BIRDS OF THE ST. CROIX RIVER VALLEY 



155 



Upland and Central Plain, uncommon and local in the Northern Highland. 

 Breeding Bird Survey data (Table 7) suggest that the region of greatest 

 abundance is the Central Plain. Unfortunately, the Hudson BBS route does 

 not traverse large expanses of northern oriole habitat as this species is a 

 common breeding bird in that area. A recent increase in breeding popu- 

 lations is suggested by Jackson's (1943) statement that this species was 

 "nowhere common in the region except at St. Croix Falls," (Polk County). 

 Goddard (1972) reported a density of 20.7 pairs per 40 ha in the Kinnickinnic 

 River Valley, Pierce County. 



Habitat: The northern oriole is primarily a species of mature deciduous 

 forest. Also fairly common in ornamental plantings in residential areas. The 

 largest breeding populations occur in mature Northern Hardwood Forest 

 and Lowland Deciduous Forest. 



Rusty Blackbird {Euphagus carolinus) 



Status: Regular migrant and occasional early winter resident. 



Migration: Common spring and abundant fall migrant throughout the 

 VaUey. Spring migrants arrive in the Western Upland about 10 March and 

 reach the Northern Highland by 25 March. Peak spring populations occur 

 1-20 April and departure is by 5 May. Fall migrants arrive about 15 Sep- 

 tember, reaching peak populations 10-25 October. Most have departed from 

 the Northern Highland by 10 November and elsewhere by 1 December. 



Winter: Early winter records of this species consist primarily of small flocks 

 associated with lowland forest habitats. Christmas Bird Count data suggest 

 that early winter occurrences are restricted largely to areas adjacent to the 

 lower St. Croix River. However, one record of an individual on the Solon 

 Springs CBC was probably of a late migrant. During January and February, 

 single birds will occasionally frequent feeding stations, including one at a 

 Polk County feeder through 17 February 1959 (Winkler 1959). 



Habitat: The rusty blackbird is primarily a species of wetland habitats. Fall 

 concentrations of these birds are typically observed in large Alder Thickets, 

 Shrub Carr, or northern bog habitats. Edges of prairie wetlands are also 

 heavily used, primarily in the Western Upland. 



Brewer's Blackbird (Euphagus cyanocephalus) 

 Status: Regular migrant and nesting species. 



Migration: Fairly common spring and uncommon fall migrant throughout 

 the Valley. Spring migrants arrive in the Western Upland 10-15 March, 

 reaching the Northern Highland by 1 April. Peak migration occurs 

 10-30 April and departure from nonbreeding areas by 10 May. Fall mi- 

 grants arrive in the Western Upland 10-15 August. Peak fall populations 

 occur 25 August to 15 September and departure is by 10 October. 



Nesting Season Distribution: Fairly common to locally uncommon nesting 

 species in the Central Plain and Northern Highland. Roberts (1932) de- 



