No Safety in Numbers
The following is a textual transcription of the passenger pigeon account in the book “The Annihilation of Nature: human extinction of birds and mammals” by Ceballos et al (2015). Available at John Hopkin’s Press and Amazon.
Two hundred years ago, the passenger pigeon was the most common bird in North America, amounting to perhaps 5 billion individuals--roughly as many as all the birds that now overwinter in the United States.
The pioneering ornithologist and bird artist John James Audubon observed a passing flock of passenger pigeons for 3 days and guessed that at times more than 300 million were passing per hour and the size of that one flock was perhaps 2 billion birds.
Passenger pigeons consumed huge quantities of seeds from oak, beech, and chestnut trees and formed dense nesting colonies that could stretch for 23 kilometers (14 miles). The sheer weight of roosting and breeding birds was said to have broken branches off large trees and toppled small ones. How do 5 billion birds disappear? The extermination began on America’s East Coast, largely through clearing of the forests. Then, after the American Civil War, railroads pushed into the pigeons’ midwestern stronghold. Telegraph lines were installed, and soon professional market hunters had a method for being kept informed of the locations of breeding colonies. Technology, growing urban appetites for meat, and plenty of professional hunters soon resulted in a relentless slaughter. The succulent squabs (young pigeons) were shipped to markets in America’s eastern cities, while adults were captured and used as targets in shooting galleries. In 1878 one hunter alone shipped 3 million pigeons from Michigan to eastern markets. An article in Forest and Stream magazine described the action in Pennsylvania in 1886: “When the birds appear all the male inhabitants of the neighborhood leave their customary occupation as farmers, bark-peelers, oil-scouts, wild-catters, and tavern loafers, and join in the work of capturing and marketing the game. The Pennsylvania law very plainly forbids the destruction of the pigeons on their nesting grounds, but no one pays any attention to the law, and the nesting birds have been killed by thousands and tens of thousands.”
The end for these superabundant birds came with astonishing speed. Market hunting ceased when it was no longer profitable, although there were still many thousands of birds living in large stretches of suitable habitat. Nonetheless, the passenger pigeon declined rapidly to extinction. The cause of the final extinction remains a mystery. Perhaps the best guess is that the birds required gigantic colonies to breed successfully. Individually, they were quite vulnerable to predators, and their breeding strategy may have evolved to swamp predators--appearing suddenly and reproducing before local predator populations could increase enough in size to pose a significant threat. As the colonies dwindled, predator saturation probably became impossible, and the birds disappeared down their enemies’ gullets.
The final living member of the species, a female named Martha, died in the Cincinnati Zoo in 1914. Martha still soldiers on, stuffed, in the U.S. Smithsonian National Museum of Natural History, and the species is memorialized in one of John James Audubon’s most evocative illustrations. But that’s not the end of the story. By devouring billions of seeds, smashing trees, and depositing vast quantities of excrement each summer, these birds shaped the ecology of eastern deciduous forests in the United States. It may be that the mobs of voracious pigeons so reduced the numbers of seeds available to the white-footed mouse (Peromyscus leucopus) that, after the pigeons vanished, big mast years (years in which forest trees produced abundant acorns and other nuts) have produced explosions of mouse populations. As noted earlier, the mice are reservoirs of the tick-transmitted Lyme disease, which now plagues human populations in the eastern United States. Could this be the passenger pigeon’s revenge?
Ectopistes migratorius was a species widely distributed in the eastern and central regions of the USA and Canada. They were occasionally seen as far as south-central Mexico and Cuba. This species, the most abundant bird in North America, became extinct in less than 40 years.
Passenger pigeons became extinct by overhunting and habitat loss. Millions of pigeons were slaughtered annually for sale in markets. Additionally, the widespread destruction of the hardwood trees that provided their food was also linked to their extinction. This species is believed to not be adapted to live in small populations, and the change in population size was so sudden that there was no adaptation that allowed them to survive. The consumption of this pigeon increased so significantly that there were specialized hunters in this species, so the decline of the passenger pigeon was inevitable until it became extinct.