A new study from Tel Aviv University and the Weizmann Institute revealed that over the last 20,000-50,000 years birds have undergone a major extinction event, inflicted chiefly by humans, which caused the disappearance of about 10%-20% of all avian species. According to the researchers, the vast majority of the extinct species shared several features: they were large, they lived on islands, and many of them were flightless.