This document provides an overview of birds, including their: - Adaptations for flight including feathers, lightweight skeletons, and specialized respiratory systems. - Global distribution in most habitats. - Varied diets and specialized beaks. - Reproduction through shelled eggs and parental care of hatchlings. - Complex social behaviors like mating systems, migration, and nesting.

1. Birds

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

3. 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 bird’s most obvious adaptations for flight are
its wings and feathers.
 Feathers are the feature that set birds apart
from other vertebrates.

5. 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 hind
limbs 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
 Archaeopteryx
 The oldest bird known.
 Skull similar to modern birds but with thecodont
teeth.
 Wings with feathers were present.

8. 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.

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

10. Living Birds
 All other birds have 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.

11. 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.

12. 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.

13. Form & Function – Feathers
 Contour feathers are vaned
feathers that cover and
streamline a bird’s 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.

14. 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.

15. 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.

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 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.

17. 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.

18. Form & Function – Skeleton
 A light, yet still strong skeleton is a
requirement for flight.
 Bird bones are laced with air cavities.

19. 19

20. 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.

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 the
gape.

22. 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.

23. 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.

24. 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.

25. Food & Feeding
 The beaks of birds are strongly adapted to
specialized food habits.

26. Digestion
 At the end of the esophagus of many
birds is the crop.
 Used for storage.

27. 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.

28. Digestion
 Owls can’t 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.

29. 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.

30. 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.

31. 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.

32. Respiratory System
 The result is that there is an almost
continuous stream of oxygenated air
passing through the highly vascularized
parabronchi.

33. 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.

34. 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.

35. Nervous System
 Birds have well
developed cerebral
hemispheres,
cerebellum
(important for
coordinating
movement &
balance), and optic
lobes.

36. 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!

37. 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.

38. 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.

39. 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.

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

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. 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

43. 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.

44. 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

45. 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?v=s2_wdMmEupQ

46. 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
female’s territory and does most of the
parental care.
 This system may have evolved in
response to high predation rates.

47. 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.

48. 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.

49. 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.