How are the unique, outlandish notes produced? I cannot profess to know. Our opinion was that the bird swallowed air into his gullet, gulping it down with each snap of the beak. To all appearance it was necessary for him to inflate the crop in this way before he could pump, or boom. As to how much of the grand booming was connected with the swallowing of the air, and how much, if any, with the expulsion of it, my friend and I did not agree, and of course neither of us could do more than guess.
I made some experiments afterwards, by way of imitating the noises; and these experiments, together with the fact that the grand booming seemed to be really nothing more than a development of the preliminary hiccoughs, and the further fact that the swelling of the breast did not go down gradually during the course of the performance, but suddenly at the close,—all these incline me to believe that the notes are mainly if not entirely caused by the inhalation or swallowing of the air; and I am somewhat strengthened in this opinion by perceiving that when a man takes air into his stomach the act is attended by a sound not altogether unlike the bittern’s note in quality, while the expulsion of it gives rise to noises of an entirely dissimilar character.
That the sounds in question were not made entirely by any ordinary action of the vocal organs was the decided opinion of both my friend and myself.
As I have said, we watched the performance for more than an hour. We were sitting squarely upon the track, and once were compelled to get up to let a train pass; but the bittern evidently paid no attention to matters on the railway, being well used to thunder in that direction, and stood his ground without wincing.
When he had pumped long enough,—and the operation surely looked like pretty hard work,—he suddenly took wing and flew a little distance down the meadow. The moment he dropped into the grass he pumped, and on making another flight he again pumped immediately upon coming to the ground. This trick, which surprised me not a little in view of the severe exertion required, is perhaps akin to the habit of smaller birds, who in seasons of excitement will very often break into song at the moment of striking a perch.
As we came down the track on our way back to the station, three bitterns were in the air at once, while a fourth was booming on the opposite side of the road. One of the flying birds persistently dangled his legs instead of drawing them up in the usual fashion and letting the feet stick out behind, parallel with the tail. Probably he was “showing off,” as is the custom of many birds during the season of mating.
Our bird across the road, by the bye, was not pumping, but driving a stake. The middle syllable was truly a mighty whack with a mallet on the head of a post, so that I could easily enough credit Mr. Samuels’s statement that he once followed the sound for half a mile, expecting to find a farmer setting a fence.
In the midst of the hurly-burly we saw a boy coming toward us on the track.
“Let’s ask him about it,” said my companion.
So, with an air of inquisitive ignorance, he stopped the fellow, and inquired, “Do you know what it is we hear making that curious noise off there in the meadow?”