I remember reading about high rise flats causing a break down in society. Everyone living on top of each other and not even knowing neighbours on the same level, never mind in the same block, whereas in the traditional form of housing people spoke to each other over the garden fence, etc. The point was put that when boxes were piled above each other the similarity was to the high rise flats. Having boxes facing each other was like the traditional housing and since the birds could see each other they would self motivate. Others have stated that when using deep litter their birds nest in the litter and often really close to each other. Pigeons are gregarious, so enjoy each others company, look under railway bridges, they live close together there. Yes, they defend their territory, but on the whole they manage to live together far better than humans do.