Wednesday, April 24, 2013
Passenger Pigeons # 2
I ended last with:
So, where were the pigeons?
They were always inhabitants of the deciduous forest, eating nuts and berries. It seems impossible for the pigeon to have existed in anything like the numbers it eventually attained. And a passenger pigeon without its niche and numbers is nothing more than a big, nut-eating mourning dove.
As the glaciers receded, radical changes began. Humans invaded. Whether small bands who hunted and gathered in the sea’s edge on the Pacific coast came earlier, or whether, even more controversially, some ice-edge hunters hopped over the margins of the retreating sea-ice from Europe, the general consensus is that most of the new Americans came from Asia over the Bering Land Bridge.
Recent investigations suggest that the people who became Clovis Man may have come down the ice-free corridor that opened along the flank of the Rockies on dogsleds, taking only a few months. And, whether or not you accept the so-called Pleistocene overkill scenario, most of the big native mammals, a charismatic megafauna that rivaled or surpassed that of the Serengeti, were gone in less than a thousand years. Today’s so- called megafauna – the modern bison, elk, moose, grizzlies, and wolves – are all from the Old World, just like humans.
A few of the new creatures had disproportionate impacts on the ecosystem. Bison of sorts had already existed in the west, but the new species, perhaps less constrained by competition or encouraged by a warmer climate, helped create a plains ecosystem that lasted until the buffalo hunters and the sodbusters destroyed it.
Meanwhile, east of the plains, the clever new immigrant from Asia began burning the forest. Most modern ecologists, following the lead of “fire historians” like Stephen Pyne, now believe that the environment first seen by Europeans was largely shaped by humans, using fire as a tool. The plains advanced in runners that would eventually reach to the east coast, carrying with it the open- country species like bison, elk, and prairie grouse. They all ranged as far as Massachusetts in the northeast, where the last pinnated grouse, a subspecies known as the heath hen, would perish in the1920’s.
How much the two species, human and pigeon, modified the landscape is hard to imagine. Human burning encouraged white oak, and pigeon feeding suppressed red oak, making white oak a dominant plant that sometimes made up nine-tenths of the forest. The same fires created “edge effects,” mixed belts of prairie and forest, rich in species and food for pigeons. Pigeons broke down the forest and renewed it, resurrected other plants from beneath snowdrifts of droppings, picked up seeds and spread them in a rain of creative destruction. Aerial predators feasted on the hordes; the large eastern peregrine was finished off by DDT, but its first and larger decline has been attributed to the loss of the pigeon. Even the burying beetle, a striking red and black creature, has become one of the rarest large species of insect in North America. It buries carcasses up to passenger pigeon size, and lays its eggs on them.
When A.W. Schorger wrote the last scientific book on the passenger pigeon, in 1955, no one knew much of the background material on is environment and history that is now slowly coming to light. He lamented:
“The life history of the passenger pigeon, including its extermination, contained many lacunae and contradictions…It is unfortunate and most regrettable that no competent ornithologist attempted to make a comprehensive study of the nesting and other phases of the life history of the passenger pigeon when it existed in large numbers.”
Now, with new tools, we can see not just a tragedy but a window into the complexity of life and systems in general. Australian mammalogist and ecologist Tim Flannery said that the ecology of North America has never been stable, at least since the glaciers. The passenger pigeon’s tale illuminates and is illuminated by the modern science of complexity, chaos, catastrophe theory, and self-organized criticality. It warns us that small incidents may trigger sudden catastrophes, an ominous lesson in a time of global warming. It may give us insights into how suddenly species can emerge, or even to the nature of species. After all, the passenger pigeon without its habits is biologically unremarkable. In the words of Jeffrey Lockwood, entomologist and ecologist: “Ecology is beginning to slowly shift focus with tentative explorations of what the world would look like if process, rather than matter, were the basis for reality. What if we defined a species in terms of its life processes?”
This book will be a kind of forensic ecology of the passenger pigeon, an inquiry into its life and life processes as well as its death. We already know who killed it, though we may not know exactly how. But what kind of an organism was it? What kind of a hole did its passing leave in the world? What can learning more about these questions and their answers teach us?
Even if we genetically reconstruct its genome in some future lab its world has vanished; we can’t ever bring back the “life processes” of the passenger pigeon. But we may be able to, in part, restore some of the things that have vanished, using lessons we learn from the pigeon and other extinctions. Above all, in contemplating the life of this unique bird, we realize not only what we have lost. We are reminded again of the strangeness and complexity of he universe that surrounds us, and of how much more there is to know.
There will be more!