1. Used to list the kinds of birds, such as "He likes to observe all kinds of birds-canaries, sparrows, red-billed gulls, etc."
Used to indicate different species or subspecies of the same bird, for example: "You can see different birds here-swallows, white-waisted swallows, red-throated swallows, etc."
3. Used to describe the living habits or behavioral characteristics of birds, such as: "This kind of bird, falcon, is good at flying and chasing prey."
4. Used to quote other people's opinions or remarks in the text, for example: "According to experts, this kind of bird, the cockatoo, is one of the smartest birds in the world."