The tradition can be traced back to President Abraham Lincoln in 1863.
Historians claim he spared a turkey’s life after his son, Tad, befriended it.
But yearly pardoning became an “official” tradition only under George H W Bush, when the former president spared a turkey’s life in 1989 as animal-rights activists protested nearby.
Many people believe the custom was started 70 years ago by Harry Truman, because he was the first president to receive a turkey on behalf of the poultry industry as a whole.
His government launched a campaign in 1947 to encourage people to forego eating poultry and eggs on Thursdays, in order to conserve supplies to send to post-war Europe.
But Thanksgiving, Christmas and New Year’s Day fell on Thursdays that year – causing outrage.
Other presidents before Bush Snr did spare birds lives, including President John F Kennedy – who gave an unofficial pardoning days before his assassination in 1963.