236 MORTALITY AMONGST SEA-BIRDS. [PART II. 
breed. This circumstance would lead to the sup- 
position that there must have been some similar 
visitation among them last year. 
The birds which were thus picked up were, I 
am told, thin, but scarcely so emaciated as to lead 
to the belief that they had become thus reduced 
merely from starvation. 
In the absence of any light which may have 
been thrown on the subject by dissection or other- 
wise, of the existence of which I am not aware, 
the actual cause of this mortality must remain a 
matter of doubt, but it may probably, without hesi- 
tation, be assigned to one of the three following— 
namely, starvation, poison, or disease. With re- 
gard to the first, it is just possible that from some 
atmospheric or other cause the fish, which form 
almost exclusively the food of these birds, may 
have kept so far out at sea, and so deep, as to 
be inaccessible to them; or again, they may have 
been by some means diverted from their usual 
course—intercepted for instance by the extraor- 
dinary plague of Dog-fish, by which the North- 
western coast of Scotland was (as mentioned in 
page 84) visited in the spring of 1858—and thus 
prevented from reaching their ordinary haunts, 
where the birds would naturally have depended on 
