The Kingdom of Rarities (10 page)

“It's really pretty ingenious,” George said later. “After the TrackTag picks up the signals of the GPS satellites, it stores hundreds, perhaps thousands, of fixes on a chip rather than attempting to
transmit the location back to us via a communication satellite, as other GPS tags do. After we recapture the animal, we swap the TrackTag and download its data. But if we don't recapture it, we can program the collar, with VHF and TrackTag, to drop off the animal. Then I can fly, locate the dropped collar using the VHF device, and send my field crew to that point to retrieve the TrackTag.” After returning it to Peter Brown, George would receive a computer file with all locations that the jaguar or puma had visited while wearing the TrackTag.

“Couldn't you learn the same thing from the VHF signals you pick up by flying each month, even with fewer locations?” I asked. “Take a look at this,” George responded, indicating an image on his laptop. Since the beginning of the radio tracking, he had been religiously plugging his jaguar locations into a database. On the screen were the location points, collected during all the flights, for Paya, a female that had recently been killed by another jaguar. The seventeen VHF fixes George had for Paya, when connected, outlined a large triangular home range of about 230 square kilometers overlaid on a map that covered vast sections of upland forest in addition to the Tambopata River.

“Now watch,” George said. He keyed in a few commands and displayed the TrackTag locations—literally hundreds of yellow dots—on top of the triangle created by the seventeen VHF fixes. “Quite a revelation, huh?” he said with a laugh. The TrackTag locations, recorded during the same period from the same animal, showed exactly the opposite pattern: Paya hugged the fifty kilometers of the river system lying within that large triangle. “She actually avoided the upland forests!” George exclaimed. “I had a hunch that the sparse VHF locations might be misleading us about how jaguars use Amazonian forests. Now we know.”

When George uploaded TrackTag results from other animals, it was clear that Paya was not the only big cat to follow that pattern. Other females largely avoided the much more abundant uplands and patrolled the riparian forest instead. Although the TrackTag
evidence was indisputable, the behavior was mystifying, since rivers have been the center of human development in this region for hundreds or even thousands of years. Why did the jaguars live so close to the water's edge? What was attractive enough to override the real threats posed by a growing human presence? In the pioneer days, the threat had been boatloads of pelt hunters. Today, the threat is thousands of gold miners and their followers who provide them with food, lodging, and pleasures. And still the jaguars hang on.

As I write, those questions remain unanswered and George still labors to crack the mystery. The evidence so far, however, casts doubt on his original assumption, that the jaguars have a taste for river-dwelling food items. Using modern DNA-sequencing techniques to analyze the jaguars' scat and identify their prey, his team has found no sign of fish or turtles or caimans. Instead, white-lipped peccaries are the primary prey. Tracking results for those animals showed that the peccaries range widely throughout the floodplain, so a steady diet of these wanderers gives no obvious clue to why the females are so attracted to river edges. Perhaps the question will remain unanswered until a researcher figures out how to add digital cameras to the TrackTag equipment in order to monitor how and where the female jaguars capture their prey. One theory holds that it is easier for cats to kill peccaries along the flat riverbanks than in the broken terrain of the uplands.

In the meantime, George has looked at the tracking data for the male jaguars to see whether they follow the same patterns. It turns out that males tend to wander more widely over the floodplain than do the females, perhaps moving from female to female in search of breeding opportunities as large cats are typically known to do. George speculated that the big males, almost twice the size of females, can more easily bring down the tusk-laden peccaries—which themselves are nearly the size of female jaguars—with less dependence on the element of surprise. This may support the view that females prowl the riverbanks because the dense understory gives them more cover from which to launch an attack. If the males,
on the other hand, depend less on short-range surprise attacks, they can focus on their second most important drive, cherchez la femme.

For assembling a picture of jaguar movements, a missing piece was knowledge of the density of jaguars far from river channels, where peccaries are few. To address this, George and his team needed a research site in the upland forest. He found a well-managed timbering operation where hunting was prohibited and obtained the local landowner's permission to use the concession as home base, allowing the team access to the vast uplands. Although this study is still under way, initial data indicate the big cats use larger home ranges in the upland areas, perhaps because of the near absence of their preferred prey, the white-lipped peccary. “My data clearly show that white-lipped peccaries are super common in the floodplain habitats, but rare in the upland forest away from the flooding,” George wrote in his journal. “I will be curious to see if plant sampling data show that the extensive upland forest is largely devoid of the large palms whose nuts the white-lippeds depend on. At least that is what we expect.”

George's inquiry into how jaguars and pumas share the range, or avoid each other entirely, was only partially answered. His preliminary data indicate that pumas seem to be similar to jaguars in their preference for riverine habitats but with the caveat that there is little or no overlap between male territories. Unfortunately, female pumas turned out to be too small to carry a TrackTag collar. (Typically, researchers try to keep telemetry devices within 5 percent of an animal's body mass, to avoid interfering with its behavior.) Thus, greater insight into how these two cats fit together in ecological space awaits yet another advance in the technology of animal tracking.

One can infer only so much about the causes of rarity by mapping jaguar or puma distributions. Perhaps greater understanding comes from looking across the ocean at another pair of large feline predators: tigers and leopards in South Asia. A common saying among old jungle-wallahs there is that “where tigers are common, leopards are scarce.” Tigers are known to kill leopards, and in areas
of high tiger density, leopards stay close to the margins of wildlands and closer to human settlements, where tigers tread less frequently. Perhaps pumas, especially the smaller females, are strongly influenced by the movements and ranging of jaguars and stay in areas avoided by jaguars.

Another important aspect of trophic rarity, or the “big, fierce animals are necessarily rare” paradigm introduced by Paul Colinvaux, is prey density. In fact, again using South Asia as an example, researchers have shown that tiger density in a given habitat can be predicted by the prey density estimated for that habitat. Tigers reach highest densities in the riverine grasslands of Asia, over 20 adults per 100 square kilometers, and an order of magnitude lower densities in mature forests, all because large prey animals—deer, wild boars, and Indian bison—do likewise. Perhaps more studies of co-occurring jaguars and pumas and their prey elsewhere in the Amazon will indicate a similar relationship between prey density and predator numbers.

Bolstered by George's TrackTag data, an answer to the initial question, “How much is enough to conserve rare nature as represented by the jaguar?” suddenly seemed more attainable, at least for this region of the Amazon. Individual jaguars in this part of Amazonian Peru have very large home ranges, as much as 400 square kilometers, the data suggested. “If we calculate the jaguar's use of habitat, while accounting for their apparent preference for floodplains and riversides,” George commented, “then maintaining genetically viable, healthy populations of jaguars of, say, 500 breeding females will probably require well above 20,000 square kilometers—perhaps between 30,000 and 40,000 square kilometers—assuming a good peccary population.” This also assumes that the areas being conserved incorporate extensive riverbank and floodplain habitat. How do the protected areas of the Amazon measure up to this task? Of the more than one hundred protected areas in the Amazon, not one is large enough, and only about a dozen are over 10,000 square kilometers; the average reserve size is only 3,500
square kilometers. Aggregates of protected areas with open passages between them—conservation landscapes, a topic explored in more depth in a moment—will clearly be required.

Studying big cats that were, for the most part, out of harm's way from humans, but not from each other, offered further insights. Each jaguar, male and female, examined by the team provided evidence of these cats' ferocity toward one another. All showed signs of struggle: cuts, old wounds, bitten ears. Several radio-collared jaguars had already perished in the lethal jaws of another: hardly a children's bedtime story, but the reality show of life in the rain forest. A visiting biologist who was familiar with California pumas had a novel view of the violence, suggesting that the frequency of scrapes, wounds, and scars indicated a healthy population as animals fought to maintain access to areas with high levels of prey. A basic law of nature drives this aggression and, ultimately, the wide spacing of jaguars in the rain forest. Perhaps the most important finding was that even where humans have less influence, as in Tambopata, jaguars have a density of only around 4 per 100 square kilometers—rare by any reckoning.

While George was tracking jaguars and pumas, Sue and her field team were searching in the same area for the elusive bald-faced saki monkey. Sakis are seed-eating primates, so the “big, fierce animals are rare” theory makes no sense as a descriptor of density. Moreover, sakis live in small family groups of fewer than ten individuals, typically including a single adult male, one to three adult females, and one or more young. At first, Sue figured that the trees whose seeds they eat must dictate the monkeys' locales and limit their range. But careful observation of their behavior and a bit of tree climbing led to a novel hypothesis to explain their rarity.

The answer lay in the architecture of the forest itself. Sue collaborated with Greg Asner, a tropical ecologist with the Carnegie Institution for Science who, together with George, had mapped
the aboveground biomass, and estimated from that, carbon density of the Madre de Dios rain forest. The tool they used to collect the biomass data was a laser scanner mounted on a small aircraft. What this innovative technology and revolutionary study showed is that a forest that looks uniform to an untrained eye from the air and even from the ground, looking up at the canopy, is actually quite variable in its three-dimensional structure and biomass. And the sakis saw the forest in a unique way: Sue and Greg found that they could predict where to find these rare canopy-dwelling primates by knowing the forest's biomass—data provided by the laser sensor. The densest branches in the canopy provided aerial concourses for these tree-running primates. In essence, Sue's work showed that the saki monkey was an Amazon old-growth forest equivalent of the famed northern spotted owl of western North America's coastal conifer forests. That nocturnal predator is a habitat specialist, persisting only where the high but open forest canopy still enables it to hunt its preferred prey (flying squirrels) and breed successfully. The main difference in habitat restrictions of the northern spotted owl and the saki monkey is that the patchy distribution of coastal old-growth conifer forests is due to logging. The distribution of sakis in unlogged Amazon forests is a natural pattern of rarity, it seems, because the structure that permits troop movement, the canopy runways of dense, wide branches, is scarce. Sakis may be very common in suitable patches but overall are rare because preferred patches, with the aerial superhighways they require, are rare. The advent of airborne laser scanning in the tropical rain forests of Colombia, Peru, Panama, and Brazil will surely enhance prediction of where rare, dense-canopy primates and other vertebrates might live over vast scales.