Science

Rich diet lowers stress in crop-eating elephants

An elephant and her calf seek refuge during the day in a forest patch near agricultural areas in Hassan, Karnataka.   | Photo Credit: Sanjeeta Sharma Pokharel

Elephants take a huge risk by feeding on agricultural crops. But this risk may be paying off in northern Karnataka: the rich diets could be lowering stress levels when compared with elephants in protected areas that don’t raid crops.

Crop-raiding by elephants is common in agricultural areas near wild spaces that support elephant populations. Though it may look easy, crop-raiding is an enormous gamble for pachyderms. They face various forms of human hostility — from the loud sounds of bursting crackers to chases — as farmers try to defend their crops. Wouldn’t resulting high elephantine stress levels be a deterrent to such behaviour?

To find out, a team of researchers from Bengaluru’s Indian Institute of Science (IISc) compared stress levels of crop-raiding elephants in human-dominated areas in Hassan with that of non-crop raiding elephants in the protected areas of Bandipur and Nagarahole national parks. They studied levels of faecal glucocorticoid metabolite (fGCM), a stress hormone, in 602 samples of elephant dung to study the animals’ stress signatures: the lower the fCGM levels, the lesser the stress. Surprisingly, non-raiding elephants in protected areas — that do not undergo the stress that crop raiding brings — showed higher stress levels than Hassan’s elephants.

Perplexed, researchers, including Sanjeeta Sharma Pokharel, decided to analyse food availability and diet quality available to these elephants. First, using maps, they examined the Normalized Difference Vegetation Index (a proxy for habitat quality or productivity, based on the values of greenness a habitat shows) of both areas. This clearly showed that agricultural zones had higher average NDVI values than the protected forests in both dry and wet seasons.

“This is obvious since the protected areas underwent the natural, seasonal differences in availability of forage while the agricultural landscape of Hassan was green throughout the year due to cultivation,” says Dr. Pokharel.

However, greenness does not necessarily mean edible food for elephants. So the team went back to the elephant poop they had collected and quantified the total carbon and nitrogen contents in each sample to check if the diets in both habitats were of a different quality. Interestingly, crop-raiders had higher nitrogen in their poop (a sign of higher protein in their diet) thanks to the high-quality forage — agricultural crops — they ate.

The study, published in Animal Conservation, suggests that it may be crucial to keep these physiological factors in mind while designing solutions to deal with man–elephant conflict, according to Dr. Pokharel.

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Printable version | Mar 7, 2021 9:39:46 PM | https://www.thehindu.com/sci-tech/science/rich-diet-lowers-stress-in-crop-eating-elephants/article25413344.ece

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