Why do biologist classify fruit bats and parrots in different animal groups?

Answer 1

Because fruit bats are flying mammals; parrots, however, are birds.

Mammals: give birth to live young, have hair, produce milk, warm blooded

Birds: lay eggs, produce no milk, warm blooded

Reptiles: lay eggs, no milk, cold blooded

There are many factors that are taken into consideration when classifying animals, most of which are based on identifying similarities with other animals/organisms.

The only thing that separates bats from other mammals is their wings... they are basically flying rats.