Moas were a diverse group of flightless birds that ruled over New Zealand up to the arrival of humans, the biggest of these mega-birds stood around 3.5 meters (12 feet) with outstretched neck. While the whole moa family—comprised of nine species—vanished shortly after the arrival of people on New Zealand in the 13th Century, scientists have long debated why the big birds went extinct. Some theories contend that the birds were already in decline due to environmental changes or volcanic activity before humans first stepped on New Zealand’s beaches. But a study released today in the Proceedings of the National Academy of Sciences (PNAS) finds no evidence of said decline, instead pointing the finger squarely at us.