I am not proposing that tags be created for all species and all families of mammals, but rather to species and families of mammals familiar to humans — such as Bovidae, Canidae, Equidae, Felidae, etc. After all, laymen seldom ask questions about animals they have never heard of.
Not everybody uses Stack Exchange the same way. For example, to read biology-related questions on Stack Exchange, I created a filter and am notified whenever new questions with the tags that I follow are posted on Biology SE, Medical Sciences SE, Bioinformatics SE, etc.
Suppose that I am particularly interested in canids. If I follow zoology I will be flooded with new questions, most of which are of little interest to me. Obviously, I would prefer to follow tag canidae.
Suppose that the mean time between new questions with the tag canidae is 2 months. It is tempting to conclude that this tag is too specific and, thus, unneeded. I believe the exact opposite is the case. The rarer, the better. I don't want to visit Biology SE for sightseeing, to read its front page hoping I will encounter something that interests me. Instead, I want to be notified whenever a new question with a tag that I follow is posted and I want to visit Biology SE mainly to read questions that I am already interested in. I don't think I am the only one with such proclivities.