Huddling is more important than rest site selection for thermoregulation in southern bamboo lemurs

Abstract

Resting site selection can have important effects on the behaviour and fitness of organisms. The maintenance of optimal body temperatures (Tb) when faced with environmental variables has often been attributed to either specific microhabitat rest site characteristics or to behavioural strategies. Among many small group-living endotherms, social thermoregulation (i.e. huddling) is utilized as an energy conservation mechanism at low ambient temperatures (Ta), thus decreasing the metabolic cost of maintaining Tb. Although unusual among primates, lemurs maintain a low metabolic rate and exhibit a diversity of thermoregulatory strategies; however, objective Tb measurements have thus far been limited to small-bodied lemurs (e.g. Cheirogaleids). As such, we sought to determine whether a medium-sized lemur model, the southern bamboo lemur, Hapalemur meridionalis, would maintain thermoregulation through microhabitat rest site selection, huddling behaviour, or potentially both strategies. Within a degraded littoral forest fragment in southeast Madagascar, we conducted full-day focal observations on three groups of H. meridionalis between January and December 2013. Adult individuals were collared with data-loggers that collected instantaneous skin temperature Tsk (°C). We calculated the mean Tsk of the focal individual during each resting bout, and the proportional rate of huddling between the focal individual and conspecifics. In addition, we recorded all resting sites utilized for at least 15 min and collected standard tree characteristics. We fitted linear mixed-effects models to determine the thermoregulatory combined effect of specific resting site characteristics, huddling behaviour and environ- mental variables on Tsk. Our results showed that lemurs selected tree sites with larger diameter at breast height; however, huddling was most predictive of increasing Tsk whereas resting site characteristics were not included in the best-fit model. It is possible that microhabitat rest site selection is not significant in a degraded forest as the potential environmental buffering is limited; thus, thermoregulatory mechanisms are probably best served by behavioural strategies, i.e. social huddling.

Eppley TM, Watzek, J, Dausmann KH, Ganzhorn JU, Donati G (2017) Huddling more important than rest site selection for thermoregulation in southern bamboo lemurs (Hapalemur meridionalis). Anim Behav 127:153-161. doi:10.1016/j.anbehav.2017.03.019

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