Lesson 2.8 "Plurals" explains some professions can have a special ending when referring to females.
I'd like to mention a couple of points that helped me understand when to use a particular suffix for a noun when referring to males and/or females.
- Question 2 of this post, “when to use a noun form when referring to a group of people?”
- This snippet from a grammar book.
- Suffix number 4 in this page: