By Jason Palmer
Science and technology reporter, BBC News
The research followed a family of Kenyan elephants for six years
The diet and behaviour of elephants evidenced by the chemical makeup of their tail hairs shows how they compete with other species, researchers say.
The six-year study, published in Proceedings of the National Academy of Sciences, followed a single family of elephants in northern Kenya.
The study shows how the elephants lost out to cattle grazing on grasses.
It also shows the rate of conception rising as food and water resources become more abundant each year.
The study, carried out by scientists from Oxford University, is part of an ongoing research programme tracking the elephant family using GPS receivers on each individual and determining a dietary history from their tail hairs.
That history is laid out chronologically in an "isotope record" along the hair. Isotopes are naturally occurring variations of atoms that are chemically identical but have a slightly different mass.
Different food or water sources that the elephants might access contain different ratios of isotopes of carbon, hydrogen or nitrogen.
The team's prior work in 2006 showed the power of the maxim "you are what you eat"; a clear record of the elephants' diets was evident in the proteins that made up their tail hairs.
"Now, we have a long-term record so we can really see what one normal family is doing over a long period of time," said Thure Cerling, the University of Utah professor who leads the research.
In the new work, the team also analysed the content of deuterium - an isotope of hydrogen - in the elephants' tails to determine the source of the water they drink.
"During the dry season, the river they're accessing comes from quite far away, so the water has had a lot of time to evaporate and change its isotope composition," Professor Cerling told BBC News.
"Then during the rainy season, the rivers come up and the whole isotope composition changes and we're able to actually see that."
But the surprise finding came from one season in which the elephants apparently did not eat grasses that should have been readily available.
"When the rainy season comes you get this big sprouting of grasses, but they can't access it until it is 30 to 50 centimetres high," Professor Cerling said. "It's got to grow tall enough before they can actually yank it off with their trunks.
"We have this one incident where they apparently missed an entire good season of grass resource; the GPS data shows that they were outside [Samburu National Reserve] in a community area where it appears that they had to compete with cattle.
"They got out-competed in that situation."
Elephants lose out to smaller cattle, who keep grasses too short to grab
The team also noted that conceptions rose sharply just a few weeks after the rainy season brought abundant food and water.
"They bulk up during the rainy season, get into good condition, right as things are starting to get good," Professor Cerling explained.
What is more, the elephants' 22-month gestation period means that the maximum birthing period is shortly before things get good again.
"That's right when they have adequate water and just about the right time to access this high-protein grass source," he added.
The approach gives an intimate look into the elephants' behaviour and diet in a way that traditionally could not be done. While that is of tremendous academic interest to wildlife ecologists, Professor Cerling says the recent findings point to an imminent problem of broader interest.
"It points out you have to worry about the conflict of how humans want to use resources and how wildlife wants to use resources," he says.
"As we have global climate change, that's going to change the available resources. As you have populations increase - and all African populations are increasing dramatically - then you'll have more competition for the resources.
"If you're concerned about preservation of wildlife then you have to worry about that competition."