In many, but not all, bird species, the male has brighter plumage than the female and uses it to attract the female’s attention and to see off rival males. Some birds also sing for the same purposes.
The female birds of most species do not need to display and are thought to have duller plumage because it makes it harder for predators to find them when they are sitting on the nest.
Not all birds keep their bright plumage all year round: male mallard ducks lose their bright green head feathers and their striking wing patterns after the breeding season. In puffins, the beak changes: after the breeding season, they lose the bright-coloured outer parts of the beak and regrow them for the following spring.