An elephant’s tale – Science Spot

Chemical analysis could help elephants and people live more harmoniously in countries such as Kenya where large free-roaming herds can wreak havoc on villages, livestock, and farmed crops. Researchers at the University of Utah analysed chemicals in elephant tail hair from those animals tagged with radio-GPS collars and so could track the diet and movements of the elephants across Kenya.

Elephants are endangered internationally, but their actual status varies from local abundance in parts of southern Africa and in some protected areas elsewhere, to critically endangered in vast regions of central Africa, despite the global ivory trade ban implemented in the 1980s. The animals need a vast territory across which to roam but increasing human population means an inevitable conflict of interest.

Thure Cerling

Geochemist Thure Cerling and colleagues determined the stable isotopes of carbon and nitrogen in African elephants’ tail hair to help them correlate what the animals ate with where they ate it on the basis of GPS (Global Positioning System) data. Isotopes are atoms of the same element, but having a different mass because of there are more or less neutrons in the nucleus. Stable isotopes are those that do not decay radioactively. Because environmental factors affects the proportions of various isotopes of hydrogen, oxygen, carbon and nitrogen in animals, plants, soil and air, stable isotope analysis has been used as a way to learn how ecosystems work.

The foot-long hairs were collected when the elephants were briefly immobilized with drug-laden dart guns so they could be fitted with GPS radio-tracking collars or new batteries for the collars. Cerling then calculated the rate of tail hair growth for the seven elephants studied. Recent hair growth contains isotopic clues to the elephant’s recent diet and environmental conditions; isotopes in older hair farther down the tail represent progressively older diet and environmental conditions.

Elephant (Credit: David Bradley)

Ratios of the rare nitrogen-15 to common nitrogen-14 in tail hair revealed information about diet and environment. Plants in dry areas like Samburu have high ratios, while plants in wetter areas – such as forests on Mount Kenya – have lower ratios.

Ratios of rare carbon-13 to common carbon-12 also reveal information about diet because plants fall into two groups with two methods of photosynthesis. Plants with so-called C3 photosynthesis include trees and shrubs, and have a relatively low carbon-13 to carbon-12 ratio. Plants with C4 photosynthesis include warm season tropical grasses, corn, millet and crabgrass, and have a fairly high ratio of carbon-13 to carbon-12. A section of elephant tail hair with a low carbon-13 to carbon-12 ratio indicates the elephant was eating trees and shrubs at the time that section of hair grew, while a high ratio indicates they ate tropical grasses – or perhaps a crop like corn.

The researchers found that isotopes in the tail hair of six elephants had high 15N:14N ratios, indicating they spent their time in the arid lowlands of Samburu. Most of the time, they had low ratios of 13C:12C, indicating they ate trees and shrubs. But during the rainy season – as indicated by satellite photos – they had higher 13C:12C ratios because they ate grasses that flourished in the wet weather.

Cerling says it is important to quantify how much of elephants’ diet comes from crops. It’s going to help resolve elephant-human conflict by quantifying the crop damage done by elephants. Areas open to elephants are getting smaller and smaller, so we need to know how important different foods are to their diets in different areas.

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