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Indian tigers more stressed than their Russian cousins, shows study

  • Indian tigers more stressed than their Russian cousins, shows study
    Indian tigers more stressed than their Russian cousins, shows study

With its bright orange coat and dark stripes, the majestic tiger strikes fear and wonder in the hearts of people, and is thus the protagonist of numerous literary works. This big cat, which is now endangered, once roamed across much of south, south-east and central Asia. Today, there are two recognised subspecies of tigers, and nine geographical populations found in a few wild havens within the historical range. Their numbers have dwindled over the years, and roughly 3,890 of them roam in the wild. Their populations in these locations face different environmental conditions, and very few studies have analysed data across these multiple populations.

In one such study, researchers from two Russian institutes—A.N.Severtsov Institute of Ecology and Evolution and Moscow State Agricultural University, and the Centre for Cellular and Molecular Biology, India, have compared the chemical contents of the faecal matter of the Amur and Bengal tigers. Amur or Siberian tigers are found in the eastern parts of Russia, while Bengal tigers are found across the Indian subcontinent. The study was published in the journal PLOS One and was partially funded by the Department of Science Technology, Government of India.

The study investigates the difference in the concentration of faecal glucocorticoid metabolites (FGCM) of the two tiger populations and tests three different extraction methods. “Faecal glucocorticoids show the welfare level of an animal. Lower levels of faecal glucocorticoids indicate fewer negative stressors in the animal's environment,” says Dr Sergey Naidenko, Deputy Director at the A.N.Severtsov Institute of Ecology and Evolution, and an author of the study.

When researchers study wild animals, they prefer to collect the samples quickly and efficiently without disturbing the animals.“The non-invasive method helps to understand the physiology of animals without collecting blood samples, it is stress-free hence allowing a long term collection of sample is possible”, adds Dr. G Umapathy one of the authors of the study. Such non-invasive methods are crucial for animals like the tiger, which are legally protected. However, many of these researchers follow various protocols for sample analysis in different labs and hence, the results of their studies cannot be directly compared. The researchers of the current study have tried to identify the best protocol for analysing faecal samples of tigers using three such methods.

In the first approach, they used the wet faecal samples directly from the field without any manipulation, while the other two methods used dried faecal matter. Faecal samples collected from tigers in India was dried and boiled multiple times in ethanol before testing it for the presence of metabolites. For those collected from Russian tigers, these steps were repeated in addition to two more methods, which involved exposing the faecal matter to methanol and then testing it directly without boiling. These steps were followed for wet and dry faecal matter, resulting in a total of three methods.

The results of the study showed that testing wet faecal matter recorded the highest concentration of FGCMs, followed by methanol, and ethanol and boiling methods for dry samples respectively. These results highlight that the method used for the Indian population which consists of boiling the sample could lead to the disintegration of some metabolites due to heat exposure.

“They are all valid, but the most suitable method or the most feasible for the technicians is wet methanol method. However, to compare the data we need to use the same method for all samples,” adds Dr Naidenko, when asked about what would be the most suitable method to record FGCMs in the future.

The researchers also found that among the Indian tigers, those in the Kanha reserve had the highest levels of FGCMs, followed by those in Bandhavghar and Sariska reserves. However, these differences were not significant. When compared with their Russian counterparts, whose samples were extracted by the same method, the researchers found that Indian tigers have a 20% higher FGCM level than the Amur tigers, indicating a higher stress.

This result has stumped the researchers too! “Previously, we showed that GC level in Amur tigers increased with the decrease of air temperature in winter. The low winter temperature, which can reach minus 40 degrees centigrade in the winter, is a big issue for Amur tiger. Actually, we hoped to show that Amur tiger suffering in comparison with Indian ones, but the results were completely different,” remarks Dr Naidenko.

The researchers suggest that the higher levels of FGCMs in Indian tigers may be a result of the stress these tigers experience in Indian jungles as they are confined to smaller territories. The visit of 300 to 500 tourists per day in the forests to have a glimpse of these cats could further stress them out, they say. The findings of the study highlight a need for better tourism management in our national parks that take the welfare of the animals into consideration.