Joel Greenberg is a research associate at the Field Museum and the Chicago Academy of Sciences Peggy Notebaert Nature Museum. His book, A Feathered River Across the Sky: The Passenger Pigeon’s Flight to Extinction (2014) effectively demonstrates that the extinction of passenger pigeons was a shocking event not simply because the species once enjoyed a population “that may have exceeded that of every other bird on earth, and its aggregations surpassed in numbers those of every other terrestrial vertebrate on the continent,” but also because its demise was so swift, with the population crashing from upwards of a billion to zero in about 40 years.
