Deer penises are sold in gift boxes in a store in Mvng La in this January 2007 photo.
The genitalia are usually made into wine or soup to supposedly restore virility and improve weak kidneys, among other benefits. Elderly men often receive them as birthday presents, according to photographer Karl Ammann.
"There is now a market for almost any volume of any vertebrate species," said Richard Corlett, a tropical ecologist at the University of Hong Kong.
"Apart from the obvious animals—big cats and rhinos—I worry most about the less obvious [species] such as pangolins," Corlett said, "where huge numbers are traded and we know nothing about [the] impacts."