Credit: Natalia Spasskaya
A scientist from the Lomonosov Moscow State University's Faculty of Biology together with her colleagues has explained the changes in modern Przewalski's horses' food reserve (diet) that have occurred since the end of the 19th century. The results were published in the Scientific Reports journal.
Przewalski's horse is a species of wild horses, which had inhabited the Dzungarian part of the Gobi Desert until the middle of the 20th century, but went extinct by human's fault. Several individuals survived in zoos and became the ancestors of every Przewalski's horse living nowadays. Until the 90s they only were kept in zoos and breeding-grounds, but with their number growing, it was decided to try and reintroduce the species to nature. Now free Przewalski's horses can be seen in Mongolia and China. It is a rare example of man rectifying his mistakes.
Since the end of the 20th century in different countries which Przewalski's horses had historically inhabited (Mongolia, China, Kazakhstan and, since 2015, Russia) several projects of reintroduction (resettlement) of the horses to nature have been implemented. Dzungarian Gobi was the last region where they lived, and the wild horses had been exterminated too fast by humans, so there was no clear understanding of whether they prefer desert or steppe communities. Thus, different natural zones were chosen for the reintroduction. However, more than 20-year existence of the horses in the nature of Mongolia has shown that in Dzungarian Gobi (with desert and near-desert conditions) the reproduction of animals was significantly slower, than in the steppe part of the country.
"The purpose of our research is to find out whether the conditions for Przewalski's horses' existence, in particular their food reserve, have changed in Dzungarian Gobi since the end of the 19th century", – says Natalia Spasskaya, one of the paper's authors, who holds a Ph. D. in Biology and works as the academic secretary of the Zoological Museum of M.V. Lomosov Moscow State University.
To answer this question, the researchers have studied the quantity of the stable carbon isotope 13C in the Przewalski's horses' tail hairs. This isotope occurs in the tissue cells of herbaceous plants in different quantities than in the cells of woody plants, and comes into herbivorous animal bodies through food, where it fits into newly-formed chemical agents. Thus, by its quantity it is possible to determine whether the animal was grass-eating or leaf-eating.
Samples of hair from the tails of adult Przewalski's horses were taken into study. These hairs grow slowly and are not affected by seasonal molting. They were taken from the coats of the animals hunted in Dzungarian Gobi in the 19th century. Such specimens are singular and are only kept in the RAS Zoological Institute in Saint-Petersburg and in the Zoological Museum of MSU. Scientists compared them to the hairs of the modern Przewalski's horses, reintroduced to Dzungaria. Also, for control of the results, a similar study, also using museum specimens, has been done on kulans, who are another Equidae species inhabiting Dzungarian Gobi.
In the course of their work the researchers found out that modern reintroduced Przewalski's horses feed on herbaceous plants at all seasons, but in the 19th century it constituted their diet only in summer. Herbaceous plants, mostly grasses, grow in the Dzungarian Gobi's plains near springs, making a kind of oases. But some places on the plain, and even more in the surrounding foothills, are also inhabited by shrubs. Their leaves were in the ration of Przewalski's horses at wintertime during the 19th century.
These seasonal characteristics of Przewalski's horses diet in the past are probably linked to the species being expelled from the steppe communities, most preferable for them, to the near-desert biotopes by the local people and their livestock. Living in the thicket helped the horses, among other things, to hide from the hunters. This fact is supported by the description of the wild horses' behavior made by the Grumm-Grzhimaylo brothers in 1890s, as well as by the memoirs of local people who still saw Przewalski's horses in 1930s-1950s. Reintroduced horses are treated differently now: they live in the protected area, where there are no people or livestock, and have become a national symbol and a tourist brand in Mongolia.
The study has also found that there were no changes in kulans eating behavior. Their usage of fodder is seasonal, like in Przewalski's horses in the 19th century. Like them, kulans are challenged by the growing numbers of people and livestock. Earlier they were hunted actively, but even now, despite them being a protected species, there is a significant level of illegal hunting, so kulans still avoid humans. At the same time, they are more fit for arid (desert) habitats: they have more near-desert plants in their diet, and they depend on watering less than horses. Thus, in the last century, this species has not changed its eating behavior.
"The results of the study also suggest that, in the future, the growing populations of Przewalski's horses will cause conflicts with the local cattle farmers. The future reintroduction projects – projects of resettling animals to their natural habitats – should be aimed at rehabilitating Przewalski's horses in herbaceous communities, most preferred for this species' subsistence, and must at the same time consider the higher risk of a man-induced pressure" – Natalia Spasskaya concluded.
It is remarkable that, using new methods of study, the scientists have managed to get the answers from more than hundred-year-old materials from a museum. This fact demonstrates one more time the enduring value of scientific museum collections.
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The work was done collaboratively with the scientists from the Vienna University of Veterinary Medicine (Austria), the RAS Zoological Institute (Saint-Petersburg, Russia), National University of Mongolia, the Leibniz Institute for Zoo and Wildlife Research (Germany), the Norwegian Institute for Nature Research, and with the members of Great Gobi B Strictly Protected Area natural reserve staff (Mongolia).
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Related Journal Article
http://dx.doi.org/10.1038/s41598-017-05329-6
