BIRDS OF THE ST. CROIX RIVER VALLEY 



51 



noticeable influx about 20 February. Spring populations build rapidly 

 through March reaching peak numbers 20-30 March and most birds have 

 departed by 30 April. Fall migrants arrive in the Northern Highland 20-30 

 September and reach the Western Upland about 10 October. Peak fall popu- 

 lations occur 10 November to 1 December and non wintering birds have 

 departed by 15 December. During peak fall periods, up to 1,000 individuals 

 have been recorded along the lower St. Croix River in Washington County. 



Winter: Uncommon winter resident of the lower St. Croix River and along 

 open stretches of water on major tributaries. The largest group recorded on 

 the Afton CBC was 65 birds on 1 January 1958. Winter populations are 

 directly related to the severity of winter weather. During 1974-75, groups of 

 30 to 35 common mergansers were regularly observed along the St. Croix 

 River through late December and early January. The record cold of 11 

 January 1975 (-40 °C), froze nearly the entire river system and common mer- 

 gansers were not observed again until mid-February when the first migrants 

 returned. 



Summer; Three common mergansers were observed in Chisago County on 16 

 June 1975 (Eckert 1976), and a lone male was observed near New Richmond, 

 St. Croix County, on 27 June 1975. These birds undoubtedly were lingering 

 migrants. 



Habitat: Primarily a species of large, deep, permanently flooded wetlands 

 and the major rivers of the VaUey. 



Red-breasted Merganser [Mergus serrator) 



Status: Regular migrant, two summer and one winter records. 



Migration: Fairly common migrant throughout the Valley, occasionally 

 common on larger lakes of the Central Plain. Goddard (1975) reported that 

 red-breasted mergansers made up only 0.3% of the total spring waterfowl 

 population in St. Croix County. This estimate indicates that censuses were 

 concentrated on smaller wetlands and were not conducted to coincide with 

 peak migration. 



Spring migrants arrive in the Western Upland about 20 March and reach 

 the Northern Highland 1-10 April. Peak spring migration occurs 10-25 

 April and departure by 15 May. Fall migrants arrive in the Northern High- 

 land 20-30 September and reach the Western Upland about 10 October. 

 Peak fall populations occur 25 October to 15 November and departure by 10 

 December. During the peak of fall migration, concentrations of 50 to 75 

 birds are typically recorded on important staging wetlands. 



Summer: A lone female was observed at Crex Meadows, Burnett County, on 

 1 July 1955. In Washington County an injured bird was observed 24 June 

 1975 (Eckert 1976). 



Winter: A group of four was observed on the St. Croix River on the Afton 

 CBC, 1 January 1975. Five were observed in St. Croix County on 5 January 

 1942 (Barger 1942). 



Habitat: Red-breasted mergansers are characteristic of large, deep-water 



