North America's Bird Population Has Plummeted The journal 'Science' says that the population has shrunk by three billion over the past 50 years. Cornell conservation scientist Ken Rosenberg, via NPR The report adds that most of the drop, around 90 percent, relates to just a handful of types. These include finches and sparrows. Other recordings show a one-third fall in shorebird numbers. The population of grassland types has also dropped over 50 percent. To get their results, the study's authors observed migration patters over a period of 10 years. They also used analyzed surveys from bird watchers in North America. Researchers say there are many reasons for the drop, including habitat loss and toxic pesticides. Michigan State University ecologist Elise Zipkin, via NPR
