Birds

Closest related animal to dinosaurs (therapod)

Divided into two groups based on keeled sternum:

• Paleognathe (large, flightless birds): Flat sternum

• Neoghathae (all other birds): Keeled sternum

Endotherms:

• Homeotherms:

  • They maintain a constant elevated body temperature

  • Flight requires massive amounts of energy

  • Metabolism produces heat

  • Very high energy/caloric requirements

• Have a very long list of derived and defining characteristics are adaptations for flight

Feathers:

• Made of beta-keratin, which is also in reptile scales

• Feather arrangement forms the wings into airfoils

Skeleton:

• Very light yet stable with pneumatic bones (air spaces)

  • Reduces weight

• With the exception of cervical (neck) vertebrae, all other vertebrae are fused to provide rigid support during flight

• Lacking teeth, have keratinized beak instead

  • Adapted to specific diets

• Main leg muscles are in the thigh, no muscles in lower legs/feet

  • Muscle mass close to birds center of gravity

  • Strong tendons in feet and toes

  • Legs are extremely resistant to cold

  • Locking mechanism

Beak adaptations:

• All birds were carnivorous

• Some modern birds are specialists, others are omnivorous

• Due to the high metabolic demands of flight, birds are voracious eaters

Wings:

• Active soaring wings: Albatross, Gannet, Gull

  • Long and narrow, gliding long distances, no spaces between feathers

• Passive soaring wings: Eagles, Buteo, Stork

  • Very long and broad with large feathers, catch wind gusts to fly, little flapping, space between feathers

• Elliptical Wings: Sparrow, Grouse, Blackbird, Thrush, Crow (generalist)

  • Short and rounded, quick takeoffs, agile flying

• High-speed wings:Swift, Falcon, Duck, Tern, Sandpiper

  • Long and pointed

  • Fast flying

Respiratory System:

• 9 air sacs are connected to the lungs, inspired air skips the lungs and instead goes to posterior air sacs (reservoir for air)

• Birds complete two inhalation/exhalation cycles for a single breath of air to pass

  • 1st inhalation: air bypass lungs and goes to posterior air sacs

  • 1st exhalation: air from 1st inhalation moves into the lungs

  • 2nd inhalation: air moves from lungs to anterior air sacs at the same time as new air moves to posterior sacs

  • 2nd exhalation: air in anterior sacs leaves the body, air in posterior sacs moves into the lungs

• Complex system, always fresh oxygenated air in the respiratory system

Excretory and Reproductive Systems

• No urinary bladder

• Have cloaca

  • Body cavity connected to digestive, urinary, and reproductive system

  • Allows for water to be absorbed from waste

    • No liquid waste

    • Urate salts expelled with feces (white)

• Females have only one “functional” ovary

• In both sexes, gonads change size throughout the year

  • They shrink in non-breeding season

  • They grow considerably during breeding seaspn

Sensory System:

• Nervous and sensory systems must meet demands of complex flight

  • Cerebrum is enlarged to control social behavior, flying, complex problem-solving

  • Intelligent birds have larger cerebrum

  • Cerebellum is enlarged to control muscle movement, equilibrium, balance

  • Very large optic lobe to process visual information associated with flight, finding food, reproductive behavior

• Acute, color vision

• Complex vocalization/communication

Reproduction:

• Internal fertilization

• Males do not have penis in most species

• Cloacal kiss

• Female is oviparous

• Significant parental care from both parents

• Nest is built or dug

  • Eggs laid in nest

  • Eggs brooded to keep warm

  • Chicks are dependent on parents

• Altricial chicks: hatch blind, no/minimal feathers, unable to move around

  • Require extended and significant parental care

• Precocial chicks: hatch with open eyes, feathers, able to move around

  • Able to leave the nest, run/swim/walk, find food within a few days, but parents still provide care until they are able to fly

  • More independent, typically flightless birds

BIRD CIRCULATORY SYSTEM:

• 4 chambered heart

• Two atria two ventricles

• Oxygenated and deoxygenated blood are completely separate

• Deoxygenated blood → right atrium → right ventricle→ lungs (oxygenated) with pulmonary circulation → heart → left atrium → left ventricle → aorta → body (systemic circulation)

• Deoxygenated on right side of heart, oxygenated on the left.