Such preening under such circumstances must, one would think, spring from a powerful incentive, and it is, I believe, chiefly when annoyed by insects that the birds preen themselves, though whether their efforts are actually to free themselves of these, or only to allay the irritation by scratching, I am not quite sure. But I noticed that a bird would often bend down its head, and with the extreme tip of its finely-pointed bill appear minutely to explore the surface of its webbed feet—and further, that when the partner of a bird doing this was beside him, it would become most interested, and do its best to assist him in the matter. One may suppose that the ledge—which is, of course, coated with a layer of guano—is covered with these pests, and that they often crawl over the bird's feet, and so ascend on to the body. If the skin of the feet were sensitive, their owner would at once know when this was the case, and with its keen eyesight and stiletto bill might guard itself fairly well, as long as it only stood. As, however, all the birds constantly sit flat on the rock, even when not incubating, the searching of the feet can be of little or no real importance to them. It is very interesting and has a very human appearance (not so much in regard to the particular act as the careful look and manner and the attitudes assumed) to see two birds thus helping to clean each other's feet, as I think must here be the case. When they nibble and preen each other they may, as a rule, I think, be rightly said to cosset and caress, the expression and pose of the bird receiving the benefit being often beatific, and the enjoyment being, no doubt, of the nature of that which a parrot receives
