Someone nominates you and the administrators approve or not. That's how you get some of the badges like Greeter, Spirit, and Educator. Then you have other badges for being a member after so many years.
Maybe not like a singular expert but maybe a badge for the area they tend to help out a lot in. For example, I've seen casportpony in Peafowl, Duck, Emergencies, and in the Chicken I believe. So place a badge for each one or maybe once you've achieved so many species you get a badge like, Mixed...
I had no idea until Dan pointed out my new badge on a thread! Thank you and congratulations to all the others! I kind of want to know who nominated me. Whoever it was, thank you!