Proximate mechanisms and relational history: the interdependence of food transfers in socially housed orang-utans (Pongo abelii)

Abstract

Animals can transfer food between each other through both competition (theft) and cooperation (sharing). Analysing patterns of food transfers can thus yield valuable insights into animals’ social dynamics, e.g. intragroup competition and cooperation. Previous studies on food transfers in our closest living relatives, the great apes, have mainly focused on ultimate explanations for food sharing and analysed food transfers as independent events with a focus on frequencies and types of transfers. In this study, we focus on the influence of contextual variables and the directly preceding interaction on food transfer attempts. We provided one monopolizable food bag per session (10 sessions each in 2010, 2012, 2014 and 2016) to orang-utans housed in the same enclosure ( N = 12) and coded the subsequent transfers and transfer attempts of food items from the bag ( N = 3207). We divided transfer attempts into four different categories (taking, co-feeding, requests, offers) and found comparable frequencies as in previous studies on food sharing in great apes. We present four models that investigate to what extent food transfer attempts influence the subsequent transfer attempt within a dyad with regards to probability of a successful transfer, choice of transfer strategy, time between two transfer attempts and probability of resistance by the food possessor. Our analyses show that characteristics of the previous interactions (e.g. success, resistance by the food possessor) and the current interaction (e.g. being in view of the food possessor, food location) affected both the behaviour of the initiator of a transfer attempt and of the food possessor. These results highlight how the behaviour of orang-utans is influenced by the preceding interaction within a dyad and by several other context-specific cues. This shows that orang-utans keep track of their most recent interaction with the same partner and take that into account towards calibrating their next interactional moves. • Orang-utans flexibly used cooperative and competitive strategies to transfer food. • Proximate mechanisms explain changes in strategies, delays, success and resistance. • Food transfers within a dyad were not independent events. • Food transfers were influenced by the preceding interaction within each dyad. • These results reveal orang-utans’ cognitive flexibility and relational intelligence.