Analysis of hair samples dating back more than 120 years have been used to reveal an important change in diet between the reintroduced Przewalski’s horses of today and their forebears.
The Przewalski’s horse, also called Takhi or Mongolian wild horse, is the only remaining wild horse species.
In 1969, the horses were officially declared extinct in the wild. However, a few animals survived in captivity. Thanks to a careful breeding programme, the first captive-bred wild horses were returned to the wild in 1992.
A team of researchers from the Research Institute of Wildlife Ecology from the University of Veterinary Medicine, Vienna, has discovered through tail-hair analysis that, before their extinction in the wild, Przewalski’s horses had been on a different diet than today.
Petra Kaczensky and Martina Burnik Šturm, reporting their findings in the journal Scientific Reports, found that before their extinction in the wild Przewalski’s horses were on a mixed diet. In summer, they only ate grass. In winter, they added less nutritious bushes to their diet.
Following their reintroduction, the animals opt to eat high-quality grass throughout the year.
The study team puts the change down to a release from the hunting pressures of the past.
“We explain this dietary shift by an improved human attitude. In the past, humans considered Przewalski’s horses as pasture competitors and hunted them as a food source,” explains Burnik Šturm.
“The nutritious pastures were reserved for domestic sheep and cattle. Thus, access to pastures in winter was difficult for wild horses. Shrubs and bushes were the only alternative.”
Unlike in former times, Przewalski’s horses are today worshipped as “holy animals” in the Gobi Desert.
They are fully protected and are no longer hunted by humans.
“The wild horses can now feed on grass throughout the year because humans allow it,” says wildlife biologist and lead author Petra Kaczensky.
In the last 120 years, the habitat of the wild horses in Southwest Gobi has hardly changed. The available food resources have remained the same. But the social acceptance of Przewalski’s horses has changed.
The situation is different for Asian wild asses, or Khulan, which also live in the Gobi Desert. Although they are also a protected species, they are less appreciated than wild horses among the people. They are still hunted by humans and chased away from nutritious pastures.
Khulan feed on grass only during summer, but in winter mainly feed on bushes and shrubs, just as the Przewalski’s horses had in the past.
“In Khulan, we clearly see the influence of humans on the animals’ way of life. The attitude towards the animals in society significantly influences their feeding behaviour,” says Kaczensky.
A common method to understand the animals’ ecology and behaviour is to analyse the chemical composition of its hair. This involves the analysis of stable isotopes, which are variants of the same chemical element with different atomic weights,containing the same number of protons, but different number of neutrons. The isotope ratios of hydrogen, oxygen, carbon and nitrogen in a sample provides essential information on the animals’ water uptake, nutrition and habitat.
Historic Przewalski’s horse and Khulan hair samples were provided by the Zoological Museums in St Petersburg and Moscow.
“These more than 120-year-old hair samples are as useful and informative as freshly collected ones,” explains Burnik Šturm.
For the isotope analysis, the tail hair is cut into one centimetre long segments and placed individually in little tin or silver cups before being burnt at high temperature. Isotopes are then measured in the developing gases using mass spectrometry, a method to sort individual atoms by mass.
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