If I had pens that size I would put a breeding pair in each, maybe a few would be used for my broody calls with their ducklings, and a the rest would be for birds that Im growing out. It really depends on how many birds he is putting in the pens. The house my call ducks live in is 4x8 with a run that is around 6x10. This house could most likely fit around 6 or so calls, would I recommend having that many in there, no way. I myself have never had more then 4 adult calls in the house at one time, now sure I could have put a few more in there but I fully believe my birds are happier and healthier b/c they have so much extra room. My breeding pen is really a rabbit hutch with 4 rooms that are 2x3 each that I open up or close off when need be. I have never housed more then a breeding trio in the hutch with every room open again my birds have enough room to be comfortable. A general rule I hear a lot is 3 feet of floor space for duck