Play Behavior Varies with Age, Sex, and Socioecological Context in Wild, Immature Orangutans (Pongo spp.)

Abstract

Play is thought to serve different purposes at different times during ontogeny. The nature and frequency of play are expected to change accordingly over the developmental trajectory and with socio-ecological context. Orangutans offer the opportunity to disentangle the ontogenetic trajectories of solitary and social play with their extended immature phase, and socio-ecological variation among populations and species. We evaluated the frequency of play in 39 immature individuals across two populations (Pongo pygmaeus wurmbii, at Tuanan, Borneo, and P. abelii at Suaq, Sumatra), age (0–11 years), sex, and social context, using more than 11 500 h of full-day focal observation data. We found independent age trajectories of different play types, with solitary object and solitary locomotor peaking before social play. Social play partners changed during ontogeny, and male immatures were more likely to engage in non-mother social play than females. Overall, social play was more frequent at Suaq than Tuanan, linked to the more frequent availability of partners. Furthermore, per time in association with conspecifics, Tuanan immatures were as likely to engage in social play as their peers at Suaq, suggesting similar intrinsic motivation. Increasing fruit availability correlated with both longer associations and increased social play frequency in the less sociable population of Tuanan, but not at Suaq. Our findings on orangutans support evidence from other species that different play types follow different developmental trajectories, vary with sex, social opportunities, and ecological context. Although drawing functional inferences is challenging, the distinct developmental trajectories reflecting adult sociability and behavioral repertoires may indicate that play serves several, non-mutually exclusive functions during ontogeny.

The ontogeny of play in a highly cooperative monkey, the common marmoset

“…We found that there was no significant difference between mothers and fathers with regard to the time they spent playing with their infants. In the species where parents do get involved in playful interactions, especially at a young age, these playful interactions are often exhibited with the primary caregiver i.e., mothers in chimpanzees Pan troglodytes (Pellegrini & Smith, 2005) or orangutans Pongo spp (Kunz et al, 2024). In species where males take an active role in immatures caretaking, they also show an important involvement in playful interactions, sometimes more than the mothers: In horses, stallions are the preferred play partners compared to the mothers and they also actively seek playful contact with their foals in contrast to the mothers (Šandlová et al, 2020).…”

“…A factor that could explain those differences between species is the presence or absence of other immatures. It has been suggested that immatures prefer playing with their peers, and will play with adults if there are no other options (Kunz et al, 2024;Pellis & Iwaniuk, 2000;Poirier, 1970). Ultimately it has been suggested that, by playing with infants, adults facilitate the immatures' acquisition of species-specific signals and skills employed in various social interactions (Enomoto, 1990;Mackey et al, 2014;Paquette & StGeorge, 2023;Sutton-Smith, 1993).…”

“…The fact that play behaviour almost disappears at a certain stage of an individual’s life indicates either that benefits from playing can only be gained during the immature period (Pellis et al, 2010) or that the costs are too high at a certain point (Pellis & Iwaniuk, 2000). Three main costs associated with play behaviour have been identified in the literature: increased predation risks (Harcourt, 1991; Hausfater, 1976), energetic expenditure (Kunz et al, 2024; Pellegrini et al, 1998) and risks of accidental and social injuries (De Oliveira et al, 2003). Unfortunately, only a few studies have directly investigated these risks and quantified the costs during play e.g., predated animals during play, energy loss in kilocalories, wounds after a play fight (Pellegrini et al, 1998).…”

“…We then explored infants’ partner preference, predicting that they would prefer to play with their parents initially and this would decrease over time to be replaced by twin play. Parent-infant play is age-sensitive and tends to be more prominent in young infants than juveniles (Amodia-Bidakowska et al, 2020; Kunz et al, 2024; Mackey et al, 2014; Paquette & StGeorge, 2023). In early studies on common marmosets (Voland, 1977) it has been found that immatures prefer to play with their twin rather than adults (Voland, 1977), but Stevenson & Poole (1982) suggested that partner preference depends on the age of the immatures and adults could be important play partners at an early stage of the infants’ development.…”