The Parsi community in India has felt the absence of vultures in a different way. Their funerary customs call for the dead to be placed in a Tower of Silence. Corpses are arranged in circles in these squat, open-topped towers where in a few hours vultures turn bodies to bones. Now, with no vultures to consume the dead and with religious proscriptions against burial or fire, the Parsi community is thrown into an extinction-induced philosophical crisis.
India has learned a hard and undeserved lesson about the valuable work of these bald-headed purifiers. The anti-inflammatory drug that caused this woe is now banned in India, but its use continues in some areas, and the vultures have yet to rebound. Regrettably, the same drug is now making inroads in African countries where vultures appear to be just as important and just as vulnerable.
Here in Tennessee, turkey vultures wheeling over the hills are a common sight. So common that it is easy to forget what a gift we have.
September 26th—Migrants
Migrant birds continue to stream over the mandala. Most are traveling south from the boreal forest, a 2.5-million-square-mile expanse of coniferous woodland that stretches from Alaska, through Canada, to Maine. This forest rivals the Amazonian rain forest in size, and it is the breeding ground for billions of songbirds. As the migrants move across the mandala, they carry the resident birds with them in agitated flocks. I watch from a rock ten meters upslope, looking down on surging groups of warblers, chickadees, and downy woodpeckers. The forest is full of their chip, chek, and cheep sounds: an army of tinkers.
The birds have shed the wariness of the breeding season and come close. Some approach almost within reach of my arm and grant me a clear gaze at their vitality. Their plumage is exquisite. Wing and tail feathers are crisp, crowns are smooth, and body feathers shine as they slide over one another. The birds’ late summer molt is complete and every feather is perfect.
For the hooded warblers in the mandala’s flock, freshly grown feathers must last a full year. The wear of vegetation, grit, and wind will grind the feathers down, and by midsummer feathers will be ragged-edged and slim. Hooded warblers turn this aging process to their advantage, however. The birds abrade themselves into their breeding costume. Their crowns and throats are muted yellow now, but as the outer edges of these feathers wear away, the black of the breeding plumage is revealed below. This is a thrifty strategy; most other bird species acquire their breeding colors by growing new feathers, each one of which is made from costly protein.
The chickadees, woodpeckers, and hooded warblers grew their fresh fall feathers here, in and around the mandala, following their summer breeding. But most birds in these flocks molted much farther north, in the spruce thickets of Canada. The names of these species, magnolia warbler and Tennessee warbler, belie their ecology. Both were first described and named from migrant “specimens” in the southern states, and this historical peculiarity is fossilized in their names. The magnolia warbler was shot as it fed in a Mississippi magnolia tree; the Tennessee warbler met its fate along the banks of the Cumberland River in Tennessee. Other boreal breeders bear the same historical baggage. Cape May warblers, Nashville warblers, and Connecticut warblers are all birds of the great northern forests. Thus the conventions of zoological nomenclature hide a great truth about the bird life of this continent. The boreal forest is the nursery of North America’s avian aristocracy, the warblers, the majority of which nest exclusively or mostly in the north. The mandala is washed twice annually by a tide whose volume and power is born in the land of the wolverine and the lynx.
A distinctly southern sound punctuates the tintinnabulation of boreal birds. A yellow-billed cuckoo clucks from the canopy then bursts into a cascade of hollow kuks, drumming out its song. I see the bird high above the mandala, jumping from branch to branch like a monkey. It barely opens its wings as it leaps and cranes its scythelike beak into leaf clusters. It grabs a katydid and gulps the fat insect down before lurching back into the high hidden canopy.
Cuckoos are abundant in the forest around the mandala, but their shyness and their penchant for tall trees mean that they are seldom seen. This bird, like other cuckoos before it, startles me with its strangeness. The cuckoo moves like a primate, sounds like a drummed hollow log, and eats insects that other birds cannot or will not. Its huge beak allows it to swallow big katydids and even small snakes. Caterpillars’ defensive hairs deter other birds but not cuckoos. Smooth or hairy, everything goes down the gullet, sometimes with a brisk beaking to snap off hairs, but more often caterpillars are swallowed whole, hairs and all. Cuckoo stomachs are apparently densely matted with caterpillar spines whose barbs lodge in the intestinal wall.
Cuckoos make it their business to break other rules of bird behavior. They don’t set up predictable territories but wander nomadically on their breeding grounds looking for clusters of food, then quickly set up camp and breed. The chicks grow rapidly and grow feathers that literally pop open, fully formed. The adults’ molt is a casual affair. Instead of shedding and growing feathers in an organized sequence and at a regular time like other birds, cuckoos molt feathers haphazardly, one by one, and spread the molt over their summer and winter grounds. Perhaps psychoactive caterpillar toxins have loosed their allegiance to the status quo or, more likely, their molt strategy is like their breeding style, designed to take advantage of local bursts of richness, then to coast through the lean times. Even their migratory behavior is loose. Ornithologists in South America have captured very young birds, strongly suggesting that some of the “migratory” cuckoos linger and breed on their wintering grounds.
Of all the birds in the mandala today, the cuckoo travels the farthest. The Amazonian forests east of the Andes are its winter home. Most warblers travel slightly less far, to southern Mexico, Central America, and the Caribbean. So the mandala connects, at this moment, nearly the entire New World. Memories of tapirs and toucans brush past thoughts of the tundra’s edge; minerals from Ecuador and Haiti fly with sugars from Manitoba and Quebec.
Tonight the warblers will link the mandala outward, beyond the earth’s bounds, bringing awareness of the stars into the forest’s matter. Having rested and fed all day, the migrants will wing southward in the cool and safety of dark. These flying birds will scan the skies, find Polaris, the North Star, and use its position to head south. The birds gained this astronomical knowledge as youngsters, sitting in the nest, peering into the night and searching for the star that did not swing across the sky. They carry this memory in the wet tangle of their brains, then gaze up in the autumn and steer by the constellations.
Remarkable as it is, knowledge of the stars is a fallible method of orientation. Stars are obscured on cloudy nights, and some first-year birds may grow up in dense forests or overcast regions. Migrant birds therefore have several extra navigational skills. They watch the sunrise and sunset, they learn to follow north-south mountain ranges, and they can detect the invisible lines of the earth’s magnetic field.
Migrant birds throw open their senses to the cosmos, integrating sun, stars, and earth as their great tide surges south.
October 5th—Alarm Waves
I sit very still. Time seeps by. A chipmunk walks across the opposite edge of the mandala, barely a meter away. The animal pauses, rummages in the litter with its paws and nose, then disappears into a jumble of rocks. This is a rare encounter. Unlike their suburban or campsite cousins, chipmunks on this mountainside are jumpy creatures. They approach me only after I have sat immobile for a long time. Encouraged by the fruit of my stillness, I settle down and melt into the rock.
Easy breeze. Distant birdsong. The forest’s waters are calm. An hour passes.
Then a sharp, hoarse exhalation of air, just a foot or two behind me. I keep still. The deer blasts out another alarm, then a double blast. A flash of white hits my eye and the animal bounds away, snorting as it goes. The deer’s alarm belly-flops into the smooth, quiet air, smacking sharp energy through the mandala.
The snorts immediately set three squir
rels chattering and whining. Eight chipmunks join in, shooting off rapid chips. The wave moves out from the mandala. A wood thrush downslope starts calling, whippa-whippo-whop, its head feathers hackled up as it hurls out the call. Distant chipmunks pick up the staccato chorus, carrying it to the edge of earshot.
The deer’s alarm at coming so suddenly on an immobile human has reached out hundreds of meters. The agitation, particularly that of the chipmunks, takes more than an hour to recede.
The mandala’s birds and mammals live embedded in an acoustic network, each individual connected to others through sound. The forest’s news ripples through this network, carrying the latest information about the location and activities of troublemakers. It takes some effort for us urbanized humans to become aware of these traveling signals. We are accustomed to ignoring “background noise,” instead taking our cues from the interior noise of our minds. Most of my time sitting or walking in the woods is spent riding waves inside my head, thinking of past or future. I suspect that this is a common experience. Only a repeated act of the will can bring us back to the present, back to our senses.
When we arrive in the acoustic now, we discover that the forest’s newsroom is focused on— surprise!—us. We’re large, noisy, and fast. And many animals have seen us in our more predatory modes. Those that haven’t had personal experience of our guns, traps, and saws quickly learn from their more experienced peers: it is in an animal’s interest to pay attention to what alarms others. We are like the hawks, owls, and foxes that seldom get to observe the forest network without triggering noisy news bulletins. Sitting low, staying still, and biding one’s time is the only way to slip in. Then we experience the alternating calm and clatter of the news wires. Hikers, for example, are preceded by bow waves that arrive minutes before their chatter and laughter. More minor disturbances, such as a branch falling or the overflight of a crow, send quieter and more short-lived pulses through the network. The deer’s alarm at stumbling upon me was, on the other hand, a surge, a bold headline.
Tuning in to the network has clear advantages for the forest’s animals. Awareness of potential danger gives listeners a head start in deciding how to react. But the advantages of actively contributing to the waves of information are not so obvious. Why call when you see a predator? Why not eavesdrop on others but keep mum? Calling attention to yourself by making a loud sound when a predator approaches seems nonsensical.
For animals with kin nearby, the costs of alarm calling may be outweighed by the need to protect family. Although it is late in the season, some chipmunks and squirrels around the mandala have youngsters with them, so their squeaks and trills give advanced warning to their offspring. But many animals use alarm calls when family are not present, so other benefits must also be in play. Some alarm signals are designed to actively communicate with the predator, drawing attention to the animal in the moment of danger. In doing so they may reap the paradoxical benefit of telling the predator who and where they are. From the predator’s perspective, prey that have seen your approach and are poised to flee are likely to be hard to catch. The predator’s time would be better spent looking for unwary prey. Alarm calling can therefore provide a direct benefit to the caller by advertising the unprofitability of an attack and thus buying safety. “I’ve seen you—you can’t catch me. Move on.”
White-tailed deer take this advertisement one step further. As they run from predators they pump their tails up and down, flashing a white rump and undertail at the pursuer. Their run is interspersed with long upward leaps, losing time that could be spent hoofing forward. Those flashing, prancing displays must have a function beyond telling the predator that it has been seen: running away is already a clear signal that the deer has detected the predator. It is possible that the deer is communicating its vigor and hence ability to escape. Only healthy deer can afford to punctuate their run with wasteful flourishes; weak or sick deer cannot risk their lives with time-wasting bounding displays. This idea has not been thoroughly tested in white-tailed deer, but similar puzzlingly exaggerated displays in gazelles do seem to be honest signals of condition.
The animals’ acoustic network has an invisible analog among the forest’s plants. When insects chew on leaves, they trigger a physiological reaction from the host plant that not only deters further damage to the host but also alerts neighboring plants. Damaged leaves turn on genes that produce a flush of chemicals. Some of the defensive chemicals evaporate and perfume the air around wounded plants. The wet interior of the neighboring plants’ leaves is soaked in these molecules and, like aroma in a human nose, the molecules dissolve and move into the surrounding cells. Here the chemicals turn on some of the same genes that produced defensive chemicals in the original plant. Unwounded plants around a damaged colleague therefore become less palatable to insects. The trees are listening.
When I sit or walk in the forest I am not a “subject” observing “objects.” I enter the mandala and am caught up in webs of communication, networks of relationships. Whether or not I am aware of it, I change these webs by alarming a deer, startling a chipmunk, or stepping on a living leaf. Dissociated observation is not possible in the mandala.
The webs change me also. Every inhalation carries hundreds of airborne molecules into my body. These molecules are the aroma of the woods, the combined fragrance of thousands of creatures. Some aromas are so pleasing to humans that we have domesticated them, extracting “perfumes.” At least one such perfume, jasmonate, is an alarm chemical, communicating danger among plants. Perhaps our olfactory aesthetics reflect a desire to be wedded to nature’s struggle?
But perfumes are the exception. Most of the forest’s molecules bypass my sense of smell and dissolve directly into my blood, entering my body and mind below the level of consciousness. The effects of our chemical interpenetration with plant aromas are largely unstudied. Western science hasn’t stooped to take seriously the possibility that the forest, or the lack of it, might be part of our being. Yet forest lovers know very well that trees affect our minds. The Japanese have named this knowledge and turned it into a practice, shinrin-yoku, or bathing in forest air. It seems that participation in the mandala’s community of information may bring us a measure of well-being at the wet chemical core of ourselves.
October 14th—Samara
The forest’s colors are gradually turning. The spicebush in the mandala is mostly green, but a few leaves are flecked with yellow. Color in the ash next to the spicebush is faded, and the outer leaves are drying and bleached. Above me, the maple and hickory still show their summer colors, but the leaves of a large hickory upslope have all turned tan and gold. A few scattered leaves have fallen, refreshing the top surface of the leaf litter and giving a quiet crunch to moving animals.
A winged maple seed flashes past my face. It whirs in a blur of light, like a flying knife at the circus. The seed helicopters down, then strikes the leaf of a toothwort herb, falls between two dead leaves on the forest floor, misses a sandstone pebble, and lodges vane up, seed down in a crevice in the humus. A fine place to germinate—this was a lucky fall.
April’s maple flowers have finally ripened and, after months of slow growth, helicopters are scattered all across the forest floor. A few nestle in dark openings in the litter, but most are exposed on the dry surfaces of leaves or rocks. For all the whirling drama of their flight from the canopy, the ultimate fate of the maple seeds is determined by the particularities of where they land. Rough surfaces excel at catching windblown seeds, so mossy rocks snare more seeds than do bare rocks. The leeward sides of trees accumulate more seeds than the windward. Animal predators destroy seeds by eating them, or inadvertently spread and sow them by storing them for a meal that never comes because of forgetfulness or death.
There is little that wind-dispersed seeds can do to select a premier germination spot. They don’t get carried to a fertile ant nest like Hepatica seeds, or deposited like cherry seeds in a pile of manure, or wiped onto a convenient branch by the beak of a mistl
etoe-carrying bird. But the maple seed’s helplessness about the choice of its final destination does not mean that the seed has no power. The seed’s skill comes before the final landing.
This morning, no seeds were falling on the mandala. Now, in the late afternoon, they rain so densely that their crackling impact on the ground sounds like a forest fire. This is no coincidence. The thin strip of tissue that holds the seed to its parent is weakest on dry afternoons. These afternoons are also when the wind is strongest—trees time the release of seeds to catch the best wind. Of course, the tree has no central air traffic controller to tell seeds when to depart. Instead, the materials used to fasten the seed to the mother tree, as well as the shape and strength of the attachment, determine when and how seeds will be released. Millions of years of natural selection have tuned the design of these release mechanisms.
There is more to the trees’ strategy than simply dumping seeds into dry air. Flying seeds have two roads ahead of them. The “low road” carries them down from the canopy to the forest floor around the parent. These seeds travel, at most, a hundred meters or so from home. The “high road” takes seeds above the canopy, into the open sky where they may travel miles.
Few seeds take the gravity-defying high road, but it is of great importance to the fate of tree species. Rare long-distance dispersers have a strong effect on the genetic structure of species, on the ability of species to persist in fragmented landscapes, and on how fast species move in response to retreating ice ages or advancing global warming. Like human history, the narratives of ecology and evolution hinge on the actions of a few individuals that travel across continents and settle far from home.
The Forest Unseen_A Year's Watch in Nature Page 19
