Fitting the bill
WINTER is a great time to look at wildfowl. Many parks will have ducks and geese that you can get close to, and larger lakes and gravel pits attract plenty of them. When you start to look more closely you will soon find that one of the greatest differences between them is their bills. Different sizes, colours and patterns, and more importantly, different shapes and structures. This last feature is, of course, related to their lifestyles, especially their diet.
Recent research looked at the evolution of wildfowl beaks, relating shape and diet of 51 species in 46 genera. The correlation between these two factors is very strong, as would be expected. Ducks which filter-feed have wide, flat bills, while those which dig up roots or graze vegetation have shorter, narrower and chunkier beaks for biting. One fossil species suggests that the ancestors of the Anseriformes probably had a duck-like bill during their evolutionary history and that the goose-like bill evolved later as grasses evolved, probably on several occasions.
The adaptation of wildfowl beaks to fit their diets has resulted in some interesting structures. Northern Shoveler has one of the most extreme examples of lamellae for filtering, with 180 lamellae on the upper mandible and about 220 on the lower, providing an effective sieve for collecting food items from beaks full of muddy water. Most other dabbling ducks have 50-70 lamellae. As a general forager, Mallard has what is regarded as a typical duck’s beak, while Northern Pintail and Gadwall have narrower beaks, with the former eating more seeds and the latter grabbing submerged vegetation.
Grazing birds have the stubbiest and narrowest beaks: Eurasian Wigeon, geese and swans being broadly similar. They may cut off short grass, but they can also dig up roots and tubers. Many diving ducks, such as Common Pochard, have typical duck-beak design, but scoter and eider, which specialise in shellfish, have stouter bills. Other specialist feeders, such as mergansers, have long, thin, serrated bills for catching fish.