I wouldn't try the gerbil yet. I have never had to go that route but I have heard of problems getting balls weaned off of them. Like I say I have never had to do that so they are stories to me. I would love to hear any stories about gerbils being used as feeders. Yes a small white mouse will do. I have a 2 and a half month old Mojave baby that just ate a hopper for me tonight for the first time. He hadn't ate for me since I got him 2 weeks ago. I am relieved for now. I juts hope he keeps it up. Good Luck