BIRD ROCK 185 
At ten o’clock at night I visited the west end of 
the Rock to see and hear the Petrels that nest there. 
The casual visitor to Bird Rock would be quite 
unaware of the presence of these birds; indeed, one 
might live there for years without knowing that 
Petrels made it their home. As far as the Rock is 
concerned, the birds are strictly nocturnal; but as 
usually only one bird—either male or female—is 
found on the nest, it is supposed that its mate is at 
sea feeding. If this supposition be true, I am at a 
loss to account for the entire absence of the birds 
during the daytime. Why should they not return 
to their nests before nightfall? And if, as stated, 
the sea bird takes the place of the nest bird, does 
the latter always feed at night and the former by 
day, or do they sometimes change about, thus mak- 
ing the same individual both nocturnal and diurnal 
in habit ? 
However this may be, I had no sooner reached 
the part of the Rock tenanted by the Petrels than I 
was given the most surprising evidence of their 
activity during the night. From the ground at my 
feet and on every side there issued the uncanny 
little song—if I may so call it—of birds doubtless 
sitting at the mouths of their burrows. It was not 
like the cry of a sea bird, but a distinctly enunciated 
call of eight notes, possessing a character wholly its 
own, and not to be compared to the notes of any 
bird I have ever heard, though at the time it 
impressed me as having a certain crowing quality. 
Such a call might be uttered by elves or brownies. 
Occasionally I saw a blur of wings as a bird passed 
between me and the lighthouse, 
