Federal Bird Safe Buildings Act of 2021 This bill requires the General Services Administration (GSA) to develop and implement strategies for reducing bird fatalities from collisions with public buildings. Specifically, the GSA must incorporate relevant features and strategies into public buildings that are newly constructed, acquired, or substantially altered so as to reduce bird fatalities. The GSA must also develop a related design guide and annually certify its active use. The bill's provisions do not apply to buildings and sites on the National Register of Historic Places, the White House and its grounds, the Supreme Court building and its grounds, or the U.S. Capitol and any buildings on its grounds.