Birds/Aves

• Birds


  Avian reptiles, part of the Phylum Chordata
• Birds


  • 2nd most abundant vertebrate group
  • Found in all habitats: forests, deserts, mountains, prairies, oceans
  • Some live in caves in total darkness
  • Even found at the north and south poles
• Smallest bird


  • Hummingbird (1.8 g)
• Largest flying bird


  • Wandering Albatross (12 ft wingspan, 25 lbs)
• Largest known flying bird

  • Eoalulavis (condor-like bird, had to run downhill into a headwind to take off)
• Largest bird


  • Elephant bird of Madagascar (2 M tall, 450 kg)
  • Extinct Moas of New Zealand (Tallest and flightless bird, related to emu, 3.6 M to 250 kg)
• Feathered theropods


  Archaeopteryx (70 kg with 6.4M wingspan)
• Birds evolved from feathered velociraptors
• Birds are classified in the same class (Reptilia) as dinosaurs
• Feathers of early birds may not have been similar to modern bird feathers
• Early birds did not have a keel for flight muscles and probably did not fly
• Early birds had bones that were not thin and hollow as in modern birds
• Early birds had a brain comparable to a reptile, not a larger bird brain
• By the Cretaceous period, fossils clearly indicate birds that could fly
• Recent genetic analysis indicates that large flightless birds like ostrich, kiwi and emu are the most ancient and most "dinosaur-like" birds
• Advantages of flight


  • Permits sudden and rapid escape from predators
  • Easier to find food, water, nesting areas, mates, etc
  • Fast straight-line travel from place to place
  • Inaccessible places become accessible; opening up new niches
  • Facilitates migrations over long distances
• Flight has evolved at least 4 different times in the history of life: insects, reptiles (pterosaurs), birds, bats
• Arboreal theory


  Wings evolved in reptiles that climbed trees to hunt for insects
• Cursorial theory


  Wings evolved in running reptiles perhaps as stabilizers
• Bird body form


  • Small compact body
  • Reduced weight
  • All heavy organs close to center of gravity
• Hollow bones


  Help reduce weight for flight
• Bird skin


  • Thin, light and flexible
  • No sweat glands (insulation and protection from elements taken over by feathers)
• Bare areas on bird skin

  • Vulture head (keeps feathers clean while feeding on carcass)
  • Ostriches & relatives (unfeathered legs used for cooling after heavy exercise)
  • Arctic birds (have NO bare areas)
• Feathers


  • Epidermal structures derived from reptile scales
  • Smooth the surface and streamline the contour of the body, making flying more efficient
• Feather structure


  • Shaft (rachis)
  • Quill part of shaft below vanes
  • Vanes
  • Barbs & hooked barbules overlapping extensions of vane (preening "zips" barbs and barbules back together)
• Types of feathers


  • Contour feathers
  • Flight feathers (primaries, secondaries, tertials)
  • Down feathers (plumules)
  • Filoplumes (decorative feathers & bristles)
• Loss of primaries


  May prevent flight
• Down feathers


  • Lack vane, barbs fan out, not hooked together
  • Hidden beneath contour feathers
  • Especially on breast and abdomen of water birds to conserve heat
• Filoplumes


  • Hairlike, degenerative feathers; simple shafts or with tuft of bristles at end
  • Bristles are sensory
  • On head, around eyes, around mouth and nostrils
• Flight muscle attachment


  • Keeled sternum
  • Furcula
• Appendages


  • Fusion of bones
  • Perching tendons
• Flight adaptations


  • Form airfoil
  • Slotting and alula reduce turbulence
• Tail


  • Balancing, steering, braking
• Kinds of flight


  • Gliding
  • Flapping
  • Soaring
  • Hovering
• Nutrition and digestive system

  • High rates of food consumption support rapid metabolic rates
  • Bill modifications
  • Crop (storage)
  • Proventriculus (secretes gastric juices)
  • Stomach
• Flight muscle attachment


  • Keeled sternum
  • Furcula
• Appendages


  • Fusion of bones
  • Perching tendons
• Flight adaptations


  • Form airfoil
  • Slotting and alula reduce turbulence
  • Tail for balancing, steering, braking
• Kinds of flight


  • Gliding
  • Flapping
  • Soaring
  • Hovering
• Bill modifications


  Support high rates of food consumption and rapid metabolic rates