The effects of late-summer wild-hay mowing on puddle-duck breeding populations, nest distribution, nest success, and breeding phenology In the year following mowing were studied at Lower Souris National Wildlife Refuge, North Dakota, during 1961-62. The effects of spring burning in 1960 are also cited. New growth on mowed meadows was only 2-6 inches tall when nesting began in residual cover (12-14 inches) on unmowed areas. Blue-winged teal (Anas discors) and gadwalls (A. strepera) made up 71 percent of the breeding puddle-duck population. During 1960-62, there were 13 percent fewer pairs of these and five other puddle-duck species along mowed and burned areas than where cover was untouched, but the difference was not statistically significant. Nest densities were greater in areas where residual cover was undisturbed. Few gadwalls nested in mowed meadows, but they nested readily In unmowed shorelines and roadsides along mowed areas. Blue-winged teal nests were common in mowed meadows. Nesting success differed significantly between cover types butnotbetween mowed and unmowed meadows. Late nest-initiation dates and reduced clutch sizes suggested that late-nesting hens used mowed areas. Mowing may have redistributed breeding ducks without reducing the total population. Regional water conditions may have been more important than mowing in determining the size of the local population.