True boss lifted cap for US singer (7)

I believe the answer is:

tanager

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'singer' is the definition.
(tanager is a kind of birdanimal)

I don't understand how the rest of the clue works.

(Other definitions for tanager that I've seen before include "A bird" , "South American singer" , "American songbird" , "Songbird of the bunting family" .)

I've seen this clue in the Sydney Morning Herald.

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