Could it be that these are animals that were hunted, fished, or herded and that there was a convention that used the singular as a sort of generic plural when going after these creatures for sport or ...

Plural of Series: English has many rules for forming word plurals. Usually, you just add "-s" or "-es" at the end. Some words ...

I've just learned a horrifying fact: I've been pluralizing the name "Prius" incorrectly, and you probably have been, too. Did you assume that the regular rules of English plural words applied, such ...