The oldest elephants wandering Mozambique’s Gorongosa National Park
bear the indelible markings of the civil war that gripped the country
for 15 years: Many are tuskless. They’re the lone survivors of a
conflict that killed about 90 percent of these beleaguered animals,
slaughtered for ivory to finance weapons and for meat to feed the
fighters.
Hunting gave elephants that didn’t grow tusks a biological advantage
in Gorongosa. Recent figures suggest that about a third of younger
females—the generation born after the war ended in 1992—never
developed tusks. Normally, tusklessness would occur only in about 2 to
4 percent of female African elephants.
Decades ago, some 4,000 elephants lived in Gorongosa, says Joyce
Poole—an elephant behavior expert and National Geographic Explorer who
studies the park’s pachyderms. But those numbers dwindled to triple
digits following the civil war. New, as yet unpublished, research
she’s compiled indicates that of the 200 known adult females, 51
percent of those that survived the war—animals 25 years or older—are
tuskless. And 32 percent of the female elephants born since the war
are tuskless.
A male elephant’s tusks are bigger and heavier than those of a female
of the same age, says Poole, who serves as scientific director of a
nonprofit called ElephantVoices. “But once there’s been heavy poaching
pressure on a population, then the poachers start to focus on the
older females as well,” she explains. “Over time, with the older age
population, you start to get this really higher proportion of tuskless
females.”
This tuskless trend isn’t limited to Mozambique, either. Other
countries with a history of substantial ivory poaching also see
similar shifts among female survivors and their daughters. In South
Africa, the effect has been particularly extreme—fully 98 percent of
the 174 females in Addo Elephant National Park were reportedly
tuskless in the early 2000s.
“The prevalence of tusklessness in Addo is truly remarkable and
underscores the fact that high levels of poaching pressure can do more
than just remove individuals from a population,” says Ryan Long, a
behavioral ecologist at the University of Idaho and a National
Geographic Explorer. The “consequences of such dramatic changes in
elephant populations are only just beginning to be explored.”
Josephine Smit, who studies elephant behavior as a researcher with the
Southern Tanzania Elephant Program, says that among the female
elephants she tracks at Ruaha National Park, an area that was heavily
poached in the 1970s and 1980s, 21 percent of females older than five
are tuskless. As in Gorongosa, the numbers are highest among older
females. About 35 percent of females older than 25 are tuskless, she
says. And among elephants ages five to 25, 13 percent of females are
tuskless. (Smit, a doctoral candidate at the University of Stirling,
in Scotland, says the data have not yet been published, though she
presented the findings at a scientific wildlife conference last
December.)
Poaching has also pushed tusk sizes down in some heavily hunted areas,
such as southern Kenya. A 2015 study conducted by Duke University and
the Kenya Wildlife Service compared the tusks of elephants captured
there between 2005 and 2013 with those of elephants culled between
1966 and 1968 (that is, before significant poaching took place in the
late 1970s and early 1980s) and found significant differences.
Survivors of that period of intense poaching had much smaller
tusks—they were about a fifth smaller in males and more than a third
smaller in females.
The pattern repeated in their offspring. On average, male elephants
born after 1995 had tusks 21 percent smaller than the males from the
1960s, and 27 percent smaller than the females from that period.
According to the study’s authors, “although our evidence for the role
of genetics on tusk size is indirect,” studies of mice, baboons, and
humans have similarly established that incisor size—homologous to a
tusk in elephants—is heritable and has “substantial genetic
influence.”
IMPLICATIONS OF TUSKLESSNESS
Despite the wave of human-influenced tusklessness in recent decades,
elephants missing their tusks are surviving and appear healthy,
according to Poole. Scientists say that the significant proportion of
elephants with this handicap may be altering how individuals and their
broader communities behave, and they want to find out if, for example,
these animals have larger home ranges than other elephants because
they might need to cover more ground to find recoverable foods.
Tusks are essentially overgrown teeth. Yet they’re typically used for
most tasks of daily living: digging for water or vital minerals in the
ground, debarking trees to secure fibrous food, and helping males
compete for females.
The work elephants do with their tusks is vital for other animals too.
Elephants’ “role as a keystone species to topple trees and dig holes
to access water is important for a variety of lower species that
depend on them,” Long says. Tusk action also helps create habitats.
Certain lizards, for example, prefer to make their homes in trees
roughed up or knocked over by browsing elephants.
If elephants are changing where they live, how quickly they move, or
where they go, it could have larger implications for the ecosystems
around them. “Any or all of these changes in behavior could result in
changes to the distribution of elephants across the landscape, and
it’s those broad-scale changes that are most likely to have
consequences for the rest of the ecosystem,” Long says.
Now, Long and a team of ecology and genetic researchers are starting
to study how tuskless elephants are navigating their lives. In June,
the team started tracking six adult females in Gorongosa—half with
tusks, half not—from three different breeding herds. They fitted them
with GPS collars, took blood and dung samples, and plan to monitor
them for a couple of years—or until the battery life in each of the
collars gives out—periodically taking more fecal samples to analyze
the elephants’ diet.
Their goal is to uncover more information about how these animals
move, eat, and what their genomes look like. Long hopes to detail how
elephants without the benefit of tusks as tools may alter their
behavior to get access to nutrients. Rob Pringle, at Princeton
University, plans to look at dung samples for insights about both diet
and the army of microbes and parasites that live inside each
elephant’s gut. Another collaborator, Shane Campbell-Staton, an
evolutionary biologist at the University of California Los Angeles,
will study blood, searching for answers about how genetics influences
the phenomenon of tusklessness.
Exactly how this trait is inherited is “puzzling,” Campbell-Staton
says. Tusklessness does seem to occur disproportionately among
females. It makes sense that tuskless males wouldn’t be able to
compete for breeding access to female elephants, he says. But if this
trait was traditionally X-linked—passed down along the X chromosome,
which helps determine sex and carries genes for various inherited
traits—we would think that because males always get their X chromosome
from their mothers that you’d have a really large population of males
that are tuskless. “But we don’t see that. Tuskless males are
extremely rare in African elephants,” he says.
Joyce Poole corroborates this. She says that in her entire career
she’s seen only three or four tuskless males—none of them in
Gorongosa.
WORK-AROUNDS
Although tuskless elephants’ nutritional and behavioral
characteristics haven’t yet been formally compared to those of tusked
elephants in any herd, Smit says anecdotally that in her research
she’s seen that elephants without tusks appear to have found
work-arounds.
“I’ve observed tuskless elephants feeding on bark, and they’re able to
strip bark with their trunks, and sometimes they use their teeth.”
They may also be relying on other elephants’ inadvertent help, she
says. Perhaps the elephants are targeting different kinds of trees
that are easier to strip, or trees that have already had some
stripping by other elephants—giving them a prepared leverage point for
tearing off bark.
Recent bans on the ivory trade in China and the U.S. may help reduce
demand for tusks, but exactly how long it could take a population with
a high proportion of tusklessness to recover some of its numbers—and
its tuskedness—varies. Among Asian elephants, for example, a long
history of hunting for ivory—as well as removing tusked elephants from
the wild for labor—likely helped contribute to higher tuskless numbers
there.
“If you look at Asian elephants, females don’t have tusks at all, and
depending on which population you look at in which country, most males
are also often tuskless,” Poole explains. Exactly why the Asian and
African elephant populations have such different rates of tusklessness
remains unexplained.
Yet Poole and others note that in areas in Asia that historically have
been targeted for ivory hunts, tuskless levels are high—just as in
Africa—underscoring that humans are leaving a lasting mark on Earth’s
largest land mammal.