Biggest risk will be in order: wild birds near them, rodents in with them, insects, especially when pen/s wet n area/s around, all initially spread by songbirds though to new areas. Parrots other hookbills, caged songbirds and other dove species "pigeons" are rock doves), also are major carriers of disease s etc.. Chickens actually are more prone to make pigeons sick with diseases they are immune to now or can fight off, than anything that hasnt killed majority of pigeons. Just keep them all dry and water fresh. For otherwise what would be real bio-security, would be inch hardware cloth covered in screen/skeeto netting, with four foot overhang on top, and raised concrete slab as bottom sloping outward.
