Frontispiece illustrating the last living Passenger Pigeon protected in the Cinncinnati Zoological Gardens. The bird was then 20 years old. That this bird was on the verge of extinction was the result of a failed program initiated in 1857.
"Estimated to have numbered three to five billion at the height of its population, it may have been the most numerous bird on Earth; researcher Arlie W. Schorger believed that it accounted for between 25 and 40 percent of the total land bird population in the United States. The passenger pigeon's historic population is roughly the equivalent of the number of birds that overwinter in the United States every year in the early 21st century. (Wikipedia article on Passenger Pigeon, accessed 9-2020).