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In ecological release, an organism escapes its home and parachutes into an ecosystem that has never encountered it before. The majority of such escapees die rapidly, unable to thrive or reproduce in novel surroundings. Most of the survivors find a quiet niche and settle in, blending inconspicuously with the locals. But a few, finding themselves in places with few or none of their natural enemies, look around with the hopeful incredulity of juvenile delinquents who discover the mall’s security cameras are broken—and wreak havoc. In their home ecosystems these species have, like all living things, a full complement of parasites, microbes, viruses, and insect predators to shorten and immiserate their lives. Suddenly free of this burden, they can burst out and overwhelm the landscape.
The Japanese grind the roots of a low vine called kuzu
(Pueraria lobata)
into a white powder that thickens soup and is alleged to have curative properties; they also plant the species on highway shoulders as erosion-preventing ground cover. In the 1930s the U.S. Civilian Conservation Corps planted millions of kuzu seedlings to fight soil loss, a major fear in the era of the Dust Bowl. Renamed “kudzu,” the vine prevented so much erosion that villages across the U.S. Southeast celebrated kudzu festivals and crowned kudzu queens. People harvested it like hay and fed it to cows; entrepreneurs marketed kudzu cereal, kudzu dog food, and kudzu ketchup. In the early 1950s rural areas suddenly awoke from their trance and discovered that kudzu was eating them alive. Without its natural enemies the plant grew so fast that southerners joked they had to close their windows at night to keep it out. Worse, the plants themselves grew bigger than is usual in Japan—nobody knows why. Engulfing fields in dense mats of root and vine, kudzu swarmed over entire farms, clambered for miles along telephone lines, wrapped up trees, barns, and houses like a green Christo. The roots sank so deep that the vine was nearly impossible to remove. In 1996 the federal government estimated that kudzu had swallowed seven million acres. The figure is now much larger.
What happened after Columbus was like a thousand kudzus everywhere. Throughout the hemisphere ecosystems cracked and heaved like winter ice. Echoes of the biological tumult resound through colonial manuscripts. Colonists in Jamestown broke off from complaining about their Indian neighbors to complain about the depredations of the rats they had accidentally imported. Not all the invaders were such obvious pests, though. Clover and bluegrass, in Europe as tame and respectable as accountants, in the Americas transformed themselves into biological Attilas, sweeping through vast areas so quickly that the first English colonists who pushed into Kentucky found both species waiting for them. Peaches, not usually regarded as a weed, proliferated in the southeast with such fervor that by the eighteenth century farmers feared that the Carolinas would become “a wilderness of peach trees.”
South America was hit especially hard. Endive and spinach escaped from colonial gardens and grew into impassable, six-foot thickets on the Peruvian coast; thousands of feet higher, mint overwhelmed Andean valleys. In the pampas of Argentina and Uruguay, the voyaging Charles Darwin discovered hundreds of square miles strangled by feral artichoke. “Over the undulating plains, where these great beds occur, nothing else can now live,” he observed. Wild peach was rampant in South America, too. Peachwood, Darwin discovered, had become “the main supply of firewood to the city of Buenos Ayres.” Some invasions cancel each other out. Peru’s plague of endive may have been checked by a simultaneous plague of rats, which the sixteenth-century writer Garcilaso de la Vega reported “bred in infinite numbers, overran the land, and destroyed the crops.”
A phenomenon much like ecological release can occur when a species suddenly loses its burden of predators. The advent of mechanized fishing in the 1920s drastically reduced the number of cod from the Gulf of Maine to the Grand Banks. With the cod gone, the sea urchins on which they fed had no enemies left. Soon a spiny carpet covered the bottom of the gulf. Sea urchins feed on kelp. As their populations boomed, they destroyed the area’s kelp beds, creating what icthyologists call a “sea urchin barrens.”
In this region, cod was the species that governed the overall composition of the ecosystem. The fish was, in ecological jargon, a “keystone” species: one “that affects the survival and abundance of many other species,” in the definition of Harvard biologist Edward O. Wilson. Keystone species have disproportionate impact on their ecosystems. Removing them, Wilson explained, “results in a relatively significant shift in the composition of the [ecological] community.”
Until Columbus, Indians were a keystone species in most of the hemisphere. Annually burning undergrowth, clearing and replanting forests, building canals and raising fields, hunting bison and netting salmon, growing maize, manioc, and the Eastern Agricultural Complex, Native Americans had been managing their environment for thousands of years. As Cahokia shows, they made mistakes. But by and large they modified their landscapes in stable, supple, resilient ways. Some
milpa
areas have been farmed for thousands of years—time in which farmers in Mesopotamia and North Africa and parts of India ruined their land. Even the wholesale transformation seen in places like Peru, where irrigated terraces cover huge areas, were exceptionally well done. But all of these efforts required close, continual oversight. In the sixteenth century, epidemics removed the boss.
American landscapes after 1492 were emptied—“widowed,” in the historian Francis Jennings’s term. Suddenly deregulated, ecosystems shook and sloshed like a cup of tea in an earthquake. Not only did invading endive and rats beset them, but native species, too, burst and blasted, freed from constraints by the disappearance of Native Americans. The forest that the first New England colonists thought was primeval and enduring was actually in the midst of violent change and demographic collapse. So catastrophic and irrevocable were the changes that it is tempting to think that almost nothing survived from the past. This is wrong: landscape and people remain, though greatly altered. And they have lessons to heed, both about the earth on which we all live, and about the mental frames we bring to it.
ONE OUT OF EVERY FOUR BIRDS
When passenger pigeons drank, they stuck their heads beneath the surface of the water until they were eye deep. When they walked, their heads bobbed awkwardly and they looked around from side to side. Passenger pigeons were greedy eaters with terrible manners; if they found some food they liked just after finishing a meal, they would vomit what they had previously eaten and dig in. Gobbling their chow, they sometimes twittered in tones musical enough that people mistook them for little girls. They gorged on so many beechnuts and acorns that they sometimes fell off their perches and burst apart when they hit the ground. But in flight they were angelic: they cut through the air with such speed and grace that they were called “blue meteors.”
When passenger pigeons found an area with grain or nuts to eat, they formed a long, linear front that advanced forward, heads peck-peck-pecking at the ground. Acorns, beechnuts, and chestnuts; strawberries, huckleberries, and blackberries; wheat, oats, and maize—all went down the pigeons’ iridescently feathered gullets. To grab their share, the pigeons at the rear constantly fluttered over the heads of their compatriots and landed at the leading edge of the front. Then the birds in the back flew over
them.
The line of birds advanced in a continuous swirl, the conservationist John Muir recalled, “revolving something like a wheel with a low buzzing wing roar that could be heard a long way off.”
Passenger pigeons traveled in massive assemblies, billions strong, that rained enough excrement to force people indoors. As a boy Muir saw a mob of birds sweep “thousands of acres perfectly clean of acorns in a few minutes.” Pigeons destroyed farm fields so often that the bishop of Quebec formally excommunicated the species in 1703. A hundred and ten years later the artist and naturalist John J. Audubon saw a flock passing overhead in a single cloud for three whole days. “The air,” Audubon wrote later, “was literally filled with Pigeons; the light of noon-day was obscured as by an eclipse.” When he visited their roost, the “dung lay almost two inches deep” for miles.
The Pigeons, arriving by thousands, alighted everywhere, one above another, until solid masses as large as hogsheads were formed on the branches all round. Here and there the perches gave way under the weight with a crash, and, falling to the ground, destroyed hundreds of the birds beneath, forcing down the dense groups with which every stick was loaded. It was a scene of uproar and confusion. I found it quite useless to speak [over the roar of wings], or even to shout to those persons who were nearest to me.
According to Arlie W. Schorger, author of a definitive study on the bird, in Audubon’s day at least one out of every four birds in North America was a passenger pigeon.
In colonial times, the Haudenosaunee celebrated pigeon roostings by gathering around the birds for a massive feast. Horatio Jones, captured as a teenager by the Seneca (one of the six nations in the alliance), participated around 1782 in a mass pigeon hunt near the Genesee River. The birds, roosting on low branches, were too full and too stupid to flee. Men knocked them down with poles or toppled the trees they were sitting on. Children wrung the birds’ necks while women stewed them in pots, smoked them over fires, and dried them to preserve in storehouses. Sometimes the Seneca ate half a dozen squabs at a time, necks tied together in a carnivorous sculpture. “It was a festival season,” Jones later recalled. “Even the meanest dog in camp had his fill of pigeon meat.” In Haudenosaunee lore, the birds represented nature’s generosity, a species literally selected by the spirit world to nourish humankind.
Non-Indians, too, saw the pigeon as a symbol of the earth’s richness—“the living, pulsing, throbbing, and picturesque illustration of the abundance of food, prepared by bountiful Nature, in all her supreme ecstasy of redundant production of life and energy,” one businessman/pigeon enthusiast gushed. Colonists grilled the birds, stewed them with salt pork, and baked them into pies; they plucked their feathers to stuff mattresses, pickled them in barrels as a winter treat, and fed them to livestock. Incredibly, hunters in the countryside captured tens of thousands of pigeons in nets and sent the living birds to urban hunting clubs for target practice.
Then, suddenly, the passenger pigeon vanished—the last bird, Martha, named after Martha Washington, died on September 1, 1914. The passenger pigeon remained an emblem of natural bounty, but now it also represented the squandering of that bounty. In 1947 the conservationist Aldo Leopold dedicated a monument to the pigeon near the site of its greatest recorded nesting, at which hunters slaughtered 1.5 million birds. The plaque read: “This species became extinct through the avarice and thoughtlessness of man.”
The pigeon should indeed stand as a rebuke and warning. But if archaeologists are right it should not be thought of as a symbol of wilderness abundance.
Passenger pigeons’ diet centered on mast, the collective name for acorns, beechnuts, hazelnuts, chestnuts, and the like; they also really liked maize. All were important foods to the Indians of eastern North America. Thus passenger pigeons and Native Americans were ecological competitors.
What would be the expected outcome of this rivalry? asked Thomas W. Neumann, a consulting archaeologist in Atlanta. Neumann noted that Indians had also vied for mast and maize with deer, raccoons, squirrels, and turkeys. Unsurprisingly, they hunted all of them with enthusiasm, as documented by the bones found in archaeological sites. Indeed, as Neumann noted, Indians actually sought out pregnant or nursing does, which hunters today are instructed to let go. They hunted wild turkey in spring, just before they laid eggs (if they had waited until the eggs hatched, the poults could have survived, because they will follow any hen). The effect was to remove competition for tree nuts. The pattern was so consistent, Neumann told me, that Indians must have been purposefully reducing the number of deer, raccoons, and turkeys.
Given passenger pigeons’ Brobdingnagian appetites for mast and maize, one would expect that Indians would also have hunted them and wanted to keep down their numbers. Thus their bones should be plentiful at archaeological sites. Instead, Neumann told me, “they almost aren’t there—it looks like people just didn’t eat them.” Pigeons, roosting en masse, were easy to harvest, as the Seneca hunt showed. “If they are so easy to hunt, and you expect people to minimize labor and maximize return, you should have archaeological sites just filled with these things. Well, you don’t.” To Neumann, the conclusion was obvious: passenger pigeons were not as numerous before Columbus. “What happened was that the impact of European contact altered the ecological dynamics in such a way that the passenger pigeon took off.” The avian throngs Audubon saw were “outbreak populations—always a symptom of an extraordinarily disrupted ecological system.”
Intrigued by Neumann’s arguments, William I. Woods, the Cahokia researcher, and Bernd Herrmann, an environmental historian at the University of Göttingen, surveyed six archaeological studies of diets at Cahokia and places nearby. All were not far from the site of the huge pigeon roost that Audubon visited. The studies examined household food trash and found that traces of passenger pigeon were rare. Given that Cahokians consumed “almost every other animal protein source,” Herrmann and Woods wrote, “one must conclude that the passenger pigeon was simply not available for exploitation in significant numbers.”