When I lived in the midst of lowland primary rain forest on the Atlantico side of Costa Rica, there was the most eerie, uncanny, unbelievable night sound one could ever imagine. It sounded so strong and nonbiological I could not imagine then, lying in my hammock, that it could issue from anything within the animal kingdom. The best I can describe it is that it sounded close to the sound when someone plays a saw on their knee, bending and warping a quavering, wailing, metallic, strangely melodic siren sound that sounds electronically synthesized.
If there were one thing I could retain from my 4 1/2-month stay in the one-room bark house filled with scorpions in the middle of the 450-hectare tract of primary rain forest, it would be a recording of the strange nighttime sounds, especially the mournful bird (?) that plays the synthesizer.
The rain forest is nearly silent during the day; but at night it's a transylvanian (double entendre) Bela Bartok symphony, with competing woodwinds and brass, of tonal beauty and timbral eeriness. That lost sound traveled through the dark woods, deep into my imagination, and resonates in me today as a mysterious Green Mansions: A Romance of the Tropical Forest (by W. H. Hudson, 1916) of dark, shaded incomprehensibility.