60 



NORTH AMERICAN FAUNA 73 



considered reasons for their decline. 



Migration: Uncommon migrant throughout the Valley, most regularly ob- 

 served adjacent to the St. Croix River. Spring migrants arrive during the 

 second week of April (earUest— 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 Wildhfe 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 im- 

 portant feeding areas for nesting ospreys. 



FAMILY FALCONIDAE: Falcons 



Gyrfalcon (Falco rusticolus) 

 Status: Accidental, one record. 



Record: One was observed near Marine-on-St. Croix, Washington County, 

 on 24 December 1973 (Honetschlager 1974). 



Peregrine Falcon (Falco peregrinus) 



Status: Regular migrant and former nesting species. The U.S. Fish and 

 Wildhfe Service and WDNR (Les 1979) have Hsted this species as en- 

 dangered. Pesticides, habitat loss, and human harassment are among the 

 major causes of the decline. 



Migration: Rare migrant throughout the Valley. Spring migrants arrive in 

 the Western Upland 10-15 April (earliest— 4 April 1974, Pierce County) and 

 the Northern Highland 15-20 April. Departure from the Valley occurs 

 15-20 May. Fall migrants arrive 5-10 September and most observations 

 occur during 15-30 September and departure by 15 October. During fall 

 migration, the restored prairie on the refuge portion of Crex Meadows is the 

 most consistent area in the Valley to observe this raptor. 



