Developmental changes in the frequency of occurrence of some 23 action patterns were studied in pairs of coyotes, wolves, dogs and their hybrids. Over 4,300 entries were recorded from days 24–42 (85.5 h observations in toto). All subjects showed a decrease in contactual behaviors from 24–30 days, and a subsequent increase in play fighting and chasing. In all species, with the exception of the coyotes, the bite was inhibited and play behavior was recorded from 24 days onwards, but only after the 30th day in the coyotes. Species differences in occurrence and frequency of certain action patterns were evident in the wolves, coyotes and dogs, and these differences were also reflected in their hybrids.