The first I will discuss is the naturalism of the biologist, now known as Natural History. Naturalism, in this sense, is concerned with observing organisms in their environments with minimal interference from humans. These generally involve the macroscopic organisms, but can include microscopic organisms. The microscopic organisms are often, in naturalist texts, referred to as “infusoria” or “animacula,” will be referred to, for the rest of this section, as “infusoria.” (I do hope you won’t mind my use of this term) Natural History concerns itself with the behaviors, interactions, and lives of organisms in a natural setting. How the organism lives, develops, reproduces, and dies, from embryonic development to decay. It involves every aspect of the organism’s life, evolutionary history, and the ecosystem in which it lives.
“Being a naturalist,” in this sense of the word, will vary depending upon who you ask. My personal notion is that anyone can be a naturalist. All which is involved is a bit of reading and a lot of careful observation. Notes are also allowed, particularly when an animal or plant you are observing has an unusual feature. For example, there was a rather large male cardinal which used to frequent my back yard when I was in high school and had quite the fondness for our small koi pond. He would often perch above the waterfall and catch small insects which would inhabit the area. Considering the Northern Cardinal’s diet is mostly (~75-80%) seeds, nuts, and fruits, this seemed quite unusual. He seemed to frequent a certain tree on our neighbor’s property and I discovered he was feeding these insects to two (maybe three) fledglings. I can only assume the female was incubating the next clutch of eggs, for I never saw her.
Field guides are a wonderful way to identify the animals being observed. I personally have several different ones covering most of the animals of North America: two fish guides, one for snakes, several for amphibians, one for birds. I also have a field guide for insects (which I rarely use). Along with these guides, I recommend a notebook, laptop, or smartphone (so long as you don’t have to look to type). You could also do as I did and put together your own field guide with lots of empty pages after the photo and description of the organism. In my original field guides, I would write the scientific names over the less common animals which I did not know, such as the following:
I was usually more careful not to obscure features of the organism in my writing, but sometimes I had to write them quickly (my handwriting is pretty horrific, but not this bad). This fish is Esox americanus. The common name and descriptive page is listed below along with the average maximum size.
Perhaps it is more important, when first getting into natural history, to develop your own method of notes, references, sketching, and organization, than is familiarity with your subject. The familiarity will be learned rather quickly in the process of observation. What you do with these observations is entirely up to you. You can share your studies with researchers or other enthusiasts. Naturalism, in this sense, is a method of observing nature.
Senses 2 and 3 are a bit more abstract.