As Susan noted, Sunday was the 90th anniversary of the Migratory Bird Treaty Act of 1918 (MBTA). The MBTA is the primary legislation protecting native birds in the United States and one of this country's earliest environmental laws. It bans "taking" any native birds; "taking" can mean killing a wild bird or possessing parts of a wild bird, including feathers, nests, or eggs. Exceptions are allowed for hunting game birds and for research purposes, both of which require permits.
This act has its roots in late nineteenth-century opposition to the millinery trade. The fashions of the 1880s and 1890s favored hats adorned with real feathers and stuffed wild birds. The most popular feathers were the long plumes of egrets and herons. The trade in feathers took a tremendous toll – 200 million wild birds per year by some estimates. Populations of the most hunted species declined precipitously.
In response to the killing, George Grinnell founded the first Audubon Society in 1886 to organize opposition. Among Grinnell's proposals were laws to protect wild birds. His organization quickly collapsed, however, largely due to financial difficulties, and it failed to have any effect on the slaughter.
In 1896, Harriet Lawrence Hemenway took up the cause of stopping the trade in bird parts. She persuaded influential friends to pledge to stop wearing bird feathers and to promote the cause among other high society women in Boston. She and her associates founded the Massachusetts Audubon Society to advocate on behalf of wild birds. Bird watching was just then becoming a popular pastime, so she found many willing to help her cause.
The example of Massachusetts Audubon inspired similar efforts elsewhere in the country; various chapters joined in 1905 to become the National Association of Audubon Societies (later renamed National Audubon Society). The organizations followed a two-pronged strategy of persuading individuals to stop wearing feathered hats through the society's publications and pushing state and federal governments to regulate market hunting. The cause took on added urgency with the sharp decline and then extinction of the once-abundant passenger pigeon (last wild bird reported in 1900; extinct in 1914) and Carolina parakeet (last wild bird killed in 1904; extinct by 1939).
Eventually activism on the part of bird watchers and ornithologists led to legislation. Several states passed laws based on Grinnell's model; however, enforcement remained spotty. The Lacey Act, in 1900, banned killing birds illegally in one state and then selling them in another. In 1913, Congress followed it with the Weeks-McLean Migratory Bird Law, which placed migratory birds under federal jurisdiction and prohibited their killing without authorization from the federal government.
Several state and federal courts struck down the 1913 law as a 10th Amendment violation. (Such a law would probably pass review today, due to changes in constitutional interpretation in the wake of the New Deal.) The Wilson administration found a way around the rulings by negotiating a treaty with the British Empire (on behalf of Canada). The 1916 treaty contained all of the protections sought under the Weeks-McLean Law and had the additional benefit of protecting birds on both sides of the U.S.-Canadian border. Congress enacted the treaty as the Migratory Bird Treaty Act in July 1918. Later revisions to the law extended its protections to include similar treaties with Mexico, Japan, and the Soviet Union (now Russia).
The MBTA still protects wild birds, even though its original target is long gone. Recent applications of the MBTA have included projects like Operation High Roller, which is directed against pigeon racing clubs that kill raptors. Corporations can be liable under the MBTA for negligently killing birds by dumping petroleum sludge or highly saline wastewater in places where birds gather. The MBTA was among the laws waived by Michael Chertoff to construct the border wall.
A list of protected birds is available here. Introduced bird species (like house sparrows and mute swans) and captive-bred game birds (like domestic mallards) are not protected by federal law.
The background history of the MBTA is included in chapter 5 of Scott Weidensaul's Of a Feather, which I reviewed in December.