Aves (Birds)

1. Aves (Birds)

2. 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

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

6. 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.

8. 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.

10. 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

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

12. Skeleton • Vertebrae fused together; • 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

14. 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

15. 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

17. Circulatory 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

20. 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

21. 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.

22. 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.

23. 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.

24. 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.

25. 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.