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  1. 1. Birds
  2. 2. Class Aves – BirdsBirds (class Aves) are archosaurs butalmost every feature of their reptiliananatomy has undergone modification intheir adaptation to flight.
  3. 3. Class Aves – BirdsBirds are found in most every habitatfrom forests to deserts, even in caves. Some birds dive in the ocean to 45 m tocatch prey. Birds have visited both the North & Southpoles. The bee hummingbird of Cuba weighs 1.8 gand is one of the smallest vertebrateendotherms.
  4. 4. Derived Characters of Birds A bird’s most obvious adaptations for flight areits wings and feathers. Feathers are the feature that set birds apartfrom other vertebrates.
  5. 5. Derived Characters of BirdsSome other theropod dinosaurs hadfeathers, but they were not capable ofsupporting flight. Insulation – provides support for the ideathat some dinosaurs were endotherms. Bright colors may have been used to attractmates.
  6. 6. Characteristics of Birds All birds also have hindlimbs adapted for walking,swimming, or perching. Foot structure in bird feetshows considerablevariation. All have keratinized beaks. All lay shelled amnioticeggs.
  7. 7. The Origin of Birds Archaeopteryx The oldest bird known. Skull similar to modern birds but with thecodontteeth. Wings with feathers were present.
  8. 8. The Origin of Birds Much of the skeleton wasthat of a theropoddinosaur. Long bony tail Clawed fingers Abdominal ribs S-shaped, mobile neck This fossil demonstratedthe connection betweentheropods & birds.
  9. 9. Living Birds The ratites, superorderPaleognathae, are allflightless. Primitive archosaurpalate. Ostriches, emus, rheas,kiwis, tinamous. Flat sternum, poorlydeveloped pectoralmuscles.
  10. 10. Living Birds All other birds have a flexiblepalate. The demands of flight haverendered the general bodyform of many flying birdssimilar to one another. Flying birds have a keeledsternum with well developedpectoral muscles.
  11. 11. Living Birds Flightlessness hasevolved in many groupsof birds. Penguins (use wings toswim through water). Many fossil formsincluding flightless owls,pigeons, parrots,cranes, ducks, & auks. Usually occurs onislands with fewpredators.
  12. 12. Form & Function – Feathers Feathers are lightweight,yet tough, consisting of: A hollow quill emergesfrom the skin. This becomes the shaftwhich bears numerousbarbs that form a flat,webbed surface, thevane. Each barb containsmany barbules.
  13. 13. Form & Function – Feathers Contour feathers are vanedfeathers that cover andstreamline a bird’s body. Called flight feathers if theyextend beyond the body. Down feathers are soft andhave no hooks on barbules. Filoplume feathers are hair-like – function unknown. Powder-down feathersdisintegrate as they grow,releasing powder that aids inwaterproofing.
  14. 14. Form & Function – FeathersFeathers are homologous to reptiles’scales.It develops from an epidermal elevationoverlying a nourishing dermal core. In reptiles, this elevation flattens into ascale. In birds, it rolls into a cylinder and sinks intothe follicle from which it will grow.
  15. 15. Form & Function – Feathers As a feather nearsthe end of its growth,keratin is depositedto make some of thestructures hard. The protectivesheath surroundingthe new feather splitsopen, and the featherunfurls.
  16. 16. Form & Function – FeathersWhen fully grown, feathers are dead –like mammalian hair.Birds molt to replace worn out feathers. Usually feathers are discarded gradually toavoid bare spots. Flight feathers & tail feathers are lost inpairs to maintain balance. Many water birds lose all their primaryfeathers at once and are grounded duringthe molt.
  17. 17. Form & Function – FeathersColors in birds may be pigmentary orstructural. Red, orange, & yellow are colored bypigments called lipochromes. Black, brown, & gray are produced by thepigment melanin. Blue is created structurally by the scatteringof shorter wavelengths of light by particleswithin the feather.
  18. 18. Form & Function – SkeletonA light, yet still strong skeleton is arequirement for flight. Bird bones are laced with air cavities.
  19. 19. 19
  20. 20. Form & Function – SkeletonBirds are archosaurs, and had ancestorswith diapsid skulls. Bird skulls are highly specialized – mostlyfused into one piece.Leg bones in birds are heavier – thishelps lower the center of gravity givingaerodynamic stability.
  21. 21. Form & Function – SkeletonModern birds are toothless. Instead they have a keratinized beak.Most birds have kinetic skulls. They have a wide gape. Upper jaw is attached loosely increasing thegape.
  22. 22. Form & Function – Skeleton All birds that can flyhave a large, thinkeel on theirsternum thatprovides area forthe large flightmuscles to attach.
  23. 23. Food & FeedingEarly birds were carnivorous, feedingmostly on insects. Many birds are still insectivores. Other foods include nectar, seeds, berries,worms, crustaceans, molluscs, fish, frogs,small birds & mammals.
  24. 24. Food & FeedingSome birds are generalists, feeding on awide range of food items. Perhaps more competition for food, but lessdanger of something happening to the foodsource.Others are specialists, only feeding onone type of food. Less competition, more danger of losing thefood source.
  25. 25. Food & Feeding The beaks of birds are strongly adapted tospecialized food habits.
  26. 26. DigestionAt the end of the esophagus of manybirds is the crop. Used for storage.
  27. 27. DigestionThe stomach has two compartments: The first secretes gastric juices. The second, the gizzard, is lined withkeratinized plates that serve as millstonesfor grinding food. Birds swallow small stones to help this process.
  28. 28. DigestionOwls can’t digest the bones & fur orfeathers of their prey. These materials are bundled together andejected through the mouth. Owl pellets can be used to determine whatthe owls in a particular area have beeneating.
  29. 29. Circulatory SystemBirds have a four-chambered heart. Separate systemic and respiratorycirculations.Fast heartbeat – faster in smaller birds.Red blood cells are nucleated andbiconvex. Mammals are enucleated and biconcave.
  30. 30. Respiratory SystemThe highly adapted respiratory systemof birds is adapted for the high metabolicdemands of flight. The finest branches of the bronchi aredeveloped as tubelike parabronchi throughwhich air can flow continuously – instead ofending in saclike alveoli as in mammals.
  31. 31. Respiratory System There is anextensive systemof nineinterconnecting airsacs that connectto the lungs. Air flows to theposterior air sacs,to the lung, thento the anterior airsacs and out.
  32. 32. Respiratory SystemThe result is that there is an almostcontinuous stream of oxygenated airpassing through the highly vascularizedparabronchi.
  33. 33. Excretory SystemUrine is formed in large, pairedmetanephric kidneys. There is no urinary bladder. Nitrogenous wastes are secreted as uricacid rather than urea. Bird kidneys can only concentrate solutes to4-8 times that of blood concentration.
  34. 34. Excretory System Some birds,including marinebirds, have a saltgland to help rid thebody of excess salts. Salt solution isexcreted from thenostrils.
  35. 35. Nervous System Birds have welldeveloped cerebralhemispheres,cerebellum(important forcoordinatingmovement &balance), and opticlobes.
  36. 36. SensesBirds usually have poor sense of smell &taste. Some, carnivores, waterfowl, flightless birdshave well developed sense of smell & taste.Birds have the keenest eyesight in theanimal kingdom and also very goodhearing. A hawk can clearly see a crouching rabbit amile away!
  37. 37. FlightTo fly, birds must generate lift forcesgreater than their own mass and theymust provide propulsion to moveforward.Bird wings are designed to provide lift.
  38. 38. Flight - Wings are Specialized forParticular Kinds of Flight Elliptical wings are good for maneuvering in forests. High speed wings are used by birds that feed duringflight or that make long migrations. Dynamic soaring wings are used by oceanic birds thatexploit the reliable sea winds. High lift wings are found in predators that carry heavyloads. Soaring over land with variable air currents.
  39. 39. Migration Many species of birdsundergo longmigrations using wellestablished routes. Some species makethe trip quickly,others stop along theway to feed. Often, they followlandmarks such asrivers and coastlines.
  40. 40. Migration The stimulus formigration has to dowith changinghormone levelsbrought about by achange in daylength.
  41. 41. MigrationBirds navigate using a number of cues: Visual cues – landmarks. Accurate sense of time. Some may use the Earth’s magnetic field. Celestial cues – sun by day, stars at night.
  42. 42. Social Behavior – Mating Systems Two types of matingsystems found inbirds: Monogamy wherean individual hasone mate. Rare in animals,common in birds. Seasonal or lifelong
  43. 43. Social Behavior – Mating SystemsBirds have a high incidence ofmonogamy because both parents areequally able to perform most aspects ofparental care. Often success of the hatchlings requirescare from two parents.
  44. 44. Social Behavior – Mating SystemsPolygamy where an individual has morethan one mate during a breedingseason. Polygyny – one male, many females Polyandry – one female, many males
  45. 45. Social Behavior – Mating Systems The most commonform of polygamy inbirds is polygyny. In some species, suchas grouse, malesgather in a displayarea or lek. Eachmale defends part ofthe lek and displaysfor the females. Only females care foryoung.
  46. 46. Social Behavior – Mating SystemsAn example of polyandry occurs inspotted sandpipers. Females defend territories and mate withseveral males. Each male incubates a nest of eggs in thefemale’s territory and does most of theparental care.This system may have evolved inresponse to high predation rates.
  47. 47. Nesting Most birds build nestsin which to lay eggs. Often great care istaken to hide the nest,or make it inaccessibleto predators. When the young hatch,they usually must befed by one or bothparents.
  48. 48. Nesting Precocial young, such asducks, water birds, fowland quail are coveredwith down when theyhatch and can run orswim as soon as theirdown dries. Most precocial youngmust still be cared for bythe parents for a time.
  49. 49. Nesting Altricial young are naked andunable to see or walk athatching. They must remain in the nestfor a week or more. Parents must spend lots oftime & energy bringing foodto hatchlings. There is a continuum with theyoung of many species fallingin between the two extremes.