282 BIRD WATCHING 



impetus of the descent. It may be a matter of 

 impetus, but to me it has often seemed more as though 

 the sound gave the idea of impetus, or added to it, 

 and that the sweeps were, sometimes, just as impetuous, 

 or even more so, when made without it. As I ob- 

 served, the birds flew to their trees at a very moderate 

 height — not very much, indeed, above the trees them- 

 selves — and, whilst many made the whizzing sound, 

 the great majority swooped down without it. It 

 seems, therefore, to be a special sound produced by 

 the rooks at pleasure, and always accompanying an 

 excited frame of mind. First one bird and then 

 another gets excited, and dashes suddenly down with 

 the whirring or whizzing noise, so that, as the sound 

 is not vocal, and is only heard upon such occasions, 

 it has all the appearance of being caused by the quick, 

 sudden motions of the wings. But it is possible that 

 some particular way of holding the quill-feathers of 

 the wing or even tail is required to produce it, in 

 combination with the general movements, and this 

 would account for its being sometimes heard and 

 sometimes not heard, when these latter are identical.* 

 The curious burring note is likewise, but far less fre- 

 quently, an accompaniment of these wild excited 

 sweepings, and this is most often the case when they 

 are from a considerable height. Here, again, the note 

 bears a clear relation to the bird's mental state, so 

 that it would appear that the degrees of pleasurable 

 excitement cannot be estimated by the motions alone. 



* With regard to the above, however, I am now no longer so sure. 

 Jc inc'cn doute. When the rooks descend from a height, the sound 

 made is often most remarkable, being that of a mighty rushing wind 

 filling the air. 



