Listening to and even learning bird songs and calls is a useful skill to learn. Some of the bird song books I mentioned in the book that are suitable for children:
This one is for more advanced birdwatchers:
Thanks to help from such resources, a birdwatcher will be able to distinguish between species, and even eventually to say whether it’s a male or female tawny owl calling:
One project for an adult and child to do together is to get up at the crack of dawn (or just before it!) and listen to the dawn chorus. Here someone has taken the effort to do that, and recorded the results in a 4-minute video.