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Birds of the St. Croix River Valley: Minnesota and Wisconsin

FAMILY PANDIONIDAE

Ospreys


Osprey

Osprey (Pandion haliaetus)

Status: Regular migrant and nesting species. The WDNR listed the species as endangered (Les 1979). Residual pesticides and loss of nesting habitat are considered reasons for their decline.

Migration: Uncommon migrant throughout the Valley, most regularly observed adjacent to the St. Croix River. Spring migrants arrive during the second week of April (earliest-22 March 1953, Burnett County and 26 March 1967, Washington County). Peak abundance of spring migrants occurs between 25 April and 5 May. Fall migration begins with departure from nesting areas in mid-August. Peak fall migration occurs 25 August to 15 September and departure by 10 October (latest-23 November 1968, Chisago County).

Nesting Season Distribution: Ospreys are rare and local nesting species north of St. Croix and Washington counties. The largest concentration of breeding adults is near the Crex Meadows Wildlife Area in Burnett County. Sindelar (1971) observed at least four nests in Burnett and three in Polk counties in the late 1960's.

Winter: M. R. Olson observed an osprey near Hudson, St. Croix County, on 31 December 1970.

Habitat: Nesting ospreys use a variety of habitat types including acid bogs, open lakes, and riverbanks. One of the most important habitat requirements is the presence of dead trees used for nest sites. Variations occur in the size of the water body that attracts breeding pairs. Most breeding pairs I have observed nest near a small lake (usually < 20 ha), within 1.6 km of larger lakes. Large bodies of water within proximity of a nesting site serve as important feeding areas for nesting ospreys.


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