1. Mammary Glands and Milk Production: Mammals have mammary glands that produce milk to nourish their young. Birds, on the other hand, do not produce milk and instead lay eggs.
2. Hair or Fur: Most mammals have hair or fur that provides insulation and protection. Birds have feathers, which serve a similar purpose but are structurally different from mammalian fur.
3. Endothermy: Mammals are endothermic, meaning they can generate their own body heat to maintain a stable internal temperature. Birds are also endothermic, but their physiological mechanisms for temperature regulation differ from those of mammals.
4. Viviparity in Most Cases: Most mammals give birth to live young (viviparity), while birds lay eggs (oviparity). There are exceptions within both groups, such as the platypus and echidna (monotremes) among mammals and a few bird species that give birth to live young.
5. Four-Chambered Heart: Mammals have a four-chambered heart (two atria and two ventricles), allowing for efficient separation of oxygenated and deoxygenated blood. Birds also have a four-chambered heart but with some differences in structure and function.
6. Red Blood Cells: Mammalian red blood cells lack nuclei and have a biconcave shape, while avian red blood cells are nucleated and oval.
7. Diaphragm: Mammals possess a diaphragm, a sheet of muscle that separates the thoracic and abdominal cavities and assists in breathing. Birds have air sacs that aid in respiration but lack a diaphragm.
8. External Ears (Pinnae): Most mammals have external ear structures called pinnae, which help capture and direct sound waves. Birds typically lack external ears and instead have ear openings covered with feathers.
9. Parental Care: Mammals generally provide extensive parental care to their offspring, including nursing, protecting, and teaching them skills. While birds also exhibit parental care, the level and nature of care may differ.
10. Three Middle Ear Bones: Mammals have three small bones (malleus, incus, and stapes) in their middle ear, which aid in transmitting sound waves. Birds have a single bone in their middle ear, the columella.
These characteristics collectively help distinguish mammals from birds and contribute to their distinct adaptations and niches in the animal kingdom.