Birds Class Aves Ch 19

Bird Characters Tetrapods Four-Chambered heart Eggs with calcareous shell Respiration by lungs Limbs usually with 4 digits 12 pairs of cranial nerves No larval stages

Birds Birds are endotherms: even body temperature: heat derived from animal’s own metabolism

Unique characters Horny toothless beaks Forelimbs modified for flying Feathers Flight

Adaptation for flight Wings (feathers) Bones Muscles Efficient digestion Respiratory system Nervous system Reproductive system

I. Feathers Contour feather –Up to 1,000 barbules on a barb –More than 1 million barbules per feather Barbs and barbules act like Velcro

II. Skeleton Modern birds have light but strong bones –Air cavities Weight of feathers > weight of bones

III. Muscles Up to 1,000 different muscles may control the flight feathers Most muscles are low in the body –Aerodynamic stability

IV. Digestion Early birds were carnivorous Now they feed on: –Insects –Nectar –Seeds –Etc… Birds have a high metabolic rate –Thus, they are voracious feeders

Beaks Beaks are highly specialized for food habitats

V. Respiratory system Must be very efficient due to high metabolism Lungs very different from reptiles and mammals Air sacs extend into body cavity –Increase gas exchange –Cools bird

VI. Reproductive System In most birds, only the left ovary and reproductive tract are functional. Structures on the right dwindle to vestiges.

The Big Picture It is almost certain that birds had a dinosaur-like ancestor Flight is what has made birds so successful The capacity to fly, however, has led to the evolution of many costly adaptations.