Wild Thoughts from Wild Places, page 12
Occasionally, though, a homer failed to return home. Maybe it had been killed by a bullet or a hawk; maybe it had lost its way; maybe it had simply gotten distracted or seduced into another path of life and ended up on the streets of a nearby city, like a runaway teenager, scuffing out its sustenance among a flock of tough and enterprising companions. To the pigeon breeder, that sort of errancy was the unavoidable cost of doing business. To the pigeon, it was a challenging reentry into the realities of natural selection.
• • •
SO PIGEONS have gotten around, and not just by wing power. The appeal that they carry among fanciers has been their ticket to worldwide distribution. They’re in Australia, they’re in Hawaii, they’re in the Arctic, they’re in Tierra del Fuego. They have even arrived in Montana.
On a brisk afternoon with snow on the ground, two thousand miles west of the west end of 46th Street, I help Steve Bodio carry water out to the pigeons in his loft. It’s a modest plywood shed divided into three rooms, each room furnished with nest alcoves and perches. At full capacity, as it is now, it holds forty-some pigeons. Although his pigeon-fancying tastes are broad, time and space impose limitations, and in this loft Steve is keeping just three breeds: Spanish pouters, English carriers, and racing homers.
The pouters are elegant birds, each of them capable of inflating its crop and hoisting itself into a proud, chesty posture, like a bodybuilder at flex in an overly tight truss. The carriers, despite their name, are also a show breed, with decorative wattles across the top of the bill and around the eyes. “I like breeds,” Steve says forthrightly. “I’m not one of these animal rights people who thinks breeding things for characteristics is wrong.” From all around us, as he speaks, come the sounds of cooing adults, peeping juveniles, wings flapping as birds resettle themselves. “On the other hand, I’m more interested in the whole gestalt of the breed—how they act, everything—than just in breeding a perfectly round wattle.”
My attention gravitates to the racing homers. I comment that they look like rock doves, with their pale gray wings, their dark bands, their highlights of shimmery green. Yes, but only superficially, Steve says. His breeder’s eye sees nuances that I don’t. Wild rock doves have a steeper forehead and a thinner bill, he explains. Also, these homers are longer legged, more deeply muscled, more streamlined than a rock dove, and half again as big. “They’ve evolved toward—or, been humanly caused to evolve toward—a fairly efficient so-called wild type,” he says. “But with actually a little more efficiency for pure flying than even the rock dove.” Besides greater speed, there’s another thing. “They’re a little more enduring as a long-distance flyer. I mean, what reason would a rock dove have to fly six hundred miles?”
The racing homers, superdoves in their own right, are the breed from which feral pigeons are mainly derived, at least in America. They have probably been a major source of European feral populations too. Those AWOL homers have brought their speed, their endurance, and their directional savvy to the gene pools of feral populations, no small contribution toward making the urban superdoves what they are.
I ask Steve Bodio, breeder of elite pigeons, historian of the fancy, what he thinks when he sees feral pigeons on a city street. “I think they’re survivors. I think they’re great,” he says generously. He appreciates any form of wildlife, he adds, that “treats human edifices as just another part of the environment. They’re just living in the human canyon.”
• • •
THE HUMAN canyon. Not being descended from cliff-dwelling ancestors myself, I can only tolerate it for short visits. After a few days of pigeon watching and other New York business, I catch a cab for the airport.
It’s early Saturday morning and, as the taxi heads east along 46th Street, I find midtown Manhattan blessedly deserted. The sidewalks are empty, except for pigeons. On the corner of 46th and Park Avenue, one bird pecks its way sedulously across the concrete, as though expecting at any moment to find a kernel of wheat. At 59th Street, where we turn east again, I notice two dozen pigeons perched along the horizontal bar of a streetlight, like a rank of cadets calmly awaiting the next war. I think of Johnston and Janiga’s book, so thorough, so authoritative, so new that even Steve Bodio hasn’t yet seen it, and of its comment about superdoves.
The two authors refer passingly to the beleaguered status of Columba livia in the wild. They note that genetic dissolution threatens those few remnant populations (which in Johnston and Janiga’s British-style terminology are Rock Pigeons, not rock doves), and that it’s a situation attributable to habitat destruction and urban encroachment throughout Europe and Asia. They offer a sober warning. “Whether or not we have a conservation program for Rock Pigeons, if there is no reduction of the absolute numbers of humans we think the disappearance of ancestral Rock Pigeons could occur as early as in the last half of the 21st century. But,” Johnston and Janiga add, in an afterthought that sounds peculiarly cheery, “we would have superdoves in their places.”
I find that cold consolation. Like Steve Bodio, I’m glad that at least some forms of avifauna are willing and able to grace the world’s cities, and I’m not aghast that feral pigeons don’t happen to carry the same array of genes as C. livia in the wild. But the feral pigeon is not—repeat, not—a satisfactory substitute for the wild rock dove.
And this relentless replacement of wild populations by feral ones, rare species by weedy ones, inconvenient beasts by convenient ones, isn’t limited to pigeons. It’s a lamentably broad trend. Humanity is changing the world’s flora and fauna—not just extinguishing many species but also transforming those that remain. We’re doing it by the force of our ecological sovereignty and by the evolutionary selection (call it natural, call it artificial) that we exercise.
To say so is to open a large topic—too large for the closing paragraphs of a small essay—but I’ll open it anyway, in the hope of leaving you with something to chew on. Consider this troubling but real possibility: that the heavy presence of Homo sapiens across all the world’s landscapes, our irrepressible self-interest, and our well-meaning management decisions may yield a global menagerie of diminished, tractable creatures. Think of “supergrizzlies” in Yellowstone that are too sensible to eat hikers, “superwolves” in Minnesota that are too prudent to mess with cows, “supertigers” in Nepal that feed dutifully on tethered goats for the edification of ecotourists in blinds, “supergorillas” on the Virunga Volcanoes that carry acquired resistance to whooping cough and prefer a PowerBar to a mouthful of nettle leaves, “superdeer” strolling imperturbably through the suburbs, “superginkgo” trees growing from holes in city sidewalks on a diet of carbon monoxide and dog piss, “supermosquitoes” that drink only from hummingbird feeders.
We’re headed toward that, and to me it’s a dreary prospect. If we come to such a point, with the surviving species (few as they may be) merely cultivated reflections of human dominance, human sufferance, human fancy, we’ll have selected away something precious. When the last beasts and the last plants left alive are all just as super as we are, the world will be a crowded and lonely place.
Before the Fall
In the tree-shaded town where I live, it seemed that autumn had come early this year—earlier even than usual for a north-country place where the cold winds begin blowing in mid-August, the cottonwoods turn color not long after Labor Day, and the first heavy snow often puts a damper on Halloween. This year was different. The leaves flushed from their buds during May and then in June, suddenly, disappeared. They hadn’t succumbed to the natural rhythm of season. They hadn’t gone yellow, fallen, piled up in the gutters as aromatic autumnal mulch. They had been eaten.
A pestilential abundance of small, hairy larvae had materialized like a plague out of Exodus, stripping the trees of their foliage. The scientific name for these voracious leaf-eaters was Malacosoma disstria, though few of us knew that at the time.
“Tent caterpillars,” said the local newspaper, vaguely but not inaccurately. “Tent caterpillars,” said the city parks people and the man at the county extension service, who were answering calls from dozens of concerned residents every day. The radio said “tent caterpillars” too. And so before long we were all out on the sidewalks, saying “tent caterpillars!” back and forth to one another. In the hubbub, we were too occupied to notice that these particular “tent caterpillars” didn’t build tents. We weren’t interested in such entomological subtleties. What we wanted to know was how we could kill the damned things before they ate all our lovely urban hardwoods down to stumps.
It was an awesome phenomenon, in its own ugly way. Not every tree was left naked, but many were, especially among the old towering elms and ashes that stand along the sidewalks, arching their canopies out over the neighborhood lanes. It happened fast. The caterpillars did much of their feeding under cover of darkness, and on those coolish June nights we could stand beneath a great tree and hear the inexorable crackle of tiny jaws: a sound like distant brushfire, but alive. In the mornings, we would find the sidewalks heavily sprinkled with their poppy-seed globules of poop. Occasionally a lone caterpillar would rappel down on a filament of silk and dangle there mockingly at eye level. On a day of chilly drizzle, too chilly for caterpillar comfort, we could spot them hunkering sociably, high up on a trunk or in a limb crotch, about two hundred fuzzy gray bodies in each pile-up. Some of us went away for a weekend, leaving the lawn freshly mowed, all seemingly fine, and came home to find that our trees had been defoliated. We climbed up on step ladders and sprayed the caterpillars with soapy dishwater from spritzer bottles. We dosed them with bacterial mists or nasty long-molecule chemicals, as variously prescribed by the local garden stores. We called in SWAT-team strikes by the men from Nitro-Green. All of these measures seemed to be marginally effective at best and, more likely, just poisonous and futile. The caterpillars continued to chomp. When they began migrating from ravaged trees to healthy ones in search of more food, we wrapped girdles of duct tape around the tree trunks and smeared on barriers of impassable goo. The caterpillars kept coming. We stepped on them as they forded the sidewalks. We mooshed them wholesale in the streets. But there were simply too many, and the infestation proceeded along its natural course. They ate, they grew, they molted repeatedly. They marched across town, treating our trees like celery.
Eventually they finished eating. They had bulked themselves up to the limits of their caterpillaroid juvenility, and now they were ready for puberty. They spun themselves up inside leaf-wrapped cocoons for a short metamorphic respite, to emerge in a few weeks as little brown moths. The crackling stopped and the treetops, what was left of them, fell silent. The caterpillars, qua caterpillars, were gone. But this vast population of pestiferous lepidoptera was still lurking over our heads, literally and otherwise, like a large gloomy hunch about the future.
• • •
BIOLOGISTS have a label for such an event. They call it an outbreak. It’s characteristic of certain types of animal but not others. Lemmings undergo outbreaks; river otters don’t. Some species of grasshopper do, some species of mouse, some species of starfish, whereas other species among the same taxonomic groups don’t. Consider reptiles: Under extraordinary conditions, certain snake species (such as the brown tree snake, Boiga irregularis, native to New Guinea but inadvertently transplanted to the island of Guam) may outbreak into staggering plenitude; desert tortoises in the American Southwest don’t. An outbreak of woodpeckers is unlikely. An outbreak of wolverines, unlikely. Among those insect species inhabiting forests, about 99 percent maintain stable populations at low density and only one percent ever experience outbreaks. What makes a species of insect—or a species of mammal or reptile or microbe—capable of the outbreak phenomenon? That’s a complicated question the experts are still trying to answer.
An entomologist named Alan A. Berryman addressed it a few years ago in a paper titled “The Theory and Classification of Outbreaks.” He began with basics: “From the ecological point of view an outbreak can be defined as an explosive increase in the abundance of a particular species that occurs over a relatively short period of time.” Then, in the bland tone of a careful scientist, he noted: “From this perspective, the most serious outbreak on the planet earth is that of the species Homo sapiens.” Berryman was alluding, of course, to the fact that we’ve increased our population by a factor of five hundred since the invention of agriculture, by a factor of five since the Industrial Revolution, by more than double within only the last century—and that there seem to be no natural limits in sight. Relative to other large-bodied mammals, we’re a grossly abundant species in the throes of an exceptional, and seemingly unsustainable, episode of proliferation and consumption. From Berryman’s viewpoint, we’re the primate equivalent of an eruption of weevils.
It’s a provocative idea, vast in its implications, majestically dour, and certainly not unique to Alan A. Berryman. In fact it’s nothing less than a theory of human history, human demography, the terminal destiny of civilization, conceived in cold-bloodedly ecological terms. But, having invoked it, Berryman let it drop. He was just a guy writing about insects for an audience of other entomologists. “From the more narrow perspective of Homo, however, an outbreak is an increase in the population of an organism that has a deleterious influence on human survival and well-being,” he hastened to add. That brings us back, from a brink of ponderous speculation, to the tent caterpillars in my little town.
Bare trees in midsummer didn’t threaten our survival but they did vitiate our sense of well-being.
Two species of Malacosoma are native hereabouts: M. californicum, the western tent caterpillar, and M. disstria, known as the forest tent caterpillar despite the fact that it doesn’t build tents. The forest tent caterpillar is the most widely distributed species of Malacosoma in North America, and by some measures it causes the greatest damage, at least partly because it feeds on a broader selection of tree species than the others. Among the intriguing facts about M. disstria is that it’s a social species, capable of reciprocal communication and collective behavior that enhance the welfare of the group. Ants, termites, and some species of bees and wasps have traditionally been considered the only social insects. But it turns out that the forest tent caterpillar, though not so elaborately social as a colony of ants or termites, does engage in cooperative activity.
The eggs are laid in single batches, roughly two hundred eggs in a batch, so that all the offspring from any one female begin life together, as an aggregate litter of siblings. The egg mass remains dormant through winter, glued onto a branch with a frothy secretion from the mother. In springtime, about when new leaves are emerging, the eggs hatch and the tiny caterpillars commence eating. As the food resource becomes scarce in their immediate vicinity, they start to move—and they move as a herd. Crawling along a branch, each caterpillar releases a fine cable of silk and a smear of some pheromonic chemical. One caterpillar locates a fresh feeding site, others arrive and join the feast, they all gorge themselves to the point of satiation, and then they withdraw a short distance to rest. Unlike the western tent caterpillar, the forest tent caterpillar does its resting without benefit of a tent. It congregates, instead, in an open-air bivouac. Even without the protection of a tent, this bivouac behavior carries certain advantages over a lone-wolf style of caterpillar self-interest. Huddling together, the forest tent caterpillars help one another stay warm. When a predator threatens, they rear up on their larval haunches and wave the front ends of their bodies back and forth in the air, showing off the long fuzzy hairs that make them unpalatable tidbits and warning their siblings to do the same. Such a tangled mob of waggling, prickly larvae is even more unattractive to hungry birds, evidently, than a single tent caterpillar would be on its lonesome.
The communication that facilitates this collective bonding is done, as in ants, with chemical trails. Two scientists named T.D. Fitzgerald and James T. Costa, working in a lab full of M. disstria and cardboard mazes, found that the pheromone smear laid down by one well-fed caterpillar “appeared to stimulate and orient trail following by siblings still at the feeding site, eventually leading the colony to aggregate at the new bivouac.” The caterpillars were enticing one another to seek safety and comfort in togetherness.
This may be one of the evolutionary secrets that allows the forest tent caterpillar to flourish, occasionally, in immense numbers. It seems that crowding is good for them, not bad. And in their dim caterpillical way, they know it.
• • •
THE WESTERN tent caterpillar, that other species of Malacosoma whose distributional range includes my little town, has its own set of adaptive tactics. Each sibling colony erects a tent, instead of relying on the more chancy (but also more economical) method of open-air bivouac. It centers its feeding excursions around the ever-enlarged tent, rather than foraging nomadically over a broad area as the forest tent caterpillar does. Whether the M. californicum set of tactics is superior to the M. disstria set of tactics is an issue that evolution hasn’t decided—except on a provisional, year-by-year basis. In a normal year, both species are present as small, sparse populations of which no one except the most vigilant entomologist takes notice. In an exceptional year, one species or the other explodes to conspicuousness as a huge population—an outbreak. Then, after a couple years of booming, the outbreak goes bust and that species collapses back to obscurity. Further years pass, with no major eruptions of either disstria or californicum, until there comes a different mix of conditions and suddenly—VWOOM!—the other species commits an outbreak. Why does one set of adaptive tactics work egregiously well in a given year, while the slightly different tactics of a slightly different species produce no conspicuous population at all? I called the county extension service and asked a fellow that question. He had no answer.
