Smaller beaks for colder winters: Thermoregulation drives beak size evolution in Australasian songbirds

Birds’ beaks play a key role in foraging, and most research on their size and shape has focused on this function. Recent findings suggest that beaks may also be important for thermoregulation, and this may drive morphological evolution as predicted by Allen's rule. However, the role of thermoregulation in the evolution of beak size across species remains largely unexplored. In particular, it remains unclear whether the need for retaining heat in the winter or dissipating heat in the summer plays the greater role in selection for beak size. Comparative studies are needed to evaluate the relative importance of these functions in beak size evolution. We addressed this question in a clade of birds exhibiting wide variation in their climatic niche: the Australasian honeyeaters and allies (Meliphagoidea). Across 158 species, we compared species’ climatic conditions extracted from their ranges to beak size measurements in a combined spatial-phylogenetic framework. We found that winter minimum ...鸟类的喙在觅食活动中发挥关键作用，现有针对喙的大小与形态的研究大多围绕这一功能展开。近期研究发现，喙在体温调节中同样具备重要功能，这或许会如艾伦法则（Allen's rule）所预测的那样，推动形态演化。然而，体温调节在跨物种喙大小演化中的作用仍未得到充分探索。具体而言，学界尚未明确：在喙大小的选择压力中，冬季保温需求与夏季散热需求何者占据主导地位。为评估这两类功能在喙大小演化中的相对重要性，需开展比较研究。本研究以气候生态位差异显著的鸟类演化支——澳新界吸蜜鸟及其近缘类群（吸蜜鸟总科Meliphagoidea）——为研究对象，解答了这一问题。研究纳入158个物种，结合空间系统发育框架，将从物种分布区提取的气候条件与喙大小测量数据进行对比分析。研究发现，冬季最低……