What defense mechanism does the Yellow Warbler use against egg-laying attempts by the Brown-headed Cowbird?

Building an entirely new nest directly on top of the existing one

The Yellow Warbler faces a significant challenge from the brood parasite, the Brown-headed Cowbird, which attempts to trick the warbler into raising its young. Instead of exhibiting behavior common to other birds, such as ejecting the foreign egg or deserting the nest, the female Yellow Warbler has developed a distinct and fascinating response. If she detects an egg laid by the cowbird, her instinct is to encase the unwanted egg by constructing a completely new nest cup constructed immediately above the original structure. This process of superimposition can occur multiple times within one breeding season, sometimes resulting in a single nest structure layered up to six times deep.