My nest bank could be a community box, dividers are removable.
Tried 2 singles and the other divider removed, and only one bird would go in the double at a time and they squabbled so I put divider back in, they've been fine with the single nests.
Tried 2 singles and the other divider removed, and only one bird would go in the double at a time and they squabbled so I put divider back in, they've been fine with the single nests.