It seems like a trivial thing, but whether and how to capitalize common names seems to trigger strong disagreements.
I prefer capitalizing all the words that comprise a common name, especially if it is a standardized English (or another language) name. Some folks prefer just capitalizing the first word in the name (e.g., Gray fox).
For example, here in North America a Green Frog is a species but a green frog might just be a frog that is green. I think the capitalization helps make clear we are talking about a particular species, subspecies, or another taxon.