There are several reasons why birds sing, especially at dusk. On the one hand we have noise pollution, and that is, when it starts to get dark, the level of noise pollution is lower, and to this it is added that the temperature is lower and the wind is calmer, which greatly improves sound transmission. . This also happens at dawn and the birds take advantage of those moments to use less energy singing. That is why it is in those hours that they are generally heard chirping.
Individuals of many species take advantage of sunrise and sunset to make their songs of territoriality, to warn about possible dangers, to communicate with each other and, the males, to attract females. The main reason for doing it at that time is the one I just explained to you, at those times they are heard better and they spend less energy singing.
In addition, many use the central hours of the day to feed themselves so they are busy with other matters. But it is important to know that it depends on the species and where it is found, because each species may have a different reason for singing at sunrise and sunset.
We, in my research group, are now studying a bird, the Canary Houbara , which does something similar, it begins to sing and show itself when it is getting dark and even does it at night and one of the reasons is that the sound is transmitted a lot better.
Singing is a very important activity: birds sing to communicate. Males do it to attract females and chickens to attract the attention of their mothers. In addition, each species has its own song that is different from the others. And all birds sing or vocalize, which is how the sounds they make are called in ornithology , both the trills or songs and the calls . The former are longer and complex and generally associated with courtship and the latter are shorter and are intended to alert or keep the flock together.
There are species that do not hear this vocalization, but that does not mean that they do not use it to communicate. For example, with the Canarian hubara we work with, I have been studying her for a long time in the field and I have never heard her chirp. I have seen her open her beak and close it so I know that she is chirping / vocalizing because, in addition, the individuals we studied have a GPS and accelerometer marking system that has allowed us to detect that they are vocalizing, but the frequency at which they are vocalizing does not lets hear it from the distance from which I observe them.
So even if they are not heard, all birds vocalize. In general, among urban birds, which are the ones we are most used to seeing and hearing, they all chirp: blackbirds, magpies , sparrows , they all sing.