The last blog post was about the fairly rigourous practice of natural history illustration. Nature journaling, on the other hand, can be as personal as a diary. The main reason to do it is to enhance your memory of your experience and to help you remember what you saw and questions to ask later, to learn even more. Graphite, colored pencils, and watercolor are all immensely portable and time-tested tools for recording the moment.
Nature journal pages from a couple hours in a park in Austin TX, watching Great-tailed Grackles and other birds. A nature journal is a personal record, not scientific or convening to standards. It's a way to remember what you saw and to ask questions to be answered later. It is not at all about creating a work of art.
The best reason to do it is to remember that experience in a completely different way than simply taking photos. I'll never forget these birds, their sounds, their actions, even the weather and the feel of the breeze that day. And I learned a lot about them later by finding answers to questions I noted in the moment.
A journal can include sketches of anything. The scene outside your window each day, the clouds in the sky, anything you would like to remember having experienced or would like to research more later. As part of our recent move to Maryland, I've been finding images of fishes that are common here and sketching them for #SundayFishSketch on Twitter. Here are a couple of those, a Bluefish and a Longnose Gar.
For more about nature journaling, I recommend John Muir Laws, his books and videos. Among the many many books on the subject, his approach worked best for me. Audubon.org has an excerpted demo on How to Draw a Lazuli Bunting, and also here's an article on How to Go from Watching Birds to Drawing Them. As it says in the article, sketching doesn't just make you a better artist, it makes you a better observer of the natural world. And you'll make unforgettable memories, whether you make "art" or not.