The passenger pigeon

"The Passenger Pigeon was no mere bird; he was a biological storm. He was the lightning that played between two biotic poles of intolerable intensity: the fat of the land and his own zest for living. Yearly the feathered tempest roared up, down, and across the continent, sucking up the laden fruits of forest and prairie, burning them in a travelling blast of life… Like any other chain reaction, the pigeon could survive no diminution of his own furious intensity. Once the pigeoners had subtracted from his numbers, and once the settlers had chopped gaps in the continuity of his fuel, his flame guttered out with hardly a sputter or even a wisp of smoke." –Aldo Leopold, 1947, On a Monument to the PigeonIn about 1806, Alexander Wilson, no casual observer of birds—the Wilson Ornithological Society was named in his honor—documented a single flock of migrating passenger pigeons near Frankfort, KY: "…From right to left as far as the eye could reach, the breadth of this vast procession extended; seeming everywhere equally crowded."Wilson estimated the column to be, at a minimum, a mile wide and 240 miles long with 3 birds per square yard of space throughout. He calculated the flock to consist of over 2.2 billion birds, a number he believed to be far lower than its actual size.Again, this was a single flock. There is no way to know how many other superflocks of the species existed at that time, but modern estimates based on historical reports of many observers suggest an overall population of 3-5 billion birds—25-40% of the nation's entire bird fauna.One nesting colony in 1878 near Petoskey MI was reported to cover some 211 to 261 square miles of deciduous forests, with many trees harboring 50 or more nests. Seven years earlier, the largest breeding colony ever observed was estimated to cover roughly 855 square miles of woodlands, extending over most of the southern third of Wisconsin and bordering parts of Minnesota.And yet, within the space of 20 years, this most abundant of all avian species in North America (some have argued in the world) had disappeared from the continent. The last wild specimen was shot in 1907 near St. Vincent Quebec and, with the demise of a female named Martha in the Cincinnati Zoo on Sept 1, 1914, the species was officially declared extinct. The passenger pigeon, Ectopistes migratorius, was not named for serving as a transport service of any kind, but as an Anglicization of the French word, passenger—to pass by—in reference to the bird's migratory behavior. Further confusion over its common name comes from misunderstanding of the term "carrier pigeon," which is just a domestic pigeon (the rock dove seen in almost every city park) trained to carry messages from point A to point B.Although similar in shape to the mourning dove, the passenger pigeon was a substantially larger bird and the male, with its slate-blue upper parts and iridescent pinkish-orange neck and chest, was more colorful. But it was the species' phenomenal life style that distinguished it from all other birds on the planet. The key to the species' former astronomical abundance was its nomadic wanderings in search of extensive stands of "mast seeding" forest. Mast is the botanical name for nuts, seeds, buds and fruits of trees and shrubs. Many species of mast-producing trees such as white oak, red oak and beech have evolved a method of reproduction involving massive synchronous (in the same year) seed production followed by an unpredictable number of years before the next mast-seeding event.During years of explosive acorn and beechnut production, there would be more food than squirrels, deer, mice, birds and other herbivores could possibly eat (a strategy ecologists call predator-satiation) and many nuts would be able to sprout into seedlings. In succeeding years, sparse mast production would keep herbivore populations from getting too large.But passenger pigeons gamed the system. Traveling in enormous flocks throughout the Eastern deciduous forests (they ranged almost exclusively east of the Rockies), they would find a mast-seeding site and clean it out in an operation that had to be seen to be believed.Observers reported a rolling wave of hundreds of thousands of pigeons in which a broad front of birds advanced along the forest floor overturning every leaf in a mad search for food. All the while, birds at the rear of the horde were continually rising up to fly over their comrades and landing at the head of scavenging crush.Like the mast-seeding trees they relied upon, passenger pigeons' primary defense against their enemies was predator-satiation. With populations numbering in the hundreds of millions, the chance of any individual pigeon falling prey to one of the species' many predators was vanishingly small.So it seemed. Next time: The demise of the most abundant of all birds.