The avian beak is increasingly recognised as an important organ for thermoregulation, particularly in disproportionately large‐beaked taxa such as toucans and hornbills. We used infrared thermography to test the prediction that southern ground‐hornbills Bucorvus leadbeateri physiologically regulate the surface temperature of their beak (T_beak), as well as that of their facial (T_facial) and gular skin (T_gular) in such a way that these surfaces provide avenues for non‐evaporative heat dissipation in warm weather. Our data, collected over air temperatures (T_a) ranging from 11°C to 36°C, supported these predictions. At T_a < 20°C, T_beak tracked T_a, but rapidly increased to values 6–12°C above T_a at T_a = 20–22°C. The T_beak–T_a gradient was maintained at approximately 7°C between T_a = 22°C and 28°C, before decreasing linearly with T_a > 28°C. We also found evidence for active regulation of T_facial and T_gular, with both surfaces regulated at approximately constant increments above T_a up to inflection T_a values of 22°C and 29°C, respectively. The presence of inflection T_a values corresponding with abrupt changes in physiological regulation of these surface areas suggests a high degree of physiological control. Estimates of heat exchange suggest that SGH may be able to dissipate up to 75% of basal metabolic rate via these surfaces, confiming the beak and areas of unfeathered skin play an important thermoregulatory role in these large, distinctive and threatened birds.

中文翻译：

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喙和无羽的皮肤作为南部犀鸟的散热器

鸟类的喙日益被认为是温度调节的重要器官，特别是在巨嘴类群中，例如巨嘴鸟和犀鸟。我们使用红外热成像来测试预测，即南方的地面犀鸟Bucorvus leadbeateri生理调节它们的喙（的表面温度Ť_喙），以及它们的面部（的Ť_面部）和gular皮肤（Ť _gular以这样的方式）这些表面为温暖天气下的非蒸发散热提供了途径。我们的数据，收集的空气温度（Ť_一范围从11℃至36℃），所支持的这些预测。在Ť_一 <20°C，T_喙跟踪T _a，但在T _a  = 20-22°C时迅速增加到比T _a高6-12°C的值。所述Ť_喙- Ť_一个梯度维持在介于约7℃下Ť_一个 = 22℃和28℃，用线性降低之前Ť_一个 > 28℃。我们还发现了主动调节T_面部和T_沟的证据，两个表面在T _a之上直至拐点T _a处以大约恒定的增量进行调节。分别为22°C和29°C。与这些表面积的生理调节的突然变化相对应的拐点T _a值的存在表明高度的生理控制。热交换的估计表明，SGH可能能够通过这些表面消散高达75％的基础代谢率，这表明喙和无羽化皮肤区域在这些大型，独特且受威胁的鸟类中起着重要的温度调节作用。