Bird Physiology

Integumentary System

  • Feathers = modified scales

    • keratinized stratum corneum of epidermis

    • claws and beak also keratinized stratum corneum

  • Scales on feet and base of beak

Feathers

  • Insulate body

  • Resistant, flexible flight surfaces

  • Specialized in form, color, and arrangement

  • Contour feathers—large firm vane, downy base

    • Pyerylae—tracts of integument with feather follicles

    • Apteria—bare patches

  • Primaries—between wrist and tip of vane

  • Secondaries—between wrist and elbow

  • Rectrices—tail feathers

  • Coverts—small feathers overlie the base of flight feathers

  • Alula—”thumb” bears 3-5 flight feathers, helps maneuver

Molting

  • Usually related to reproduction

  • Most molt annually

  • Postnuptial molt—after breeding/nesting, before migration

  • Prenuptial molt—some males, breeding plumage

  • Triggered by photoperiod

Skeletal System

  • Specialized for lightness and strength

  • Thin, strutted bones

  • Fusion of bones=strength

  • Beak (bill) formed by elongation of premaxillary and dentary bones

  • Highly flexible neck

  • Synsacrum—fused vertebrae just above tail, rigid for flight and bipedalism

  • Highly keeled sternum

  • Variable bills and feet due to function

Cardiovascular System

  • 4 chambered heart

  • Larger birds= slower, smaller heart

    • turkey < 100 beats/minute

    • sparrow = 500 beats/minute

  • Countercurrent heat exchange—blood flows in opposite directions to reduce energy loss

Respiratory System

  • No muscular diaphragm

  • Lungs in pleural cavities

  • Membrane between pleural cavities acts as diaphragm

  • Muscles contract to create low pressure and draw air into lungs, second contraction pulls air into air sacs

  • During flight, contraction of flight muscles draws in air

  • Air sacs

    • 3x the respiratory volume of similar size mammal

Digestive System

  • No teeth

  • non-muscular tongue with tactile sensors

  • Crop—storage in grain eating birds

  • Muscular gizzard + grit/stones to grind food

  • Ceca—paired, at junction of small and large intestine, range of digestive functions

Nervous system

  • Reduced olfactory portion of brain

  • Optic lobes greatly enlarged and well developed

    • Best vision of all vertebrates

    • Flying, foraging, mate selection, navigation

    • Eyes may equal or exceed weight of brain

    • Eye position based on predator/prey

    • Some perceive ultraviolet and polarized light

  • Good hearing

    • “ears” are feathers, tympanum part of inner ear

    • very well developed in owls

    • some birds use echolocation