Depending on where you live, there are some natural sounds that follow the changing of the seasons. We live in Pa. on a mountain, with several acres and tons of forest all around. I can tell summer is growing long since the cicadas have started droning away during the day and into the evening. They'll only get stronger. Cicadas are out every year, not just the 17 year ones. When they do come out on that 17th year, it's pretty incredible. Also, the grasshoppers are becoming louder as well, droning away from the high grass. There are a lot of species around with very distinct sounds. Some other insects that signal the advent of fall include the leaf hoppers and katydids, which will become louder as we approach the end of summer and move into fall.
I've done a lot of research to identify different species and find it really interesting to learn more about them, identifying them by their calls. Also, I see and hear more owls during the fall and winter. Around here we have mostly screech and barn owls, the former with a very distinct call. Anyone else keep their ears open like I do or live in the country?