There are seabirds as well as land-birds. The most ordinary seabird is the seagull. It has a white body, a white head and a yellow beak. There is a very, very spot of red at the very end of the beak, underneath. All gulls have very strong wings so that they can fly far out to sea. If a gull flies out too far, so that it is too tired to fly back to the shore , it does not get frightened, for it can sit and rest upon the waves . A seagull's wings do not get wet because all its feathers have a kind of oil over them, so that when the water gets on to the feathers, it just runs off again. Gulls can even sleep upon the waves. Sailors  know a lot about seagulls and they never kill them. When the gulls fly a long way out to sea, sailors say that it means fine weather is coming. When the gulls stay near the shore, sailors say they there will be much wind and rain, and perhaps a storm, for the gulls know more about the weather than sailors do. The water can't make the seagull's feathers wet because the feathers are   _  .
thick long light oily