Use the resources provided by the various Nature in Your Neighborhood Lead Naturalists, guide books, iNaturalist.org, or other online resources to look up the various names of your species.
There may be several common names for your focal species that have been collected over time. When referring to a species, as you will do in your sketch, it is best to include as many as you can for cross-referencing purposes.
Scientific names usually comprise two words: 1) the genus, which is always capitalized, and 2) the species, which is not capitalized. Sometimes there is a third word, which indicates a subspecies, which is also not capitalized, e.g., Orcinus orca, Homo sapiens, Tamias amoenus caurinus.
Make sure you use capital letters correctly. Common names are generally not capitalized, e.g., bracken fern, flying squirrel, mountain lion — unless they include a proper noun, such as a specific location, e.g., California sea lion, Olympic marmot, Sitka spruce or a person’s name, e.g., Steller sea lion (named after Georg Wilhelm Steller), Douglas fir (named after David Douglas), Townsend’s vole (named after John Kirk Townsend). The exception is that bird names ARE ALWAYS capitalized, e.g., Red-tailed Hawk, Yellow Warbler, Pacific Wren.