50 



NORTH AMERICAN FAUNA 73 



Habitat: Ruddy ducks are characteristic of semipermanently and perma- 

 nently flooded wetlands that are dominated by cattail, hardstem bulrush, 

 and river bulrush. Most wetlands occupied by breeding ruddy ducks vary 

 from 1-3 m deep. 



Hooded Merganser (Lophodytes cucullatus) 



Status: Regular migrant and nesting species, two winter records. 



Migration: Uncommon migrant throughout the Valley, fairly common 

 locally along heavily wooded lakes and streams in the Northern Highland. 

 Goddard (1972) reported that hooded mergansers made up 0.2% of the total 

 spring waterfowl population in St. Croix County. This low percentage 

 resulted from censusing prairie wetlands that are not utilized regularly by 

 hooded mergansers. Spring migrants arrive in the Western Upland 1-10 

 April (earliest— 23 March 1968, St. Croix County) and the Northern High- 

 land about 10 April (earUest— 14 March 1966, Burnett County). Peak abun- 

 dance occurs 20 April to 5 May and departure from nonbreeding areas 

 occurs by 15 May. FaU migration begins in early September in the Northern 

 Highland and migrants reach the Western Upland about 15 September. 

 Peak fall populations occur 15 October to 1 November and departure by 

 20 November. Peak fall populations in western Wisconsin range from 50 to 

 75 birds on important staging wetlands. 



Nesting Season Distribution: Fairly common (and local) breeding duck 

 throughout the VaUey. Hooded mergansers make up a small proportion of 

 the breeding population on prairie wetlands where the most intensive sur- 

 veys have been conducted. Lack of survey work along streams and in 

 wooded lake regions contributes to the poor understanding of their breeding 

 distribution. 



Winter: There are two winter records including one bird along the St. Croix 

 River near Grantsburg, Burnett County, on 9 January 1956 and one bird on 

 the Afton CBC on 1 January 1975. 



Habitat: In the Western Upland and Central Plain, breeding hooded mer- 

 gansers use heavily wooded river and stream habitats for breeding. An 

 abundance of dead trees providing natural nesting cavities is an important 

 component of their breeding habitat. In the Northern Highland, breeding 

 birds occupy large forest-bordered lakes and acidic bog-type lakes in addi- 

 tion to riverine habitats. 



Common Merganser {Mergus merganser) 



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



Migration: Common migrant throughout the Valley. Goddard (1975) 

 reported that common mergansers made up 0.1% of the total spring water- 

 fowl population in St. Croix County. This estimate reflects late dates of 

 censusing, which did not coincide with the peak migration period of this 

 bird, rather than an actual low population. Spring migration begins with a 



