Are the 50 that spend their time in the barn the youngest? I'm thinking that if you don't feed them more, it may force them to venture outside. How old are they and how long have they been doing this?
I know my Andalusians, in the summer, hardly come outside at all but I don't have any shade for them to hang out in. I'm working on getting some shrubbery between 6-10 feet tall for them to lounge under. My daughter's birds will spend time outside. I found out last summer that its because the ground is hot as one ran out into the yard one afternoon because she got caught between me and the doorway, and she started the craziest dance trying to get back to the barn!
Maybe the older birds pick on the 50?