Aves (Birds)

Characteristics Over 9900 species Outnumber all other vertebrates except fishes Single unique feature set apart birds from other animals Feathers - If it has feathers it’s a bird Entire anatomy is designed around flight Wings for support & propulsion Bones rigid, light, & hollow Highly efficient respiratory system High-pressure circulatory system Finely tuned nervous system

Living Birds Two groups Palaeognathae Neognathae Large, flightless ostrich-like birds & kiwis Flat sternum & poorly developed pectoral muscles Neognathae Flying birds with a keeled sternum where flight muscles attach

Feathers The most distinct characteristic of birds is the presence of feathers. Feathers have multiple purposes, including enabling flight. Develop from follicles in the skin generally arranged in tracts (or pterylae), which are separated by patches of bare skin (the apteria). Some species, such as penguins, lack pterylae and instead the feathers are uniformly distributed over the skin.

Feather Parts Feathers are anchored in the skin by a short, tubular base, the calamus remains firmly implanted within the follicle until molt occurs. Barbs closely spaced side branches Barbules branch from the barbs, and proximal and distal barbules branch from opposite sides of the barbules. Ends of the distal barbules have hooks that insert into the grooves of proximal barbules of the adjacent barb. hooks and grooves act like Velcro to hold adjacent barbs together, forming a flexible vane.

Electron microscope image of a body-contour feather that shows the barbs, and how barbules on adjacent barbs Velcro together. When barbs and barbules are stiff and held tightly together, the feathers together form a tight, sheet-like, surface = Pennaceous texture When barbs are flexible and the barbules lack hooks, the feather has a soft, loose, fluffy texture = plumulaceous texture

Skeleton Pneumatized bones Skulls Horny (keratinous) beak Light, delicate, laced with air cavities, & strong Skulls Built light & mostly fused into one piece kinetic Horny (keratinous) beak toothless

Skeleton Vertebrae fused together; Bones of forelimbs Sternum ribs are mostly fused with vertebrae, pectoral girdle, & sternum Promotes rigidity Bones of forelimbs Modified for flight Reduced in number Several fused together Sternum Bears a large, thin keel to provide muscle attachment

Muscular System Muscles are relatively massive Largest is the pectoralis Depresses the wings in flight Supracoracoideus is the antagonist muscle Creates a rope-and-pulley system

Digestive System Insects the largest component of the diet Grinding of food occur in the gizzard Lack teeth Short pharynx Long, muscular, elastic esophagus Many birds have an enlargement at the lower end (crop) that acts as a storage chamber Stomach Proventriculus – secretes gastric juice Gizzard – grinds food Intestines Cloaca – terminal part Also receives genital ducts & ureters

Circulatory System Respiratory System 4-chambered heart Strong ventricular walls Heartbeat is extremely fast Respiratory System Parabronchi Ends of bronchi which air flows continuously Extensive system of nine interconnecting air sacs

Nervous & Sensory System Well-developed brain Cerebral hemispheres, cerebellum, & optic lobes Relatively intelligent birds (crows & parrots) have larger cerebral hemispheres then less intelligent birds (chickens & pigeons) Cerebellum – coordinates muscles, equilibrium Optic lobes – form a visual apparatus

Flight a balance between two sets of forces lift and weight, and thrust and drag Weight is the result of gravity and is reduced as much as possible in birds (anatomy). Lift is generated by the flow of air over the wings.

Basic Forms of Wings Elliptical Wings most small forest and scrub-dwelling birds, such as robins and sparrows Low aspect ratio Ratio of length to average width These wings allow a high degree of control and manoeuvrability in confined spaces minimize drag to allow rapid ascent and descent Wing beat is usually rapid highly slotted between the primary feathers helps to prevent stalling during sharp turns, low-speed flight, and frequent landing and takeoff.

Basic Forms of Wings High speed wings found on swallows, falcons, shore birds, and ducks Birds that feed on the wing or make long migrations. bones are relatively long, wings taper to a point to allow for high flight speed with low drag, and low energy consumption during flight. wings are also thin must be flapped for short glides and during descent, and flaps are fairly rapid but small. aerodynamically efficient for high-speed flight Cannot keep a bird airborne at low speeds.

Basic Forms of Wings Long soaring wings found on terns, albatrosses, gannets, frigate birds, gulls and other sea birds. high aspect ratio resembling those of sailplanes. open spaces allow for long wings to create good lift with little energy expenditure. adapted for high speed and dynamic soaring less manoeuvrable than the wide, slotted wings of land soarers Birds can glide easily over large expanses of water and have exploited the sea winds birds must usually run and take off into the wind to get off the ground, and usually land easily on water.

Basic Forms of Wings High-lift/Broad soaring wings found on vultures, condors, hawks, ospreys, pelicans and eagles wings are broad and only relatively long takeoff and landing in fairly confined areas, high lift, low speed soaring, and slow descents. Many of these birds are land soarers good manoeuvrability required for tactic soaring in the air currents over land.