Identification

Perching: Large raptor with dark brown back, white breast, white head with prominent dark eye stripe, long beak.

Flying: Mostly white underneath with dark wing tips and dark patches at the wrists. Narrow wings with distinctive crook at the wrists give this raptor a gull-like appearance in flight. Wings are slightly arched when soaring.

Nesting Habitat

Near lakes on the plains or beside rivers, lakes, or beaver ponds in the mountains. They build a large stick nest in a tall tree, in a broken-topped snag, on a power pole, or on an artificial nest platform. In the mountains they frequently nest in flooded groves of trees on islands. They take readily to artificial nest platforms. Young breeding pairs have a high rate of nest failure.

Nesting Dates

Courtship: March to May

Incubation: early May to mid-July

Dependent nestlings: early June to late July

Incubation period is 34-40 days. Young fledge 50-60 days after hatching. Fledged young remain dependent on parents for about three months.

Statewide Distribution and Population

Osprey nest primarily in mountain parks and western valleys, but pairs have begun to breed on artificial platforms around prairie reservoirs along the Front Range especially between Denver and Fort Collins. The statewide population has increased from about 10 pairs in 1965 to around 100 pairs in 2000. DDT and other pesticide use in Mexico continue to affect North American nesting osprey populations.

State and Federal Status

Not listed. Formerly federal sensitive.

Search and Nest Monitoring Protocol

Beginning in mid-April, visit potential nest sites (lakes, reservoirs, and mountain marshes) every two weeks for 1-2 hours. Continue monitoring until young have fledged. Observation points should be located at least 400 m from active nests and perches.

Recommended Nest Buffer Area

CPW recommends no surface occupancy (beyond that which historically occurred in the area) within 400 m of the nest site and no human encroachment within 400 m of the nest site between 1 April and 31 August.

References

Bent, A. C. 1937. Life histories of North American birds of prey, part 1. U.S. National Museum Bulletin 167, Washington, D.C.

Johnsgard, P. A. 1990. Hawks, eagles, and falcons of North America. Smithsonian Institution press, Washington, D.C.

Kingery, H. E., ed. 1998. Colorado breeding bird atlas. Colorado Bird Atlas Partnership, Denver.

Peck, G. K., and R.D. James. 1983. Breeding birds of Ontario: Nidiology and distribution. Volume 1: Nonpasserines. Royal Ontario Museum, Toronto.

Swenson, J. E. 1981. Osprey nest site selection in Yellowstone National Park. Journal of Field Ornithology 52: 67-69.

Wickersham, L.E. 2016. The Second Colorado Breeding Bird Atlas. Colorado Bird Atlas Partnership, Denver.