Diet changes do not synchronize precisely with vegetation changes.

Your hair is what you eat. As it grows, hair incorporates carbon, hydrogen and other elements from food and water. So a single strand is like a core sample: chop it into short lengths, analyze each, and you have a record of dietary changes over time.

That might not be of much use for humans — the technique can’t determine, for instance, if you switched from Cheerios to Froot Loops last month. But for certain animals, the ratio of isotopes of carbon and other elements in the hair can indicate whether the animals are eating grasses or trees and shrubs and how the water supply is changing.

Thure E. Cerling of the University of Utah and colleagues have used this technique in a long-term study of elephants, analyzing the tail hair of four members of a family unit in Kenya over six years. Combining the analyses with GPS logs of the animals’ movements, rainfall records and satellite data on regional vegetation patterns, the researchers have compiled a week-by-week dietary record for the elephants. Their findings are published in The Proceedings of the National Academy of Sciences.

The researchers found that the elephants’ main food sources changed over time. During rainy seasons, the animals grazed mostly on grasses, while in drier seasons they ate mostly trees and shrubs. But the shifts did not synchronize precisely with vegetation changes. Peak grass consumption, for example, occurred about two weeks after the peak in grass growth. The researchers suggest this is because it takes a while for grass to grow high enough so the elephants can grab it with their trunks.

The study revealed other trends that have implications for conservation efforts. During one rainy season, for example, the elephants did not shift to a diet of mostly grass. The researchers suggest this was because during that time the elephants migrated into an area that was heavily grazed by cattle and lost the competition for their usual food source.

Courtesy of Mark Rosenthal