BirdsClass: Aves

Characteristics

• Well adapted to marine, freshwater, & terrestrial habitats

• Bodies adapted for flight• Endothermic - body temperature controlled by

metabolism (40 to 41 degrees Celsius body temperature) )

Evolution

• Evolved from reptiles • Few fossils due to lack of preservation of

feathers or thin, hollow bones

Characteristics of Birds

• Body covered with feathers made of protein called keratin

• Thin, hollow bones • Some bones fused for extra strength • Forelimbs modified into wings for flight • Two hind limbs with claws to support upright

body • Scales on legs

• Toothless, horny beak • Additional air sacs with lungs for more oxygen

• Amniote egg with calcium carbonate shell • Oviparity with both parents often caring for

eggs • Eggs usually incubated within a nest

Feathers!!!

Feathers:

• Modified scales • Function to provide lift for flight & help

conserve body heat • Five kinds of feathers ----- down, contour,

flight, filoplume, & bristles

Down feathers:

1. Soft & fluffy2. Cover the body of nestlings3. Provide an undercoat insulating adult birds

Down feathers

Contour Feathers:

1. Give streamline shape to body2. Provide coloration to adult birds3. Give additional insulation to body

Contour

Flight Feathers:

1. Specialized contour feathers2. Found on wings & tail

Flight feathers

Filoplumes:

•1. Called pin feathers2. Hair like feathers under contour feathers on body

Filoplumes

Parts of a feather

• Develop from tiny pits in the skin called follicles

• Shaft emerges from the follicle • Two vanes develop on either side of shaft • Barbs branch off of each vane & have

projections called barbules • Barbules have microscopic hooks to hold

barbules together

Parts of a Flight Feather

Microscopic Hooks on Barbules

Feathers

• Birds preen their feathers to clean them & coat them with oil

• Preen glands - oil glands located at the base of the tail

• Birds shed or molt feathers periodically:1. Molting usually in late summer between breeding & migration2. Flight feathers replaced3. Some birds molt before courtship

Beaks and Feet

• Adapted to habitat & feeding • Hawks & eagles have hooked beaks & talons

for tearing meat

• Swifts have tiny beaks that open wide to catch insects in midair

• Flightless birds like ostriches have legs & feet modified for running & walking

• Penguins have wings modified into flippers for swimming

• Ducks & geese with webbed feet

• Legs of some birds such as herons & egrets turn vivid colors to attract mates

Muscles

• Flight muscles called pectorals & are attached to wing & keeled sternum

• When large pectorals contract, wings move down

• When large pectorals relax & small pectorals contract, wings move upward

Body Temperature

• Metabolism generates body heat (endothermic)

• Enables birds to survive in warm & cold environments

• Rapid breathing & increased air sacs in lungs bring in more oxygen

• Ingest large amounts of food for energy • Fluff out feathers to trap air for insulation • Aquatic birds have thin layer of fat for

insulation

Digestive System

• Fast & efficient digestion• No chewing • Crop for temporary food storage • Two part stomach --- proventriculus & gizzard • Proventriculus is 1st chamber where digestive

juices added • Gizzard is 2nd part for crushing food

• Pyloric sphincter valve at lower end of gizzard controls food movement into intestines

• Duodenum - beginning of small intestine where bile (digests fats) & pancreatic juice are added & digested food is absorbed

Respiration

• Fly at high altitudes where there is less oxygen so need efficient respiratory system

• High metabolic rate requires large amount of oxygen

• Nine air sacs associated with lungs increase oxygen level & decrease density

• Air pathway:air enters body through nostrils on beak trachea (windpipe) syrinx (voice box) 2 primary bronchi 75% of air into two posterior air sacs and 25% of air into lungs air from lungs into other seven air sacs

Circulatory system

• Four chambered heart • Right side of heart pumps deoxygenated blood from

body cells to lungs • Left side of heart receives oxygenated blood from

lungs & pumps it to the body cells • Single aortic arch • Rapid heartbeat (hummingbird 600X/minute &

chickadee 1000X/minute) • Less active birds such as ostrich have slower heart

rates (70X/minute)

Nervous System

• Large brains relative to size of bird• Cerebellum coordinates movement • Cerebrum controls navigation, mating, nest

building, & care of young • Optic lobes receive & interpret visual stimuli • Have color vision for locating food

Reproductive System:

• Testes in males produces sperm that travels by the vas deferens to cloaca

• Females have single ovary that makes eggs • Eggs are fertilized in the oviducts • In mating, male presses cloaca to female to

transfer sperm (internal fertilization)

amniote egg

• 1. Embryo suspended in fluid called albumen (white of egg)2. Chalaza - rope like strands suspending embryo in albumen3. Chorion is membrane inside of shell4. Yolk is stored food surrounded by yolk sac

http://www.enchantedlearning.com/subjects/birds/label/chickenegg2/

• Eggs incubated by one or both parents • Brood patch - thickened, featherless patch of

skin on abdomen of bird used to warm eggs

• Yolk sac has blood vessels to carry food to embryo

• Wastes from embryo collect in membrane called allantois

• Chorion membrane lines the shell & allows gas exchange

Young birds may be precocial or altricial

Precocial young:

• 1. Have longer incubations2. More eggs laid3. Active as soon as hatch4. Nestlings can swim, walk, & feed themselves5. Need some parental care6. Includes ducks, geese, & swans

Altricial young:

• 1.Lay fewer eggs2. Hatch quickly3. Hatchlings are blind, naked, & helpless4. Depend on parents for warmth & food for several weeks5. Includes songbirds, woodpeckers, hawks, pigeons, doves, raptors

Behavior:

• Longer parental care allows more complex learning (courtship, nesting, migration, etc.)

• Territoriality allows males to establish & defend breeding areas

Courtship

• behaviors used by males to attract mates:1. Brightly colored feathers2. Flight displays3. Songs

Courtship

• Nest building holds eggs, conceals & shelters young birds, may help attract mates

• Nests are built in sheltered, well-hidden spots in trees, on the ground, etc. & are made of twigs, mud, grass, feathers...

nests

Migration

• triggered by dropping temperatures & dwindling food supplies

• Birds use migration clues including:1. Position of sun & stars2. Topographical landmarks3. Magnetic clues4.Air pressure changes5. Low frequency sounds