What are the similarities and differences between bats and birds?

Bats and birds have few characteristics in common. They are united only by the ability to fly and warm-bloodedness. In birds, flight is carried out thanks to altered forelimbs, which have turned into wings. Also birds are covered with feathers, have a beak and lay eggs. Bats do not have true wings, they only have a skin membrane between the front and hind limbs. Bats are viviparous and, like all mammals, feed their offspring with milk. They have no beak, and instead of feathers, they have hair.