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NORTH AMERICAN FAUNA 73 



of young, and the first migrants reach the Western Upland 15-20 August. 

 Peak migration occurs 1-15 September. Departure from the Northern High- 

 land occurs 15-20 September and elsewhere by 1 October (latest— 5 October 

 1973, St. Croix County). 



Nesting Season Distribution: Common breeding bird in the Northern High- 

 land and that part of the Central Plain north of St. Croix Falls and Taylor's 

 Falls. South of that line, they are uncommon and local, and rare and local in 

 the Western Upland. Green and Janssen (1975) showed that the breeding 

 range of this warbler extended through the three Minnesota counties. On 

 26 June 1979, I heard and saw territorial males 4.8 km west of Taylor's 

 Falls, Chisago County. Although nests or young were not observed, I have 

 no doubt they nested in this area. 



Nests or young have been recorded in all subject Wisconsin counties 

 except Pierce. An area near the Cylon Marsh WildHfe Area (Sec. 15, T. 31 N., 

 R. 16 W.) and at the mouth of the Apple River (Sec. 20, T. 31 N., R. 19 W.), 

 St. Croix County, are the most southerly locations of regular occurrence. 

 Jackson (1943) recorded this warbler only "occasionally" in the Northern 

 Highland near Solon Springs in 1919, but BBS data (Table 6) show that 

 breeding chestnut-sided warblers occur commonly throughout the Valley 

 and that largest densities are in the Northern Highland. 



Habitat: Early successional stages of deciduous and coniferous habitats are 

 used for nesting. Deciduous Clear Cuts that are predominantly aspen sup- 

 port the greatest density of breeding chestnut-sided warblers. Northern 

 Hardwood Forest that is dominated by maple-basswood-aspen is also im- 

 portant. Recent attempts by State wildlife agencies to retard vegetational 

 succession by clear-cutting or selectively logging mature deciduous forest 

 are beneficial for this warbler. 



Bay -breasted Warbler {Dendroica castanea) 

 Status: Regular migrant. 



Migration: Uncommon to rare spring migrant in the Western Upland and 

 Central Plain; fairly common in the Northern Highland. Common fall 

 migrant throughout the VaUey. Spring migrants arrive in the Western 

 Upland 8-12 May, reaching the Northern Highland about 15 May. Peak 

 migration occurs 15-25 May and departure by 1 June. Jackson (1943) re- 

 ported that the collection of a female bay-breasted warbler at Danbury, 

 Douglas County, on 27 May 1919 was the only spring record obtained in 

 northwestern Wisconsin that year. Fall migrants arrive in the Northern 

 Highland in late July, reaching the Western Upland 10-15 August. Peak fall 

 migration occurs 1-20 September. Departure from the Northern Highland 

 occurs 20-25 September and elsewhere by 1 October (latest— 19 October 

 1968, Chisago County). 



Habitat: Bay-breasted warblers occupy a wide range of deciduous and conif- 

 erous habitats. In the Northern Highland they are most regularly observed 

 in Lowland Coniferous Forest or Black Spruce- Tamarack Bog. 



