Birds Class Aves Ch 19 Bird Characters Tetrapods

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.