the theory I have just laid down, since such generalised and legitimate longings are only indirectly related to the bird's special instinct.
I do not myself see how these curious relations of robber and robbed could have arisen, unless there had been, from the beginning, a marked difference in the relative powers of flight possessed by each. The skua, originally, must have caught fish, like the birds on whose angling it is now dependent, and only an easy mastery over the latter could have induced it to abandon the one way of living for the other. This superiority was probably first impressed upon the weaker species through bodily suffering, but it would have been less trouble for the stronger one could it have succeeded without coming to extremities, and this, and its constantly doing so, might in time have made it forget, as it were, the last act of the drama. But say that the skua has forgotten this, then it is likely that a certain number of the persecuted birds have by practice discovered that it has, and so emancipated themselves from the tyranny. Whether this be the reason or not, I have often noticed the persistence with which some terns refuse to yield the fish, though the nearness of the skua, and its sweeping rushes, seem quite sufficient to induce them to. Those, on the other hand, who drop it quickly, often do so whilst the enemy is still at a distance, in which case the fish falls upon the water before the skua can catch it. Upon this, the latter—if not invariably, as the fishermen assert, yet certainly in the greater number
