170 Mr. J.Blackwall's Ornithological Notes. 



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 re- 

 sult 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 ante- 

 rior region of the head were cast off, and have not been renewed 

 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 disengaged from the 

 egg may be inferred from the fact, that although numerous indi- 

 viduals, 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 phsenomenon 

 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 conclu- 

 sion 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 earlier denudation of the more prominent parts 

 may be occasioned by the friction consequent upon the manner 

 in which the bill is employed in procming food. The short fili- 

 form processes so common on the depressed and less-exposed 

 parts present a difficulty of which no satisfactory solution sug- 

 gests 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 Natm-al History,' p. 136-139, been successful, this question, 

 upon which pubhc 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 un- 

 timely deaths, one before it had begun to moult, and the other 

 soon after it had commenced moulting. On Mr. Waterton's re- 

 turn from Bavaria, his gamekeeper, to whose care the latter bird 



