If someone calls you an early bird, it means that you tend to get up very early in the morning. It's usually a compliment to be called an early bird.
Early birds are people with a natural habit of waking early, and often also going to bed before it gets too late. You can also call someone who arrives early to events, movies, the airport, or appointments as an early bird. Early bird comes from a seventeenth century English proverb, "The early bird catches the worm," which means that people who are well prepared are usually the most successful.