BIRDS OF THE ST. CROIX RIVER VALLEY 



37 



populations occur 5-15 April; 6,000 to 8,000 birds are commonly observed in 

 St. Croix County. Movement of nonbreeding mallards is rapid after peak 

 periods; departure is by 1 May. 



Fall migration begins 1-10 September with formation of local feeding 

 flocks of adults and juveniles. Movements of migrants into the region begins 

 about 20 September; peak populations occur 20 October to 1 November, 

 Concentrations at Crex Meadows, Burnett County, have surpassed 11,000 

 twice (11,500 on 30 October 1967 and 15,000 on 3 November 1964). 

 Recently, use of two refuges in St. Croix County has resulted in large num- 

 bers of mallards exceeding 10,000 (largest, 13,500 on 20 October 1977). 

 Movement from the region is dependent on weather conditions. Departure of 

 the largest number of birds occurs by 20 November and those not wintering 

 have departed by 15 December. 



Nesting Season Distribution: Common breeding duck throughout the 

 region; nesting has been reported from all counties. Most research has cen- 

 tered on breeding populations in the pothole region of St. Croix and southern 

 Polk counties, and at Crex Meadows. In the former area, Peterson (1978) 

 estimated a breeding population of mallards of nearly 1.4 pairs per km^ At 

 Crex Meadows, the estimated number of mallard breeding pairs on water- 

 fowl survey transects ranged from 7 in 1973 to 55 in 1977 (WDNR files). 



Winter: Common wintering duck wherever open water is available. Large 

 early winter flocks are usually associated with open water areas along the 

 St. Croix River. Cooper and Johnson (1977) reported that 75 to 200 mallards 

 wintered near Afton, Washington County, from 1974 to 1977. Substantial 

 wintering populations are also known to occur along the Kinnickinnic River 

 in Pierce County and southern St. Croix County. 



Habitat: Nesting mallards occupy a variety of wetland classes ranging from 

 sedge meadows and acidic bogs to permanently flooded wetlands. Nesting 

 pairs also use lowland forest habitat along rivers and streams, man-made 

 impoundments, and stock-watering ponds created by the Soil Conservation 

 Service. With the almost complete destruction of native grassland habitat, 

 these ducks now commonly nest in hay lands and oat and corn fields. Several 

 thousand acres of Managed Grasslands have been established by govern- 

 ment agencies to provide dense waterfowl nesting cover. 



Black Duck {Anas rubripes) 



Status: Regular migrant, nesting species, and winter resident. 



Migration: Uncommon spring migrant in all regions; fairly common in the 

 fall in the Northern Highland and locally at the Crex Meadows WildUfe 

 Area, Burnett County. Spring migrants arrive along the St. Croix River 

 about 15 March, generally moving to natural basin wetlands 1-10 April. No 

 peak spring concentrations of black ducks have been noted, although they 

 are most frequently observed 10-25 April. Departure from nonbreeding 

 areas usually occurs by 15 May. Stragglers have been noted during late May 

 and throughout the summer, primarily in the Western Upland. 

 Fall migrants arrive in the Western Upland 5-10 September. Peak fall 



