An analysis of tail hairs has revealed the dietary choices of three horse species in the Mongolian swathe of the Gobi Desert.
The endangered Przewalski’s horse, a species of wild horse that has been successfully reintroduced to the desert region, shares its pasture grounds with wild asses and free-roaming domestic horses.
Food competition among the different species had the potential to arise if supplies got scarce, especially if they made the same dietary choices.
A team led by researchers from Vetmeduni Vienna – the University of Veterinary Medicine Vienna – set out to chemically analyse the tail hairs of the animals to determine the seasonal dietary habits of the three species.
The study team, reporting in the the Journal of Applied Ecology, found that while the wild asses switched from being a grazer in the summer (eating grasses and other ground plants) to also browsing in the winter (that is, nipping foliage from trees and shrubs), the wild and domestic horses ate exclusively grass all year round. In the lean winter months, this led to increased food competition between wild and domestic horses.
This realisation could help improve wildlife management measures for the Przewalski’s horse in the future.
Przewalski’s horses were considered extinct in the wild in 1968.
Successful breeding efforts at zoos around the world helped to reintroduce the animals in the Great Gobi B protected area in southwestern Mongolia in a program which began in 1992.
The wild horses share the extreme habitat of the desert with the Asiatic wild ass, also called khulan, and the free-ranging domestic horses of local nomads.
For the preservation of the Przewalski’s horse, it is important to understand if and how the three related species compete for food in the protected area.
Martina Burnik Šturm and Petra Kaczensky, from the Research Institute of Wildlife Ecology at Vetmeduni Vienna, in cooperation with the Leibnitz Institute for Zoo and Wildlife Research in Berlin, used a special method based on the chemical analysis of tail hairs to investigate their dietary habits.
Their analysis allowed them to determine the composition of the diet of each of the three species, which led to the discovery of increased dietary competition in the winter months.
The chemical analysis of the tail hairs painted a clear picture: Przewalski’s horses and domestic horses were year-round grazers. Khulan, on the other hand, switched from grazing in the summer to a high proportion of foliage in the winter.
“When food becomes scarce in the long winter months, competition can be expected especially between the two species of horse,” explains Burnick Šturm.
In the summer, the food supply is relatively high. At the same time, the local nomads leave the Gobi and take their horses to the high pastures of the surrounding mountains.
“In the hot season, Przewalski’s horses mainly graze near sources of water,” explains Kaczensky.
“Khulan, on the other hand, also graze on pastures far from water sources as they are better able to conserve water. The potential for pasture competition in the summer is therefore relatively low among the three species in the Great Gobi B protected area,” she says.
The chemical analysis used by Burnik Šturm and Kaczensky measured stable isotopes in the tail hairs.
Burnik Šturm explains: “Stable isotopes are atoms of the same chemical element with the same number of protons but different number of neutrons and thus with different masses. The isotope values in the body tissue of living organisms are the result of the isotope values in the environment and of the animal’s metabolism.”
Grasses and shrubs in the Gobi Desert exhibit different values of carbon isotopes, which make it possible to differentiate between grazers and browsers.
Because the tail hairs of horses grow at a regular rate, they act as an archive, storing the isotope values at each growth stage. The longer the hair, the farther back into the past the researchers can look.
“If you know how fast the hairs grow, you can date specific hair segments and clearly assign them to a certain season. Consecutive hair segments therefore provide valuable information about the diet and water balance of an individual animal,” Burnik Šturm says.
International research teams, under the direction of Vetmeduni Vienna and in close cooperation with the administrators of the Great Gobi B protected area have for years been committed to the reintroduction program in the region.
The long-term goal is to establish a self-sustaining and viable population of Przewalski’s horses, but also to protect other key species such as the khulan.
An exact understanding of the dietary behaviour of the Przewalski’s horse and the khulan are important for improving the conditions in the protected area.
The high potential for pasture competition between domestic and wild horses highlights the need for stricter regulation and a restriction on the grazing of domestic horses, the researchers said. The establishment of artificial water sources should be considered to avoid infringing on the khulan’s areas of retreat.
They concluded: “In the light of increasing livestock numbers throughout Mongolia and Central Asia, we see a great need for future studies to better understand pasture competition between the full range of wild and domestic ungulates.”
Burnick Šturm and Kaczensky were joined in the research by Oyunsaikhan Ganbaatar and Christian Voigt.
Sequential stable isotope analysis reveals differences in dietary history of three sympatric equid species in the Mongolian Gobi
Martina Burnik Šturm, Oyunsaikhan Ganbaatar, Christian C. Voigt, and Petra Kaczensky
Journal of Applied Ecology DOI: 10.1111/1365-2664.12825
The study can be read in full here.