Cornell Lab of Ornithology conservation scientist Dr. Ken Rosenberg led an international team of 12 scientists in an analysis of decades of data on bird population — and the conclusion is disturbing. In the last 50 years, one in four birds in North America has disappeared. Pesticide use and loss of habitat to farmland are some of the most significant contributors to the decline in bird populations, according to Rosenberg. Although scientists have known for a long time that certain bird species were threatened by human activities, this study reveals that these issues apply to birds of nearly all species. “Seeing this net loss of three billion birds was shocking,” Rosenberg said.