Birds

1
Birds

• Chapter 27

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Class Aves Birds

• Birds (class Aves) are archosaurs but almost
  every feature of their reptilian anatomy has
  undergone modification in their adaptation to
  flight.

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Class Aves Birds

• Birds are found in most every habitat from
  forests to deserts, even in caves.
• Some birds dive in the ocean to 45 m to catch
  prey.
• Birds have visited both the North South poles.
• The bee hummingbird of Cuba weighs 1.8 g and is
  one of the smallest vertebrate endotherms.

4
Derived Characters of Birds

• A birds most obvious adaptations for flight are
  its wings and feathers.
• Feathers are the feature that set birds apart
  from other vertebrates.

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Derived Characters of Birds

• Some other theropod dinosaurs had feathers, but
  they were not capable of supporting flight.
• Insulation provides support for the idea that
  some dinosaurs were endotherms.
• Bright colors may have been used to attract mates.

6
Characteristics of Birds

• All birds also have hindlimbs adapted for
  walking, swimming, or perching.
• Foot structure in bird feet shows considerable
  variation.
• All have keratinized beaks.
• All lay shelled amniotic eggs.

7
The Origin of Birds

• Birds descended from theropods a group of
  small, carnivorous dinosaurs.
• By 147 million years ago, feathered theropods had
  evolved into birds.

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The Origin of Birds

• Archaeopteryx
• The oldest bird known.
• Skull similar to modern birds but with thecodont
  teeth.
• Wings with feathers were present.

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The Origin of Birds

• Much of the skeleton was that of a theropod
  dinosaur.
• Long bony tail
• Clawed fingers
• Abdominal ribs
• S-shaped, mobile neck
• This fossil demonstrated the connection between
  theropods birds.

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The Origin of Birds

• Archaeopteryx arose from the theropod lineage.
• Closely related to Dromaeosaurs.
• More shared derived characters.
• Many had feathers used for insulation and/or
  social display.

11
Living Birds

• The ratites, superorder Paleognathae, are all
  flightless.
• Primitive archosaur palate.
• Ostriches, emus, rheas, kiwis, tinamous.
• Flat sternum, poorly developed pectoral muscles.

12
Living Birds

• All other birds are superorder Neognathae, having
  a flexible palate.
• The demands of flight have rendered the general
  body form of many flying birds similar to one
  another.
• Flying birds have a keeled sternum with well
  developed pectoral muscles.

13
Living Birds

• Flightlessness has evolved in many groups of
  birds.
• Penguins (use wings to swim through water).
• Many fossil forms including flightless owls,
  pigeons, parrots, cranes, ducks, auks.
• Usually occurs on islands with few predators.

14
Form Function Feathers

• Feathers are lightweight, yet tough, consisting
  of
• A hollow quill emerges from the skin.
• This becomes the shaft which bears numerous barbs
  that form a flat, webbed surface, the vane.
• Each barb contains many barbules.

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Form Function Feathers

• Contour feathers are vaned feathers that cover
  and streamline a birds body.
• Called flight feathers if they extend beyond the
  body.
• Down feathers are soft and have no hooks on
  barbules.
• Filoplume feathers are hair-like function
  unknown.
• Powder-down feathers disintegrate as they grow,
  releasing powder that aids in waterproofing.

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Form Function Feathers

• Feathers are homologous to reptiles scales.
• It develops from an epidermal elevation overlying
  a nourishing dermal core.
• In reptiles, this elevation flattens into a
  scale.
• In birds, it rolls into a cylinder and sinks into
  the follicle from which it will grow.

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Form Function Feathers

• As a feather nears the end of its growth, keratin
  is deposited to make some of the structures hard.
• The protective sheath surrounding the new feather
  splits open, and the feather unfurls.

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Form Function Feathers

• When fully grown, feathers are dead like
  mammalian hair.
• Birds molt to replace worn out feathers.
• Usually feathers are discarded gradually to avoid
  bare spots.
• Flight feathers tail feathers are lost in pairs
  to maintain balance.
• Many water birds lose all their primary feathers
  at once and are grounded during the molt.

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Form Function Feathers

• Colors in birds may be pigmentary or structural.
• Red, orange, yellow are colored by pigments
  called lipochromes.
• Black, brown, gray are produced by the pigment
  melanin.
• Blue is created structurally by the scattering of
  shorter wavelengths of light by particles within
  the feather.

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Form Function Skeleton

• A light, yet still strong skeleton is a
  requirement for flight.
• Bird bones are laced with air cavities.

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Form Function Skeleton

• Birds are archosaurs, and had ancestors with
  diapsid skulls.
• Bird skulls are highly specialized mostly fused
  into one piece.
• Leg bones in birds are heavier this helps lower
  the center of gravity giving aerodynamic
  stability.

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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 the gape.

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Form Function Skeleton

• All birds that can fly have a large, thin keel on
  their sternum that provides area for the large
  flight muscles to attach.

24
Food Feeding

• Early birds were carnivorous, feeding mostly on
  insects.
• Many birds are still insectivores.
• Other foods include nectar, seeds, berries,
  worms, crustaceans, molluscs, fish, frogs, small
  birds mammals.

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Food Feeding

• Some birds are generalists, feeding on a wide
  range of food items.
• Perhaps more competition for food, but less
  danger of something happening to the food source.
• Others are specialists, only feeding on one type
  of food.
• Less competition, more danger of losing the food
  source.

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Food Feeding

• The beaks of birds are strongly adapted to
  specialized food habits.

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Digestion

• At the end of the esophagus of many birds is the
  crop.
• Used for storage.

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Digestion

• The stomach has two compartments
• The first secretes gastric juices.
• The second, the gizzard, is lined with
  keratinized plates that serve as millstones for
  grinding food.
• Birds swallow small stones to help this process.

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Digestion

• Owls cant digest the bones fur or feathers of
  their prey.
• These materials are bundled together and ejected
  through the mouth.
• Owl pellets can be used to determine what the
  owls in a particular area have been eating.

30
Circulatory System

• Birds have a four-chambered heart.
• Separate systemic and respiratory circulations.
• Fast heartbeat faster in smaller birds.
• Red blood cells are nucleated and biconvex.
• Mammals are enucleated and biconcave.

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Respiratory System

• The highly adapted respiratory system of birds is
  adapted for the high metabolic demands of flight.
• The finest branches of the bronchi are developed
  as tubelike parabronchi through which air can
  flow continuously instead of ending in saclike
  alveoli as in mammals.

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Respiratory System

• There is an extensive system of nine
  interconnecting air sacs that connect to the
  lungs.
• Air flows to the posterior air sacs, to the lung,
  then to the anterior air sacs and out.

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Respiratory System

• The result is that there is an almost continuous
  stream of oxygenated air passing through the
  highly vascularized parabronchi.

34
Excretory System

• Urine is formed in large, paired metanephric
  kidneys.
• There is no urinary bladder.
• Nitrogenous wastes are secreted as uric acid
  rather than urea.
• Bird kidneys can only concentrate solutes to 4-8
  times that of blood concentration.

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Excretory System

• Some birds, including marine birds, have a salt
  gland to help rid the body of excess salts.
• Salt solution is excreted from the nostrils.

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Nervous System

• Birds have well developed cerebral hemispheres,
  cerebellum (important for coordinating movement
  balance), and optic lobes.

37
Senses

• Birds usually have poor sense of smell taste.
• Some, carnivores, waterfowl, flightless birds
  have well developed sense of smell taste.
• Birds have the keenest eyesight in the animal
  kingdom and also very good hearing.
• A hawk can clearly see a crouching rabbit a mile
  away!

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Flight

• To fly, birds must generate lift forces greater
  than their own mass and they must provide
  propulsion to move forward.
• Bird wings are designed to provide lift.

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Flight - Wings are Specialized for Particular
Kinds of Flight

• Elliptical wings are good for maneuvering in
  forests.
• High speed wings are used by birds that feed
  during flight or that make long migrations.
• Dynamic soaring wings are used by oceanic birds
  that exploit the reliable sea winds.
• High lift wings are found in predators that carry
  heavy loads. Soaring over land with variable air
  currents.

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Migration

• Many species of birds undergo long migrations
  using well established routes.
• Some species make the trip quickly, others stop
  along the way to feed.
• Often, they follow landmarks such as rivers and
  coastlines.

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Migration

• The stimulus for migration has to do with
  changing hormone levels brought about by a change
  in day length.

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Migration

• Birds navigate using a number of cues
• Visual cues landmarks.
• Accurate sense of time.
• Some may use the Earths magnetic field.
• Celestial cues sun by day, stars at night.

43
Social Behavior Mating Systems

• Two types of mating systems found in birds
• Monogamy where an individual has one mate.
• Rare in animals, common in birds.
• Seasonal or lifelong

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Social Behavior Mating Systems

• Birds have a high incidence of monogamy because
  both parents are equally able to perform most
  aspects of parental care.
• Often success of the hatchlings requires care
  from two parents.

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Social Behavior Mating Systems

• Polygamy where an individual has more than one
  mate during a breeding season.
• Polygyny one male, many females
• Polyandry one female, many males

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Social Behavior Mating Systems

• The most common form of polygamy in birds is
  polygyny.
• In some species, such as grouse, males gather in
  a display area or lek. Each male defends part of
  the lek and displays for the females.
• Only females care for young.

http//www.youtube.com/watch?vs2_wdMmEupQ
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Social Behavior Mating Systems

• An example of polyandry occurs in spotted
  sandpipers.
• Females defend territories and mate with several
  males.
• Each male incubates a nest of eggs in the
  females territory and does most of the parental
  care.
• This system may have evolved in response to high
  predation rates.

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Nesting

• Most birds build nests in which to lay eggs.
• Often great care is taken to hide the nest, or
  make it inaccessible to predators.
• When the young hatch, they usually must be fed by
  one or both parents.

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Nesting

• Precocial young, such as ducks, water birds, fowl
  and quail are covered with down when they hatch
  and can run or swim as soon as their down dries.
• Most precocial young must still be cared for by
  the parents for a time.

50
Nesting

• Altricial young are naked and unable to see or
  walk at hatching.
• They must remain in the nest for a week or more.
• Parents must spend lots of time energy bringing
  food to hatchlings.
• There is a continuum with the young of many
  species falling in between the two extremes.