A new study has revealed that over the last 20,000 to 50,000 years, birds have undergone a major extinction event, inflicted chiefly by humans, which caused the disappearance of about 10 to 20 percent 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.

Source: Where have all the birds gone?