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Heck also played an important part in saving the European bison (wisent) from extinction when the majority of its population of about 90 survived in captivity in Germany following great losses to the species during World War I. To help manage the survival of the European bison from the remaining captive population, he commenced the first studbook for a non-domestic species, initially as a card index in 1923, leading to a full publication in 1932. Thanks to Heck's efforts, the European bison population has significantly increased and the species has been re-released into the wild.