chordates
Bird Beaks
Bird beaks, in particular, reflect the variation not only in the types of foods these animals consume but in where and how they get their food. Some birds, for example, catch their prey in water. Stilts, herons, spoonbills, and oystercatchers wade in shallow water, searching for fish, crustaceans, and mollusks. Stilts and herons have long, pointed beaks to snatch fish they've spotted, while spoonbills move their broad, rounded beaks through the water to catch their prey by feel. As their name implies, oystercatchers eat oysters, clams, and mussels. Their beaks, not surprisingly, are very strong and stiff, enabling them to pry open mollusk shells and extract their contents in a matter of seconds.
The size of a bird's prey also presents tremendous challenges. Pelicans and bald eagles, for instance, both rely on the element of surprise, ambushing fish swimming just below the water's surface. The pelican typically dives into the water from great heights and uses its gaping mouth and the pouch at the base of its lower jaw as a fishnet. When it surfaces, the bird tips its beak down to drain the water out, and then up to swallow the fish whole. Bald eagles also grab fish just below the surface but do so with the sharp talons on their feet instead of with their beaks. Because the eagle's prey is often too large to swallow whole, it uses its sharp, hooked beak to tear off bite-sized strips.
Some bird beaks, like those of the woodpecker, the flycatcher, and the bunting, are pincerlike, perfect for grasping tiny objects (usually insects) with great precision. These beak types are specialized further still, relative to each bird's method of foraging. The woodpecker's beak is tough and chisel-like, enabling the bird to excavate holes in trees in search of insects inside. The flycatcher's beak is long, with a slight hook at the tip and flanked with stiff hairlike feathers, all of which help the flycatcher capture insects on the wing. The bunting's beak is less specialized. It allows this species to eat a wider variety of foods, including insects and seeds.
The beak of the crossbill is one of the most specialized of all bird beaks. The upper and lower portions of its beak are curved in opposite directions and cross each other when the beak is closed, making the bird look deformed and the beak unusable. This shape, however, is perfectly suited to prying open the cones of conifers for the seeds they contain.
The beak, bill or rostrum is an external anatomical structure of birds which is used for eating and for grooming, manipulating objects, killing prey, probing for food, courtship and feeding young. The term also refers to a similar mouthpart in some cephalopods, cetaceans, pufferfishes, turtles, Anurantadpoles and sirens.
Anatomy
Beaks vary significantly in size and shape from species to species. The beak is composed of an upper jaw, called the maxilla, and a lower jaw, called the mandible. The jaw is made of bone, typically hollow or porous to conserve weight for flying. The outside surface of the beak is covered by a thin horny sheath of keratin called the rhamphotheca. Between the hard outer layer and the bone is a vascular layer containing blood vessels and nerve endings. The rhamphotheca can includes knob, which is found above the beak of some swans, such as the Mute Swan, and some domesticated Chinese geese (pictured).
The beak has two holes called nares (nostrils) which connect to the hollow inner beak and thence to the respiratory system.The nares are usually directly above the beak. In some birds, they are in a fleshy, often waxy structure at the base of the beak called the cere (from Latin cera, meaning wax). The cere is an indicator of the reproductive cycle of budgerigars.
Petrels and albatrosses have external horny sheaths called naricorns that protect the nares. These are separately placed on either side of the base of the upper mandible in albatrosses, but fused, with an internal septum, on the top of the base of the upper mandible in petrels.. In the mallard, and perhaps in other ducks, there is no cere, and the nostrils are in the hard part of the beak, as a soft cere would be liable to injury when the duck dredges for food among submerged debris and stones.
On some birds, the tip of the beak is hard, dead tissue used for heavy-duty tasks such as cracking nuts or killing prey. On other birds, such as ducks, the tip of the bill is sensitive and contains nerves, for locating things by touch. The beak is worn down by use, so it grows continually throughout the bird's life.
Uses of beaks
As noted by Darwin in his observations on Galapagos Finches, birds' beaks have evolved to suit the ecological niche they fill: Raptors have decurved (downward curving) beaks for ripping up meat. Hummingbirds have long thin beaks for reaching nectar. The spoonbills' beaks allow them to filter-feed in shallow water. Unlike jaws with teeth, beaks are not used for chewing. Birds swallow their food whole, and it is broken up in the gizzard
Anna's Hummingbirds have long, tubular bills that resemble straws, which they use to sip nectar from flowers.
Acorn Woodpeckers have a strong, long, chisel-like bill to make holes in oak trees.
Vermilion Flycatchers have a wide bill surrounded by a net of bristles that works to funnel flying insects into it's mouth while the flycatcher is in the air.
Mergansers have a long bill with serrated edges and a hooked point, adapted for grabbing fish.
The edges of a Mallard's bill are fringed to strain plants, seeds, and small animals from mud and water
Western Meadowlarks use their long pointed bills to probe for insects in the ground.
The Evening Grosbeak has a thick, conical beak, which is necessary for opening the hard outer shells of seeds to reach the nutritious interior.
Eagles tear prey, such as mice, into bite-sized pieces with their strong, hooked bill
Many shore birds have long, thin probing bills. These bills come in a variety of sizes to jab at different depths in the muck, allowing many species to live together without directly competing for food.
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