In the world of bird breeding, refers to the specialized "education lesson sounds" used to train Waterslager canaries (often called Malinois canaries in Turkey). These birds are legendary for their ability to mimic the sound of bubbling water, known as "water notes".
Küçük sat in the darkness of his covered cage, his head tilted. This "darkness training" was essential; without visual distractions, the young bird had nothing to do but listen and mimic.
Finally, the : the gentle, rhythmic flow of a cradle-like stream.