Save Vanishing Species semipostal stamp sales were extended under a government funding bill that took effect late last month.
The stamp, which features the image of an Amur tiger cub, has brought in $6.1 million since its introduction in 2011. More than 55 million stamps have been sold so far.
The proceeds are given to the U.S. Fish and Wildlife Service, which distributes them to a variety of species preservation funds. These include the Great Ape Conservation Fund, the Marine Turtle Conservation Fund and the Rhinoceros and Tiger Conservation Fund.
Usps.com has more information about the organization’s semipostal stamps.