Okay. I just wasn't 100% sure if nipping unaccompanied by other dominance behaviors like rumblestrutting or mounting was a possible sign of aggression rather than dominance. The original 2 pigs are about 5 1/2. New piggie is bigger but the shelter I got her from estimates she is 1 to 2 years old, though it is impossible to know for sure. The piggy she usually nips at is the submissive one, which I thought would be odd if she is trying to establish dominance. One of the hiding spots has double exits. New pig usually nips when they are out in the open. They were introduced in neutral territory, such as it could be (2 towels on my living room floor directly next to where their cage is). Also, the cage I keep them in is new, and the night they were introduced was also the first night being in the new cage for all the pigs. Admittedly, I did cut the floor time short by mistake - it was only around 30 minutes and the pigs were ignoring each other so I got cocky. A lot of places I looked at on cage size was that 2x4 would work for 3 females, but I am always open to the possibility of being wrong - we'd never learn anything otherwise! I physically don't have the space for anything bigger, unfortunately.
