Diel and infradian (7‐day) activity rhythms in Mexican spider monkeys (Ateles geoffroyi) kept with and without visitor contact

Abstract

Diel activity rhythms in mammals are regulated by an endogenous (circadian) timing system which is synchronized by environmental 24-hr periodicities called zeitgebers.Additional direct responses to stochastic environmental factors ensure the fine-tuning to the actual situation and may mask the circadian time course. Following an observational study on behavioral effects of visitor activities in a group of spider monkeys (Ateles geoffroyi) kept free-ranging on a small island of Lake Catemaco, Veracruz, Mexico, we analyzed the effect of weekly varying numbers of visiting tourist boats on the monkeys' diel activity rhythm. With small accelerometer-data logger devices we recorded the monkeys' locomotor activity continuously for several months each. Then we compared the data with those from spider monkeys living without tourist contact. Neither the duration of the monkeys' activity time (α) nor its phase relationship to the 24-hr solar day did change on different weekdays in either site. However, their activity level showed a clear 7-day rhythm. The monkeys of the tourist site showed highest activity on Saturday and Sunday, when the frequency of visiting tourist boats was highest, whereas those of the non-tourist site were least active on Sunday and Monday, when human activities were lowest there. While the monkeys of the nontourist site usually displayed a distinct bimodal activity pattern peaking in the morning and late afternoon, the pattern in those of the tourist site mostly lacked a morning peak and varied more over time. Based on our results, we suggest that circadian entrainment is not involved in the differences between the diel activity rhythms of the spider monkeys from the two keeping sites and the differing 7-day variation in their activity level. Rather, these differences seemingly reflect direct responses to the differing human activities and thus may correspond to circadian masking effects. K E Y W O R D Sactivity pattern, circadian rhythm, circaseptan rhythm, masking effect, zoo visitor effect

Ethological studies of native Mexican mammals: A review

“…Other studies found interspecific differences in the way primates allocate time to different activities: the mantled howler monkey, A. palliata, spent a considerable amount of time resting, feeding, and moving around (Muñoz et al 2001); Guatemalan black howlers (A. pigra), rested more frequently in highquality habitats (Rangel-Negrín et al 2018); separately, the periods of rest and activity of spider monkeys (A. geoffroyi), were mainly driven by light-darkness periods and environmental factors such as temperature, precipitation, and humidity (Muñoz-Delgado et al 2004). In this last species, in Catemaco, Veracruz, Muñoz-Delgado et al (2014) studied the impact of housing conditions and season on the daily timing and pattern, and Muñoz-Delgado et al (2018), recorded that these primates respond to visitor (tourist) activity since it modified their normally pronounced bimodal diel activity pattern and developed a superimposed infradian activity rhythm peaking on Saturday and Sunday.…”

External environmental conditions impact nocturnal activity levels in proboscis monkeys (Nasalis larvatus) living in Sabah, Malaysia

“…">We expected that smaller distances to plantations would trigger proboscis monkeys' activity (positively masking activity patterns). Nights spent near plantations may be associated with higher human density, which could disrupt sleep or cause increased vigilance in proboscis monkeys (Gaynor et al, 2018; Leasor & Macgregor, 2004; Muñoz‐Delgado et al, 2018; Tagg et al, 2018). Proboscis monkeys avoid sleeping sites near high human activity, which could indicate increased stress in the presence of humans and, thus, presence of nocturnal activity around plantations (Boonratana, 2013).…”

“…Nights spent near plantations may be associated with higher human density, which could disrupt sleep or cause increased vigilance in proboscis monkeys (Gaynor et al, 2018;Leasor & Macgregor, 2004;Muñoz-Delgado et al, 2018;Tagg et al, 2018).…”