Data from: Feeding ecology is the primary driver of beak shape diversification in waterfowl

The diversity of beak shapes among birds is often assumed to be largely the result of adaptations to different feeding behaviors and diets. However, this assumption has only been tested for a small subset of avian diversity, primarily within the order Passeriformes. Moreover, given the role of the beak in behaviors other than feeding and given that most previously identified beak-feeding associations concern beak size rather than shape, it remains unclear how much of beak shape diversity is explained by feeding ecology and what functional explanations account for these differences in shape.
I quantified the association between beak shape and feeding ecology for 42 species in the bird order Anseriformes (waterfowl) using 3D curvature of the upper beak collected from museum specimens and continuous dietary data compiled from the literature. I also tested whether leverage or stress resistance of the beak explains the association between beak shape and feeding ecology. Diet is strongly and significantly correlated with beak shape in waterfowl. An ancestral beak shape reconstruction and the reconstructed diet of the anseriform fossil Presbyornis both support filter-feeding as ancestral for most waterfowl, followed by multiple, significantly convergent transitions from a duck-like beak toward a more goose-like beak. The evolution of a more goose-like beak is associated with increased consumption of leaves, decreased consumption of invertebrates, and an increase in mechanical advantage of the beak. Moreover, no association was identified between size (measured as either beak size or body mass) and feeding ecology nor between size and beak shape.
These results demonstrate that feeding ecology has acted as the primary selective force in the diversification of waterfowl beak shapes, including the convergent originations of geese. Thus, rapid and convergent adaptation of the beak to feeding is not limited to passerines nor is it limited to size-correlated shape changes. The positive evolutionary correlation between mechanical advantage and herbivory shows that lever mechanics can explain the functional evolution of the kinetic upper beak in birds. These results also suggest that functions of the beak other than feeding may play a minor role in explaining overall beak shape diversity.

鸟类喙形的多样性通常被认为主要是对不同取食行为与食性适应的结果。然而，这一假说仅在鸟类多样性的一小部分类群中得到了验证，且主要集中于雀形目（Passeriformes）。此外，鉴于喙除取食外还承担其他行为功能，且此前已探明的喙与取食关联大多聚焦于喙大小而非喙形，目前仍不明确取食生态能够解释多大比例的喙形多样性，以及何种功能机制可阐释喙形的这些差异。本研究针对雁形目（Anseriformes，即水禽）的42个物种，利用从博物馆标本获取的上喙三维曲率数据，以及从文献中汇编得到的连续型食性数据，量化了喙形与取食生态之间的关联。本研究同时检验了喙的杠杆效率或抗应力性能是否能够解释喙形与取食生态间的关联。结果显示，水禽的食性与喙形存在显著且强相关的关联。对祖先喙形的重建，以及对雁形目已灭绝化石物种毕氏鸟（Presbyornis）的食性重建结果均表明，多数水禽的祖先取食方式为滤食，随后从鸭类喙形向更接近鹅类的喙形发生了多次显著的趋同演化转变。更接近鹅类的喙形演化，与叶片取食量增加、无脊椎动物取食量减少，以及喙的机械优势提升相关。此外，研究未发现体型（以喙大小或体质量衡量）与取食生态之间存在关联，也未发现体型与喙形之间存在关联。这些研究结果表明，取食生态是驱动水禽喙形多样化的主要选择压力，包括鹅类喙形的趋同演化。由此可见，鸟类喙部针对取食的快速趋同适应并非仅局限于雀形目，也并非仅局限于与体型相关的喙形改变。机械优势与植食性之间的正向演化关联表明，杠杆力学机制可以阐释鸟类可动上喙的功能演化。本研究结果同时提示，喙除取食外的其他功能，对整体喙形多样性的解释作用相对有限。