Is It an Elephant? Is It a Shrew?
No, It’s a Sengi!
No, It’s a Sengi!
When Western scientists first described these unusual animals in the 19th century, they classified them with shrews in the order Insectivora. Later biologists recognized that they were not closely related to shrews and variously classified them with rabbits, primates, and ungulates (hoofed mammals). In fact, they look like miniature versions of duikers or dik-diks, which are small African antelope. Recent genetic studies, however, suggest all of these ideas are wrong.
Elephant-shrews are an ancient group that arose in Africa and never expanded beyond that continent. Elephant-shrews share a common ancestor, estimated to have lived about 100 million years ago, with tenrecs and golden-moles, the aardvark, and, most surprising, sea cows (manatees and dugongs), hyraxes, and their namesake elephants! These superficially very different species are united under the name Afrotheria, all more closely related to each other than to any other mammals.
Scientists believe that the Afrotherians evolved and diversified in Africa, isolated for millions of years from all other mammals. Many more—and more diverse—species once comprised this group; today only about 80 species of Afrotheria survive (one aardvark, two or three elephants, four sea cows, six hyraxes, 15 sengis, 21 golden-moles, and 30 tenrecs).
Mammals we now think of as typically African, including cats and other carnivores, zebras, and antelope, arose in what are now the continents of North America, Asia, and Europe, and entered Africa only after roughly 25 million or so years ago. These competitors may have squeezed out most of the Afrotheria species, including species in four additional families of elephant-shrews that are now extinct. Elephants and sea cows expanded far out of Africa, and tenrecs reached Madagascar, but hyraxes, elephant-shrews, and golden-moles all stayed put.
Elephant-shrews are among the mere three percent of all mammal species that are monogamous, forming exclusive mating pairs. But they don’t live as cozy couples sharing food and beds. The pair spends little time together, although they occupy the same territory, which they defend against all intruders—males chase out male interlopers, females chase out females. Even mating is a brief and fairly infrequent affair, and males don’t help females care for their young.
Monogamy in elephant-shrews was first described by Galen Rathbun in the 1970s. Rathbun conducted field studies of two species—the rufous elephant-shrew (Elephantulus rufescens) and the golden-rumped elephant-shrew (Rynchocyon chrysopygus)—in Kenya. In 1976, he brought 22 of the rufous species to the National Zoo for further study. Using the insights he had gained in the field to develop appropriate husbandry techniques—in particular, housing the animals as monogamous pairs rather than in groups—Rathbun established the world’s first viable breeding colony of captive elephant-shrews.
Although they enjoy good vision and hearing, elephant-shrews explore their world nose first. The noses twitch constantly, probing and sniffing every detail of their forest floor habitats, searching for crickets, spiders, termites, ants, and other invertebrates to eat. The noses are also busy investigating the scent messages left by other elephant-shrews. As elephant-shrews travel about their territories, they rub various glands along the ground, depositing odorous secretions for other elephant-shrews to “read.”
The Nose Knows
The Nose Knows
In the early 1980s, Fred Koontz studied rufous elephant shrews in the Zoo’s collection to earn his Ph.D. He wanted to understand the messages contained in the odors produced by a large gland on their chest called the sternal gland. Males and female sternal mark, on average 15 and seven times per hour, respectively. But when defining a new territory or interacting with a new mate, both may mark as often as five times a minute.
Through an elaborate series of experiments, Koontz broke the sternal gland code. Smelling the secretions, one elephant-shrew can determine the sex of another—the sexes look identical but smell very different. Koontz himself learned to tell males and females apart by their odor—males, he found, smell “fruity,” and females “sulfurous.”
Further, he found that elephant-shrews recognize the sternal gland odors of different individuals. This is how a female knows her mate and vice versa. With both sexes constantly marking and sniffing in their territories, paired elephant-shrews regularly send and receive olfactory images of each other. So while mates spend little time physically together, they are always enveloped in each other’s olfactory aura.
While most of the small elephant-shrews are active primarily at dawn and dusk (the technical word is crepuscular), the giant elephant-shrews are diurnal—active during most of the day. At the Zoo, you will see our giants foraging for crickets and mealworms, and gathering simulated leaf litter to form the nests that they rest in at night.
Day and Night
Day and Night
Various species of elephant-shrew live throughout Africa except in western Africa and the Sahara, where they inhabit forests and dense woodlands or savannas, scrubland, and deserts. Many of the species have small or fragmented distributions, however, and of the 15 elephant-shrews, three are listed on the IUCN Red List of Threatened Species—one is near threatened, one is vulnerable, and the other is endangered.
The black and rufous giant elephant-shrew is vulnerable. It lives in only forests and dense woodlands in parts of eastern Kenya and Tanzania, habitat that is rapidly disappearing due to human development activities. People also catch and kill them for food. The Association of Zoos and Aquariums (AZA) is coordinating a conservation breeding program for the species in North American zoos.
Along with these elephant-shrews, many of the other Afrotherians are vulnerable or endangered, including all the elephants and sea cows, half of the hyraxes, and several golden-moles and tenrecs. As Galen Rathbun, now at the California Academy of Sciences and chair of the IUCN’s Afrotheria Specialist Group, points out, “By one count, the seven groups that make up the Afrotheria represent nearly a third of all the living orders of mammals. This means that with relatively few species extinctions, entire groups of Afrotherian mammals would cease to exist, thus terminating over 100 million years of evolution in Africa and drastically reducing that region's biodiversity.”
Fast Facts on the Black and Rufous Elephant-Shrew (Rhynchocyon petersi)
Parts of eastern Kenya and Tanzania
Lowland and mountain forests, dense woodlands, and coastal forest
17 to 21 ounces; nine to 12 inches head and body length plus a ten-inch tail
Estimated four to five years in the wild. Birds of prey and snakes are predators.
One or two relatively large young that are weaned at about two weeks of age.
ALL Photo by Heidi Hellmuth, Philadelphia Zoo. ALL RIGHT RESERVED