Do pairs exhibit similar behaviours? Evaluating inter-individual synchrony in activities of Magellanic penguins

Animal welfare is a key priority in modern zoos and aquariums, with behavioural observations widely adapted as practical and effective methods for its assessment. Although increasing attention has been given to inter-individual interactions within a group, which can enhance animal welfare, such studies remain limited due to logistical constraints associated with conducting continuous behavioural observations alongside individual identification. Penguins, in particular, present significant challenges, as they are typically housed in groups and spend part of their time in aquatic environment. In this study, we employed animal-borne data loggers to record the on-water and on-land activities of captive Magellanic penguins Spheniscus magellanicus . The aim was to examine the behavioural synchrony of paired individuals, presumed to share close bonds, and consequently to explore which behavioural parameter could serve as a proxy for inter-individual affinity. On-water and on-land activities were monitored using immersion sensors attached to the flipper bands of 23 penguins, including three bonded pairs, at Sumida Aquarium, Tokyo, Japan, from 11 October 2022–9 October 2023. To assess inter-individual synchrony, kappa coefficient values were calculated for all unique pairwise combinations. Synchrony within pairs was relatively low during the breeding period but increased significantly during the non-breeding period, with on-water activity showing a marked tendency to be distinctly higher within pairs compared to non-paired individuals, serving as a proxy for inter-individual affinity in penguins. Additionally, simulated pseudo-observations suggested that approximately 250 intermittent observations of on-water instances are required to reliably detect substantial behavioural synchrony among individuals, which offers an alternative methodology that is both practical and suitable for daily observation settings by keepers. This study revealed significant synchrony in on-water activity during the non-breeding period within pairs; however, no data were available regarding inter-individual distances or other relevant interactions. Therefore, further research is needed to investigate spatial proximity and social interactions in greater detail to gain deeper insights. • Activities of multiple penguins were recorded simultaneously by animal-borne devices. • Pairs exhibited marked synchrony in aquatic activity during the non-breeding period. • Synchrony in on-water activity serves as a proxy for affinity among individuals. • Ad hoc observations of co-occurring frequency on water may reveal social affinity.