Under Zinke, the Interior Department adopted a restrictive interpretation of the Migratory Bird Treaty Act, issuing a guidance document stating that the killing of birds "resulting from an activity is not prohibited by the Migratory Bird Treaty Act when the underlying purpose of that activity is not to take birds."[95] The move was opposed by a bipartisan group of 17 former top Interior Department officials, including seven former heads of migratory bird management at the U.S. Fish and Wildlife Service, who served in each administrations from Nixon to Obama. In a letter sent to Zinke and members of Congress, the former officials wrote that "This legal opinion is contrary to the long-standing interpretation by every administration (Republican and Democrat) since at least the 1970’s."[96][97]