I zoomed in to try to see what’s going on and it’s neck still looks puffed out, but I can’t really verify if sound is still coming out. I mainly wanted to show off how low the voice is. I wasn’t able to find the original comment I saw about the last hoot rolls off to the limits of human hearing.

I did find a description of its larger cousin, the Blakiston’s Fish Owl:

I listened under the sound of the wind for the distinctive call of the fish owl. Fish owls hoot at frequencies in the low-200-hertz range, in the same ballpark as a great gray owl and twice as low as a great horned owl. In fact, the frequency is so low that the sound can be difficult to capture well with a microphone.

On the tapes I’d later make, the owls always sounded far away, muffled, lost, even if they were close by. The low frequency of the vocalizations served a purpose: it ensured that sound passed cleanly through dense forest and could be heard some distance away, up to several kilometers. This was especially true in winter and early spring, when there was little tree cover and the crisp air facilitated movement of sound waves.

Fish owl pairs vocalize in duets. This is an uncommon attribute recognized in less than 4 percent of bird species globally, most of which are in the tropics. The male usually initiates a fish owl duet, filling an air sac in his throat until it’s swollen like some monstrous, feathered bullfrog. He holds that position, the white patch of his throat now a conspicuous orb contrasting against the browns of his body and the grays of the gathering dusk, a signal to his mate that the vocalization is impending. After a moment he exhales a short and wheezy hoot—the sound of someone having the breath knocked out of him—and she answers immediately with one of her own, but deeper in tone. This is unusual among owl species, where females usually have the higher voice. The male then pushes out a longer, slightly higher hoot, which the female also responds to. This four-note call-and-response is over in three seconds, and they repeat the duet at regular intervals for anywhere from one minute to two hours. It is so synchronized that many people, hearing a fish owl pair vocalize, assume it is one bird.

From Scientific American: A Duet of Fish Owls