform nests after 3 years of age, as high water levels, storms or winter ice activity destroyed some of these low nests between breeding seasons. Ospreys were able to attain greater productivity in these stump nests than on man-made nesting substrates.