Yesterday I went for a walk and saw a skylark; I would not have seen it if I had not heard it singing first. It is the same with goldfinches as, when I recognise their call, I look out for them. However, I find it hard to learn to recognise bird song; it can be difficult to locate sounds and connect them to their source. Especially when there are many birds singing at once.
Listening out for bird song is a great activity to do with children. It helps their concentration and general listening skills, as well as helping them to identify birds in their environment. It links well with literacy lessons. A brilliant resource to help you and your class learn to recognise different birds is the RSPB bird identifier which not only has pictures and descriptions of birds but audio clips of their song. One difficulty is that it is not possible to look up a sound in the same way that one can use an identification key to identify a bird by appearance. The way I have used it is to listen to a recording of a bird which I know is common in my locality, and then go outside and listen out for that song. Children have enjoyed doing this too, and are very excited when they recognise a song that they have heard in class.
There is rarely time in a crowded curriculum to do this with older children. However, I have found that some children, once introduced to this free resource are keen to use it in their own time. It is often surprising how much bird song one can hear even during a noisy playtime. I would love to hear how you get on if you do decide to listen for bird song with your class.