It’s called the Dawn Chorus...that hour or so before sunrise when the air is thick with bird song. It is at its most prominent in spring as birds mark their territory and began to mate. Or at least, they used to. These days the Dawn Chorus is a shadow of its former winged self.
A lot of research has been conducted into the loss of bird life in the UK, with depressing results. The number of birds in the UK has fallen from 210 million to 166 million since 1966. It is estimated that the UK loses one breeding pair of birds every minute.