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.