feral

Hiroko Oyamada の "The Hole" を読んでいます。

They were brought to Japan in the 1930s for their fur, which the military used for coats. People also cooked and ate them. After the Second World War, Japan no longer needed military clothing, therefore graybacks were no longer useful. The graybacks that remained went feral, and now inhabit river areas throughout Japan.

graybacksは毛皮を利用する為に戦前に輸入したが、戦後 "feral" となった、とあるので、これは野生化したことだと推測します。辞書で確認します。

・Oxford English Dictionary: (of animals) living wild, especially after escaping from life as a pet or on a farm: feral cats
・Collins Dictionary: Feral animals are wild animals that are not owned or controlled by anyone, especially ones that belong to species which are normally owned and kept by people.: The feral animals have begun venturing into towns in the hunt for food as winter bites.
・Cambridge English Dictionary: existing in a wild state, especially describing an animal that was previously kept by people: feral dogs/cats