i havnt intorduced any new pigeons but have split my hens and cocks and all stock and young pigeons are together. i did have 2 young pigeons die with the same symtoms earlier in the year but nothing since and no other problems so put it down to yound bird sickness.
today all other pigeons look in great health and no loose droppings at all.
the birds just went really light stopped eating and within a few days died.