Play behaviour during early ontogeny in free-ranging dogs (Canis familiaris)

Twenty-four free-ranging dog puppies belonging to six litters were observed from birth to 13 weeks of age to study the play behaviour in early ontogeny. Only a single annual breeding cycle with synchronized breeding season was recorded in this study. Mean litter size was 6.67 ranging from 5 to 8 with a male-biased sex ratio of 1.22:1. Social investigation was first observed with 3 weeks of age, and then subsequently developed other play behaviours (play-fighting, play-mounting, aggressive play, objects play and pseudo-sexual play). The litters were significantly different from each other in relation to the number of total play bouts (χ2 = 475.42, d.f. = 5, P < 0.005). The puppies within the litters as well as among the litters were significantly different from each other in relation to the frequency of play bouts. There was a positive correlation between the frequency of play bouts and the number of the puppies within the litters (r = 9970, P < 0.005). All the play behaviours showing weekly variations increased with the age of the puppies, but it suddenly decreased in weeks 9 or 10, and continued thereafter. Male puppies initiated playful interactions with a greater frequency than did female puppies. Except in the case of aggressive play, male puppies initiated play more often with female puppies and vice versa showing the evidence of inter-sexual play in free-ranging dogs. Intra-sexual dominance relationships among the littermates developed between 5 and 13 weeks of age.