34.1 The Natural History of Birds
| Birds are the only animals with feathers. |
| Evolutionary links between reptiles and birds have been shown in fossils. |
| Fossil record of birds is fragmented and incomplete becasue their feathers and fragile bones don't fossilize well. |
| Archaeopteryx is the earliest fossil known to have feathers. |
| Perching songbirds have the greatest range of adaptation and live in nearly every environment. |
34.2 Movement and Support
| Differences between a bird's body and reptiles are the result of structural adaptations for flight. |
| Down feathers insulate the bird by trapping layers of air. |
| Fused bones also reduce the need for heavy ligaments to hold them together. |
34.3 Energy Needs
| Endotherms are animals that maintain a constant internal body temperature. |
| Birds have more efficient respiratory, circulatory and digestive systems than reptiles which enables them to meet energy needs. |
| Crocodiles and birds are closely related because they have a four-chambered heart. |
| Respiratory system is unique in that flow of air through lungs is a one-way flow. |
| There is no urinary bladder in which to store liquid wastes. |
| Crop is a storage area in digestive tract where food is softened. |
| Muscular action of the gizzard combined with stones breaks the food into very small pieces. |
| Villi are fingerlike projections of intestinal wall that increase the surface area across which nutrients are absorbed. |
34.4 Reproduction
| Since birds are endothermic, their eggs must be incubated while the embryo develops. |
| Many animals must learn the characteristics of their species during a critical period immediately after birth called imprinting. |
| Most birds are monogamous only during one particular breeding season. |
| Mating, nest-building and migration are annual events of instinctive behavior that are triggered by the amount of daylight. |
34.5 Adaptations for Getting Food
| Birds eat almost anything, from seeds and insects to fish and small land animals. |
| They must use their feet to grasp food. |
| Many birds use their beaks to break or tear food into pieces small enough to swallow. |