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.

中文翻译：

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马来亚太阳熊（Helarctos malayanus）的体温调节及其对原地保护的影响

马来亚太阳熊的体温调节尚未完全了解。因此，在本研究中，研究了气象变量对太阳熊行为和自主体温调节机制的影响，以确定激活各种体温调节机制的温度阈值。红外热像仪用于非侵入性地确定与环境温度 (TA) 相关的体表温度 (TS) 分布，并确定太阳熊的热中性区 (TNZ)。在三个欧洲动物园的 5 °C 到 30 °C 之间，对 10 只成年太阳熊进行了热成像测量。为了评估有助于体温调节的行为，通过以 60 秒为间隔的瞬时扫描采样，在 5 °C 到 34 °C 的温度范围内观察了 9 只成年太阳熊，总共 787 小时。热成像测量显示，太阳熊的 TNZ 介于 24 °C 和 28 °C 之间，并且热量在体表上均匀消散。行为数据表明，与体温调节相关的行为发生在能量消耗巨大的自主神经机制之前，并且与 TA 和太阳辐射高度相关。虽然低于 TNZ 的体温调节行为开始的温度阈值约为 15°C，远低于热成像评估的下临界温度 (TLC)，但防止过热行为的开始发生在 28°C，更接近到估计的太阳熊的上临界温度 (TUC)。这些发现提供了有关太阳熊的热需求的有用数据，这些数据涉及物种应对自然范围内发生的气候变化和森林砍伐影响的潜力。此外，这些结果可能对圈养熊的照料和福利具有重要意义，在设计和管理设施时应予以考虑。