Great egrets and snowy egrets grow aigrettes, long filamentous plumes, only during the breeding season. Plume hunters therefore shot birds at the nest, leaving chicks to starve, and North American and European colonies were stripped. At the peak of the trade, plumes commanded prices comparable with precious metals by weight.
The reaction shaped conservation. Audubon societies formed in the United States from the 1890s, the Society for the Protection of Birds in Britain campaigned against feathered hats, and legislation followed: the Lacey Act of 1900, the Migratory Bird Treaty Act of 1918 in the United States, and Britain's Importation of Plumage Prohibition Act of 1921. Wardens were hired to guard colonies, and at least two were killed doing it. The great egret became the emblem of the National Audubon Society.
What is less often noted is that the trade was industrial rather than merely fashionable, and other species suffered as badly. Egret populations recovered; some of the herons and terns taken alongside them did less well.