The very first time I use symbolism comes in chapter one of book one (Red Oak Fall): the mourning dove that lands in the tree that Jonah seems to talk to. The dove is symbolic of the Holy Spirit (see Luke 3: 21,22* where the dove lands on Jesus after he's baptized)

I was inspired to use the dove coming to Jonah with a message based on a real-life experience. It was 8 years ago this week (July 21-27) that we had something similar happen at our home. I had stopped cutting firewood on a Saturday morning for a lunch break when an adult mourning dove came down our driveway and walked right up to me! The dove didn't seem to mind what I did and preceded to walk right around me. My family came out to see where I was and for the next 10-15 minutes the dove walked around all 4 of us! It even flew away once and returned before it flew away one last time.

None of us had an explanation for why the dove did what it did that day. It wasn't hurt, it wasn't young or learning to fly. But the next day I was grilling burgers just a short distance from where this took place and I was thinking about the incident when I remembered something. On the Thursday before this I had ended my morning prayer by saying "Lord, my family really needs a touch from your Holy Spirit".  Just then, when I remember my prayer - a dove, somewhere close by "cooed" 3 times as if to say "Now do you understand?" I immediately felt the awesomeness of God and started crying and thanking Him for such a blessing. Now 8 years later I still get tears in my eyes or feel the hairs on the back of my neck stand up whenever I think of that day.

So, that's where I got the idea from. I believe the Holy Spirit used the dove to deliver us a message, and in a similar way (in my book) He uses the dove to deliver a message to Jonah.

*Now when all the people were baptized, and when Jesus also had been baptized and was praying, the heavens were opened, and the Holy Spirit descended on him in bodily form, like a dove; and a voice came from heaven, "You are my beloved Son with you I am well pleased." Luke 3: 21-22 ESV