Lewis the Elephant's Hair Raising Tale

Elephant B1013, known affectionately as Lewis, marched to the beat of his own drummer. One of the subjects of a recent study of migratory patterns in African elephants, Lewis behaved very differently from the other test elephants-and in doing so, helped prove the effectiveness of a brand-new technique for tracking the endangered pachyderms. The method, which measures ratios of isotopes (varieties of an element that differ in the number of neutrons in the nucleus) in elephant tail hairs, provides detailed information on one particular area of elephant activity: eating. Analyzing a single hair can give researchers the equivalent of an elephant food diary, divulging what a beast ate and where he ate it for a year or more. Lewis's particular food preferences ultimately doomed him, but the information his isotope analysis provided may help conservationists prevent future elephants from meeting a similar fate.

African elephants are endangered, and Kenya, among other nations, has set aside land for sanctuaries to try to protect the elephants that remain. But elephants do not always cooperate by staying within the sanctuaries. When they venture out of bounds, they often have run-ins with humans, especially farmers who don't take well to elephants raiding their crops-and these encounters rarely end well for the elephant. Tracking elephant movement is important for conservationists' efforts to keep the animals out of danger, and for a number of years, scientists have followed elephants using global positioning system (GPS) technology. While GPS provides detailed information on where an animal goes, it tells researchers nothing about why the animal travels or what it does in various locations. Thure Cerling, a geochemist at the University of Utah who headed the new isotope study, set out to supplement satellite data with information on what motivates elephants to migrate.

Cerling's technique relies upon two well-established scientific factors. First, different types of plants, and plants in different geographic regions, contain distinct ratios of certain isotopes. Vegetation in and around the Samburu National Reserve in Kenya, where the research took place, can be broken into two broad categories: grasses, and trees and shrubs. One factor that distinguishes these families of plants is the way they photosynthesize-grasses utilize a system called the C4 pathway, while trees and shrubs (called browse plants) use the C3 pathway. Photosynthesis fixes carbon, meaning that it changes it from being part of a gas (CO2) to being part of a solid (glucose). It turns out when plants fix carbon, they favor a certain carbon isotope, 13C (carbon with 7 neutrons and 6 protons) or 12C (carbon with 6 neutrons and 6 protons), depending on which photosynthetic pathway they use. As a result, grasses and browse plants end up with a different ratio of the two isotopes in their cells. In other words, grasses and shrubs leave distinct, discernible chemical traces behind, even long after the plants are completely broken down.

The second factor crucial to isotope tracking is what happens to these isotopes when they enter an animal's body. Animals use nutrients from the food they consume to assemble new cells and tissues, and since no mammalian biochemical processes make any distinction between carbon isotopes, they use whatever happens to be floating around. If an elephant is eating mostly grasses, the 13C/12C ratio in its new cells will be roughly the same as in grass. By measuring isotope levels in animal cells, scientists can figure out what the animal has been eating.

In most cells of the body, isotopes turn over pretty quickly, meaning that scientists would have to get samples frequently to develop a picture of what an animal ate over time. Cerling's team found an ingenious solution to this logistical challenge-they analyzed hair. Hair is almost entirely dead tissue, with new, live material added only at the root. A single elephant tail hair can be half a meter (1.6 ft) long, and will typically have been growing for over a year. Since new material is added to hair at a steady rate, and the new hair growth always reflects the isotopes in the animal's system at that moment, a single tail hair encodes a record of an elephant's diet for a full year or more.

Cerling's team chopped tail hairs collected from Lewis and the 6 resident elephants into tiny sections and measured the 13C/12C ratios in each section. They also analyzed isotopes of a second element, nitrogen, because it has been found that plants in different geographic areas fix the nitrogen isotopes 15N (8 neutrons and 7 protons) and 14N (7 neutrons and 7 protons) in distinct quantities. Researchers used this data to chart the animals' grass and browse consumption, as well as the locations in which they were eating, over a six-month period.

The results showed a striking difference between Lewis and the other elephants. Resident elephant diets followed a clear seasonal pattern, with grasses making up the bulk of their diet during the wet season, when those plants are abundant in the Samburu Reserve. During the dry season, when grass was sparse, the resident elephants switched to trees and shrubs. Lewis, however, showed a high level of grass consumption even during the dry season. From 15N/14N ratios, the scientists could tell that the grasses he was eating during the two seasons did not come from the same place; when dry weather hit, Lewis abandoned the reserve and headed for the Imenti forest, a region bordering farmland. Based on his isotope record, the researchers concluded that while other elephants made do with sub-par browse food in the reserve, Lewis spent the dry season feasting on corn, the most abundant crop in the Imenti region.

Iain Douglas-Hamilton, a member of Cerling's team, explained to Scientific American what would motivate bull elephants like Lewis to migrate in search of food. "If they are to succeed in sexual contests for females, they need high-quality food to build up their strength, hence the reason for high-risk crop raiding" he said. But while Lewis's adventures might have helped him in the short run (isotope analysis doesn't provide any information on mating habits, so there's no way to know for sure), ultimately they did not pay off. That's because in seeking out nutritious food, Lewis ended up in a face-off with humans, and the humans had guns. He was shot several times, and died a year after the study ended.

The researchers hope that Lewis's sad demise could lead to better conservation programs for African elephants, and perhaps prevent deadly human-elephant encounters in the future. "Tracking stable isotopes in an elephant's diet.provide a powerful new tool for conservationists," Douglas-Hamilton said. By shedding light on elephant motivation, it should help environmental policymakers "see how management plans can be focused on understanding [elephants'] basic needs for space." In the meantime, the research has proven that you really are what you eat- at least if you're an elephant.

Sources

Carey, Bjorn. "Elephant Tails Tell Tale of Diet, Migration." LiveScience, (January 3, 2006) www.livescience.com/ animalworld/ 060103_ elephant _tails.html.

Cerling, Thure E. et al. "Stable Isotopes in Elephant Hair Document Migration Patterns and Diet Changes." Proceedings of the National Academy of Sciences, January 10, 2006, page 371.

Wong, Kate. "Isotopes and GPS Reveal Secrets of Elephant Migration and Diet." Scientific American, (January 3, 2006) www.sciam.com/ article.cfm? articleID= 00075A66- C7DB- 13B9- 87DB83414B7F0000& c=I100322.