Mysteries and surprises abound in the nocturnal world of Leopards of Yala.

For more than a century, Yala National Park in Sri Lanka has been one of Asia’s most celebrated wildlife preserves, a lush windswept tropical forest rich in rare aquatic birds and abundant with ferocious predators, such as crocodiles and sloth bears. But only in very recent years has Yala’s big cat distinction been brought to light: It contains one of the world’s largest concentrations of leopards. NATURE takes viewers deep into the jungle habitat of these elusive animals, in Leopards of Yala.

Over a period of six years, Jehan Kumara, a businessman from Sri Lanka’s capital city of Colombo, and Dr. Ravi Samarasinha, a physician from the local countryside, devoted their spare time to tracking leopards in Yala. In the course of their work, they are joined by Scottish cameraman Gordon Buchanan, attracted to Yala by the lure of finding the only big cat he had never captured on film.

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Online content for Leopards of Yala was originally posted April 2003.

Researchers Daniel Mulcahy and Gerald Garner of the Alaska Biological Sciences Center (ABSC) in Anchorage, for instance, wanted to solve an annoying problem: the repeated loss of radio transmitters that researchers had attached to male polar bears in order to track them by satellite. Whether the transmitters were glued to a bear’s fur or attached to an ear or collar, they consistently went silent soon after the bear was out of the trackers’ sight.

Researchers guess the bears found ways of ridding themselves of the uninvited eavesdropping devices. To solve the problem, Mulcahy and Garner decided to try implanting a tiny transmitter below a bear’s skin, with just a short antenna sticking out. While the idea was promising — it had worked in other animals — it posed a significant challenge: performing a half-hour surgical operation on a potentially angry animal in the middle of a freezing ice field. “The major challenge was to find methods permitting the surgeries to be done in the outside on the sea ice of the northern coast of Alaska, where the temperatures experienced during surgery were as low as -22 degrees Fahrenheit,” the researchers dryly explained.

Still, the two men were game. After surveying the area in a low-flying helicopter, they spotted a bear and then shot a tranquilizing dart into it. Once the animal was asleep, they landed the helicopter and unloaded their portable surgical gear — all the time watching over their shoulders for the unwanted arrival of other bears. To keep their hands from freezing, the surgeons wore warm linings under their rubber surgical gloves. But they couldn’t keep other items from getting chilled. “Injectable drugs froze in vials and syringes,” Mulcahy and Garner recalled. “Instruments froze to blood on the surgeon’s hands. Plastic or paper drapes shattered and tore when used.” It was so cold, in fact, that the small incision they made in the bear’s skin never stopped bleeding, probably because temperatures were too low to allow the chemical reactions that promote clotting to occur. To make things work, the scientists had to move extremely fast: “Speed was the best overall solution to the problems,” they concluded.

It’s too soon to know if implanted transmitters will ultimately prove more reliable — or practical — than previous techniques. But there is no question that tracking polar bears by satellite has yielded valuable information. One scientist, for instance, used a satellite to track a bear on a record-setting 3,000 mile trek across the Arctic in search of food. The female bear started near Alaska’s Prudhoe Bay oil fields and then ambled across the polar cap to Greenland, where she spent a winter before continuing on to Canada’s Ellesmere Island. Eventually, the bear returned to Greenland. The researcher, in contrast, didn’t have to move from the cozy confines of his computer terminal once the transmitter had been attached.

Satellites aren’t the only high-tech tool researchers are using to study polar bears. Recently, other Alaskan researchers used sensors that can detect infrared radiation, which is produced by warm objects, to detect polar bear dens buried beneath the snow. Because from the surface, the dens look no different from snowdrifts, the spotting technique could help biologists protect the nurseries from development activities. It could also be used to warn people away from dens and potentially dangerous mother bears, who can become aggressive when they believe their cubs are in danger.

Though such technologies will bring new insights into the lives of polar bears, they probably won’t change one fact of life: if you want to study polar bears, you need to be prepared to expose yourself to the elements.

In the forests of the Central African Republic, Italian primatologist Chloe Cipolletta is trying to make friends. Cipolleta isn’t seeking ordinary companions; she’s trying to befriend a group of western lowland gorillas in order to learn more about how to protect these endangered and poorly understood primates.

“I was born with a passion for animals and nature,” Cipolletta told NATURE. “Working in a conservation project is, for me, the ultimate fulfillment because it gives me the chance to contribute to their protection while having the opportunity to work directly with them.”

If you’ve been to a zoo, you’ve probably seen a lowland gorilla. Despite their ubiquity in captivity, in the wild, lowland gorillas have proven far harder to study than their better-known cousins, the mountain gorillas. Lowland gorillas are hard to approach and live in thick, brushy forests that make it difficult for researchers to follow the animals.

Working under the auspices of the World Wildlife Fund, Cipolletta went to the Dzanga-Sangha region to learn more about western lowland gorillas. Her work is part of a larger effort to protect the region, where conservation groups and the government have established a 1,250-square-mile system of protected lands. These areas are filled with dense tropical forests and small, wet clearings called bais which attract animals, including gorillas.

To gain the gorillas’ trust, Cipolletta asked for help from the BaAka (Bi-AK-uh), local tribes people who have an intimate understanding of the forest and an extraordinary ability to find their way around it. Although the BaAka sometimes hunt gorillas they are generally afraid to get near them. So Chloe’s idea of tracking and then trying to get close to them must have seemed like madness. But eventually the BaAka, including Nbanda and Ngombo, two of their best trackers, agreed to help her. She admits she could not have found the gorillas without them.

The idea was to get the gorillas habituated to people, thereby enabling researchers to more easily study the primates, and to turn the area into an ecotourism destination, which might benefit the local economy. Planners hope such tourism will create an incentive to preserve the ecosystem and make the BaAka allies in protecting the gorillas.

In Deep Jungle, viewers watch as Cipolletta and her colleagues pick up the trail of a male gorilla silverback and his son, eventually ending up face to face with the pair. It was a memorable moment years in the making, but things have changed since the film was made, Cipolletta explains.

“Mlima (the silverback in the film) succeeded in acquiring a female, and was in [his] best shape ever,” she wrote. “But that attracted the attention of a lone silverback who opposed him, and wanted to attract the female. They fought and Mlima died as a result of the wounds.”

“The juvenile featured in the film, Ndimbe, was wounded too but survived,” Cipolletta wrote. “It was dramatic, but we also know that Mlima had a few very happy weeks with his new female before dying.” Cipolletta says tourists are able to watch the Makumba group of gorillas, “a family of 13 individuals with many kids.”

There are also signs that the BaAka have gained a new perspective on gorillas. “I still get surprised about many things while working here, and that’s one of the things keeping me here,” Cipolletta says. “Certainly a most encouraging moment was after the death of the silverback. I received so many condolences from people in the villages. The way so many people responded surprised me a lot and gave me much hope.”