Play behaviour of wild grey seals (Halichoerus grypus) : effects of haulout group size and composition

Burghardt’s Surplus Resource Theory of Play states that long periods of immaturity and parental care are among the most important conditions for play to occur among young individuals. Grey seals (Halichoerus grypus) are polygynous, sexually dimorphic marine mammals. Young individuals are known to be social and playful—especially males, who do not take an overt part in breeding colonies until they are at least 8 y old. However, unlike most other social species, the lactation period of grey seals is short, with abrupt weaning, and no parental provisioning is provided afterward. We hypothesized that haulout group size of grey seals should have a positive effect on their social play because it provides indirect protection of young playful individuals. Social play behavior of a haulout group of grey seals of various ages and both sexes was observed during the nonbreeding season in Abertay Sands, Scotland. Adult individuals made up approximately 80% of the haulout group, and males were predominant. There was a moderate positive relationship (R = 0.46, p < 0.0001) between social contacts (number of play interactions between two individuals) and group size. The majority of play interactions were observed during the second hour of group formation when young individuals started to join the group. Group size is an important factor that increases vigilance, provides indirect protection for young individuals, and helps them acquire the necessary skills and physical condition for the breeding season.