Massachusetts Curriculum Frameworks. What are Birds? Birds are warm-blooded animals that have: wings, feathers, a beak, no teeth, bones. Birds lay eggs. Their young hatch from those eggs. What Are Mammals? Mammals are animals that have hair. Mammals are the only animals with hair. Mammals are also warm-blooded. This means their body temperature stays the same, even if it is very cold or hot outside. Read More...