warble

US /ˈwɔːr.bəl/
UK /ˈwɔːr.bəl/
"warble" picture
1.

to sing in a soft, low voice, especially with a trilling or quavering sound

:
The bird began to warble a sweet melody.
She would often warble old folk songs.
1.

a trilling or quavering vocal sound, especially that of a bird

:
The sweet warble of the nightingale filled the air.
She listened to the gentle warble of the stream.