The world has 50 billion birds, a team of Australian researchers has concluded, but most species are rare and in need of greater conservation efforts. In a study published in the Proceedings of the National Academy of Sciences, biologists examined global occurrences and population estimates for about 92% of all existing bird species using data from 2010 to 2019. They found most birds occupy the vast stretch of land across Eurasia and North Africa known as the Palearctic and the region across North America known as the Nearctic. But most species have small populations, they found, with 12% of species having fewer than 5,000 individuals. Perching birds, shorebirds and waterfowl are the most abundant. Only three species—the house sparrow, European starling and ring-billed gull number more than 1 billion. “We conclude that there are many rare species, highlighting the need to continue to refine global population estimates for all taxa and the role that global citizen science data can play in this effort,” the authors concluded.