I've been a birdwatcher since high school. I have worked as an educator and field ornithologist throughout my career. I've always enjoyed drawing but have not used it as a regular part of my field notes, a thing for which I'm a bit embarrassed to admit. I'm now 60 and recently retired and would like to develop my nature journaling to include illustrating my observations. I'm a licensed bander and often take photos of various unusual things I observe in the birds I capture (unusual plumage, deformities, etc.). I can imagine drawing some of these phenomena would be a valuable way to notice minutia that might be missed with a photograph.
As far as choosing a style of journaling is concerned, I think I'm going to have to just start doing and see what works for me.