The Polish Academy of Sciences now maintains that "from a purely scientific perspective," domesticated house cats in Europe, and therefore in Poland, should be considered an "invasive alien species."
Felis catus, the domestic cat, was only domesticated roughly 10,000 years ago in the ancient civilizations of the Near East. The presence of cats in Europe is only due to human activity, meaning it can be classified as an alien or non-native species to Europe. The Institute of Nature Conservation in Poland noted the "clear scientific evidence" of the negative impact that domesticated cats have on native biodiversity, leading to their classification as invasive.
Poland's alien species database includes almost 1,800 species', including raccoons, mandarin ducks, and more. According to accepted definitions, the majority are also invasive, though this does not mean they are a threat to Poland or the European Union (EU). As such, no regulation requires domesticated cats to have their population controlled or permits needed for ownership.
However, the Institute stresses that one of the easiest ways pet owners can reduce the impact of their cats on native wildlife is to limit how much time cats can roam freely, especially during bird breeding seasons.
You can read more from the Institute's frequently asked questions (FAQs) here.