BIRDS OF THE ST. CROIX RIVER VALLEY 



141 



near Afton State Park (Washington County). Occasional breeding season 

 records have been obtained at the mouth of the Apple River (St. Croix 

 County) and from lowland forest at Marine-on-St. Croix (Washington 

 County). Records away from the typical range of this warbler in the Valley 

 include two singing males on 2 June 1968 at Franconia, Chisago County, one 

 in Chisago County on 6 June 1971, and one male near Range, Polk County, 

 on 15 June 1968. 



Habitat: Breeding season observations of this warbler have been restricted 

 to Lowland Deciduous Forest. Predominant vegetation of these areas in- 

 clude mature stands of American elm, cottonwood, and green ash. 



Blackburnian Warbler {Dendroica fusca) 

 Status: Regular migrant and nesting species. 



Migration: Fairly common migrant in the Western Upland and Central 

 Plain, common in the Northern Highland. Spring migrants arrive 5-10 May, 

 reaching the Northern Highland 10-12 May. Peak spring migration occurs 

 15-25 May and departure from nonbreeding areas by 30 May. Jackson 

 (1943) considered this warbler "abundant" at St. Croix Falls (Polk County) 

 21-25 May 1919. Fall migration begins 10-15 August and the first birds 

 reach the Western Upland about 20 August. Peak fall migration occurs 

 5-15 September and birds depart by 25 September. 



Nesting Season Distribution: Uncommon breeding bird, restricted to the 

 Northern Highland. Breeding season records exist for Burnett, Douglas, 

 and Pine counties. The only confirmed nest records are from Pine (Green and 

 Janssen 1975) and Douglas (Chambers 1944) counties. However, it undoubt- 

 edly nests elsewhere in the Northern Highland. Jackson (1943) reported that 

 courting Blackburnian warblers were observed at St. Croix Falls on 24 May 

 1919. He noted that "although no nests were discovered . . . , the environ- 

 ment is favorable for nesting." Breeding Bird Survey data (Table 6) indicate 

 that this bird occurs in relatively low densities during the breeding season in 

 the Northern Highland. 



Habitat: The Blackburnian warbler is characteristic of northern coniferous 

 forests. Territorial birds are encountered most regularly in large tracts of 

 Lowland Coniferous Forest dominated by black spruce, white cedar, and 

 hemlock. Breeding birds also use Black Spruce-Tamarack Bogs and white 

 pine forest where remnants still exist. 



Chestnut-sided Warbler (Dendroica pensylvanica) 

 Status: Regular migrant and nesting species. 



Migration: Common migrant throughout the Valley. The mean date of 

 spring arrival in the Western Upland is 8 May (earliest— 2 May 1974, Pierce 

 County) and arrival in the Northern Highland by 12 May. Peak migration 

 occurs 10-25 May and birds have departed nonbreeding areas by 30 May. 

 Fall migration begins in the Northern Highland 5-10 August with dispersal 



