Abstract: Historic overlap zones of wild equids were small in Africa but extensive for Przewalski`s horses and Asiatic wild asses in Asia. Currently the Great Gobi B Strictly Protected Area in SW Mongolia is the only place where sympatric, free-ranging populations of these equids occur. This provides an unique opportunity to examine the co-existence of these little studied species and test the hypothesis that Przewalski`s horses are primarily adapted to mesic steppe habitats, whereas Asiatic wild asses are adapted to arid desert steppes and semi-deserts.
We monitored 9 Przewalski`s horses and 7 wild asses with satellite telemetry and superimposed the data on a habitat map derived from remote sensing (LANDSAT TM & ETM+-data) and ground sample plots. We tested for habitat preferences comparing use and availability with a logistic regression mixed model approach. Individuals were treated as random factors. Factor variables were tested for significant differences in subsequent Tukey post-hoc tests. Przewalski`s horses had non-exclusive home ranges of 152-826 km² and heavily selected for the most productive riparian plant communities. Asiatic wild asses also had non-exclusive home ranges, but with 4,449-6,835 km² they were 10 times larger than those of Przewalski`s horses. Asiatic wild asses seem to use plant communities more or less relative to their availability. Our results provide evidence for two parallel resource selection strategies. Our findings indicate that the Gobi areas provide an edge, rather than an optimal habitat for Przewalski`s horses. This leaves only small and isolated pockets of suitable habitat for future re-introductions. Asiatic wild asses, on the other hand, need access to large tracts of land to cope with the unpredictable resource distribution of the Gobi. Thus, Asiatic wild ass conservation requires a large scale approach.

Abstract: The Przewalski's horse (Equus caballus przewalskii) was extinct in the wild by the mid 1960s. The species has survived because of captive breeding only. The Takhin Tal reintroduction project is run by the International Takhi Group; it is one of two projects reintroducing horses to the wild in Mongolia. In 1997 the first harem group was released. The first foals were successfully raised in the wild in 1999. Currently, 63 Przewalski's horses live in Takhin Tal. Little information exists on causes of mortality before the implementation of a disease-monitoring program in 1998. Since 1999, all dead horses recovered (n = 28) have been examined and samples collected and submitted for further investigation. Equine piroplasmosis, a tick-transmitted disease caused by Babesia caballi or Theileria equi, is endemic in Takhin Tal and was identified as the cause of death of four stallions and one stillborn foal. In December 2000, wolf predation was implicated in the loss of several Przewalski's horses. However, thorough clinical, pathologic, and bacteriologic investigations performed on dead and surviving horses of this group revealed lesions compatible with strangles. The extreme Mongolian winter of 2000-2001 is thought to have most probably weakened the horses, making them more susceptible to opportunistic infection and subsequent wolf predation. Other occasional causes of death since 1999 were trauma, exhaustion, wasting, urolithiasis, pneumonia, abortion, and stillbirth. The pathologic examination of the Przewalski's horses did not result in a definitive diagnosis in each case. Several disease factors were found to be important in the initial phase of the reintroduction, which could potentially jeopardize the establishment of a self-sustaining population.