R.E. Johnson 1967 March 19 Stinson Beach, Marin County, California - waterways adjacent to mudflats exposed by low tide. 2:00 PM. Warm, scattered clouds. Groups of ruddy ducks (mixed ?♀?♂) move together, first swimming south down waterway & then turning more or less as a group and swimming back again. Turns are often concurrent with meeting another group coming toward them. There may be some interchange of group members or groups may join. If groups both turn, some individuals appear undecided as to which group to follow since they will turn & follow each briefly before finally joining one group. Males (white cheek patch) are in various stages of plumage. Some have blue bills, others do not (a few have reddish feathers on back). Birds are mostly floating with head out, but a few have bills tucked in behind wing. Birds with bills tucked swim with group & appear to have no trouble navigating or turning with group. Why, then, do they tuck their bill? Only 2 or 3 dives were noticed in an hour among a group of 30+ ducks. Some birds swim with tail up (angle differs between individuals) and others with tail beneath water level (but visible just below water). This does not appear to be correlated with stage in molt or with sex. No individual was seen to swim with tail under - tail out.