We tested the concept that moose (Alces alces) begin to show signs of thermal stress at ambient air temperatures as low as 14 °C. We determined the response of Alaskan female moose to environmental conditions from May through September by measuring core body temperature, heart rate, respiration rate, rate of heat loss from exhaled air, skin temperature, and fecal and salivary glucocorticoids. Seasonal and daily patterns in moose body temperature did not passively follow the same patterns as environmental variables. We used large changes in body temperature (≥1.25 °C in 24hr) to indicate days of physiological tolerance to thermal stressors. Thermal tolerance correlated with high ambient air temperatures from the prior day and with seasonal peaks in solar radiation (June), ambient air temperature and vapor pressure (July). At midday (12:00hr), moose exhibited daily minima of body temperature, heart rate and skin temperature (difference between the ear artery and pinna) that coincided with daily maxima in respiration rate and the rate of heat lost through respiration. Salivary cortisol measured in moose during the morning was positively related to the change in air temperature during the hour prior to sample collection, while fecal glucocorticoid levels increased with increasing solar radiation during the prior day. Our results suggest that free-ranging moose do not have a static threshold of ambient air temperature at which they become heat stressed during the warm season. In early summer, body temperature of moose is influenced by the interaction of ambient temperature during the prior day with the seasonal peak of solar radiation. In late summer, moose body temperature is influenced by the interaction between ambient temperature and vapor pressure. Thermal tolerance of moose depends on the intensity and duration of daily weather parameters and the ability of the animal to use physiological and behavioral responses to dissipate heat loads.

中文翻译：

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重新定义驼鹿（Alces alces）对温暖环境条件的生理反应

我们测试了驼鹿 (Alces alces) 在环境空气温度低至 14 °C 时开始显示热应力迹象的概念。我们通过测量核心体温、心率、呼吸频率、呼出空气的热量散失率、皮肤温度以及粪便和唾液中的糖皮质激素，确定了阿拉斯加雌性驼鹿对 5 月至 9 月环境条件的反应。驼鹿体温的季节性和日常模式并未被动地遵循与环境变量相同的模式。我们使用体温的大幅变化（24 小时内≥1.25 °C）来表示对热应激源的生理耐受天数。耐热性与前一天的高环境空气温度以及太阳辐射（6 月）、环境空气温度和蒸汽压力（7 月）的季节性峰值相关。中午（12:00），驼鹿表现出体温、心率和皮肤温度（耳动脉和耳廓之间的差异）的每日最小值，这与呼吸速率和通过呼吸损失的热量速率的每日最大值一致。早晨在驼鹿中测量的唾液皮质醇与样品收集前一小时内的气温变化呈正相关，而粪便糖皮质激素水平随着前一天太阳辐射的增加而增加。我们的结果表明，自由放养的驼鹿没有环境气温的静态阈值，在温暖季节它们会受到热应激。在初夏，驼鹿的体温受到前一天环境温度与太阳辐射季节性峰值的相互作用的影响。在夏末，驼鹿的体温受环境温度和蒸气压之间相互作用的影响。驼鹿的耐热性取决于日常天气参数的强度和持续时间，以及动物利用生理和行为反应来散发热负荷的能力。