I've read about this on here but never experienced it. There is something called a dwarf gene, and also, some chicks are just slow to develop. The outcome varies -- sometimes they end up looking like everyone else, sometimes not. It's true I gather that roos develop feathers more slowly, but that seems extreme, to just be because it might be a roo. There is probably more than one cause of what is called failure to thrive, too, so I suppose this could be one outcome of it.