Meanwhile, the pair noted, indigenous trackers could often identify individual animals by their footprints, which vary slightly, much like human fingerprints.
WildTrack takes advantage of this variation to identify and monitor animals in the wild. All human trackers need, the researchers say, is a digital camera and a global positioning system (GPS) device.
When trackers locate animal prints in the field, they simply take a digital photo of the print and record its GPS map coordinates.
Trackers send the information to the researchers electronically. Software then characterizes the footprint, and the data is stored a digital library.
Eventually prints sent from the field can be matched to the archived records of known individuals.
Jewell and Alibhai have begun using WildTrack to census tapirs in Argentina, Bengal tigers in India and Bangladesh, and Iberian lynxes in Spain and Portugal.
Next month the researchers will start gathering data about a subspecies of black rhinos found in Cameroon, West Africa.
The scientists chose the animal because there are estimated to be just 15 individuals left, making it possibly the most endangered subspecies in the world. (Subspecies are members of an animal species found in a distinct geographic area.)
The rhinos, which are black only because of the mud caked on their hides, have largely disappeared as a result of habitat destruction and slaughter for their horns.
There are only about 2,600 black rhinos in central and southern Africa and a total of 18,000 rhinos in the world. There were 70,000 rhinos just 30 years ago.
The black rhino is known for its aggressiveness and its nimble upper lip, which it uses to grasp and browse on shrubs. The animals live to be 40 to 60 years old.
WildTrack's goal in Cameroon is to get an accurate count of the number of individuals. Some philanthropists have said they will contribute money to preserve the black rhinos only if it can first be proven that a viable population exists, the researchers say.
If WildTrack can confirm a population, the resulting donations could be used to hire armed guards to protect the animals, the scientists say.
"We hold the key to unlocking this funding," Jewell said, adding that groups have been trying to get an accurate count for about 20 years. "This is a last-ditch effort."
Because WildTrack is noninvasive, "if this [approach] doesn't work, then there is no harm done," she said.
In April WildTrack will be used to study rare Sumatran rhinos on the Southeast Asian island of Borneo.
The animals are the only rhinos with a hairy coat. They live in small bands in dense jungle, where they eat fruit, leaves, twigs, and bark.
The species's population has declined 50 percent during the past 15 years, and past monitoring efforts have been fraught with difficulties.
There are only about 30 of the rhinos left, and they "are very, very elusive," Jewell said. "We're really talking about a remnant population."
"It's a three-day trek to get to them through the jungle from base camp. It will definitely be a challenge."
WildTrack receives help from Friends of Conservation, a nonprofit based in Cambridge, England, and SAS, a U.S. software company. The project's rhino research is funded by the National Geographic Society's Conservation Trust.
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