MAROJEJY NATIONAL PARK, Madagascar -- Since daybreak he has been scanning the treetops for the creatures that move as if by pogo stick and look as if they wear white fur coats and big, black, round sunglasses.
It is after 2 p.m., and the dense, hilly rain forest has yet to give primatologist Erik Patel a glimpse of Propithecus candidus, the rare monkeylike lemur known as the silky sifaka. It is one of the world's 25 most-endangered primates, the animal order that includes humans. Fewer than 1,000 silky sifakas are thought to exist, all of them in this rugged patch of northeast Madagascar.
Finally, a guide working with him spots a flash of white deep in a ravine. Within minutes Patel skitters and slides down the root-covered slope, where he hears a familiar sound: the sneezelike "zzuss" call the animals emit when alarmed.
"It's Pink Face," he says, wiping sweat from his forehead. "I know it's him."
Patel, 35, is a scientific pioneer, the planet's foremost expert on the silky sifaka. Until 2001, when he began work on a doctorate at Cornell University, the sum of knowledge about these animals was as fleeting as their ghostlike visage. He chose this path because he would have to blaze it.
Across Africa, animal researchers have long pitched tents in forests and deserts, on mountains and seashores. They have sought to map the lives of hundreds of species, data point by data point. It is a form of research that relies as much on a tolerance for bug bites and a steady diet of beans as on advanced equipment and observation skills.
Captive animals can yield some secrets of their species. But only in the wild are they completely themselves, whether the great apes of Uganda, baboons in Botswana, wild dogs in South Africa or the lemurs of Madagascar.
Patel and the continent's dozens of other animal researchers represent the newest chapter of scientific discovery. Using a wide variety of methods and approaches, they are continuing a tradition made famous by chimpanzee expert Jane Goodall and the late Dian Fossey, who studied and lived among mountain gorillas for nearly 20 years.
The work can be lonely and tedious. During his months in the forest, Patel favored his work over his health and his personal life. But he is on a mission, not unlike earlier explorers who, having mapped the coastline of an unknown shore, ventured into the interior without being certain of what they would find.
Over the past four years, Patel has spent 14 1/2 months camping in this forest. He is back for a few weeks to observe Pink Face and the others in this community of six lemurs. He hopes new data will shed more light on how the animals communicate, information that may one day yield clues about how speech evolved in humans, the lemur's distant cousins.
And he feels a sense of urgency. Despite an increase in conservation efforts, including Patel's own, no one knows how much longer the silky sifakas can survive persistent hunting and deforestation. They may need him as much as he needs them.
No one can mistake these animals for any other kind of lemur. Only the silky sifakas have fluffy white fur covering their body except for the face, which is slate gray or pinkish. Their eyes are reddish orange.
They have been dubbed flying angels for the way they soar from tree to tree. In reality, they use their powerful legs and fingerlike toes to grasp a tree trunk or branch and quickly push off to the next one, up to 10 feet away. They have had lots of practice.
Lemurs have been eating tree leaves and exploring the forest canopy for perhaps 50 million years.
How they got here remains a mystery. Madagascar, along with India, split off from Africa about 125 million years ago, and Madagascar parted ways with India 88 million years ago - before lemurs existed - to take its place as the planet's fourth-largest island.
One theory holds that a storm washed some lemurs off the coast of Africa and that some of the animals then "rafted" on floating vegetation before chancing on Madagascar. It is conceivable, writes Peter Tyson in The Eighth Continent: Life, Death, and Discovery in the Lost World of Madagascar, that all of Madagascar's lemur species, from one as tiny as a mouse to a gorilla-size kind that is now extinct, "arose from a single pregnant female that crawled ashore 40 or 50 million years ago."
The island's long isolation meant that most of its plants and animals evolved separately from the wider world. Biologists estimate that eight in 10 of its species - plants as well as animals, including its birds, reptiles and frogs - are found nowhere else, an astonishing rate of uniqueness. People arrived 2,000 years ago, likely from Indonesia, making this one of the last-settled major land masses on Earth.
The most striking example of the island's species diversity may be the lemurs.