Abstract: Twenty-five years ago, the snow leopard Uncia uncia, an endangered large cat, was eliminated from what is now Sagarmatha National Park (SNP). Heavy hunting pressure depleted that area of most medium-large mammals, before it became a park. After three decades of protection, the cessation of hunting and the recovery of wild ungulate populations, snow leopards have recently returned (four individuals). We have documented the effects of the return of the snow leopard on the population of its main wild prey, the Himalayan tahr Hemitragus jemlahicus, a 'near-threatened' caprin. Signs of snow leopard presence were recorded and scats were collected along a fixed trail (130 km) to assess the presence and food habits of the snow leopard in the Park, from 2004 to 2006. Himalayan tahr, the staple of the diet, had a relative occurrence of 48% in summer and 37% in autumn, compared with the next most frequent prey, musk deer Moschus chrysogaster (summer: 20%; autumn: 15%) and cattle (summer: 15%; autumn: 27%). In early summer, the birth rate of tahr (young-to-female ratio: 0.8-0.9) was high. The decrease of this ratio to 0.1-0.2 in autumn implied that summer predation concentrated on young tahr, eventually altering the population by removing the kid cohort. Small populations of wild Caprinae, for example the Himalayan tahr population in SNP, are sensitive to stochastic predation events and may be led to almost local extinction. If predation on livestock keeps growing, together with the decrease of Himalayan tahr, retaliatory killing of snow leopards by local people may be expected, and the snow leopard could again be at risk of local extinction. Restoration of biodiversity through the return of a large predator has to be monitored carefully, especially in areas affected by humans, where the lack of important environmental components, for example key prey species, may make the return of a predator a challenging event.

Abstract: An inverse relationship between individual vigilance level and group size is widely reported in many behavioral studies on animals across several taxa. It is generally held that such a relationship is due to a reduced probability of an individual being killed in larger groups. in the present investigation, I studied the vigilance behavior of the endangered Tibetan argali Ovis ammon hodgsoni in relation to group size and escape terrain. I hypothesized that an individual argali has a higher vigilance level in smaller groups and in habitats closer to cliffs than individuals living in larger groups and open areas (escape terrain). The results show that the vigilance of argali decreased with increasing group size, but there was no effect of escape terrain on its vigilance behavior. There were significant differences between age-sex groups: male, female and yearling in their time budgets. Females, compared to males and yearlings, spent more time being vigilant. They also foraged more and moved less than males. It is suggested that vigilance is an important anti-predator behavior amongst argali sheep.