Feathers and Flight |
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| Flight Some raptors fly to ctach their prey or to reach a safe roosting or nesting site, in some instances to escape from other predators or to display to a possible partner. Flight is very strenuous and demands of flight impose strict limitations of the size and shape of raptors. Their bodies must combine extreme lightness with compact, robust construction. Their bones are hollow, criss-crossed with struts to give both strength and lightness. The largest muscles beign the breast of pectoral muscle can account for up to 15 per cent of the total bid’s body weight. These are situated near the bird’s centre of gravity, an arrangement that gives stability in flight. Wings must be able to spread, fold, flap and twist. Flight feathers provide an unbroken surface which when flapped, acts as a resistance against the air allowing the bird to lift. The speed, angle of the wings and position of the flight feathers decides how fast or manoeuvrable the bird can be.
Feathers The feather probably developed from the scales of the bird’s reptile ancestors. Feathers are made from keratin, the same horny material that forms a reptile’s scales. They are highly complex structures, which combine both strength and lightness. The centre of the feather consists of a long thin hollow tube called a quill; on either side of the quill is an inner and outer web or vane, the thing we normally call a feather. The vane is made up of a number of small branches called barbs that interlock with each other to form a strong supple surface, essential for flight. There are several types of feathers, but the main ones are the contour feathers which cover the birds head and body. The primary and secondary feathers that make up the wing structure and finally the large feathers that go to make up the tail are called recites. All diurnal raptors, once feathered, have ten primary win feathers, 11-25 secondary and 12-14 tail feathers. Feather care is very important, which is why birds spend so much time preening, zipping the barbs of the feathers together with its beak. The bird also uses its beak to remove dirt or parasites and conditions and waterproofs its feather using organic oil which it gets from a gland above the base of its tail. Feathers have a limited life as they wear out and need to be replaced. Old ones fall out and new ones grow in a process called moulting. All raptors moult, this normally occurs once a year, after the breeding season. Some birds such as eagles can take as long as three years to complete the moult, depending on the bird’s general condition. The barn owl has the softest feathers of all raptors. Loose fringes on wing feathers deaden any sound and help silent flight. |
