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31st July 2019 - It's not just humans that get bills!

Bills in the bird world are a lot more helpful than the ones we are used to receiving through the letterbox.

A birds' 'bill' or 'beak' is an impressive entity.  Not just used for eating food, they are also used for catching it, prying up bark that conceals it, filtering it from water, killing it, carrying it, cutting it up, and so on. Bills can also preen, nest build, excavate, turn eggs, defend, attack, display courtship, scratch, climb, and more. It is small wonder that bill size and shape are characteristics that vary enormously from species to species.

In most birds, their bills consist of the upper and lower jaws (mandibles) and are often covered in a layer of toughened skin.  The outer layer tends to be especially thick near the tip, where the most wear occurs. The edges of the bill may be sharpened for cutting, or serrated for grasping, but the edges of some bills, including those of ducks, are blunt and relatively soft except at the tip, which is hardened. Ducks must often sort insects and seeds from murky water, and the edges of their bills are richly supplied with touch receptors that help them to detect their food.

For many birds, the upper jaw is perforated by nostrils, although in some high-diving birds like gannets the external nostrils are missing.  Gannets avoid flooding by breathing through the mouth and keeping it shut when they hit the ocean. Similarly, the nostrils of woodpeckers are protected from being flooded with "sawdust" by feathers or by being reduced to narrow slits.

The most obvious adaptations of bills are those related to feeding. Birds that catch fish with their bills must maintain a tenacious grip on slippery prey. Thus, albatrosses and pelicans have hooked upper bill tips, and mergansers have serrated edges. Most waders hunt by probing in mud and sand, and have long, slender, forceps-like bills for finding and grasping their prey. Avocets, however, tend to feed more at the water's surface and swing their upward-curved bills from side to side. Oystercatchers have especially stout bills designed for hammering and prying open molluscs.

How we marvel at a bird in flight, think of geese flying in formation, the speed of a swift or the guile of a kestrel, yet birds pick up a big bill for this privilege. With their forelimbs almost entirely committed to the act of flying, beaks often assume the responsibility for many diverse functions that mammals will use their forelimbs to undertake.