Introduction to the Birds Class = Aves ≈ 9600 species, 27 orders, far outnumber all other vertebrates except: fishes Distribution = worldwide Ratites = flightless birds, 4 orders Carinate = birds that fly , 23 orders Single unique feature of birds = feathers Forelimbs modified into wings Hindlimbs adapted for walking, swimming, or perching All have horny beaks All lay eggs Most have body adapted for flight (mode of locomotion) Characteristics 1. Body - head, neck, trunk, & tail 2. Paired forelimbs - modified into wings for flight 3. Epidermis Feathers on body, scales on legs Down – Insulation Molting – loss of feathers Water birds molt all feathers @ once 4. Skeleton Fully ossified w/ air cavities (reduce weight for flight) Beak w/o teeth Sternum (breastbone) w/ or w/o keel (for attachment of flight muscles) 5. Nervous system – well developed Sight – excellent Hearing – bird song, courtship Smell - limited 6. Heart – 4 chambers 7. Endothermic = “heat from w/in” = warm-blooded 8. Respiration – expandable lungs - Air sacs throughout body - Permit steady delivery of O2 to tissues - Reduce weight of body for better flight 9. Syrinx = voice box for vocalizations 10. Kidneys, no bladder – semisolid excreta 11. Reproduction - Oviparous - Internal fertilization - Egg incubation external - Nest building - Parental care