Migratory birds have enjoyed federal protection since 1918 under the Migratory Bird Treaty Act. The law makes it illegal to capture, kill, trade, or otherwise transport wild birds without the express permission of the U.S. Fish and Wildlife Service. It also holds companies or corporations accountable who cause the death of migratory birds through environmental accidents such as oil spills. But a proposed revision to the law rolls back some of these protections if entities can prove the deaths were unintentional.