Birds are not mammals; they are a different class of animals within the animal kingdom. Mammals and birds are distinct groups with different characteristics and evolutionary histories.
Mammals are warm-blooded vertebrates with mammary glands, allowing them to nurse their young with milk. They typically have hair or fur on their bodies and give birth to live young (although there are exceptions like monotremes, such as the platypus, which lay eggs). Mammals have a range of adaptations that set them apart from birds and other animals.
On the other hand, birds are warm-blooded vertebrates characterized by features such as feathers, beaks, lightweight bones, and the ability to lay eggs. Their unique respiratory system enables efficient oxygen exchange, which is essential for their high-energy activities, including flying.
In summary, birds are not mammals; the two groups are distinguished by their distinct characteristics and evolutionary lineages.