How old is this bird? I know for a fact that quails produce MUCH less eggs as they get older...(from about 1 every day to 1 every week lol)
Still...not sure if that applies to pigeons. You sure nothing is disturbing them- no overhandling, new birds, aggressive male "crushinators/squabzillas" who will chase them off the nest (I'm looking at you Adolf )
And how is their diet?