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BIRD NOTES. EXTERNAL STRUCTURE AND MOVEMENT. The covering of feathers on a bird is called the plumage . Feathers have 2 primary functions that are essential for flight . They form the flight surfaces that provide lift and aid in steering . They prevent excessive heat loss.
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EXTERNAL STRUCTURE AND MOVEMENT • The covering of feathers on a bird is called the plumage. • Feathers have 2 primary functions that are essential for flight. • They form the flight surfaces that provide lift and aid in steering. • They prevent excessive heat loss.
EXTERNAL STRUCTURE • Feathers are also important in courtship, incubation, and water proofing. • As feathers mature, their blood supply is cut off, and the feathers become dead.
EXTERNAL STRUCTURE • The most obvious feathers are contour feathers, which cover the body, wings, and tail. • These feathers consist of a vane and a supportive shaft. • Feather barbs branch off the shaft, and barbules branch off the barbs. • Barbules of adjacent barbs overlap one another. • The ends of barbules lock together with hamuli, which are like little hooks. • Interlocking barbs keep contour feathers firm and smooth.
EXTERNAL STRUCTURE • Other types of feathers include down feathers, which act as insulation, and filoplume feathers, which have sensory functions.
EXTERNAL STRUCTURE • Birds keep a clean plumage to rid the feathers and skin of parasites. • Preening, which is done by rubbing the bill over the feathers, keeps the feathers smooth, clean, and in place.
EXTERNAL STRUCTURE • Secretions from an oil gland at the base of the tail of many birds are spread over the feathers during preening to keep the plumage water repellant. • Secretions also lubricate the bill and legs to prevent chafing. • Anting is a behavior common to many songbirds and involves picking up ants in the bill and rubbing them over the feathers. • The formic acid that ants secrete is toxic to feather mites.
EXTERNAL STRUCTURE • Feather pigments deposited during feather formation produce most colors in a bird’s plumage. • Color patterns are involved in cryptic coloration, species and sex recognition, and sexual attraction.
EXTERNAL STRUCTURE • All birds periodically shed and replace their feathers in a process called molting. • A typical molting pattern for songbirds begins after hatching when the chick is covered with down. • Juvenile feathers replace the down at the juvenile molt. • A postjuvenile molt in the fall result in plumage similar to that of an adult. • Once sexual maturity is reached, a prenuptial molt occurs late in winter or early spring, prior to the mating season. • A postnuptial molt usually occurs between July and October.
EXTERNAL STRUCTURE • Flight feathers are often lost in a certain order so that birds are not completely deprived of flight during molt periods. • Many birds, however, such as ducks, coots, and rails cannot fly during molt periods and will hide in thick marsh grasses.
The Skeleton • The bones of most birds are lightweight but very strong. • Some bones, like the humerus (forearm), have large air spaces and internal strutting (reinforcing bony bars), which helps increase strength. • Birds also have a reduced number of skull bones, and a lighter structure, the bill, which replaces the teeth. • Some aquatic birds, like the loon, have dense bones, which helps reduce buoyancy during diving.
The Skeleton • The appendages involved in flight cannot manipulate nesting materials or feed young. • The bill and very flexible neck and feet make these activities possible. • The cervical vertebrae have a saddle-shaped surface that allows great freedom of movement. • This flexibility allows the bill and neck to function as a 5thappendage.
The Skeleton • The pelvic girdle, vertebral column, and ribs are strengthened for flight. • Most ribs overlap the next rib to help strengthen the rib cage. • Fusion of the thoracic, lumbar, and sacral vertebrae helps maintain the proper flight posture, and supports the hind appendages during landing, hopping, and walking.
The Skeleton • The posterior caudal vertebrae are fused into a pygostyle, which helps support the tail feathers that are important in steering.
The Skeleton • The sternum of most birds is very large for the attachment of flight muscles.
The Skeleton • The appendages of most birds have also been modified. • Some bones of the front appendages have been lost or fused, and are points of attachment for flight feathers. • The rear appendages are used for hopping, walking, running, and perching.
The Skeleton • Perching tendons run from the toes across the back of the ankle joint to muscles of the lower leg. • When the ankle joint is flexed, as in landing on a perch, these tendons contract and the foot grips the perch. • This automatic grasp helps a bird perch even while sleeping.
Muscles • The largest, strongest muscles of most birds are the flight muscles. • Muscles of most birds are adapted physiologically for flight. • These muscles must be able to contract quickly and fatigue slowly. • They also have many mitochondria and produce large amounts of ATP to provide energy needed for flight, especially long-distance migrations.
Muscles • Domestic fowl have been selectively bred for massive amounts of muscle (white meat). • This is good for food, but poorly adapted for flight because it doesn’t have enough mitochondria for energy.
Flight • The wings of birds are adapted for different kinds of flight. • Bird wings form an airfoil, which is a surface that provides lift.
Flight • Air passing over the wing travels farther and faster than air passing under the wing, decreasing air pressure on the upper surface of the wing and creating lift.
Flight • The lift must overcome the bird’s weight, and the forces that propel the bird forward must overcome the drag that the bird moving through the air creates. • Increasing the angle that the leading edge of the wing makes with the oncoming air (angle of attack) increases lift. • As the angle of attack increases, the flow of air over the upper surface becomes turbulent, reducing lift. • Turbulence is reduced if air can flow rapidly through slots at the leading edge of the wing. • Slotting the feathers at the wing tips and the presence of an alula (groups of small feathers that bones of the wing support) help reduce turbulence.
Flight • The tail of a bird helps with many things such as steering and braking during flight. • During horizontal flight, spreading the tail feathers increase lift at the rear of the bird and causes the head to dip for descent. • Tilting the tail sideways turns the bird.
Flight • When a bird lands, its tail deflects downward, serving as an air brake. • In the males of some species, like sunbirds and widow birds, tails have dramatic ornamentation that attracts females and improves reproductive success.
Flight • Different birds have different kinds of flight. • During gliding flight, the wing is stationary, and a bird loses altitude. • Waterfowl come in for a landing using gliding flight.
Flight • Flapping flight generates the power for flight and is the most common type of flying. • Soaring flight allows some birds to remain airborne without using too much energy. • Ocean soarers, such as albatrosses and frigate birds, have long, narrow wings that provide maximum lift at high speeds.
Flight • Hummingbirds perform hovering flight. • They hover in air by fanning their wings back and forth 50-80 beats per second. • The wings move in a figure 8 pattern.
NUTRITION AND DIGESTIVE SYSTEM • Most birds have huge appetites!! • This appetite supports a high metabolism that makes endothermy and flight possible. • Bird bills and tongues are modified for many different feeding habits and food sources. • For example, a woodpecker tongue is barbed for getting grubs from tree bark. • Sapsuckers make holes in trees and use a brushlike tongue for licking the sap that builds up in these holes.
NUTRITION AND DIGESTIVE SYSTEM • The tongues of hummingbirds and other nectar feeders roll into a tube for getting nectar from flowers.
NUTRITION AND DIGESTIVE SYSTEM • Birds’ bills are used for feeding, preening, nest building, courtship, and defense. • Modifications of the bill reflect specific functions. • The bill of an eagle is modified for tearing prey, the bill of a cardinal is specialized for cracking seeds, and the bill of a flamingo is used to strain food from the water.
NUTRITION AND DIGESTIVE SYSTEM • In many birds, the crop is a storage structure that allows birds to quickly ingest large quantities of locally abundant food. • They can then seek safety while digesting their food.
NUTRTION AND DIGESTIVE SYSTEM • The crop of pigeons produces “pigeon’s milk”, a cheesy secretion that young pigeons (squabs) feed on until they can eat grain. • Crops are less developed in insect eating birds because they typically eat all day long.
