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Gibbon sleep quantified: the influence of lunar phase and meteorological variables on activity in Hylobates moloch and Hylobates pileatus

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Abstract

Sleep in the primate order remains understudied, with quantitative estimates of sleep duration available for less than 10% of primate species. Even fewer species have had their sleep synchronously quantified with meteorological data, which have been shown to influence sleep–wake regulatory behaviors. We report the first sleep duration estimates in two captive gibbon species, the Javan gibbon (Hylobates moloch) and the pileated gibbon (Hylobates pileatus) (N = 52 nights). We also investigated how wind speed, humidity, temperature, lunar phase, and illumination from moonlight influence sleep–wake regulation, including sleep duration, sleep fragmentation, and sleep efficiency. Gibbons exhibited strict diurnal behavior with little nighttime activity and mean total average sleep duration of 11 h and 53 min for Hylobates moloch and 12 h and 29 min for Hylobates pileatus. Gibbons had notably high sleep efficiency (i.e., time score asleep divided by the time they spent in their sleeping site, mean of 98.3%). We found illumination from moonlight in relation to lunar phase and amount of wind speed to be the strongest predictors of sleep duration and high-quality sleep, with increased moonlight and increased wind causing more fragmentation and less sleep efficiency. We conclude that arousal threshold is sensitive to nighttime illumination and wind speed. Sensitivity to wind speed may reflect adaptations to counter the risk of falling during arboreal sleep.

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Acknowledgements

University of Toronto and Duke University are acknowledged for providing funding for this research. Gratitude is extended to Gabi Skollar and the Gibbon Conservation Center of Santa Clarita, California, USA, for allowing our research to take place, and thanks is extended to Reg and Violet for their participation in this study.

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  1. Department of Anthropology, University of Toronto Mississauga, 19 Russell Street, Mississauga, ON, M5S 2S2, Canada

    Kaleigh R. Reyes, Ujas A. Patel & David R. Samson

  2. Department of Evolutionary Anthropology, Duke University, Durham, NC, USA

    Charles L. Nunn

  3. Duke Global Health Institute, Duke University, Durham North Carolina, USA

    Charles L. Nunn

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  1. Kaleigh R. Reyes
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Reyes, K.R., Patel, U.A., Nunn, C.L. et al. Gibbon sleep quantified: the influence of lunar phase and meteorological variables on activity in Hylobates moloch and Hylobates pileatus. Primates 62, 749–759 (2021). https://doi.org/10.1007/s10329-021-00920-y

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