Key changes identified in the diet of Przewalski’s horses, but why?

 

Przewalski's horses became extinct across their natural rangelands, but have been reintroduced from captive stock. Photo: Natalia Spasskaya
Przewalski’s horses became extinct across their natural rangelands, but have since been reintroduced from captive stock. Photo: Natalia Spasskaya

Analysis of tail hairs from Przewalski’s horses from more than 120 years ago have identified key changes in their natural diet since their reintroduction.

Work by scientists from Lomonosov Moscow State University’s Faculty of Biology and the University of Veterinary Medicine in Vienna have shown that important changes in the horses’ diet have occurred since the end of the 19th century.

The Przewalski’s horse is a species of wild horse which inhabited the Dzungarian part of the Gobi Desert until the middle of the 20th century, before their extinction in the wild.

Several individuals survived in zoos and became the ancestors of every Przewalski’s horse living today. Until the 1990s they were kept only in zoos and breeding-grounds, but with their number growing, it was decided to try and reintroduce the species to the wild.

Now, free Przewalski’s horses can be seen in Mongolia and China.

Since the end of the 20th century, several reintroduction projects have been implemented in countries historically inhabitated by the species (Mongolia, China, Kazakhstan and, since 2015, Russia).

Dzungarian Gobi was the last region where they lived before their extinction in the wild.

There was no clear understanding of whether they preferred the desert or the steppe. Thus, different natural zones were chosen for the reintroduction.

However, after more than 20 years in Mongolia, it was found that the reproduction of animals was significantly slower in Dzungarian Gobi, with its desert and near-desert conditions, 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,” explains Natalia Spasskaya, one of the paper’s authors, who holds a doctorate. 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 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 used in the study, the findings of which have been published in the journal Scientific Reports. These hairs grow slowly and are not affected by seasonal moulting.

They were taken from the coats of the animals hunted in Dzungarian Gobi in the 19th century.

Scientists compared them to the hairs of the modern Przewalski’s horses reintroduced to Dzungaria.

For control purposes, a similar study was undertaken using museum specimens from kulans, another equidae inhabiting Dzungarian Gobi.

The researchers found that modern reintroduced Przewalski’s horses fed on herbaceous plants across 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 oasis-like areas.

But some places on the plain, and even more in the surrounding foothills, support the growth of shrubs. Their leaves were found to have been in the diets of Przewalski’s horses during winter in the 19th century.

These seasonal characteristics of Przewalski’s horses diet in the past were probably linked to the species being expelled from the steppes, most preferable to them, to the near-desert regions by the local people and their livestock.

Living in the thicket helped the horses, among other things, to hide from the hunters. This is supported by the description of the wild horses’ behavior given 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 use of fodder is seasonal, just like the Przewalski’s horses of 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 suited to desert habitats – they have more near-desert plants in their diet, and need less water 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,” Spasskaya says.

“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.”

Other collaborators in the research were the the RAS Zoological Institute in (Saint Petersburg, Russia; the National University of Mongolia; the Leibniz Institute for Zoo and Wildlife Research in Germany; the Norwegian Institute for Nature Research; and staff members of the Great Gobi B Strictly Protected Area natural reserve.

Stable isotopes reveal diet shift from pre-extinction to reintroduced Przewalski’s horses
Petra Kaczensky, Martina Burnik Šturm, Mikhail V. Sablin, Christian C. Voigt, Steve Smith, Oyunsaikhan Ganbaatar, Boglarka Balint, Chris Walzer and Natalia N. Spasskaya.
Scientific Reports 7, Article number: 5950 (2017) doi: 10.1038/s41598-017-05329-6

The study, published under a Creative Commons License, can be read here

Earlier report 

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