Lecture 22

• Respiratory system of birds

  • Differs radically from the lungs of other reptiles and mammals

  Marvelously adapted for meeting the high metabolic demands of flight

  Finest branches of the bronchi are developed as tubelike parabronchi through which air flows continuously

  Nine interconnecting air sacs located in pairs in the thorax

  Almost continuous stream of oxygenated air is passed through the richly vascularized parabronchi

  
• Bird flight


  Birds generate lift during flight when air passes angled or curved (cambered) wings

  Downward-deflected air pushes the wing (and bird) upward

  Birds fly by applying the same aerodynamic principles as an airplane and using similar equipment: wings for lift and propulsion, a tail for steering and landing control, and wing slots for control at the slow speed of take-offs and landings

  
• Bird wing anatomy


  • Slower-flying, highly maneuverable birds have short, rounded wings with high camber and prominent slots

  The fastest birds have long, pointed wings with flat profiles and no slots

  
• Bird migration


  Regular movements between summer nesting places and wintering regions

  Most birds migrate north in spring and south in fall

  Birds use many cues to navigate during migration, including using geographic landmarks, the position of the sun or stars, and the Earth's magnetic field

  
• Social behavior of birds

  • Highly developed, manifested in vivid courtship displays, mate selection, territorial behavior, and incubation of eggs and care of young
• Monogamy in birds


  Most birds are monogamous during the reproductive season, when a male and female form a pair-bond

  Many are only socially monogamous—pairing is maintained, but mating is not restricted to the partner
• Polygyny and polyandry in birds

  Some birds are polygynous, where one male mates with multiple females

  Some birds are polyandrous, where one female mates with multiple males
• Nesting and parental care in birds

  • Most birds build a nest to incubate their eggs

  For some species, only the mother cares for the eggs and young; but in many species, both parents participate in care

  Young hatch at various levels of development: altricial young are naked and helpless, whereas precocial young are feathered and able to walk and feed themselves
• Characteristics of mammals


  • Endothermic

  Have hair on their bodies

  Nurse their young with milk

  Extant mammals are in three clades: Monotremata (egg-laying mammals), Metatheria (marsupials), and Eutheria (placentals)
• Mammary glands


  Occur on all female mammals and in a rudimentary form on all male mammals

  Develop from downward-growing epidermal cells that form a branching system of ducts, surrounded by milk-producing cells

  Grow rapidly during the late stage of pregnancy, in response to hormones

  The number of mammary glands varies from 2 in primates to about 20 in some marsupials

  In human females, adipose tissue begins to accumulate around the mammary glands at puberty to form the breast
• Mammalian skin and associated structures

  • Skin is thicker in mammals than in other classes of vertebrates

  Epidermis is thinner where it is well protected by hair, but in places subject to much contact and use, its outer layers become thickened with keratin

  Hair is especially characteristic of mammals and grows from hair follicles sunk into the dermis of the skin

  Hair may provide mechanical protection, thermal insulation, protective coloration, and waterproofing
• Types of hair in mammals

  • Dense and soft underhair for insulation, trapping a layer of insulating air

  Coarse and longer guard hair for protection against wear and to provide coloration
• Most mammals have two annual molts, one in the spring and one in the fall

  Summer coats are always much thinner than winter coats and in some mammals may be a different color