According to J.P.Brooke-Little, the Heron, Crane and Stork are almost always interchanged because not many heraldic artists would know the difference between them. Althouigh ornithologically these three birds belong to different families, it would require specialist knowledge to differentiate between them. The heron is usually distinguished from the stork by a crest of elongated feathers at the back of the head and the crane is unlike both the stork and heron in that it has a longer neck and tail feathers. When standing on one leg and grasping a stone in the other claw, the crane is said to be 'in its vigilance' - so I would also suppose that both a heron or a stork would also be described in the same manner if it were to be presented in the same way. The terminology referring to 'in its vigilance' pertains to its position with the stone in the claw - however, if it is something else in its claw, I do not think that the terminology can be used.