Survival, Movements, and Habitat Use of Mallard Broods Produced on Overwater Nesting Structures in Eastern South Dakota

Survival, movements, and habitat use of mallard (Anas platyrhynchos) broods produced from overwater nesting structures in eastern South Dakota were evaluated during spring and summer 1998-99. Two study sites with overwater nesting structures were chosen in 1998, representing a large semipermanent marsh (Mickelson) and a complex of wetlands (Oakwood). A third site, representing a medium-sized semi-permanent marsh (Redetzke), was added in 1999. Eighty-six females and 58 day-old ducklings were radiomarked. Brood survival was high at Oakwood (71%), Mickelson (100%), and Redetzke (80%). Duckling survival was 0. 424 ± 0. 057 to 38 ± 18 �ays at Oakwood (years pooled), 0. 733 ± 0. 035 to 40. 5 ± 14.S days at Mickelson (years pooled), and 0. 467 ± 0.077 to 42 ± 22 days at Redetzke. Survival was significantly higher at Mickelson than at Oakwood (X2 = 21.341, ldf, P \u3c 0.001) or Redetzke (X2 = 9. 890, ldf, P = 0. 002). Date of nest exodus and initial brood size were identified as potentially affecting brood survival. No broods left Mickelson during rearing. Twenty of 23 (86. 9%) and 16 of 18 (88. 9%) made interwetland moves at Oakwood and Redetzke, respectively. Broods averaged between 1 and 2. 250 overland and 1. 143 and 2. 2 non-overland moves per week during rearing. Per brood overland movement distance was highest in weeks 1 - 3 and 8, while non-overland movement distance per brood peaked in weeks 1 and 4. Eleven of 36 broods moved \u3e 1 km. Broods at Oakwood and Redetzke used 1 - 6 different wetlands during rearing (x = 2. 355 ± 0. 189), and utilized semi-permanent wetlands 100% and 64. 7% of the time, respectively (Stewart and Kantrud 1971). Use of seasonal, semi-permanent and permanent wetland basins matched basin availability at Oakwood and Redetzke. Broods at Oakwood used wetlands with mean percent vegetative coverage of 30 - 39% percent cover, while percent cover at Redetzke brood marshes averaged 60 - 69%. Cattail dominated all sites. Brood and duckling survival appear higher than previously reported in peer reviewed literature. Numerous factors, including interspersion of emergent cover and presence of off shore loafing areas, may have contributed to higher survival at Mickelson. Throughout the rearing period, broods made similar numbers of interwetland moves, but for shorter distances than previously documented. High wetland densities and high water conditions likely contributed to short movements and high use of semipermanent wetlands. These data reinforce the need to protect a variety of wetland habitats, though large areas with water control structures may provide quality brood rearing areas when properly managed. Additional research evaluating micro-habitat use by mallard broods may allow for better determination of factors affecting survival, and would provide greater insight into mallard brood ecology