Listen for a thin run of notes that will not sit still — it slides up, dips down, and on the way. English has a verb for exactly that sound, warble, and a warbler is simply whatever makes it. Usually that is a small bird in a hedge. But the name follows the sound, so it can also land on a person at a microphone or a part inside a machine.
Warbler is warble plus -er, so the word names whatever produces that wavering song.
warbler 由 warble（發出顫抖起伏的歌聲）加上 -er 組成，字面上就是「發出那種歌聲的那一個」。因為 -er 不限於人，所以這個名字可以給鳥、給人，也可以給一個零件。
Wiktionary etymology for warbler: "From warble + -er." (kaikki:3f6f69a190036ae4:372367149)
Three branches
發出顫音的鳥
英文最早把這個名字給了鳥，所以這是離核心畫面最近的一層。
noun · B2
A small bird that sings in a high, shaky, up-and-down way. In birdwatching, warbler is also the group name for many of these small songbirds, such as the Old World warblers and the New World warblers.
鶯；會唱歌的小鳥
發出顫音的人
名字跟著聲音走，於是落到唱歌的人身上；被比成鳥，玩笑的味道就跑出來了。
noun · C1
A person who sings. It is usually said in a joking way, often about someone whose singing is not very good.
（開玩笑說的）歌手
發出顫音的裝置
-er 從來不只用在活的東西上，所以同一個名字也可以給一個會發抖音的零件。
noun · C1
A small part inside a machine that makes a wavering, up-and-down sound, used instead of a bell to call your attention.
顫音發聲器