This story appears in the October 2013 issue of National Geographic magazine.
Dr. Terri Roth got into her scrubs, pinned her long brown hair up in a bun, and pulled on a clear plastic glove that stretched over her right forearm, past the elbow, and almost to her shoulder. Her 1,500-pound patient, a rhinoceros named Suci, was maneuvered into a narrow stall. While one of her colleagues fed Suci apple slices out of a pail, Roth pulled a second glove over the first and grabbed what looked like a video game remote. Then she stuck her arm deep into the rhino’s rectum.
Two days earlier, Roth, director of the Center for Conservation and Research of Endangered Wildlife at the Cincinnati Zoo, had tried to inseminate Suci, a Sumatran rhino born at the zoo in 2004. The artificial insemination (AI), which Roth had also performed wearing a shoulder-length glove, had involved threading a long, skinny tube through the complicated folds of Suci’s cervix. According to Roth’s notes, Suci had “behaved very well” during the procedure. Now it was time for a follow-up ultrasound. Grainy images appeared on a computer screen propped near Suci’s substantial rump. Roth located the rhino’s bladder, which appeared on the screen as a dark bubble, then continued on. At the time of the AI, an egg in Suci’s right ovary seemed to be on the verge of being released. If, indeed, it had been, there was a chance Suci could have become pregnant this cycle. But the egg was still there, right where Roth had last seen it, a black circle in a cloud of gray.
“Suci did not ovulate,” Roth announced to the half dozen zookeepers who had gathered to help with the ultrasound. The group let out a collective sigh. “Oh no,” someone said. Though clearly disappointed, Roth immediately began to plan for Suci’s next cycle.
If giving a rhino an ultrasound seems extreme, consider this: When the Cincinnati Zoo opened its gates, in 1875, there were perhaps as many as a million Sumatran rhinos browsing forests from Bhutan to Borneo. Today there may be fewer than a hundred left in the world. Three of these—Suci and her brothers, Harapan and Andalas—were born in Cincinnati. Six years ago the zoo sent Andalas to Sumatra, where he has since sired a calf at Way Kambas National Park. If the species survives, it will in no small part be thanks to the 16 years Roth has spent collecting blood samples, testing hormones, and doing ultrasounds on animals in captivity.
And what goes for the Sumatran rhino goes for a growing list of species saved from oblivion. As the wild shrinks, zoos are increasingly being looked to as modern-day arks: the last refuge against a rising tide of extinction.
Although collections of exotic animals have existed for thousands of years—in the 15th century B.C., Hatshepsut, one of ancient Egypt’s few female pharaohs, presided over a menagerie of monkeys, leopards, and giraffes—the zoo, both as a concept and a reality, is a relatively recent invention. The first zoological society in the United States was formed in 1859, in Philadelphia, with the goal of creating something grander and more edifying than the traveling animal shows and city menageries popular at the time. The Civil War intervened, and it took another 15 years for the Philadelphia Zoo to open. It was soon joined by the Cincinnati Zoo and the Cleveland Zoo.
From early on, American zoos had a hand in conservation. At the end of the 19th century the Cincinnati Zoo tried—unsuccessfully—to breed passenger pigeons, whose numbers were in steep decline. (The bird that’s believed to have been the very last passenger pigeon, named Martha, died at the zoo in 1914, and the building where she lived is now a memorial.) And in the early years of the 20th century, when one count showed just 325 wild bison left in North America, the Bronx Zoo started a captive-breeding program that helped save the species. But zoos have to support themselves, and the sorts of animals that draw crowds are not necessarily the sorts that most need help.
Robert Lacy, a conservation biologist at the Chicago Zoological Society, says that zoos are going to have to make “some really difficult prioritization decisions. Do you save a small number of big furry things, because that’s what will draw the public? Or do you focus on a whole lot more little creatures that it’s harder to get the public interested in, but you might be able to save a whole lot more of for the same amount of money?”
Others argue that the situation is becoming so dire in the 21st century that zoos are going to have to fundamentally rethink their mission. Why devote any resources to species that are doing fine on their own?
“I think it’s a bit of a cop-out to say the public wants to see x, y, or z,” says Onnie Byers, chair of the Conservation Breeding Specialist Group, part of the International Union for Conservation of Nature (IUCN) Species Survival Commission. “Plenty of species need exactly the expertise that zoos can provide. I would love to see a trend toward zoos’ phasing out species that don’t need that care and using the spaces for species that do.”
Among the animals that owe their continued existence to captive-breeding efforts by American zoos are the Arabian oryx, the black-footed ferret, the red wolf, the Guam rail, and perhaps most famous of all, the California condor. By 1982 the California condor population had dwindled to just 22 birds. Soon after, every one left in the wild was caught and taken to either the Los Angeles Zoo or the San Diego Zoo. Although the reintroduction of the birds has been plagued by problems—among other things, the zoos have found they need to train the animals to avoid electrocuting themselves on power lines—there are now more than 200 condors living outside of captivity.
Because such programs tend to be expensive—the condor recovery effort costs participating institutions up to two million dollars a year—they’re usually led by large big-city zoos. But littler zoos are increasingly joining in. The Miller Park Zoo, in Bloomington, Illinois, is one of the smallest accredited zoos in the country—just four acres. It has bred red wolves and is hoping to figure out how to breed an endangered subspecies of squirrel known as the Mount Graham red squirrel.
“It’s a small animal that doesn’t require a huge amount of space,” says Jay Tetzloff, superintendent of the zoo. “And one of the zookeepers looked at me and said, ‘Wouldn’t it be cool to be the first zoo to breed that animal?’ ”
Right now, as a class, the world’s most threatened group of animals is probably amphibians. According to the IUCN, which maintains what’s known as the Red List, more than a third of the world’s frog, toad, and salamander species are at risk of extinction. Amphibians lack even the marginal charisma of a condor or a red wolf, and they clearly are no match for big-draw zoo species such as pandas or lions, which are not (yet) facing imminent extinction in the wild. But there are advantages to being small. For one thing a whole population of amphibians can be preserved in less space than that required by a single three-quarter-ton rhinoceros like Suci.
“It’s an amazing responsibility to have half the remaining members of a species in your care,” says Jim Breheny, the director of the Wildlife Conservation Society’s Bronx Zoo. He’s standing in what used to be the zoo’s veterinary hospital and is now a state-of-the-art breeding facility stacked with tanks of Kihanzi spray toads—mustardy yellow amphibians about the size of a quarter. He sounds like a new dad after a difficult delivery—proud and more than a little bit relieved.
Depending on how you look at things, the Kihanzi spray toad is either one of the most unfortunate or one of the luckiest species around. Until the late 1990s the toad was unknown to science. It was not described until a hydroelectric project was already ripping through its tiny habitat—five acres of mist-soaked wetlands in the Kihanzi River Gorge, in eastern Tanzania. In 2000, recognizing that the project would probably harm the newly discovered species, the Tanzanian government invited the Bronx Zoo to collect some of the animals to maintain as an “assurance colony.”
Exactly 499 spray toads were captured; half stayed in the Bronx, and the others wound up at the Toledo Zoo. A few years later a deadly fungus that had been decimating amphibian populations worldwide showed up in the Kihanzi gorge. Between the pathogen and the effects of the hydro project, the toad’s numbers plummeted. In 2004 researchers combing the area spotted only three tiny toads, and over the next few years, they found none. In 2009 the Kihanzi spray toad was declared extinct in the wild.
As all this was happening, the zoos were struggling to figure out how to re-create in a captive setting the highly specialized microhabitat that gives the toad its name. In the gorge a series of waterfalls had provided the toads with round-the-clock spray. In the Bronx each tank was fitted with its own little spray nozzle to mimic this effect. Among amphibians, Kihanzi toads are unusual in that they bear live young, which at birth are no bigger than a match head. For the tiny young, the zoo had to find even tinier prey; eventually they lit on minute arthropods known as springtails, which the researchers also had to figure out how to raise. The keepers noticed that the toads seemed to be suffering from a nutritional deficiency, so a special vitamin supplement had to be designed.
After some initial—and rather scary—losses, the toads began to thrive and reproduce. By 2010 there were several thousand of them in New York and Toledo. That year a hundred toads were sent back to Tanzania, to the University of Dar es Salaam. Meanwhile, with the help of the World Bank, the Tanzanians were working in the gorge. By diverting water from the falls, the hydro project had eliminated the mist that the toads depend on. The Tanzanians outfitted the gorge with a sort of giant sprinkler system and managed to restore the spray. In 2012 the first captive-bred toads were released back into the wild.
But for every success story like the Kihanzi toad, there are dozens of other species hanging on the edge of extinction. After checking in on the spray toads at the Bronx Zoo, Breheny showed off some recently hatched yellow-headed box turtles. The turtle, from China, is critically endangered; no more than 150 are estimated to exist in the wild. Not long ago the zoo announced it was going to try to breed half the species on the list of the world’s 25 most endangered turtles. It has appealed to other zoos to take on the remaining half.
“This can’t be a missed opportunity,” Breheny says. “Even if you’re a small zoo, you can house one species or several species of turtles and really make a difference.”
On the other side of the country, at the San Diego Zoo Institute for Conservation Research, Marlys Houck pulls a box of small plastic vials from a vat of liquid nitrogen. To protect her hands from the cold—the temperature inside the vat is minus 320°F—she’s wearing what look like heavy-duty oven mitts. The vials are arranged upright, in little slots. Houck locates the two she wants and places them on a steel table. “There they are,” she says.
Inside the vials is much of what’s left of the po‘ouli, a chunky bird with a sweet black face and a light chest that lived on Maui. The po‘ouli probably went extinct a year or two after the San Diego Zoo and the U.S. Fish and Wildlife Service made a last-ditch effort to save it, in 2004. At that point a mere three individuals were thought to exist, and the idea was to capture all of them and try to breed them. But only one bird—a male—allowed himself to be netted.
When he died, two months later, his body was immediately sent to the San Diego Zoo. It was Thanksgiving weekend, and Houck rushed to the institute to harvest still living cells from the carcass. “This is our last chance,” she remembers thinking. “This is the dodo.” She succeeded in culturing some of the cells from the bird’s eye, and the results of that effort now make up the contents of the vials. (The po‘ouli’s skin is now at the Smithsonian.) Houck doesn’t want the cells to get so warm that they are damaged, so after about a minute, she places the vials back in the box and returns them to the vat. The liquid nitrogen gives off a misty, ghostlike vapor.
Along with thousands of other identical-looking vials, the tubes of po‘ouli cells represent what might be described as a beyond-the-last-ditch conservation effort: the Frozen Zoo. Nearly a thousand species are represented in the Frozen Zoo, which occupies a single room on the institute’s ground floor.
For now, at least, all but one of the species in deep freeze still have flesh-and-blood members. But it seems safe to predict that in the coming years, more and more will go the way of the po‘ouli. Many of the animals in the “zoo” are highly endangered; these include the Sumatran orangutan, the Amur leopard, and the puaiohi, a songbird from Kauai. As I watch Houck put away the little vials, I wonder about a future in which what counts as conservation all too often involves liquid nitrogen. Though frogs and toads enjoy the dubious distinction of belonging to the world’s most endangered group, it’s worth noting that extinction rates among many other classes are approaching amphibian levels: It’s estimated that a third of all reef-forming corals, a quarter of all mammals, a fifth of all reptiles, and a sixth of all birds are headed toward oblivion.
“I think there are going to be more and more species where the only living material left is going to be cells in the Frozen Zoo,” Oliver Ryder, the institute’s director of genetics, tells me. As it happens, one such species, or really, in this case, subspecies—the northern white rhino—can be found just a few hundred yards from Ryder’s office. Native to central Africa, the northern white rhino is down to its last seven individuals, and its extinction is at this point considered inevitable. Two of the seven—Nola, a female, and Angalifu, a male—live at the San Diego Zoo Safari Park, and when I leave the institute to go visit them, I find them basking in the late afternoon sun. The animals are both nearing 40 and too old to breed. But after they die, they will, in a manner of speaking, live on—one last hope, suspended in a frozen cloud.