1. Birds Class Aves Ch 19

2. 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

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

4. Unique characters Horny toothless beaks Forelimbs modified for flying Feathers Flight

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

6. 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

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

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

9. 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

10. Beaks Beaks are highly specialized for food habitats

11. 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

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

13. 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.