1. Class Aves Birds are reptile like animals that maintain a constant
internal body temperature.
They have an outer covering of feathers, 2 legs that
are covered with scales and front limbs modified
into wings.

2. Characteristic that separates birds from other
animals = feathers
Most paleontologists think that birds evolved from
extinct reptiles like dinosaurs.
Part of the evidence:
Archaeopteryx:
First birdlike
fossil discovered

3. Well developed feathers like
a modern bird.
Teeth, bony tail,
Toes and claws on its wings
like dinosaurs.

4. Body temperature control:
Endotherms - ‘warm blooded’ – they control their
Internal body temperature.
Feathers help to insulate the body.
Most birds internal temperature is about 41C
(105.8F) even on cold days.
Down – trap air to keep bird warm
Contour – provide lifting, force and balance needed for flight

5. Feeding:
Bird’s beaks or bills are adapted to the type of food they
eat.
Insect eating – fine, short beaks
Seed eating – short, thick beaks
Long, thin beaks – gather nectar
Carnivores – strong, hooked beaks

6. No teeth – have specialized structures to help break down
food.
Crop – food is stored and moistened.
Gizzard – In birds that eat insects and birds, help further
digestion by grinding it. Usually small stones inside.

7. Respiration:
Inhales – most of air first enters large air sacs in the body
cavity and bones and then flows to the lungs.
Air travels through the lungs in a series of small tubes
where gas exchange takes place.

8. Circulation:
4 Chambered heart.
Heart beats quickly – from 150 to more than 1000
beats per minute!

9. Excretion:
Nitrogenous wastes are removed by the kidneys
and converted into uric acid.
Most water is reabsorbed and excretion is in a
white pasty form (bird droppings)
Response:
Well developed brain that can interpret and respond to
A lot of incoming signals.
Well developed eyes – can see color well.

10. Movement:
Flight less birds – walk, run
Cassowary

11. Adaptations for flight:
Most other birds fly.
Adaptations for flight:
Long bones are very strong (strengthened by internal
struts) and light (air spaces)
Large chest muscles
Enlarged breast bone or sternum where muscles are
attached to.
Feathers

12. Internal fertilization Lay eggs – oviparous
Reproduction:
Internal fertilization
Lay eggs – oviparous
Eggs have hard outer shells.
Most birds incubate their eggs until they hatch.
Both parents often provide food for their young.