Feathers are made of keratin, a protein that is also found in human hair and nails. Keratin is water-resistant, meaning that it does not absorb water easily. This is important for birds because they spend a lot of time in water, either swimming or flying through rain.
The feathers of water-resistant birds have a special structure that helps them to shed water. The feathers are arranged in a way that creates tiny air pockets between them. These air pockets trap air and help to keep the bird dry.
In addition, the feathers of water-resistant birds are coated in a waxy substance called preening oil. This oil helps to further waterproof the feathers and makes them more flexible.
The combination of water-resistant feathers and preening oil helps to keep birds dry and comfortable, even when they are in water. This is important for birds because they need to be able to maintain their body temperature in order to survive.