The chickadee gargle is generally termed a call but it has some characteristics of song: it is complex, is learned, has dialects and is used mostly by males. The gargle has been most studied in the Black-capped Chickadee, where each bird has a repertoire of about 20 gargles. It is used as a close-range aggressive vocalization year-round.
These are recordings of a Carolina Chickadee singing before sunrise in mid-March (on two different days at the same location, probably the same bird). The song consists of gargles and the regular four part song in an eventual variety pattern. The bird was singing alone with no evidence of any agonistic encounter, so it appears that in this case the gargle was being used as an advertising song.
Sequence: gargle, a second gargle, four part song, then the second gargle again.
Sequence: gargle, four part song, a different gargle, then the four part song again.
The Gargling Chickadees (Earbirding)
Ficken, M. S. 1981b. What is the song of the Black-capped Chickadee? Condor 83:384-386