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NORTH AMERICAN FAUNA 73 



val in the Western Upland is 8 May (earliest— 1 May 1976, St. Croix County) 

 and migrants reach the Northern Highland 10-15 May. Peak migration 

 through the Valley occurs 15-25 May. Fall migration begins 10-15 August. 

 Peak fall migration occurs 20 August to 5 September and departure by 

 20 September. Peak fall migration in the Western Upland occurs 10-20 Sep- 

 tember and departure by 1 October. 



Nesting Season Distribution: Fairly common to locally common nesting 

 species in the Western Upland and Central Plain, rare to locally uncommon 

 in the Northern Highland. Jackson (1943) considered this vireo to be un- 

 common when compared with the red-eyed vireo in northwestern Wisconsin. 

 Bernard (1967) described this species as a "regular but generally uncommon 

 summer resident" in Douglas County. Breeding Bird Survey data (Table 6) 

 indicate a fairly constant abundance throughout the Valley. Nesting has 

 been documented in all counties. 



Habitat: Characteristic nesting species of mature Lowland Deciduous 

 Forest. Highest breeding densities occur in that habitat and mature North- 

 ern Hardwood Forest. Other habitats frequently used include Southern 

 Deciduous Forest, Deciduous Clear Cuts, and Residential Habitats. 



FAMILY PARULIDAE: Wood Warblers 



Black-and-white Warbler (Mniotilta varia) 

 Status: Regular migrant and nesting species. 



Migration: Fairly common migrant throughout the Valley. Jackson (1943) 

 reported that the black-and-white warbler was "the most abundant of 

 warblers" during the 1919 spring migration in Polk and Burnett counties. 

 EarUest spring migrants arrive in the Western Upland during the last 

 5 days of April, reaching the Northern Highland 1-5 May. Peak migration 

 occurs 10-20 May, and nonbreeders depart by 25 May. Fall migration 

 begins in mid- August and birds reach the Western Upland 20-25 August. 

 Peak fall migration occurs 10-20 September, and most have departed by 

 5 October. 



Nesting Season Distribution: Uncommon and local nesting species, most fre- 

 quently encountered in the Northern Highland. Green and Janssen (1975) 

 indicated the breeding range of this warbler extended into northern Wash- 

 ington County. My Minnesota breeding season records have been obtained 

 only in southern Pine County. Confirmed nesting records exist only for Polk 

 County (12 June 1975). Breeding Bird Survey data (Table 6) suggest a rapid 

 increase in relative abundance moving northeast through the Valley. The 12- 

 year mean number of males recorded on Dresser BBS is <0.1, increasing to 

 1.3 on the Loraine BBS, and 6.9 on Minong. 



Habitat: Territorial males have been recorded in both deciduous and conif- 

 erous habitats during the breeding season. In deciduous areas, a preference 

 is shown for mature Northern Deciduous Forest, characterized by extensive 

 stands of maple and basswood. This species apparently prefers Northern 



