Sleep duration is affected by social relationships among sleeping partners in wild Japanese macaques.
Co-sleeping behaviour, such as sharing a sleeping site or bed, should play an important role in determining sleep structure in mammals by mitigating predation pressure and harsh abiotic conditions during sleep. Although environmental factors surrounding sleeping sites have been studied, there is very little information on the effects of the social environment within the site on sleep in animals other than humans. Here, we quantified the duration of nighttime sleep of wild primates during behavioural observations. Wild Japanese macaques (Macaca fuscata yakui) form clusters at sleeping sites, where they huddle with group members. Macaques slept for longer when huddled in sleeping clusters with natal members than in those with non-natal members. A high degree of synchronisation of wakefulness in pairs of macaques huddling in non-natal clusters suggested that their sleep was often interrupted by the wakefulness of huddling members at night. Our results suggest that familiarity and closeness to huddling partners influence sleep duration.
Department of Zoology, Graduate School of Science, Kyoto University, Sakyo-Ku, Kyoto 606-8502, Japan; Tropical Biosphere Research Center, University of Ryukyus, Nishihara, Okinawa 903-0213, Japan. Electronic address: kj.mochida@gmail.com.
Koji
K
Mochida
Department of Zoology, Graduate School of Science, Kyoto University, Sakyo-Ku, Kyoto 606-8502, Japan.
Mari
M
Nishikawa
D000375:Aging / Q000502:physiology; D000818:Animals; D005260:Female; D007398:Interpersonal Relations; D008251:Macaca / Q000502:physiology*; D008297:Male; D012621:Seasons; D012890:Sleep / Q000502:physiology*; D012919:Social Behavior; D014851:Wakefulness / Q000502:physiology
Macaca fuscata; Sleep disturbance; Sleeping partner; Social buffering; Social sleep behaviour