Anseriformes

Ferrying in Anseriformes Unlike grebes, whose common ancestor can be inferred to ferry because the behaviour is present in all living species, we found that the last common ancestor of waterfowl did not ferry (likelihood = 0.03). Ferrying is rare across the anseriform tree, showing up unexpectedly in the evolutionarily distinct B. lobata (likelihood = 0.007), and more recently in the lineage leading to S. waigiuensis (likelihood = 0.34), whose close relatives in the genera Aix and Cairina do not ferry (Figure 5). In contrast, we found stronger evidence at the basal node of the genus Mergus, of which three species ferry (likelihood = 0.46) and at the basal node of the swans (Cygnus), of which four species ferry (likelihood = 0.22). Ferrying has nonetheless been lost in at least one species within each genus: M. squamatus (likelihood = 0.61), C. cygnus (likelihood = 0.26), and C. columbianus (likelihood = 0.30). The strong and significant phylogenetic signal that we found for ferrying (D = −0.32, α = 0.001) revealed that this behaviour has been highly phylogenetically determined across waterbird clades.