What makes wild chimpanzees wake up at night?

Abstract

I examined the possible cause of night awakening among wild chimpanzees (Pan troglodytes) in Mahale Mountains National Park, Tanzania. Chimpanzee vocalizations and activity-related sounds (CVSs) were used to indicate awakening because I was unable to visually observe them. Over a 5-night observation period, CVSs (n = 128) were heard every night, and most (n = 91) were observed within 5 min of previous CVSs. Chimpanzees use CVSs as social communication to maintain spatial contact with other chimpanzees who occasionally travel at night. The first sound in a sequence of CVSs (CVS bout) was heard immediately following the vocalization or sound of another animal (n = 11), defecation or urination by a chimpanzee (n = 7), or unknown (n = 19). CVS bouts were longer when preceded by defecation or urination than when preceded by the vocalization or sound of other animals or an unknown factor. This suggests that the degree of wakefulness varies according to the possible cause of the disturbance. CVSs at night may be provoked by various factors, and awakening during the night is probably common among diurnal primates.

Nocturnal behavior by a diurnal ape, the West African chimpanzee (Pan troglodytes verus), in a savanna environment at Fongoli, Senegal

“…I began data collection when low‐light conditions required using a flashlight (with red bulb) to write. Unlike Zamma (), I did not use chimpanzees’ nesting behavior as an indication to start data collection on nocturnal behavior, as Fongoli chimpanzees often nested well after dark, especially during the dry season. Therefore, data collection included behavior that occurred before nesting began but after darkness fell as well as behavior following nesting, presumed sleeping and then waking.…”

“…Reports of nocturnal activity by wild, diurnal primates are mainly anecdotal and include reports of vocalizations as well as activity such as foraging or traveling. Numerous studies have reported nocturnal movement for diurnal primates ( Alouatta pigra : Dahl & Hemingway, ; Cebus capucinus : cited in Bearder et al, ; Theropithecus gelada : Kawai & Iwamoto, ; Macaca mulatta : Vessey, ; M. fuscata : Nishikawa & Mochida, ; M. sinica : cited in Bearder et al, ; Pongo pygmaeus : MacKinnon, ; Pan troglodytes : Goodall, ; Pruetz & Bertolani, ; Zamma, ) as well as diurnal strepsirhines ( Lemur catta : Donati et al, 2013). Primates heard vocalizing at night include Barbary macaques ( M. sylvanus : Hammerschmidt et al, ) and chimpanzees (Goodall, ; Izawa & Itani, ; Tutin et al, ), and gorillas ( Gorilla beringei ) chest‐beat at night (Schaller, ).…”

“…Chimpanzees exhibit REM sleep, and studies of these apes in captivity indicate variation in whether they remain relatively stationary (Riss & Goodall, 1976) or move around at night and sleep in bouts of a few hours at a time (Morimura et al, ). Zamma () found that wild chimpanzees at Mahale, Tanzania, were frequently disturbed at night. Although occasional nocturnal activity because of disturbance is expected, other circumstances such as nocturnal crop raiding by chimpanzees ( P.t.…”

What volume of seeds can a chimpanzee carry in its body?

“…Although the study reporting this volume did not specify how this value was acquired, it is possible that this value represents defecations only during the daytime and does not include those at night. A recent study of nighttime behaviors of Mahale chimpanzees (Zamma 2014) revealed that they frequently defecate at night-even at midnight. If we calculate chimpanzee defecations using V obs and the average number of seeds contained in a fecal clump, the estimate is 11.8 defecations 24 h -1 .…”

Orangutan Night-Time Long Call Behavior: Sleep Quality Costs Associated with Vocalizations in Captive Pongo

“…It has been noted that the forager pattern may be polyphasic [50,51]; even preindustrial, preelectric western populations divided the night into "first sleep" and "second sleep, " indicating a polyphasic pattern [52]. Chimpanzees night-time vocalizations at Mahale have been recorded to be especially active during the periods of 23:00-02:00, with a predominance of pant-hoots associated with night-time defecation and urination [53]. With respect to orangutans, it may also be the case that the cost of night-time vocalizations can be made up during the day with "siesta napping, " which has been observed in all ape populations [54] and is characteristic of equatorial forager's daily inactivity patterns [55,56].…”