BIRDS OF THE ST. CROIX RIVER VALLEY 



33 



Migration: Uncommon migrant in the Western Upland and Central Plain. 

 First spring migrants arrive 5-10 May and are most frequently observed 

 20-25 May. Fall migration begins 15-25 August and departure by 25 Sep- 

 tember. 



Nesting Season Distribution: Uncommon nesting species in the Western 

 Upland, uncommon to rare and local in the Central Plain. Documented 

 breeding records exist for St. Croix County (three nests), Polk County (one 

 nest), and Burnett County (one nest). Summer observations of adults in Chi- 

 sago and Washington counties provide inferred evidence of nesting in those 

 counties. 



Habitat: Principal nesting habitat of the least bittern includes semiperma- 

 nently and permanently flooded wetlands. Nests observed in St. Croix and 

 Polk counties were in extensive stands of hardstem bulrush and river bul- 

 rush. The Burnett County nest was in a mixed stand of cattail and river 

 bulrush. 



American Bittern (Botaurus lentiginosus) 



Status: Regular migrant and nesting species, accidental in winter. 



Migration: Fairly common spring and fall migrant in the Western Upland 

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

 migrants arrive 10-20 April (earUest— 4 April 1974, Burnett County), reach- 

 ing peak abundance 1-5 May. Fall migration begins about 15 August in the 

 Northern Highland and 25 August to 1 September elsewhere. Peak numbers 

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

 20 September to 1 October; departure elsewhere is 10-25 October. 



Nesting Season Distribution: Fairly common and well distributed in all 

 regions. Breeding pairs occur with greatest frequency in the prairie wetland 

 region of St. Croix, Polk, and Washington counties, and at Crex Meadows, 

 Burnett County. Documented nest records exist for St. Croix, Polk, Bur- 

 nett, and Washington counties. Evidence of nesting exists for the remaining 

 counties. Jackson (1941) reported flushing one American bittern from a 

 marsh at the headwaters of the St. Croix River in Douglas County on 8 Au- 

 gust 1919. 



Winter: Wayne Norhng observed a single bird at Crex Meadows, Burnett 

 County, on 9 January 1976. 



Habitat: American bittern breeding habitat use varies with geographic 

 province. Typical breeding habitat in Western Upland includes seasonally, 

 semipermanently, and permanently flooded wetlands. Vegetation associated 

 with these wetlands includes river bulrush, cattail, softstem bulrush, hard- 

 stem bulrush, and phragmites. Preferred habitat in the Central Plain is simi- 

 lar with a higher percentage of reed canary grass in seasonally flooded wet- 

 lands. Occasionally this species uses upland fields including Haylands, oat 

 fields. Managed Grasslands, and retired cropland for nesting. In the north- 

 ern regions of the Central Plain and throughout the Northern Highland, 

 breeding habitat includes cattail-bulrush marshes. A high percentage of 



