938 Birds. 



dible. In addition to these facts I may remark, that an opportunity had presented 

 itself of inspecting- a rook whose mandibles were so greatly curved in opposite direc- 

 tions, and, consequently, so much crossed at the extremities, that it could not possibly 

 thrust its bill into the ground, and the base of that organ and the anterior part of the 

 head did not manifest the least deficiency of plumage. With such evidence in its 

 favour, I was induced to adopt the popular hypothesis, which I now abandon, in con- 

 sequence of having recently proved by experiment that it is erroneous. Being sup- 

 plied by George Davies, Esq., with two young rooks, taken from a nest in his rookery 

 at Cyffdu, on the 17th of May, 1843, I put them into a large wooden chicken-pen, pur- 

 posing, when they could take their food without assistance, to remove one of them to a 

 garden enclosed with walls, where it might have an opportunity of employing the means 

 of procuring sustenance common to the species, and to let the other remain in the pen. 

 This plan was frustrated by the unexpected death of one of the young birds soon 

 after it came into my possession ; but the result of the experiment, as* will be seen in 

 the sequel, was not at all affected by this untoward circumstance. In the month of 

 August, the surviving rook lost only a few feathers from various parts of its body, but 

 did not moult regularly till July and August, 1844, when the feathers at the base of 

 the bill and on the anterior region of the head were cast off, and have not been re- 

 newed to the present hour, though the bird has always been remarkably healthy, and 

 has never, on any occasion, been suffered to leave the pen for a moment. That rooks 

 in a state of liberty usually moult in the autumn of the year in which they are disen- 

 gaged from the egg may be inferred from the fact, that although numerous individuals, 

 whose shrill voices evidently denote that they are young birds of the season, may be 

 seen in the months of June and July with the base of the bill and anterior part of 

 the head abundantly supplied with feathers, yet for several months prior to the breed- 

 ing-season not one can be perceived, at least as far as my own observations extend, 

 which has not those parts denuded. From what has been stated, it is evident that the 

 phenomenon under consideration has a physiological, not a mechanical cause, though 

 the removal of the plumage may be facilitated by the frequently repeated act of 

 thrusting the bill into the ground ; and the circumstances which seemed to support the 

 opposite conclusion admit, for the most part, of an easy explanation upon this view of 

 the subject. The difference observable in the extent and completeness of the nudity 

 at the base of the bill and the anterior part of the head of the rook, probably depends 

 upon the progress which has been made in moulting, especially among the younger 

 birds; and the early denudation of the more prominent parts may be occasioned by 

 the friction consequent upon the manner in which the bill is employed in procuring 

 food. The short filiform processes so common on the depressed and less exposed parts 

 present a difficulty of which no satisfactory solution suggests itself; but the state of 

 the plumage on the head of that rook whose mandibles were greatly crossed, may be 

 accounted for on the supposition that it was a young bird which had not moulted. 

 Had the experiment recorded by Mr. Waterton, in his ' Essays on Natural History,' 

 p. 136-139, been successful, this question, upon which public opinion has been so 

 long divided, would have been settled some years earlier; unfortunately, however, 

 both the young rooks selected for the purpose of deciding it met with untimely deaths, 

 one before it had begun to moult, and the other soon after it had commenced moulting. 

 On Mr. Waterton's return from Bavaria, his gamekeeper, to whose care the latter bird 

 had been consigned, informed him that at the period when its existence terminated, 

 " the lower mandible had begun to put on a white scurfy appearance, while here and 



