140 



NORTH AMERICAN FAUNA 73 



1 January 1975 (Washington County). It is not known if these birds re- 

 mained throughout the winter. 



Habitat: During migration, this warbler is ubiquitous, occurring in essen- 

 tially all available habitats. Breeding season records include birds from 

 extensive stands of Lowland Coniferous Forest, dominated by white spruce, 

 from Black Spruce-Tamarack Bogs, Jack Pine Barren, and areas of mature 

 white pine. Both habitats are used extensively by nesting yellow-rumped 

 warblers within their normal breeding range in northern Minnesota and Wis- 

 consin. 



Black-throated Green Warbler {Dendroica virens) 

 Status: Regular migrant and nesting species. 



Migration: Uncommon migrant throughout the Valley, locally common in 

 the Northern Highland. Spring migrants arrive in the Western Upland 

 5-10 May, reaching the Northern Highland 10-15 May. Peak spring migra- 

 tion occurs 15-25 May and nonbreeders have departed by 30 May. Fall 

 migration begins in the Northern Highland 15-20 August and the first 

 migrants reach the Western Upland 25-30 August. Peak fall migration 

 occurs 5-20 September and departure by 5 October (latest— 7 October 1973, 

 St. Croix County). 



Nesting Season Distribution: Uncommon breeding bird in the Northern 

 Highland. Rare and local in southern Pine, Burnett, and northern Polk and 

 Chisago Counties. Jackson (1943) reported this warbler as "not uncommon" 

 at Solon Springs, Douglas County. On BBS transects (Table 6) black- 

 throated green warblers have been recorded only on the Minong route, 

 Douglas County. This warbler was recorded on 9 June 1973 in Chisago 

 County (Longley 19736), but no evidence of nesting was obtained. 



Habitat: Mature Northern Hardwood Forest dominated by sugar maple, 

 basswood, and trembUng aspen is used extensively. The large expanses of 

 Lowland Coniferous Forest, primarily adjacent to the upper St. Croix River, 

 are also important. 



Cerulean Warbler (Dendroica cerulea) 

 Status: Regular migrant and nesting species. 



Migration: Rare spring and fall migrant, restricted primarily to the Western 

 Upland and a small region of the Central Plain. Spring migrants begin to 

 arrive 10-15 May. Most observations are after 15 May and are probably of 

 birds on breeding territories. Data are too few to establish fall migration 

 periods. The latest date available is 16 August 1974 in St. Croix County. 



Nesting Season Distribution: Rare and local breeding bird. Confirmed nest 

 records exist only for St. Croix County. On 23 June 1976, I observed adults 

 feeding two young in the nest along the Willow River near Hudson (T. 29 N., 

 R. 19 W.). Cerulean warblers occur regularly only in the lower reaches of the 

 Kinnickinnic River (Pierce County) and Willow River (St. Croix County) and 



