How the Great White Egret Inspired Bird Conservation in the Smithsonian says:
One particular group of birds suffered near extermination at the hands of feather hunters, and their plight helped awaken a conservation ethic that still resonates in the modern environmental movement. With striking white plumes and crowded, conspicuous nesting colonies, Great Egrets and Snowy Egrets faced an unfortunate double jeopardy: their feathers fetched a high price, and their breeding habits made them an easy mark.
To make matters worse, both sexes bore the fancy plumage, so hunters didn’t just target the males; they decimated entire rookeries. At the peak of the trade, an ounce of egret plume fetched the modern equivalent of two thousand dollars, and successful hunters could net a cool hundred grand in a single season. But every ounce of breeding plumes represented six dead adults, and each slain pair left behind three to five starving nestlings. Millions of birds died, and by the turn of the century this once common species survived only in the deep Everglades and other remote wetlands.
This slaughter inspired Audubon members to campaign for environmental protections and bird preservation, at the state, national and international levels. The Lacey Act passed Congress in 1900, restricting interstate transport of wild fowl and game. In 1911 New York State outlawed the sale of all native birds and their feathers, and other states soon followed suit. Passage of the Weeks-McLean Act (1913) and the Migratory Bird Act (1918) took the protections nationwide and mirrored legislation in Canada, Britain, and Europe, effectively ending the fancy-feather era.
More about Great Egrets on the UM Animal Diversity Web.