Predation by mink (Mustela vison) on three types of ducks (captive, pen-reared-released and wild) was documented in two studies at the Northern Prairie Wildlife Research Center, Jamestown, North Dakota. In the first study, 36 of 60 flightless adult and juvenile ducks held on eight 0.1-acre experimental ponds disappeared between 10 July and 4 August 1969. Available evidence indicated that all were killed by a large adult mink. The mink selected recently released incubator-hatched ducklings, females in the process of incubating, and adults and juveniles on a marginal food supply.In the second study, 152 wood duck ducklings (Aix sponsa) were released on a 76-acre marsh during 1971. Half of the ducklings, when 24 to 27 days old, were placed at weekly intervals in four floating pens and allowed to escape after 4 days. Each time birds were placed in the floating pens, a comparable group was placed in a predator-proof shoreline pen. Birds in the shoreline pen escaped as they learned to fly when approximately 60 days old. The shoreline of the marsh was periodically searched, and the remains of 21 (28%) of the floating-pen birds were identified in food remains found at 16 mink dens. No remains of birds from the shoreline pen were found at the dens. Coots (Fulica americana) were also taken commonly. Wild ducklings appeared to have been almost totally consumed, but the legs and feet of the wood ducks were often left uneaten because of bands and tags.