Elephant population numbers dropped from 2, individuals to around in the early s, reports Nicola Jones for Nature. However, many female elephants that survived poaching during wartime were overlooked because they were already naturally tuskless. So, after the war ended, female elephants that naturally lacked tusks were more likely to pass down genes coding for tusklessness, per the New York Times. To see how the ivory trade and poaching pressures may have amplified natural selection towards tuskless elephants, researchers started collecting data on the elephants at Gorongosa National Park.
However, they noticed that the elephants with no incisors were usually female. The park has never seen a tuskless male, suggesting the trait related to tusklessness is sex-linked. Females are smaller, weighing up to 3, Kg 7, lb. Elephants are unusual among mammals in that they continue to grow throughout their life, although their rate of growth slows after they reach sexual maturity.
Elephant home ranges vary from population to population and habitat to habitat. Individual home ranges vary from 15 to 3, square kilometers , square miles. Elephants are not territorial although they utilize specific home areas during particular times of the year. Elephants communicate with each other in many ways and with all their senses.
They rely less on their eyes than humans do but visual signals are important and the position of their ears and trunks show what mood they are in. Their sense of smell can tell them something about another elephant's health or sexual condition. Touch can also be used to convey some information. However, the main way an elephant communicates deliberately is by sound. Elephant vocalizations range from high-pitched squeaks to deep rumbles, two-thirds of which are emitted at a frequency too low for the human ear to detect.
Such low frequency calls may be heard by other elephants at distances of at least eight kilometers. Recent studies also show that foot stomping and low rumbling emitted by elephants generate seismic waves in the ground that can travel nearly 20 miles along the surface of the Earth.
Elephants may be able to sense these vibrations through their feet and interpret them as warning signals of a distant danger. They may therefore be communicating at much farther distances than previously thought. Elephants do have remarkable memories. In the wild, elephants appear to remember for years the relationships with dozens, perhaps hundreds of other elephants, some of whom they may see only occasionally.
They also have an impressive memory for places to drink and to find food. This information gets passed on from generation to generation.
Elephants live in a social hierarchy dominated by older females. Females travel in long-lasting social units of about half a dozen adult females and their offspring, with the unit being led by a single older female, the matriarch. Males do not maintain long-term social bonds, remaining in the unit only into their teens. They then live out their lives in loose bachelor groups or wandering on their own.
To test the importance of the age of the female leader of the individual units, researchers from the University of Sussex, the Institute of Zoology in London and the Amboseli Elephant Research Project in Kenya used high-powered hi-fi equipment to play back the sounds of elephant calls.
Calls from complete elephant strangers prompted the mothers to cluster around their young defensively, while familiar calls were ignored. The units led by the oldest matriarchs, those with the most experience, were best able to distinguish between friends and those that might present problems by harassing calves or starting disputes. If these key individuals cannot immediately distinguish between potential threats, their families may spend too much time being defensive and not enough time reproducing.
In fact, the scientists found the age of the matriarch to be a significant predictor of the number of calves produced by the family per female reproductive year. These findings present important implications for conservation of elephants because older, larger animals are more likely to be targets for hunters and poachers, and killing these individuals could weaken entire family units for years.
That is 5kg more than the average weight of an adult human. Thanks to protection from the president of Kenya at the time, Ahmed got to live out his life in full, dying of old age in Sadly this is not the case for many elephants. Humans have long been attracted to the beautiful tusks of elephants. Ivory remains one of the most highly prized materials in the natural world. Those targeted are often the oldest and largest animals — because they have the biggest and therefore most valuable tusks.
This is not only tragic for individual animals, but also for the wider elephant population , as the oldest and wisest elephants play a key leadership role in elephant society. In fact, we conducted experiments showing that the oldest elephant matriarchs — the female leaders of the family groups — were much better than younger matriarchs at distinguishing more dangerous male lions from female lions using just the sound of their roars. Now, these elephants are likely to be at an advantage as they are much less likely to be targeted by poachers.
A greater chance of surviving and breeding might explain why these tuskless animals have become more common in the population. Studies are underway to determine whether that is the case. 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.
Elephants are highly social and form tight family groups. 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. 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.
Tusklessness does seem to occur disproportionately among females. Joyce Poole corroborates this. 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. 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.
Exactly why the Asian and African elephant populations have such different rates of tusklessness remains unexplained. All rights reserved. Wildlife Watch is an investigative reporting project between National Geographic Society and National Geographic Partners focusing on wildlife crime and exploitation. Send tips, feedback, and story ideas to ngwildlife natgeo.
Share Tweet Email. Why it's so hard to treat pain in infants.
0コメント