Each female with young defended a brood territory, but the sizes were not estimated. Monogamous, solitary nester, although 2 nests occasionally found in the same tree. Clutch size usually 6-11, most often 9. Precocial young tended by female only, but early broods may be accompanied by the male as well. Attains flight at 50-55 days, but may be abandoned long before that.
Drake sometimes defends territory against other species of ducks.
Most competition for nest cavities is from flickers and starlings, but mountain bluebirds, tree swallows, and flying squirrels also compete for nest sites. In 4 instances, Barrow's goldeneye has killed buffleheads attempting to use their nests. There are 5 records of nests containing eggs of buffleheads and eggs of common or Barrow's goldeneyes. Predation on nests is infrequent, and most predation probably is on fightless young. Tends to frequent shallow lakes with few or no fish.