Why are flippers

Homologous organs are organs that have common basic structure but perform different functions and appearance.

Flippers of whales and wings of birds considered as homologous organs because they both have the same anatomy, i.e., they have same skeletal structures, and they perform different functions. Flippers of whales are used to swim whereas the wings of birds are used for flight.

As whales and birds have flippers as homologous organs show that they have evolved from very closely related ancestors. Even though they have the same origin, they both have been adapted for different functions.