What is the defense mechanism documented in the Yellow Warbler when a Brown-headed Cowbird lays an egg in its nest?

Answer

Building an entirely new nest floor on top of the existing eggs

The Yellow Warbler has been observed dealing with brood parasites by constructing a new nest floor directly over the cowbird's egg, sometimes resulting in nests layered up to six deep.

What is the defense mechanism documented in the Yellow Warbler when a Brown-headed Cowbird lays an egg in its nest?

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Fun & Interesting Facts About Warblers - YouTube

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