Characteristics of Wetlands Used by Breeding Diving Ducks in Eastern South Dakota

Two extensive roadside surveys were conducted along 29 east-west transect routes in 1 995 to determine the distribution and habitats of diving ducks in eastern South Dakota. Redheads (Aythya americana) and ruddy ducks (Oxyurajamaicensis) were the primary breeding species of diving ducks in eastern South Dakota in 1995 and 1996. Canvasback (Aythya valisineria) and lesser scaup (Aythya affinis) broods were uncommon. Distributions of diving ducks were clumped in the northern portions of the Missouri and Prairie Coteau while voids in distributions occurred in the Big Sioux River drainage, and the west-central and southeastern portions of eastern South Dakota. Wetland water regime was the only significant variable in a stepwise logistic regression of wetland habitats. Permanent, semipermanent, and seasonal wetlands with vegetation structure were the primary habitats of both diving duck adults and broods. Two assumptions of the annual USFWS Breeding Population Survey were shown to be erroneous for diving ducks in eastern South Dakota in 1 995 and 1 996. The timing of the survey did not accurately assess eastern South Dakota\u27s breeding diving duck populations. During the USFWS Breeding Population Survey, lesser scaup and ringnecked duck (Aythya collaris) breeding numbers were overestimated while ruddy ducks were underestimated. In 1995, species composition changed dramatically for lesser scaup from the annual USFWS Breding Population Survey (42.2%) to brood data from survey 2 (4.9%). In 1996, 5 consecutive surveys were conducted along 11 transect routes from 1995 routes to confirm and evaluate when migrant lesser scaup and ring-necked ducks exited the state. Lesser scaup showed a precipitous drop in numbers counted (n=2,096) in survey 1 (l 3 May - 16 May) to numbers counted (n=l 92) in survey 2 (22 May - 31 May), suggesting an exodus from the state in late May. Distributions of diving ducks in eastern South Dakota show voids in large areas (southeastern South Dakota) and clumping in the northern portion of the coteau regions. Differences were found in densities of diving ducks when the survey transect counts were divided into three nearly equal units from south to north. The findings of this study suggest that densities of diving ducks are not homogeneous across large areas. Land use changes may have altered wetland habitats available to waterfowl since strata boundaries were delineated warranting further investigation into the assumption of homogeneous duck density across large areas. Managers should also recognize that lesser scaup and ring-necked ducks are not breeding in the numbers estimated during the annual USFWS Breeding Population Survey. The inclusion of transient lesser scaup and ring-necked ducks into the population indices inflates breeding population estimates. Waterfowl managers rely on population estimates as a tool in monitoring population trends and the setting of hunting regulations. Effective species management for all ducks relies on the validity of the information provided. Our findings indicate that assumptions for the annual USFWS Breeding Population Survey warrant further investigation in order to provide accurate information to base management decisions