Birdsong has stimulated a great deal of research in recent years, and the question of why many birds deliver the majority of their daily output early in the morning is the one that has attracted the most attention says Mike Toms.
Why do birds sing early in the morning?
The two main functions of birdsong - to attract a mate and to repel rivals - are likely to exert an influence on the timing of its production, and changes in its output over the course of the breeding season have been recorded.
However, other factors may also exert an influence, such as the need to feed or watch out for predators. Many researchers believe that early morning song (what we know as the dawn chorus) is really just a trade-off between the conflicting needs of defending a territory and finding sufficient food to replace overnight losses.
The timing of the dawn chorus matches the period when territorial incursions are at their peak, and also happens to be when low light levels may limit feeding opportunities.
So if a bird cannot feed effectively, and rival males are making threats, then it makes sense for that individual to sing more at that time of the day. rather than later on.