Swans
A Mute Swan preening its feathers
Not actually mute, this species is native to Britain and Europe.
A Mute Swan preening its feathers
Not actually mute, this species is native to Britain and Europe.
■ Many aggressive displays are designed to make the bird look larger. The threat display of the Mute Swan is a prime example. The swan lifts its wings up above its back, fluffs out the tiny feathers on its neck, and surges forward across the water. This is accompanied by some fearsome hissing. In most cases, birds are bluffing when they threaten a human like this, but the Mute Swan, at about twenty pounds, can deliver a powerful blow with the bony leading edge of its wing or with its bill, and you should give it a wide berth.
The aggressive display of a Mute Swan
■ Swans and geese have long slender necks that must be kept warm in any weather, and especially when exposed to freezing wind and submerged repeatedly in water. To reduce exposure and retain heat, long-necked birds coil their necks tightly against the body when they can. The countercurrent circulation birds have in their legs (see this page) is not practical in the neck, because the brain requires a steady supply of warm oxygenated blood. So these species have evolved a dense coat of tiny downy feathers over their entire neck. In fact, a Tundra Swan holds the record for the most feathers ever counted on an individual bird—just over twenty-five thousand in all, with 80 percent of those (about twenty thousand feathers) on the head and neck.
A Mute Swan curling its neck to keep warm
■ What is a bill? A bird’s bill is a very lightweight structure supported by a framework of two types of bone. A core of spongy bone is encased in a thin shell of more solid bone, making the bill both strong and light. Covering the bones is a hard outer shell of keratin (like our fingernails). Because it is living tissue, the bill can change color, though gradually. The keratin layer is constantly growing to heal nicks and scratches and to maintain the shape of the bill, including the sharp edges and hooked tip, which are worn down by use.
A Mute Swan’s bill structure, with the bones in gray and the thin covering of keratin in orange and black