Now the southern end of the Common is always inhabited by individuals belonging to one of these species, or to others of close affinity; so that wherever these travellers settle whilst passing across it, the chances are that they will find the ground occupied--and their behaviour under such circumstances is no less interesting than the behaviour of the bird upon whose ground they are trespassing. We will take the case of the Whinchat. It arrives from the south-west, and, flying from bush to bush, works its way in a north-easterly direction. In doing so it intrudes upon the territory of a Stonechat; and the Stonechat, becoming excited, flies towards it, and it retires for a short distance in the direction from whence it came. Here again it is followed and attacked and again moves on, and then, flying in a circle as if to avoid the territory which blocked the path, resumes its former line of flight, though still followed by the Stonechat, which after continuing the pursuit for perhaps a quarter of a mile, suddenly turns in the air and returns to its headquarters. It is difficult to put oneself in the place of the Stonechat or of the Whinchat. But even after making due allowance for the danger inseparable from any attempt to do so, there remains the unquestionable fact that whereas the impulse to attack was strong in the one, the impulse to defend itself was wholly lacking in the other. Yet a Whinchat, when it has established itself, is most pugnacious; it not only attacks every bird of a similar size that approaches its position, but its behaviour under such circumstances bears the impress of unusual determination; and if we were to take a male and place it in the position of the Stonechat, we should find that its nature would change, that the presence of the Stonechat would evoke a hostile response, and, conversely, that the instinct of the Stonechat would not be susceptible to stimulation. Hence it is clear that the nature of a bird when on migration is not quite the same as it is when its destination is reached; that the positions occupied from time to time during the journey carry no meaning, or, rather, are not brought into relation with its life in quite the same way as is the position which it finally occupies; and further, it is clear that the interest it displays in other species undergoes a somewhat remarkable transformation when at length its destination is reached.