BIRDS OF THE ST. CROIX RIVER VALLEY 



57 



tion records are fewer and range from 6 August 1975 (Burnett County) to 

 12 October 1968 (Polk County). Most fall migration records occur 25 August 

 to 10 September. 



Nesting Season Distribution: During June and July 1978, up to three sepa- 

 rate pairs were observed regularly in St. Croix and northern Pierce counties. 

 Specifically, these pairs were near Oakridge Lake and near Erin Corners in 

 St. Croix County, and near the junction of County Highway W and Highway 

 29, 10 km west of River Falls in Pierce County. Attempts to locate nests 

 failed. These summer records are especially noteworthy because nesting 

 occurs yearly in nearby areas of Dakota County, Minnesota (Green and 

 Janssen 1975). 



Habitat: Most Swainson's hawks observed during migration are associated 

 with open habitats including Managed Grasslands and agricultural fields. 

 The birds observed in June and July 1978 were in an ecotone between 

 Managed Grassland and Southern Deciduous Forest. The Pierce County 

 pair was using a hayfield-woods ecotone. 



Rough-legged Hawk (Buteo lagopus) 



Status: Regular migrant and winter resident, accidental in summer. 



Migration: Fairly common migrant throughout the Valley, becoming common 

 at Crex Meadows, Burnett County, during the fall and early winter. Fall mi- 

 grants arrive about 20 September (earliest— 4 September 1974, Burnett 

 County; 15 September 1968, Pine County). Peak fall migration occurs 

 20 October to 15 November, with a gradual exodus from most northerly 

 locations occurring until 1 January. Spring migration begins in late Feb- 

 ruary in the Western Upland and migrants have reached the Northern High- 

 land by 20 March. Peak spring migration occurs 15 March to 15 April and 

 departure by 15 May (latest— 7 June 1975, Burnett County; 12 June 1975, 

 St. Croix County). 



Winter: Regular winter resident in the Western Upland and Central Plain. 

 Sporadic midwinter resident in the Northern Highland. Distribution and 

 abundance of wintering birds is highly dependent on small mammal popu- 

 lations and the severity of the weather. 



Habitat: Rough-legged hawks occupy open habitats almost exclusively. 

 Edges of agricultural fields, hayfields, native grasslands, and wet meadows 

 receive primary use. Occasionally, this hawk will be found in Northern Hard- 

 wood and Lowland Deciduous Forests. 



Ferruginous Hawk {Buteo regalis) 

 Status: Casual fall visitor. 



Records: W. Norling observed an adult at the Fish Lake Wildhfe Area, Bur- 

 nett County, on 25 October 1974. I observed an adult flying over the Oak- 

 ridge Waterfowl Production Area, St. Croix County, on 24 September 1978. 

 A 30 December 1967 record of a ferruginous hawk on the Suburban St. Paul 



