Peter Berthold of the Max Planck Institute for Ornithology said each year cats kill some 50 million birds in Germany, The Local.de reported.
"Sometimes they kill a wonderful red-colored bullfinch, or a wryneck, which could be the last in the district," Berthold said.
He suggested instituting an "ecological compensation tax."
Thomas Schroder, president of the German animal protection association, warned such a move could backfire.
"Considering the experience we have had with a dog tax, we would fear the introduction of a cat tax would mean many animals could suddenly be thrown out, or given to animal shelters," he said.
That, said Schroder, could lead to more feral cats on the prowl feeding on feathered victims.