The ‘dawn chorus’ is the name given to the sound of many birds singing together for a short period of time as dawn breaks in spring.
Usually it is only male birds which sing and it is thought the dawn chorus is a way to announce their presence to other rival birds of the same species. This could be to make territorial claims and also to impress the ladies by showing off their vocal skills as this is the time of year that mating starts. Why at that time of day? There is no point in waiting for every other bird to claim its territory before you so it’s first out their gets patch and as soon as the sun starts to rise is as early as it gets after a night’s sleep. Different birds start to sing at different times.
The dawn chorus starts from as early as 4am whilst still dark with blackbirds, robins, and song thrushes usually being the first to start. As the sky lightens they are joined by finches, dunnocks and wrens. It is speculated that this is because of their food requirements. Thrushes, robins and blackbirds all eat worms which can often be found above ground early in the morning so these birds sing before it is light enough to see their breakfast whilst the other birds which are insect eaters have a lie in as they don’t start to feed until the insects have warmed up enough to become active and become easier to find.
For whatever reason they start to sing at that time you won’t hear them unless you get up, but I have now saved you the trouble of having to do that, you can watch the dawn arrive and listen to the dawn chorus on this video.