The gray-faced sengi is good at hiding out.
It was not until 2005 that scientists discovered this species of elephant shrew, a mammal found only in Tanzania. First captured in a camera trap image, the species was later named Rhynchocyon udzungwensis by tropical ecologist Francesco Rovero and his collaborators.
The gray-faced sengi (sengi is a Swahili name) lives in the country's Eastern Arc Mountains in the protected areas of the Udzungwa Mountains National Park and the Kilombero Nature Reserve.
Native only to Africa, elephant shrews are small mammals with long, trunk-like noses. Eighteen species of them are found in a variety of habitats, ranging from rain forests to coastal deserts, and they vary in color and size. (Related: "New Species of Giant Elephant Shrew Discovered?")
The gray-faced sengi is the biggest of the four known species of giant elephant shrews, weighing in at about 1.75 pounds (0.8 kilogram)—that's at least 25 percent larger than any other elephant shrew.
The species also has a more unfortunate distinction: It's the second most threatened of all elephant shrews—the first being the endangered golden-rumped species, which lives in drier coastal forests.
An estimated 15,000 to 24,000 gray-faced sengi exist in the wild—historic population data is unknown—and the International Union for Conservation of Nature lists them as vulnerable.
A Rain Forest Home
Little is known about the gray-faced sengi, though scientists are learning more. It's thought that they are monogamous, shy animals that make their nests among leaf litter on the forest floor. They may be one of the most ancient species of elephant shrew, but scientists lack fossil evidence to know for sure.
In an August 2013 paper published in the Journal of Mammalogy, Rovero reported an increase in the elephant shrew's range based on new camera-trap data: The species is now known to live in two distinct areas of mountainous rain forest across 150 square miles (390 square kilometers) in the Udzungwa Mountains, the Ndundulu-Luhomero, and part of the Mwanihana Forest. (See Tanzania pictures.)
Gray-faced sengi prefer gently sloping forest interiors, Rovero said, and seek areas with abundant leaf litter to build their nests, affording them protection from predators. Dense forest helps them hide from terrestrial hunters like leopards, honey badgers, and mongooses. The tree canopy also provides gray-faced sengi with good coverage from aerial predators like raptors.
To find food, elephant shrews remove leaf litter with their long foreclaws and use their specialized, elongated snouts to sniff out their next meal, likely insects and other invertebrates such as spiders and worms. Many species of elephant shrew clear pathways beneath the leaf litter in their quest for food. (Watch a video of the gray-faced sengi in Tanzania.)
To build nests, the animals collect dead leaves near the base of trees with their hind limbs and pile them up into a dome.
The gray-faced sengi's habitat of the Eastern Arc Mountains "is a biogeographically unique area, and is considered a biodiversity 'hot spot,'" said Jorge Ahumada, a tropical ecologist. Ahumada is part of a team of tropical scientists from Conservation International who are monitoring the gray-faced sengi and other species through camera traps as part of the Tropical Ecology Assessment and Monitoring (TEAM) Network, which collaborates with the Udzungwa Ecological Monitoring Centre to monitor animals in the area.
In 2008 the TEAM Network set up its first site in Africa in the Udzungwa Mountains, working with the Udzungwa center, a field station established in 2006 by an Italian museum now known as Museo delle Scienze, or MUSE, where Rovero is the curator of tropical biodiversity. The field station and TEAM site are managed by the museum in partnership with Tanzania National Parks.
Habitat protection is key to this species' survival and that of others in this species-rich area. Working in concert with the Tanzanian government and non-governmental organizations, scientists such as Rovero continue to assess the elephant shrew's population figures and range so that the animal's vital forest habitat can be conserved and protected.
"Ensuring that parks are functioning at protecting their biodiversity is the single most important action to preserve tropical forest biodiversity," said Rovero, whose 2006 elephant shrew expedition, as well as much of his subsequent evolutionary and ecological work, was partially funded by the National Geographic Society.
Though most of the elephant shrew's home is located in protected areas, the animal is still threatened by drought-driven fires and increasing pressure from people.
"Habitat loss, illegal fuel wood collection, and poaching pressures from human settlements surrounding the park are the main [threats]," Ahumada said.
In response, TEAM has set up camera-trap surveys to assess elephant shrew population numbers and data for other animals in the area.
So far the scientists have recorded as many as 30 different species through their monitoring efforts.
Other mammals in the forest include an endangered forest antelope known as the Abbott's duiker, leopards, and elephants, to which the elephant shrew is distantly related. (See pictures of more animals that live in tropical rain forests.)
The TEAM data gathered in Udzungwa provides an "early warning system to park authorities," Ahumada said, so they can better understand how these species' populations and distributions are changing in real time.
This way, "managers can react accordingly and modify their management practices," he said.
Still, the gray-faced sengi's natural ability to remain elusive and disappear into the forest floor may be the key to its survival.
Christy Ullrich Barcus is editor of National Geographic's Polar Bear Watch.