Yes Damon! It's very common. Most of my videos start anywhere between 8-15% CTR and within a couple of weeks they decline to a steady 5-8%. The reason is that when you first upload, you get a BIG initial rush of people who are subscribed clicking and watching, or seeing it in their feeds and they click and watch so your CTR is typically going to be really high quickly. Then as YouTube continues to push your content out over time, less people tend to click (this is why thumbnails are so crucial to keep getting that click) and so your % will decline a fair bit. My first videos hurt me the most because they were awful thumbnails and I had only like 3-5% CTRs to start, now they're like 1-3% BUT my new style gets tons of compliments and I know it's working because my CTR's are much higher and stay a lot higher later. Don't be discouraged because even if they tail off to around 5%, that's a decent CTR and will still get you views! Just keep on working to improve your CTR in every way you can!