Science

Population Collapse

Forget extinctions. Population decline is a much greater crisis.

Animal population decline.
Photo illustration by Holly Allen. Images by iStock/Thinkstock.

The first great extinction crisis in the United States was the fall of the passenger pigeon, the last of whom, a bird named Martha, died at the Cincinnati Zoo in 1914. There had really been nothing special about the passenger pigeon prior to about 1900; on the contrary, the pigeon had recently been as common a bird as we had in America. Many people held memories of its abundance, and the sentiment on Martha’s passing was less mourning for the bird than astonishment at its rapid decline. John James Audubon had described the great flocks by their sound, a noise like “a hard gale at sea” passing through a ship’s rigging. When they landed, flapping their wings to alight, the sound was like “distant thunder.” The magazine Field and Stream wrote of Martha’s death, “Millions and millions, reduced to one and now naught but history.” Americans remembered shooting into clouds of passenger pigeons so thick that a town could eat for weeks on the spoils.

Then they were gone. “The conscience balm has always been, ‘They will be ever common,’ ” wrote the Cornell biologist Albert Hazen Wright at the time. The extinction was a reckoning on mankind’s destructive power. The attention paid to Martha, who was stuffed and now lives in a box at the Smithsonian Institution, showed how an ecological crisis could capture Americans’ imaginations—regardless of the creature’s particular stature—if the path of change were impossible to ignore. But it now resonates in a different way, as the first of several extinction crises that have drawn our attention to a particular animal with a human name. Every extinction needs a good character. Take Sudan, the 45-year-old northern white rhino whose sexual prowess took a precipitous dive toward the end of his life. The last male of his subspecies, his plight has drawn international attention to rhinoceros conservation. When Sudan died at a conservancy in Kenya on Monday, it was trending on Facebook by Tuesday morning. He was the face of his species.

We watch for extinctions like those with the thought that, like Noah, we only need two of each species to preserve biodiversity assembled over millions of years. In the meantime, though, animals and plants are rapidly declining all around us. The Living Planet Index, which monitors more than 14,000 populations of 3,706 species of vertebrates, reports that populations fell by 58 percent on average from 1970–2012. On land, habitat loss is the greatest culprit: Mangroves, to take one example, are estimated to have lost as much as 35 percent of their mass since just the 1990s. It’s a much more serious crisis than generally acknowledged, especially compared to its lamented endpoint, extinction.

This is not to fault the environmental movement. Our focus on preserving pairs for our ark represents a hopeful impulse that jibes with an understandable preference: Charismatic beasts (and eye-catching landscapes) command more attention than the faceless fisheries, flocks, and permafrost that are quietly disappearing. We are paralyzed in the face of this crisis of abundance because it’s something we don’t see, not in the way our ancestors could see the decline of the passenger pigeon. Fixing it will require a new way of looking.

I called Billy from the back of the sept-places, one of the thousands of station-wagon taxis that ply intercity routes in Senegal, to say that we were getting into Toubacouta. We’d arranged a room at his guesthouse just the night before. The late notice was typical for us, and apparently no problem for him.

Toubacouta sits on the southern edge of the Sine-Saloum delta, a 700-square-mile mangrove forest where the Sine and Saloum rivers meet the Atlantic near Africa’s westernmost point. The town is a base for delta tourism. There are backpacker hostels and fancy hotels. It is sandwiched between a highway and a harbor—on the latter end is a mud beach where fishing boats take visitors into the mangroves.

Billy showed up in a gray Mitsubishi to drive us into town. Keur Billy was a little walled compound with a handful of single-room structures—a guesthouse with our bedroom, the building where Billy and his wife slept, a kitchen—clustered around a stagnant swimming pool. Apologizing, Billy told us he didn’t keep the pool up. He had few guests. Keur Billy, which he had built a few years ago as a business venture, was empty most of the time.
He’d opened it up for us for the night.

The Senegalese will tell you the Sine-Saloum is a jewel. It’s a UNESCO World Heritage site. It is one of the best places in West Africa to fish. But a decade after it got the Times travel-section treatment, for a handful of luxe beach resorts that had opened on the delta perimeter, the Sine-Saloum still draws few visitors. Too few, Billy would say.

The Sine-Saloum is a landscape of abundance. I could feel this as we boarded a pirogue and motored into the delta the next day. My eyes, camera-trained to see beauty as a still slice of space in time, were not prepared for this kind of spectacle. At first I sat in the prow, peering into the landscape, looking for … I don’t know. Parrots? But soon I realized I had to change my approach. Just as your eyes need to recalibrate to see in a darkened room, seeing the sublime monotony of abundance requires a patient, elongated gaze. Topography was visible only through clusters of baobabs marking higher ground; distance measured by the little nubs of green coastline, one after another like false peaks, marking by their receding size the contours of the strait. The undifferentiated mass of water took shape as the presence of herons, martins, egrets, and pelicans delineated sand bars. This is what hundreds of square miles of mangroves looks like; they stretch as far as they eye can see, as the cliché goes, but the eye can’t see far because the landscape is so flat.

The monotony was my problem, not the Sine-Saloum’s. The delta is awe-inspiring, but not stimulating. It doesn’t photograph well. Its scale—the thing that makes it both impressive, distinctive, and valuable as a habitat for 200 species of birds and 100 species of mollusks—is almost impossible to perceive in one glance. Its majesty does not translate into human terms. Like many such places, it is undervalued.

That the serpentine paths of the Sine-Saloum, walled in by endless mangrove trees, continuous green leaves, and blue water, are less alluring than a safari peppered with zoolike concentrations of megafauna may seem obvious. The comparison deftly illustrates a broader taste: We value diversity over abundance. This manifests in both what we think is worth looking at and in what we think is worth preserving.

One problem we have with abundance is that we’re not very good with numbers, and the larger the numbers get, the more trouble we have telling the difference between them. Perhaps it’s this, environmental journalist Michael McCarthy posits in his book The Moth Snowstorm, that explains how the “Great Thinning” has gone largely unnoticed. McCarthy’s book is an ode to abundance for its own sake, its title derived from his childhood memory of driving at night through clouds of insects. Entomologists refer to this as the “windshield phenomenon,” an experience McCarthy believes is increasingly rare.

His instinct appears to be correct. British bug researchers have recorded dramatic declines in the weight of bugs getting caught in traps. In Germany, researchers using similar traps reported in October that insect populations have declined by 75 percent in the past 25 years. Fewer bugs means less food for songbirds, whose populations have also collapsed. Twenty-four common land-bird species in North America have lost 50–90 percent of their population since 1970. The numbers are similar for other bird species in other parts of the world. For fish, the situation is even more ominous. We removed two-thirds of the biomass of predatory fish from the ocean in the 20th century, mostly since the 1970s. New estimates reveal that fisheries, ruined by overfishing, have been in decline for much longer than we thought.

Before species disappear from the earth entirely, they disappear from a particular segment of the map. These local extinctions, called extirpations, do not make as many headlines. But they are naturally much more common than extinctions, and happening rapidly, as a recent study by researchers in Mexico and California highlights. They sampled 177 mammal species from across the five continents, finding that most had lost more than 40 percent of their geographic range compared to historical norms. Almost half had their territory reduced by more than 80 percent. A third of all land-based vertebrates are in decline. Giraffe counts may have fallen by as much as 40 percent since the 1980s; savanna elephants by 30 percent. Extirpations can have tremendous ripple effects on local ecosystems, as the departure of wolves from Yellowstone National Park—and their subsequent reintroduction—has demonstrated. Species can be revived from tiny numbers—your grandparents probably never saw a deer growing up—but the Noah’s Ark fantasy that you just need two is challenged by the extraordinary effort we have spent reviving species like the California condor.

Extinctions hurt, but the decline in populations induces its own sorrow. There are places you can go to assuage this pain, if abundance is your thing and money no object: distant Alaskan rivers where there’s nothing to see but salmon leaping upstream, or the microclimates of the Patagonian Andes, where whole valleys are carpeted with tiny-leafed beech trees, some of them hundreds of years old. That majesty could once be found closer to home. How impossibly lucky we were to have clouds of monarch butterflies drift through our backyards. Their numbers have fallen by 90 percent in just two decades. Nineteenth-century accounts of California tree branches drooping and snapping under the weight of butterflies now seem far-fetched.

The slow sadness of the thinning goes down easier than the tragedy of extinction. That it took so many generations for light pollution to wash the stars from the night sky puts the loss a little beyond the power of human memory. “If the stars should appear one night in a thousand years, how would men believe and adore!” Emerson observed. Or, as Neil Young put it, it’s better, for recognition’s sake, to burn out than to fade away.

There are technical reasons to care about thinning. Colony collapse disorder, a crisis in honeybee populations that seems to have abated in recent years, and the melting of the polar ice caps are two crises of abundance whose perceived seriousness is fueled by a sense of interconnection, the ominous sense of a looming natural domino effect. The early, technocratic stirrings of American conservation policy were similarly motivated by a sense that the decline in the continent’s massive numbers of moose, deer, and salmon might combine to make Americans less prosperous.

There is also logic for being less concerned by an enormous bird population falling by half than by a much smaller population dwindling to almost zero. Bigger populations can more easily recover—honeybee numbers, for example, seem to have stabilized after the crisis of colony collapse disorder. In species that reproduce more quickly than we do, sharp declines don’t have to always be cause for concern.

But, I think, a greater appreciation of abundance could help the environmental movement, displacing activism from distant rural fights over government land and putting it at the heart of daily life, especially urban life. (Two forces that devastate bird populations, for example, are house cats and glass-walled skyscrapers.) Urbanites have the most to gain from the replenishment of once-common plants and animals. Abundance doesn’t have to be an African mangrove forest. It is flocks of geese, and butterflies, and the oysters that once thronged New York Harbor. It’s clouds of migratory birds bringing commuters to a standstill in the streets of Washington or Houston.

At the edge of the Sine-Saloum, the monoculture is broken down by the cellphone towers, minarets, and salt ships that mark the limits of human civilization. These margins are what to watch when the thing itself—be it a fishery, a forest, or a cloud of moths in the headlights—feels so full from the inside.

There are fishermen on the delta, men with nets casting for fish, and women who moor their pirogues at a parting of the mangroves. We saw their whelks on the beach in Djifer, where the pétoncles shells rattle in the waves, but the nets wash up in tangles of neon green with catches of plastic and Styrofoam and diapers.

In her book The Triumph of Human Empire, the historian Rosalind Williams writes about moments when humans’ slow, imperceptible dominance over nature is recognized. “Even slow changes may quite suddenly crystallize into events of consciousness, when individuals recognize the extent and significance of human domination of the planet,” she writes. Outrage grows from personal familiarity. It did with Martha. These days, most of us cannot even recognize the scale that we’ve already lost.