It'll probably rely on 1. how flighty/socialized/scared they are and 2. individual bird :'(
I've had bantam cochins and silkies who break the standard of 'not flighty' who have jumped our 4' fence lol! If these birds were hand raised and not scared of people they'll probably at least not jump out to get away from you! : D
I'm assuming the fence is for your run or an outside area, if the silkies were to bug them (which I dont think they would, unless you have a particularly spicy one!) they may try to jump out to avoid the other birds. They could also just get curious! or want to try some different tasting grass, if they do try to jump out you could probably get some netting to put over the top of the run/outside area : D