by Sue Halpern
Truth used to be wings pinned to foamcore, properly named. That was when Lincoln Brower was a boy in western New Jersey, roaming the farmland his family owned, and the surrounding woods. He was a collector, a boy who took pride in finding and identifying and displaying. There was an old German entomologist in the neighborhood who took him collecting in the Great Swamp. When the man died, Brower inherited his business, collecting and selling cocoons. He was a boy, making a couple of hundred dollars a year. His parents had been through the Depression. There was a lesson here: you could make a life and a living doing what you loved to do.
AS A GRADUATE STUDENT at Yale in the 1950s, Brower found himself raising butterflies for a project that his first wife, Jane, was working on: the first controlled studies of mimicry in animal coloring, looking at bird predation on butterflies. The theory was that monarchs were distasteful, even poisonous, to certain birds because their larvae fed on milkweed. Their unpalatability moreover protected not only them but other, similarly colored butterflies such as viceroys, which were not thought to have their own inherent chemical defense. Birds, which rely on sight more than on smell when seeking prey, would see any one of these other orange-and-black butterflies, assume it was toxic, and leave it alone. (“Sometime just pick up a monarch butterfly and pinch it. It will regurgitate. Put a drop on your tongue and taste it; it’s really bitter,” Lincoln told me.) So Brower raised viceroys, which look a lot like monarchs but are smaller; and monarchs, which are the largest of the black-and-orange butterflies and whose caterpillars feed on milkweed, which makes the cardiac glycosides that are toxic to certain bird species; and tiger swallowtails, which are yellow and black and nontoxic.
The study was a success. Jane Brower was able to show that monarchs were indeed unpalatable. By feeding them to blue jays under controlled conditions, she demonstrated not only that the birds vomited when they ate monarchs reared on particularly toxic milkweed varieties, but that once they did, they learned not to eat them or butterflies that looked like them. It was a learned response.
“Sure enough,” Lincoln said, “the monarch butterflies were toxic, and the jays wouldn’t eat them or the viceroys. But they did eat the palatable butterflies, the swallowtails. But birds that had had no experience with monarch butterflies ate them. And got sick.”
That was the expected, and hoped-for, result. But to the Browers’ surprise, the experiment revealed something else as well: different species of milkweed contain different concentrations of the noxious chemical cardiac glycoside, which in lower doses may be unpleasant to the birds but does not cause them to throw up or die. “If we hadn’t thought the tuberosa milkweed was more toxic than the other varieties and had fed the monarchs the nontoxic kind, the experiment would not have worked, and we might have given up,” Brower explained. Instead, it set him on a different path altogether, away from his graduate studies in larval cannibalism, through a study of chemical defense in monarchs, to, ultimately, the development of a procedure called cardenolide fingerprinting, which enables scientists to tell where each butterfly comes from by determining what species of milkweed it fed on as a caterpillar.
But in the 1950s, the discovery that different milkweed varieties had different toxicities led Brower to another observation—that there was a kind of protection within the species itself that operated like Batesian mimicry (wherein nontoxic species colored almost identically to toxic ones are able to use their coloring to deter predators, which can’t tell which is which). Monarchs that were not especially unpalatable were being protected by the jays’ conditioning through eating more toxic monarchs—monarchs that caused “retching, vomiting, excessive bill-wiping, alternate fluffing and flattening of feathers, erratic movements, head and wing jerking, partial eye closure, and a generally sick appearance.” In the annals of natural history, it was ground-breaking research.
Not all birds were equally or even adversely affected by cardiac glycosides, however. In Mexico, Bill Calvert had noticed that black-backed orioles and grosbeaks did not shy away from eating monarchs. Indeed, he estimated that in one colony alone, they were killing about thirty-four thousand butterflies a day—or more than a million in that single season.
Predator and prey—that, of course, is how nature works. But it’s not hard to see how a scientist might move from an uninflected observation to something more emphatic and urgent—how Brower could easily assimilate this number, one million, and model what it would be if the forests were thinned and the butterflies had less tree cover, or what it might be if they were simply more exposed and vulnerable to attack. Then it would be not just nature running its course but nature with a tipped hand. Clearly the butterflies were at risk if the forest lost its density. Brower was coming to understand that. From there it was not much of a stretch to go from being a research scientist to being an environmental advocate. In a way, the facts demanded it. If the monarchs were going to be protected, then the forest had to be, as well.
“My whole career, up until we confronted the deforestation of the overwintering sites in Mexico, was pursuing questions purely because they were interesting and because there was a historical basis for the research,” Brower said the morning we went to his lab. “Even the question ‘How do monarchs survive the winter in Mexico?’ is a pretty basic biological question. Right now my research is bouncing back and forth between what I can do to show we can’t cut these trees and what interesting biological questions I can address.”
Later he said something more telling: “I grew up on a large farm in New Jersey. Every place I collected butterflies as a boy has now been turned into a housing development. I had a wonderful trail through the woods where I’d collect underwing moths. I’d paint the trees with sugar, which would attract the moths. Have you ever seen one? They are gorgeous. That land was all sold off and turned into a golf course. One day not long afterward I was out playing golf and I spotted a few white marks from the sugar trail on trees that had been cut down. That just did it. I never played golf again.”
In the years since, Brower has made it a point of pride to testify against land development and developers, to take positions on conservation issues across the country and abroad, to marshal the information he has garnered by doing science to push particular political points of view. The science may be neutral, but the scientist is not.
SO BROWER WAS not pleased, the way everyone else seemed to be, with the 1997 bumper crop of monarchs. Amid all the caviling voices on Monarch Watch and the other monarch migration tracking site, Journey North, his was noticeably flat. When monarchs reached Texas in March, much to the excitement of people who lived in Dallas and Uvalde and Johnson City, Brower cautioned, “That’s too early. They’ll be in the Midwest in April. I don’t think the milkweed will be up yet.” His point was that the monarchs had to be supported by habitat. They had to eat, or else they would starve. And that was not all. In all the years he had been doing research, he had noticed that monarchs kept to a regular schedule. In Florida, for instance, “they came the last week of March and the first week of April every year, like clockwork.” Butterflies that had jumped the calendar worried him.
As respected as Brower was, his worry was largely disregarded. He was like those market analysts who see the Dow cresting 12,000 and say “Correction, correction”—words that no one wants to hear except people selling short. But in biology, no one was selling short, so Lincoln Brower was simply ignored. “Lincoln was just being Lincoln,” more than one of the monarch watchers told me, with a “can we get back to the party now?” kind of impatience. In their estimation he was by nature an alarmist.
To some extent this attitude was justified. Although Professor Brower had been the first research scientist (along with the natural historian and lepidopterist Bob Pyle) to make the distinction between an endangered species, which the monarch was not, and an endangered phenomenon, which the monarch migration appeared to be, and though that distinction was accepted and formed the basis for a lot of other research and advocacy, he
had squandered a certain amount of goodwill the year before, in a six-hundred-word New York Times op-ed piece. Written with the poet Homero Aridjis and entitled “Twilight of the Monarchs,” the essay was published just days after an unseasonable snowstorm in the Neovolcanic Belt. Although winter temperatures in the overwintering sites typically hover around freezing, it rarely snows there. That was one of the reasons, it was surmised, that the butterflies migrated there in the first place. Freezing temperatures could be deadly. Rain could be deadly. Snow most certainly would be deadly.
Lincoln Brower and his colleagues, in fact, had done the definitive studies on the monarch’s (lack of) tolerance for low temperatures. As Brower described it, “I wanted to determine the temperature butterflies freeze at, so I inserted a thermal probe into their bodies, put them into a vial, put the vial in solution, and dropped the temperature. When the water in the butterfly freezes, it releases the heat of crystallization. You know that’s the freezing point. I did that for several hundred and found that the freezing point is minus eight degrees centigrade. Then I wet the butterflies and did the same thing. They could only go down to one degree centigrade before they froze.”
What this told him was that if trees were cut down and the canopy was opened up, and it rained or snowed and the butterflies got wet, they would “lose their cryoprotection.” Big trees—that is, trees with bigger trunks—are more protective than small trees. In winter they are warmer than the ambient temperature, and they also hold their warmth even as the air temperature falls. In summer they are cooler. In both cases this explained why so many monarchs could be found clustered on tree trunks.
“That’s a complicated, nifty adaptation that’s interesting in its own right,” Brower exclaimed after describing it.
Nifty as it was, it wasn’t nifty enough to stop the illegal loggers, who were paid a premium for big, old trees. Their taking them out meant that the monarchs were losing not only their heater effect but their overhead cover as well—what Brower called their cryoprotection. But this—the cryoprotection theory—was speculative. Taking out trees was not. It produced real, hard cash.
And then it snowed. Up in the highlands in the last days of 1995, on the flanks of the Neovolcanics, the snows fell, and then they accumulated. This was unusual. More typically it stayed cold in the mountains and sometimes rained, creating the right microclimate, with sufficient moisture, for monarchs to spend the winter without drawing down all their lipid reserves. Snow was disastrous to the monarch colonies, especially colonies sequestered in forests that had been thinned. And this was a big snow.
The reports from Mexico were dire. Butterflies were dying in numbers that were exponential. They were falling off trees, frozen. They were lying on the ground, frozen. Everything Brower had been saying for years about the dangers of cutting the oyamel trees was, sadly, coming to fruition. The forest, which had been the winter home of the monarch for ten thousand years, was suddenly no longer able to sustain it. There were reports in the Houston Chronicle, the Mexico City Times, Toronto’s Globe and Mail, the New York Times. On the D-Plex list the mood was somber. People shared what bits of information they could glean from Reuters and sources in Mexico. They were like people whose loved ones might have gone down in a crash, waiting for some kind of confirmation. And then it came. Brower and Aridjis published their article in the New York Times. The first line said it all: “As many as 30 million monarch butterflies—perhaps 30 percent of the North American monarch population—died after a snowstorm hit their sanctuaries in Mexico on December 30.”
Thirty million butterflies. Thirty percent of the North American monarch population. The numbers were staggering.
But then the sun came out. The snow began to melt. And millions of butterflies that had been lying on the ground began to warm up and wake from the dead. Not just millions—tens of millions. An estimated thirty million had fallen and been left for dead when the researchers first hiked in during the storm, but when they returned and the final count was done, it was estimated that the winter storm had actually killed far fewer—about ten million butterflies. It was not an inconsiderable number, to be sure, but it was so much less than thirty million that it seemed, by comparison, negligible. Brower looked like a hysteric, the biologist who cried wolf.
Fifteen months later, here he was again, raising his voice, questioning the health of the fecund and apparently robust spring migration. This time his concern was perceived as a kind of intellectual tic, something he could not help himself from doing, and not a serious biological problem at all.
To Lincoln Brower’s studied eye, however, the numbers suggested real trouble in Mexico. As he saw it, the butterflies had left Mexico early, unable to find sufficient water and nectar because land clearing right up to the edge of the preserves had eliminated their sources.
“In February they started moving down the mountains to get closer to moisture, but instead of finding a mixed pine zone with a rich understory, they found the land cleared out,” Brower speculated. “On hot days they would be coming down in droves and there would be no place for them to spread out. With their usual staging ground for the spring migration disrupted, the monarchs simply took off and went much farther than usual.
“It’s my hypothesis,” he added, “and I can’t prove it.”
Because of their early departure, the monarchs were able to produce more generations in the north prior to the return trip—hence the unusually high numbers. To Brower, then, those numbers spoke not of health but of a decimated habitat. It had been an uncommonly mild spring, ideal for breeding monarchs. But what if it hadn’t been? What if there had been hurricanes and tornadoes and late snowfalls? What would have happened to that early generation of monarchs then? These were the questions Brower was raising, and nobody, it seemed, wanted to answer them.
“I REJECT the argument that since we have starving people, we can’t save the butterflies. I totally reject that. Save the butterflies, and you improve the quality of life for those people. And they’re going to starve anyway.” More vintage Brower. It was getting on to the end of the year. The massive spring migration had turned into what appeared to be a massive fall migration, and now Brower was back in the Mexican mountains, astride an impatient brown mare, waiting to begin an ascent of Cerro Altamirano with Homero Aridjis, the poet laureate of monarchs and the coauthor, with Brower, of the much-maligned article in the Times. Aridjis was also on horseback, as was his wife, Betty. Aridjis had grown up in Contepec, a market town that sits at the bottom of the ten-thousand-foot mountain. As a boy, he would hike with his friends up to a field called Llano de la Mula—the “Plain of the Mule”—to picnic and watch the butterflies, which were so thick they bowed the trees. Later he convinced the president of Mexico to protect Cerro Altamirano as well as four other overwintering sites. It had been protected since 1986 because of his efforts; now he wanted to show it to his friend Brower.
The region had been experiencing a drought, and the trail up the mountain was dry and soft as ash. If dirt could be ephemeral, this dirt was, eroding one step at a time so that it disappeared as soon as you touched it. Dust rose like smoke, so much dust you could draw your name in it on the flank of your horse. The animals were walking slowly, losing their footing as the scree dropped out beneath their hooves and rattled away, small avalanches falling behind them, loosening other rocks, making more dust. There were eleven in our party. The trail was disappearing, but we were leaving our mark.
Then the path leveled out, and we scanned the air, the trees, the ground for evidence that this was the way to the monarchs. We saw none. No butterfly wings, no dead butterflies, no butterflies overhead. The oak forest gave way to oyamel fir, and still nothing. Even the birds were still. Homero was somber. He had come to revisit the past but found instead what he imagined to be the future.
And it wasn’t just butterflies, the poet said later, when we were resting at Llano de la Mula, a slightly canted alpine meadow ringed by tall oyamel trees. This place used t
o be full of coyotes, skunks, and rabbits. Armadillo, too. All we were seeing now was ladybugs—thousands of them, crawling and flying in great clusters. Wrong biomass: no one was interested. Homero got up and walked around, back into the forest, looking for the clusters of butterflies he’d been expecting to find. No butterflies, but evidence everywhere of the fires that had devastated this forest fifteen years before, fires started by people attempting to clear land for agriculture, fires that had happened to get out of control. Since then the local monarch population had been smaller and less reliable, Homero said; it was perhaps a direct result of the fires, as well as of logging.
“I feel very frustrated,” he admitted, mounting his horse for the ride down. “Every time I come, there are fewer and fewer trees.”
“It is very depressing for Homero to see what has happened year after year,” Betty added. In his work she often served as his translator, but this was beyond words.
THE TRIP DOWN the mountain was no less treacherous than the trip up. The horses slipped. The trail kept crumbling away till there was no trail, just dust and rocks. Homero had gone on ahead; Brower was walking and pointing out trees that had gashes in their trunks the size and shape of ax blades. There were many: it was nearly epidemic.
“These flesh wounds will invite disease,” Brower explained, “and eventually the trees will die.” When they do, they may be hauled out legally, for though it is illegal to take down living trees in this forest because it is protected by the 1986 presidential decree, there is no such injunction against moving dead or diseased timber.
Later, at about five thousand feet, we heard the sound of a chain saw, distant but distinct. A whine, a pause, a whine again. Wood cracked and a tree crashed through the understory. Half an hour farther down the mountain and there was the tree, cut in thirds and tied to the flanks of five donkeys. The donkeys were being led by two men and a boy. “How much will you get for these?” Homero Aridjis asked them.
