The Migratory Bird Treaty Act (MBTA), 16 U.S.C. § 703, made killing certain types of birds a misdemeanor. The MBTA did not contain any mens rea provision. Upon the inspection of several heater-treaters, or vessels used to prepare oil for transport, the U.S. Fish and Wildlife Service (FWS) found hundreds of protected birds that had been caught and killed in the heater-treaters. FWS began educating oil companies of this danger. In 2006, FWS sent a notice of the danger to the companies involved in the initial heater-treater inspections, including Apollo Energies, Inc. (Apollo) (defendant). Dale Walker (defendant), doing business as Red Cedar Oil (Red Cedar), did not receive the notice. Given the general lack of awareness of the heater-treater danger prior to its education campaign, FWS decided not to pursue criminal action under the MBTA against any company until 2007. In April 2007, FWS found a protected bird dead in a heater-treater owned by Apollo, and multiple protected birds dead in heater-treaters owned by Walker. Upon being informed of the dead birds, Walker placed caps on the exhaust pipes of Red Cedar’s heater-treaters. Nevertheless, FWS found a protected bird dead in one of Walker’s heater-treaters in April 2008. Apollo was convicted of violating the MBTA, and Walker was convicted of two counts of violating the MBTA. Apollo and Walker appealed, arguing that they had no intent to kill the birds and that only the unmanned oil equipment had resulted in the birds’ deaths.