Differences in Plumulaceous Feather Characters of Dabbling and Diving Ducks

We examined variation in five microscopic plumulaceous (downy) feather characters of eighteen species of dabbling (Anatini) and diving (Aythyini, Mergini) ducks to quantify the differences between these tribes, and to explain how the plumulaceous feather ultrastructure in ducks may be influenced by different ecological requirements. Over 75% of the variation in feather characters among these ducks was explained by the first two components of a principal components analysis (PCA). Component 1 explained 51% of the variation and was positively correlated with the characters that quantified the number of barbules with expanded nodes and the number of expanded nodes on barbules. The microscopic feather characters of dabbling ducks (Anatini) have triangular-shaped, expanded nodes on most proximal barbules, whereas diving ducks (Aythyini and Mergini) lack expanded nodes on some barbules. Anatini also have a greater density of expanded nodes per barbule, wider nodes, shorter distance between expanded nodes, and longer barbule length. Further analysis of node density across all taxa showed that as dive depths increase, the number of expanded nodes per barbule decreases, and in the deepest divers many of the barbules completely lack expanded nodes. The significantly greater density of expanded nodes in dabbling ducks suggests that the downy nodes may function to trap more air. Diving species have fewer expanded nodes, less buoyant plumage, and are more efficient at foraging in deeper water than dabbling ducks.