Thermoregulation in Malayan sun bears (Helarctos malayanus) and its consequences for in situ conservation. (July 2020)

• Record Type: Journal Article
• Authors: Schneider, Marion; Ziegler, Thomas; Kolter, Lydia
• Is Part Of: Journal of thermal biology. Volume 91(2020)
• Publication Date: 2020-07
• Subjects: Thermoregulation -- Climate change -- Helarctos malayanus -- Infrared thermography -- Malayan sun bear -- Thermoneutral zone; Thermobiology -- Periodicals; Temperature -- Periodicals; Biology -- Periodicals; Thermobiologie -- Périodiques; Thermobiology; Periodicals; 571.46
• DOI: 10.1016/j.jtherbio.2020.102646
• Languages: English
• ISSNs: 0306-4565

Abstract

Abstract: Thermoregulation in Malayan sun bears is not fully understood. Therefore, in this study the effect of meteorological variables on both behavioural and autonomic thermoregulatory mechanisms in sun bears was examined in order to identify temperature thresholds for the activation of various thermoregulatory mechanisms. Infrared thermography was used to non‒invasively determine body surface temperature (TS ) distribution in relation to ambient temperature (TA ) and to determine the thermoneutral zone (TNZ) of sun bears. Thermographic measurements were performed on 10 adult sun bears at TA between 5 °C and 30 °C in three European zoos. To assess behaviours that contribute to thermoregulation, nine adult sun bears were observed at TA ranging from 5 °C to 34 °C by instantaneous scan sampling in 60 s intervals for a total of 787 h. Thermographic measurements revealed that the TNZ of sun bears lies between 24 °C and 28 °C and that heat is equally dissipated over the body surface. Behavioural data showed that behaviours related to thermoregulation occurred in advance of energetically costly autonomic mechanisms, and were highly correlated with TA and solar radiation. While the temperature threshold for the onset of thermoregulatory behaviours below the TNZ lies around 15 °C, which is well below the lower critical temperature (TLC ) assessed by thermography, the onset for behaviours to prevent overheating occurred at 28 °C, which was closer to the estimated upper critical temperature (TUC ) of sun bears. These findings provide useful data on the thermal requirements of sun bears with respect to the species potential to cope with the effects of climate change and deforestation which are occurring in their natural range. Furthermore, these results may have important implications for the care and welfare of bears in captivity and should be taken into consideration, when designing and managing facilities. Highlights: It is estimated that the thermoneutral zone of Malayan sun bears lies between 24 °C and 28 °C. Behaviours related to thermoregulation occur in advance of energetically costly autonomic mechanisms. Behavioural thermoregulation is highly correlated to ambient temperature and solar radiation. The onset of thermoregulatory behaviours below the TNZ is 15 °C, which is 9 °C below the estimated TLC of sun bears. The onset of thermoregulatory behaviours above the TNZ is closely linked to 28 °C, the estimated TUC of sun bears.