Every time I have encountered wood pigeons or city pigeons (rock doves) on the ground at night, they were sick or injured - probably not long for this world.
Birds go downhill fast when they get sick, because any sign of weakness marks them as easy prey, so they sort of carry on bravely and don’t outwardly display any symptoms - in the case of pet birds, this often means it’s too late to save them once they begin to look sick.