How and how did the birds adapt to different environmental conditions?

Birds have adapted to different habitats and environmental conditions.
There are birds that have adapted to the hot climate (bustard, ostrich). They have not too dense plumage, fast legs to escape from predators.
Birds that have a connection with water (ducks, geese, penguins) lubricate their feathers with the secretion of the coccygeal gland (so that the feathers do not get wet), there are swimming membranes on their legs between the toes.
Birds living in the tundra, in very cold places (snowy owl), have a protective white color, thick plumage, powerful wings, and sharp claws.