Tiercel; if that is wrong, then all my observations of the inverted vole of the sexes in their care of the young goes by the board. Owing to constant association I soon found myself able to tell which bird was present, though, as in the shepherd's ability to distinguish different members of his flock, it would not be easy to at once reduce the process to writing. The Tiercel of this pair had a much larger cere than the Falcon, i.e., the yellow bare skin round the eye showing, as I have learned since, that he was the older of the pair. The cere, owing to foreshortening, disappears when the bird is seen full-face, and in the same way the pose and condition of the plumage, as well as changing expression, help to make identification difficult, but there is also a massiveness about the Falcon which helps to distinguish her from the Tiercel.
As regards the prey, there seemed no selection as to kind; it looked as if with the Falcon the only rule were first come, first served. In the same way I failed to trace any design in the condition of the quarry as delivered. As far as I could make out, if she kept the Tiercel waiting, and presumably turned up with a freshly killed bird, it was intact, whereas the longer she had it in her keeping, the more thoroughly was it plucked and skinned; but this is purely surmise, as from my circumscribed outlook I got no proof of the Falcon waiting to be called. The natural way of feeding the young is for the adult to divide the prey among the young. If it were usu4l for the prey to be simply dropped into the eyrie, as happened when on occasions the Falcon brought a bird during the Tiercel's absence, I think the young males would have stood a very poor chance beside their voracious sisters—that is, presuming I am right in concluding that the larger young are females. My friend, the late Colonel Moore, when I pointed out the difference in size among the 1910 brood, said that in the Raptores generally incubation starts with the first egg laid, and that the young vary in size accordingly. From what I had seen of two young ravens in the previous year, I dissented. I do not know what the books say about it, but I have since satisfied myself that as regards Peregrines this is a sexual difference, although I have not gone to the length of dissecting them. As I said at the beginning of the book, from the early appearance of this difference in size I
