Yes - gerbils need the company of other gerbils in order to be happy. They are social creatures who naturally live together in the wild, and without gerbil friends they’ll feel lonely and depressed. Wild gerbils, whether of the Mongolian or fat-tailed species, live in colonies or family groups, usually consisting of a breeding pair and several generations of pups. These little families will live together in a big burrow, and go about their lives side-by-side every day. They’ll eat together, communicate, and sleep in the same chambers. Without this constant companionship they will be really unhappy, even if their owner plays with them a lot.
If your gerbil has been kept on its own and you’ve tried to introduce another gerbil, it’s natural that they will react badly to this newcomer, even if your pet is lonely - after all, there’s an animal they don’t know coming into their home. If a strange gerbil came into their burrow in the wild, they would usually have to try to drive them out of their territory, so if your pet has a negative reaction to the new gerbil, don’t take this as any indication of how your pet feels. Instead, stay calm and try some different introduction techniques. We’ve included a page of them here, on our How To Introduce Gerbils page.