IPA: /ˈbɜːrdˌsɔːŋ/
KK: /ˈbɜrdˌsɔŋ/
A pleasant sound that birds make, often in the morning or during mating season.
I love waking up to the sound of birdsong outside my window.
Birdsong is formed from "bird" (from Old English "bridde", meaning a young bird or fledgling) and "song" (from Old English "sang", meaning a vocal musical composition). The word "birdsong" refers to the musical sounds made by birds.
Think of a young 'bird' ('bridde') making a 'song' ('sang') — that's why birdsong means the music that birds create.