Well, I have five buttons that I bought as chicks from a breeder. I estimate that they were a week old when I got them (Jan 3rd). I think that some may have been late hatchers or from a different hatch, as two of them were behind in development. Now, I noticed that the two biggest buttons are beating the daylights out of the two smallest. I haven't noticed the other big one beating them up, but s/he may be as well. The two bullies are both whites, and just about fully feathered (they have a tiny mask around their eyes that is still baby fuzz), the other biggest is a silver, and again, almost fully feathered. The two little guys are what I believe are a red breasted silver male and a red breasted hen. What's going on? I'd like to keep them as a community to get mixed eggs from, but if worst comes to worse, I can seperate. These five guys are in a 20L tank, but certainly don't seem to be crowded. They still have a brooder light on them (75w lightbulb, on the top of the tank screen), plus they always have fresh water and fresh food (24% chick crumbles, plus the leftover parakeet food, plus they sometimes get mealworms and certain leftovers from our table).