Dorota Suminska, the author of a book titled "The Happy Cat," pointed to other causes of shrinking biodiversity, including a polluted environment and urban building facades that can kill birds in flight.
"Ask if man is on the list of non-invasive alien species," Suminska said, arguing that cats were unfairly assigned too much blame.
Solarz told the AP that some media reports about the listing created a false impression that the institute was calling for feral and other cats to be euthanized.
Earlier this month, his institute published a post on its website citing the "controversy" and seeking to clarify its position. The institute stressed that it was "opposed to any cruelty towards animals." It also argued that its classification was in line with European Union guidelines.
As far as categorizing cats as "alien," the institute noted that "Felis catus" was domesticated probably around 10,000 years ago in the cradle of the great civilizations of the ancient Middle East, making the species alien to Europe from a strictly scientific point of view.
The institute also stressed that all it was recommending was for cat owners to limit the time their pets spend outdoors during bird breeding season.
"I have a dog, but I don't have anything against cats," Solarz said.
