Knowledge is the antidote to fear. - Ralph Waldo Emerson
Introduction • Birds are grouped into a class called Aves. • Because they have unique adaptations for flight. • It is believed that birds first evolved from the archosaur of reptiles. • Birds have the following things in common with reptiles: one occipital condyle, one ear ossicle, the lower jaw structure, nucleated red blood cells, nesting behavior, and parental care.
Introduction • Birds however have some things that are unique to them: • Feathers, wings, endothermy, modified vertebral column, light bones, horny bill without teeth.
Fossil Records • Evidence from Archaeopteryx • Shows that these ancient reptiles may have climbed up trees with claws and then glided a flew short distances. • Another idea is that birds ran or hopped along the ground and then trapped prey with their wings. • There have been fossils found to show flight and some that show flightless birds.
Today • In the bird group there are about 9,100 different species, divided into 27 orders. • See page 329, the table will be on the test
Characteristics • Feathers- also called plumage • Function to: allow flight, help species recognize one another, mate attraction, endothermy, and waterproofing. • Color of Feathers • May be due to pigments, reflected light, or iridescence. • Feathers are keratinized • Contour feathers cover the body, wings, and tail.
Contour Feathers • Structure of Contour Feathers • 1. Consist of a vane with its inner and outer webs, and a supportive shaft. • 2. Feather barbs branch off the shaft. • 3. Barbules branch off the barbs. • 4. Barbules of adjacent barbs overlap one another. The ends lock with the hook like hamuli (see picture on next slide). • 5. The interlocking of barbs keep contour feathers firm and smooth.
Contour feathers give the bird its characteristic smooth round shape. They also give the bird its visual coloring and provide a first level of defense against physical objects, sunlight, wind and rain. They are very important.
Down feathersare smaller and lack the barbules and their accompanying hooklets so they are not zipped together and do not look as neat. In fact they are soft and fluffy. They provide most of the insulation and are so good at this that mankind for many years collected down feathers from various birds to put into sleeping bags and jackets to help keep us warm.
Semiplumes are half-way between a contour feather and a down feather. These occur between the contour feathers and help to supply insulation and a certain amount of form as well.
Filoplumes are very small and have only a very few barbs at their tips. They are believed to have a sensory function, helping birds keep their feathers in order.
Feather Maintenance • Birds clean their feathers by preening (rubbing the bill over the feathers, keeps the feathers smooth, clean and in place. • Secretions from the oil gland at the base of the tail are spread all over the body which help keep the plumage water repellent and supple. This keeps the bill and legs from chafing. • Anting- many songbirds pick up ants with their bill and rub them all over the feathers. The formic acid that ants secrete is toxic to feather mites. So birds use them to keep parasites away.
Color of Feathers • Feather pigments are deposited during feather formation most colors in a bird’s plumage. • Other colors arise from irregularities on the surface of the feather that diffract white light. • An example of iridescence is the perception of interchanging colors on the neck and back of hummingbirds.
Iridescent feathers change color when seen from different angles or in different light conditions. The tips of the feathers have tiny platelets that either allow light to pass through or reflect it. The result is an amazing light show that has the viewer seeing a lustrous rainbow of colors. The peacock is the most famous of birds with iridescent feathers, but many of the more drab colored birds also display iridescence. The black parts of magpies and starlings sometimes appears to be blue or green.
Molting • Molting- the periodic shedding of feathers • The timing of molt periods varies. • Flight feather are frequently lost in a particular sequence so that birds are not wholly deprived of flight during molt periods. • However some birds like ducks can not fly during molt periods and have to hide in thick march grass until the molt is completed.
Birds Skeleton • Characteristics: • Lightweight, large bones have air spaces, other bones are smaller in size. • Like reptiles they have uncinate processes, that strengthen the rib cage. • The rear of the bird is adapted for running, hopping, or perching. • The neck is flexible • The synsacrum and pygostyle support and steady the pelvic region while walking, hopping, and flying.
1) Skull 2) Cervical Vertebrae 3) Humerus 4) Second digit 5) Metacarpals 6) Fourth digit 7) Third Digit 8) Radius 9) Ulna 10) Scapula 11) Synsacrum 12) Pygostyle 13) Ischium 14) Ilium 15) Pubis 16) Pelvic girdle 17) Uncinate process 18) Femur 19) Halux 20) Digits 21) Tarsometatarsus 22) Tibiotarsus 23) Keeled sternum 24) Coracoid 25) Furcula (or wishbone) Key to worksheet
The bonesWhile maintaining strength, most of the bones are pneumatic, meaning they are hollow and filled with air spaces connected to the respiratory system. • Skull • The bones of the skull are generally fused providing protection to the brain while being of light weight. A light, toothless beak replaces the bony, heavy toothed jaw of reptiles. Beaks, of course, can be highly modified for different types of food and feeding behavior Note the large orbits, as sight is an important sensory mechanism for birds.
Neck • The necks of birds are very important for body maintenance and eyesight. Modification for flight has rendered avian forelimbs almost useless for any task other than flight. To make up for this lack of forelimb dexterity, the beak is used for many tasks such as preening feathers. To access hard-to-reach feathers on the back and tail birds require a flexible neck. Furthermore, as birds have immobile eyes, head movement and flexibility is required to focus on objects at various distances.
Thorax and Sternum • Overlying flaps projecting off the ribs called uncinate processes help to stiffen the rib cage so it will not collapse during the powerful strokes required for flight. The sternum is the highly modified breastbone. In flying and swimming birds the keel is enlarged for flight muscle attachment. Flightless birds such as Ostriches have a sternum without a keel.
Pectoral Girdle • The pectoral girdle is made up of the sternum, clavicle, coracoid and scapula. The clavicles come together to form the furcula, or "wishbone". The furcula provides a flexible attachment site for the breast muscles and along with the coracoids act as struts that resist pressure created by the wing stroke during flight. Flight muscles running from the sternum to the relatively short and stiff humerus elevate and depress the wing.
Pelvic Girdle • There is an extensive fusion of bones of the pelvic region to provide stiff support for the legs in order to deal with the stress of take-off and landing. The synsacrum is a fusion of the pelvic and 6 caudal (tail) vertebrae. At the end of the spinal column is the pygostyle, a fusion of the final few caudal vertebrae. The pygostyle supports the tail feathers and musculature.
Wing • The avian wing contains the usual arm bones of reptiles and mammals, but in a highly modified form. The humerus is rather short compared to the total length of the wing, as it must withstand the pulling of the flight muscles. The radius and ulna form the support for the mid-wing. The outer wing or "hand" bones are highly fused for strength and feather support. The first digit or pollex supports the alula, a small feather used to control air flow around the wing.
Leg and Foot • The upper leg is composed of a fairly standard femur, but the lower leg and foot are highly modified by fusion of bones. Of course, between the femur and the fibula and tibiotarsus is the knee, whose location in birds is often confused. The tarsometatarsus is an extended fusion of the foot bones. This lengthening adds extra leverage for running, landing and take-off.
SONG BIRDS or PERCHING BIRDS (warblers, thrushes, wrens, etc.) have independent, flexible toes, with one pointing backwards, ideal for grasping perches. Why don't perching birds fall out of trees when they sleep? When perching birds sit, a tendon on the backside of the ankle automatically flexes locking their toes around the branch. With feet locked, sleeping birds don't fall. As the bird stands up its feet release.
WOODPECKERS have two toes pointing forwards and two backwards; for climbing up, down, and sideways on tree trunks.
WATER BIRDS such as ducks have webbing between their toes for swimming. GULLS also have feet similar to these so they don't sink while walking in the soft sand or mud near the water's edge.
WADING BIRDS. The long toes of herons, which spreads the bird's weight over a large surface area, facilitates walking on soft surfaces near the water's edge (where wading birds like to eat).
RAPTORS such as hawks, eagles, and owls use large claws (called talons) to capture, kill, and carry prey with their feet.
Pheasants and chickens use their strong feet to scratch the dirt and leaf litter to uncover seeds and insects.
Strong-legged flightless birds, like the Cassowary, protect themselves by kicking with their powerful feet and sharp claws.
Skeleton Continued • Bird flight alternates between gliding and flapping flight. • It requires a lot of energy also called ATP. • The keel on the sternum is enlarged for the attachment of the strong pectoral flight muscles. • Airfoil design allows or creates lift.
Types of Nests • Ground nests were probably the first nests made by birds. They are usually just "scrapes' on the ground forming a depression. Birds shape these type of nests by rotating their abdomen in the same place many times. Shorebirds typically employ this type of nest. The picture to the left is a ground nest of a Killdeer. An interesting note about shorebirds is that they almost always lay four eggs.
Types of Nests • Platform nests were probably the first elevated nests. Platforms eliminate risk from most ground predators. These type of nests, built by herons, cormorants, eagles and osprey (right) are very simple in structure. Essentially they are a collection of loosely gathered sticks and twigs with a slight depression to hold the eggs. Platforms can get quite large because some birds use the same platform year after year adding more material to the existing nest each year.
Types of Nests • Insulated cavity-nests shelter eggs from cooling winds and allow the parent's body heat to warm the eggs more efficiently. Many species use cavities as their nesting location, including woodpeckers, titmice, chickadees, owls, and bluebirds just to name a few. Nest cavities also serve as a valuable roosting spot, giving birds a place to "hide-out" during inclement weather. Cavity-nesting species have a keystone role in the environment because many other types of animals use old cavities for their homes. For example, southern flying squirrels often use old red-cockaded woodpecker cavities for their nesting location.