The evening chirping signals the rest of the flock to come home before it’s time to be quiet and rest through the night. The birds continue singing until the last rays of light have faded in the evening.
You may have noticed a cacophony of birdsong in the wee hours of the morning. Scientists call this the dawn chorus. It can start as early as 4:00 a.m. and last several hours.
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.
The songs of birds are learned, not inherited, much as with humans.
Usually a male that is defending a territory or attracting a mate will sing from one of the highest or most conspicuous spots available.
Birds usually do not sing around their nests. a few may sing a quiet "whisper song" that can be heard for only a few yards.
A bird may sing a song because it is well fed, stress free and happy.