Data from: 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 temperature was positively correlated with beak size, while summer maximum temperature was not. This suggests that while diet and foraging behavior may drive evolutionary changes in beak shape, changes in beak size can also be explained by the beak’s role in thermoregulation, and winter heat retention in particular.

鸟类的喙在觅食活动中发挥关键作用，目前针对喙尺寸与形态的多数研究均围绕这一功能展开。近期研究表明，喙在体温调节过程中同样具有重要作用，这一效应或可如艾伦法则（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尺寸演化中的作用，目前仍未得到充分探索。具体而言，学界尚未明确在喙尺寸的自然选择进程中，冬季保温需求与夏季散热需求何者占据主导地位。亟需开展比较研究，以评估这两类功能在喙尺寸演化中的相对重要性。本研究以气候生态位差异显著的鸟类演化支——澳新大陆吸蜜鸟及其近缘类群（吸蜜鸟总科Meliphagoidea）——为研究对象，解答上述问题。我们针对158个物种，结合空间系统发育分析框架，将从各物种分布区提取的气候条件数据与喙尺寸测量数据进行比对分析。研究结果显示，冬季最低气温与喙尺寸呈显著正相关，而夏季最高气温则未表现出此类关联。这表明，尽管饮食与觅食行为或可推动喙形态的演化改变，但喙尺寸的变化同样可通过其体温调节功能得到解释，其中尤以冬季保温的作用最为突出。