The early bird considered

What annoys me most is that it is so loud for the first hour, and then it stops to acceptable daytime levels.  In Brisbane at this time of year, it means being woken up, often, at between 4.30 and 5 am.

So, why do they do it?  See this - Why do birds sing in the morning?

But why choose the hours around sunrise to sing? There are a number of theories, and they're not necessarily mutually exclusive.

One idea is that in the early morning, light levels are too dim for birds to do much foraging. Since light levels don't affect social interactions as much, it's a great opportunity to sing, instead.

Another idea is that early morning singing signals to other birds about the strength and vitality of the singer. Singing is an essential part of bird life, but it's costly in terms of time and energy. Singing loud and proud first thing in the morning tells everyone within hearing distance that you were strong and healthy enough to survive the night. This is attractive to potential mates, and lets your competitors know you're still around and in charge of your territory.

For many years, scientists theorized that the atmospheric conditions in the early morning — typically cooler and drier than later in the day — might allow birdsong to travel further through the air. However, recent research shows this isn't the case. Birdsong travels just as far, if not farther, at noon as at dawn.