Koltrast is ‘blackbird’. Kol is coal, a common Germanic word. Trast is thrush, going all the way back to an Indoeuropean root *trozdo- from which also stems Latin turdus, with the same meaning. In the early hours of a spring morning ten thousand years ago our ancestors listened to the same song.
This time of the year they don’t sing, they do as everybody, try to fatten up as soon as possible before winter comes.