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for many hours at a time—I never suspected its true origin. These particular birds never uttered any sound more extraordinary than a kind of "ik, ik, ik!" and this though they were constantly fighting, whilst the performance of the nuptial rite was frequent amongst them. The note which so astonished me never came from very near; I heard it, as I have said before, only occasionally, and it always seemed to come from a part of the rock where a few pairs of fulmar petrels were sitting. When I mentioned it to the watcher, who occupied the little sentry-box on the ness, during the daytime, when I was out, leaving it for me to sleep in at night, he said nothing about guillemots, but expressed his opinion that the sound was produced by these fulmar petrels. Now the fulmar petrel, though I have never met with any reference to it, does utter, when on the breeding-ledges—or at least, it does in the Shetlands—a note which is sufficiently marked and striking, a sort of angry, hoarse, gruff interjection—guttural too—several times repeated, and sounding sometimes like a laugh. Often too, these notes are not divided, or else are so quickly repeated that they sound like one, continuously uttered for some little space of time. As I now think, I must sometimes have caught this note at the beginning or end of the cry of the guillemot, and put it down as a part of it. Then, when, with this idea in my mind, I watched the petrels at but a few yards' distance, and heard them uttering the note they do utter, to my heart's content—swelling