In the 19th century, wild African elephants roamed free of fences. The
migratory mega-herbivores had vast impacts on the ecology and flora of
East African habitats. But humans, in pursuit of ivory, hunted
elephants relentlessly—and continue to do so. According to the Great
Elephant Census, the savanna elephant population declined 30 percent
in 15 countries between 2007 and 2014.
Scientists have had trouble tracing the geographic origins of most
ivory from the 19th century, when the international trade intensified.
But a new study, published last month in PLoS ONE, made headway in
classifying the sources of historic ivory in natural history and
museum collections. This led to an improved picture of 19th century
trade patterns, illustrating that most ivory came from East Africa’s
tropical interior. Using the study’s methodology to analyze modern
ivory, scientists can trace elephants most at risk of poaching or
habitat loss today.
“Humans have sought after elephants for millennia for their ivory.
It’s had a major impact,” said lead scientist Ashley Coutu, an
archaeologist at the University of York in the U.K.
The analysis by Coutu’s team relied on different chemical structures
of each element, such as carbon and oxygen, called isotopes. These
variations exist naturally, and are stored in both living and
nonliving things.
When animals eat and drink, they “incorporate varying amounts of each
isotope and metabolize them differently,” said Coutu. By analyzing the
levels of these isotopes preserved in tusks, hair and other tissues
from elephants, scientists can trace their diets, habitats, and
migration patterns across the East African landscape.
East Africa features strikingly different settings: lush coastal
forests, dry open savannas, and tropical inland forests. Each dynamic
habitat has a unique patchwork of trees and grasses, which normally
carry different mixtures of the isotopes measured by Coutu’s team.
Elephants aren’t picky eaters; they’ll munch on most vegetation. And
as the pachyderms feed and drink from watering holes, they take up
elements and their isotopes into their hair, teeth, and tusks.
In the study, the researchers analyzed carbon, oxygen, nitrogen, and
strontium isotopes from poached elephant tusk, bone, and tooth
samples. Carbon, oxygen, and nitrogen contain clues about the climate,
rainfall, and distance from the Indian Ocean where an elephant lived
and ate. Strontium preserves hints of the geologic landscapes where an
elephant roamed.
The team picked away at old billiard balls, piano keys, cutlery
handles, and other ivory commodities from African, European, and
American collections—sourced from about 100 elephants—and analyzed the
remnants of tissue within.
“We could see patterns in the isotope data across the East African
region that helped us characterize elephants to different habitats,”
said Coutu. She added that many piano keys and ivory cutlery handles
“had isotope values that matched elephants which lived in tropical
rainforests” in East Africa’s interior, supporting earlier evidence
that hunting eradicated elephants from the coastal areas of southern
Kenya and northern Tanzania by the mid-1800s, pushing poaching inland.
But isotopes are only one tool; they are limited in what they can reveal.
“We’re never going to use these isotopes alone to map everything out,”
said Matt Sponheimer, a biological anthropologist at the University of
Colorado, Boulder in the U.S., who has conducted similar research.
But the study contributes to a growing body of data that helps
scientists track and grasp the unique life history of the African
elephant. The more scientists learn about this, the better they can
work toward protecting modern-day elephants.
“This is something that began and was acceptable for so many years. If
you look around and look at the poaching today, it’s in the same
places,” said Nancy Cohn, a trustee at the Deep River Historical
Society in Connecticut.