Aves (Birds)

CharacteristicsOver 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 BirdsTwo 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

FeathersThe 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 PartsFeathers 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 branchesBarbules

◦ 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

SkeletonPneumatized bones

◦Light, delicate, laced with air cavities, & strong

Skulls◦Built light & mostly

fused into one piece◦kinetic

Horny (keratinous) beak◦toothless

SkeletonVertebrae 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

Muscular SystemMuscles are relatively massive

◦Largest is the pectoralis Depresses the wings in flight

◦Supracoracoideus is the antagonist muscle Creates a rope-and-pulley system

Digestive SystemInsects the largest component of the dietGrinding of food occur in the gizzard

◦Lack teethShort pharynxLong, 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

IntestinesCloaca – terminal part

◦Also receives genital ducts & ureters

Circulatory System4-chambered heart

◦Strong ventricular wallsHeartbeat is extremely fastRespiratory SystemParabronchi

Ends of bronchi which air flows continuously

Extensive system of nine interconnecting air sacs

Nervous & Sensory SystemWell-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

Flighta 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 WingsElliptical 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 WingsHigh 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 WingsLong 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 WingsHigh-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.