I am picking up duck eggs on Saturday but won't have enough to fill my incubator. I might be getting chicken eggs next week (trying to turn them down since I only have the one 'bator but it might end up me or the frying pan if my friend can't find a broody hen) so there's a possibly the other half will be filled but, if not, do you put something (rocks? wooden eggs?) in to fill the empty part? Does it matter? Also, any tips for hatching ducks and chickens together?