My mom had a bird call whistle when I was growing up that I absolutely loved to play with. If you haven't tried it, you must. It's kind of amazing how many different calls you can make with one whistle.
So my mom finally got me a set of bird call whistles, hoping it would encourage me to get in to birdwatching. It's great fun to listen to bird calls and try to imitate them with your own whistles. Check out some whistles like the ones below; they're not expensive.
Bird call whistle set
Hand-carved bird callers
“It's great fun to listen to bird calls and imitate them.”