[LINK] "Massacres Alter Social Structure of Africa’s Elephants"
Writing about elephants, ScienceNOW's Virginia Morell notes the sociological and demographic impacts of poaching on elephant populations. They're worrisome: leaving aside the actual decreases in the number of elephants, the selective killing of older elephants destabilizes the family groups that form the nuclei of elephant society. Even the baby boom that the researchers note is worrisome, indicating that the elephants' habitat can support far more elephants than actually live.
Poachers are slaughtering elephants across Africa at an unprecedented pace. But scientists tracking the animals’ carcasses—their faces and ivory hacked away—are seldom able to explain in detail what these deaths mean to the pachyderms’ populations and social structure. Now, a 14-year study of elephants in northern Kenya concludes that the adult behemoths are more likely to die at the hands of humans than from natural causes. At the same time, the elephants have responded to the heavy poaching with a baby boom, providing the researchers some hope for the jumbos’ survival.
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In 1997, the scientists began a study on elephant behavior in two adjacent national reserves, Samburu and Buffalo Springs, which together measure 220 square kilometers. The parks’ elephants were accustomed to vehicles and easy to study; they had also recovered from heavy poaching in the 1970s. At the beginning of the study, illegal killing was rare. “We might lose one big male a year,” says George Wittemyer, a wildlife biologist at Colorado State University, Fort Collins, and the study’s lead author. “We thought the population was stable.” That changed in 2009 as poachers began shooting elephants en masse. The scientists then shifted their study to look at the effects the poaching was having on the elephants they knew.
At the study’s outset, the researchers focused on 934 individuals (509 females and 425 males). The team used a standard method for identifying each elephant, noting each animal’s unique markings on its ears and face, as well as the shape of its tusks. Then each week, from 1997 to 2011, the researchers drove along five, 20-kilometer routes inside the reserves and recorded the presence or absence of the study elephants. They considered any animals that they didn’t spot for more than 3 years to be dead. The scientists seldom found the carcasses of these animals, but they investigated any dead elephants reported by tourists or rangers that were inside the parks or within 10 kilometers of the reserves’ boundaries.
Although the elephant population was increasing when the study began, it began to decline as poachers targeted the animals. The older elephants, which have larger tusks, were especially hard hit. In 2000, there were 38 males over 30 years old in the study population. By 2011, their number had dropped to 12—and of those, seven had matured into this age class. Older females also suffered huge losses, with almost half of those 30 years old dying between 2006 and 2011. By 2011, 56% of the elephants that were found dead had been poached, the team reports online today in PLOS ONE.
The poaching spree has also altered the elephants’ social organization, the study shows. When the work began, males made up 42% of the population; by 2011, they had been cut down to only 32%. And 10 of the 50 elephant family groups that the scientists were studying were effectively wiped out. “They no longer have any breeding females,” Wittemyer explains. “And so, the family group has disappeared, leaving surviving juveniles on their own.” These youngsters may join other families, or, without a leader to guide them, try to survive in sibling groups typically led by the oldest sister.
“Some elephants died from a bad drought that hit the region between 2009 and 2010,” Wittemyer adds. “But at least half of these deaths were due to poaching.” The poaching took place outside the reserves on lands that are largely unpatrolled. In addition to the reserve, the elephants roam over a vast area of more than 3500 square kilometers.