CLASS CLASS AVESAVES

ZOOLOGY

CLASS AVESCLASS AVES

• 9,700 species

• the largest class of terrestrial vertebrates.

• Among living vertebrates, only birds and bats can fly.

• The bodies of birds are well adapted to flight.

CLASS AVESCLASS AVES

• Birds are so distinctive that it is difficult to mistake one for any other kind of vertebrate.

• There are seven important characteristics of birds.

FEATHERSFEATHERS

• Feathers are unique to birds, and all birds have them.

• Like hair, feathers are composed mainly of the versatile protein keratin.

• Feathers serve two functions:

1. Essential for flight2. Insulate a bird’s body

against heat loss

WINGSWINGS

• A bird’s forelimbs are modified into a pair of wings.

• Feathers cover most of the surface area of the wing.

SKELETONSKELETON• Skeleton is lightweight and rigid• Reflects the requirements of

flight.– Many of the bones are thin-walled

and hollow, making them lighter than the bones of nonflying animals.

– Air sacs from the respiratory system penetrate some of the bones.

• Because many bones are fused, the skeleton is rigid and can resist the forces produced by the strong flight muscles.

ENDOTHERMIC METABOLISMENDOTHERMIC METABOLISM

• A bird’s rapid metabolism supplies the energy needed for flight.

• Birds maintain a high body temperature of 40–41°C (104–106°F).

UNIQUE RESPIRATORY SYSTEMUNIQUE RESPIRATORY SYSTEM• Rapid metabolism requires

an abundant supply of oxygen, and birds have the most efficient respiratory system of any terrestrial vertebrates.

• The lungs are connected to several sets of air sacs, an arrangement that ensures that oxygen-rich air is always in the lungs.

BEAKBEAK

• No modern bird has teeth, but the jaws are covered by a tough, horny sheath called a beak.

OVIPARITYOVIPARITY

• All birds lay amniotic eggs encased in a hard, calcium-containing shell.

• In most species, the eggs are incubated in a nest by one or both parents.