How is the adaptation of mammals of the reservoir to life conditions visible?

They have a streamlined body shape needed to reduce drag and energy costs. Beavers, otters, frogs, and swimming birds have webbing between their toes to make it easier to row. The limbs of walruses and seals are equipped with flippers; in penguins, wings are also transformed in the water into flippers, which help to swim faster. Animals have a subcutaneous layer of fat so as not to freeze in water. They breathe with gills.