BIRDS OF THE ST. CROIX RIVER VALLEY 



119 



grants arrive in the Western Upland during the first 10 days of March, 

 reaching the Northern Highland 15-25 March. Peak spring migration 

 through the Valley occurs 25 March to 15 April. Fall migration begins 

 during late August with the formation of loose feeding flocks. Peak fall 

 migration occurs 15 September to 10 October and most have departed by 

 1 November. During the peak of fall migration, flocks of 50 to 75 individuals 

 are regularly encountered and occasional groups of 200 to 250 have been re- 

 corded. 



Nesting Season Distribution: Abundant nesting species in the Western 

 Upland and Central Plain, common in the Northern Highland. Jackson 

 (1943) considered the American robin abundant throughout northwestern 

 Wisconsin in 1919. Breeding Bird Survey data (Table 5) show that the Amer- 

 ican robin is by far the most numerous nesting thrush in the Valley. God- 

 dard (1972) recorded a nesting density of 18.4 pairs per 40 ha in the Kin- 

 nickinnic River Valley, Pierce County. 



Winter: This species is fairly well distributed throughout the Valley; several 

 midwinter records exist from Burnett, Douglas, and Pine counties. Amer- 

 ican robins are regularly observed during midwinter in the Western Upland 

 and appear to be dependent on trees and shrubs (mountain ash, cedar) that 

 retain their fruits throughout the period. 



Habitat: Breeding American robins are found in nearly all habitat types in 

 the Valley. This species has adapted well to man's continued alteration of 

 the Valley and is a common breeding species in park-like Residential Habi- 

 tats. The estabUshment of Pine Plantations, particularly in the Western 

 Upland and Central Plain, has provided increased areas of excellent 

 nesting habitat. 



Varied Thrush (Ixoreus naevius) 

 Status: Casual winter visitor. 



Records: This western thrush has been recorded in the Valley at least seven 

 times. Minnesota records include one at Stillwater, Washington County, 

 from mid-December to 30 March 1974 (Eckert 1974). Additional Wash- 

 ington County records include single birds on 3 January 1976, late No- 

 vember 1976, and 9 January 1977. Longley (1967) observed a single bird in 

 Chisago County on 13 November 1966. Records from the Wisconsin 

 counties include one bird at Osceola, Polk County, from early December 

 1948 until 21 April 1949 (Simmons 1949). One apparently wintering bird re- 

 mained near Grantsburg, Burnett County, from 12 November 1963 to mid- 

 March 1964 (Bauers 1964). 



Habitat: Varied thrushes in this region are usually found at feeding stations. 

 Surrounding habitats include Southern Deciduous Forest composed pri- 

 marily of Hill's and white oak and brushy edges. 



Wood Thrush {Hylocichla mustelina) 

 Status: Regular migrant and nesting species. 



