Estimation of blue sheep population parameters in the Dhorpatan Hunting Reserve, Nepal

Achyut Aryal^1,2*, Sven Gastaur², Steffen Menzel², Til Bahadur Chhetri² and Jack B. Hopkins³

¹Ecology and Conservation Group, Institute of Nature Sciences, Massey University, New Zealand.

²The Biodiversity Research and Training Forum (BRTF), Nepal.

³Department of Ecology, Montana State University, Bozeman, MT 59717-3460, USA.

*Corresponding author. E-mail: savefauna@yahoo.com.

Accepted 7 January, 2010

Abstract

Blue sheep (Pseudois nayaur) are the main prey species of snow leopards (Uncia uncia) and are a highly coveted species in Nepal. Currently, the conservation of blue sheep in Nepal is a national concern because it is not clear if populations were affected by the Maoist insurgency beginning in 1996. For this study, we estimated population parameters for blue sheep in the Dhorpatan Hunting Reserve and compared these estimates to studies conducted pre-insurgency. We found that the number (206 sheep) and density (1.8 sheep/km) of sheep in the Barse and Phagune Blocks (study area) have not changed since 1993 and 1976, respectively. A mean of 7 animals/herd from 29 herds were classified by sex. The mean sex ratio was higher for 2006 and 2008 counts (4.82 males/female, SD = 2.52) than pre-insurgency counts (0.82 males/female, SD = 0.06) however there was no significant difference between sex ratios. The proportion of ewes in the population was lower than a 2006 count, but similar to pre-insurgency counts. Population age structure was less variable in 2008 than previous counts. More young rams and fewer ewes were counted since 2006, which may have been due to misclassification of females and/or less poaching pressure on young males. Recent hunting pressure by insurgents may have reduced ewe population numbers, and as a result, lambs numbers.

Key words: Blue sheep, Dhorpatan Hunting Reserve, herd size, population density, population size, Pseudois nayaur, sex ratio.