Estimating seasonal density of blue sheep (Pseudois nayaur) in the Helan Mountain region using distance sampling methods

Abstract

The monitoring of animal populations is necessary to conserve and manage the rare or harvest species and to understand the population change over several years. We used distance sampling methods to estimate seasonal density of blue sheep in a 2,740 km 2 area of Helan Mountain region by walking along 32 transect lines from winter 2003 to autumn 2005. In all, 367-780 blue sheep were observed in 91-143 groups in the surveys during the seasons. Observed mean group size ranged from 3.42 to 8.35 individuals; encounter rate, the number of groups detected per kilometre, varied from 0.19 to 0.30 during the seasons. A hazard rate key function with cosine series expansion and a half-normal key function with either cosine or simple polynomial series expansion were the best fitting models based on the lowest value of Akaike's information criterion (AIC). Density estimates varied between 3.627 sheep per square kilometre in spring 2004 and 4.635 per square kilometre in summer 2005. There were no detectable differences in estimated density among seasons (P = 0.887). The estimated density of blue sheep was negatively correlated with the total number of deaths (P < 0.05), number of sub-adult males' deaths (P < 0.05), number of sub-adult females' deaths (P < 0.05), and number of male lambs' deaths (P < 0.05). We concluded that distance sampling surveys should be used to monitor long-term population trends to provide the best quantitative estimates of blue sheep populations in the Helan Mountains region.

Nocturnal line transect sampling of wild boar (Sus scrofa) in a Mediterranean forest: long-term comparison with capture–mark–resight population estimates

“…Line transect sampling (LTS) has been widely used for direct and indirect surveys of wild ungulates (Marques et al 2001;Walter and Hone 2003;Liu et al 2008;Acevedo et al 2008;Wegge and Storaas 2009). This method implicitly takes into account variables influencing visibility by estimating the probability of detection as a function of distances between objects of interest and transects .…”

Evaluating dall's sheep habitat use via camera traps

“…Conventional sampling techniques for mountain ungulates typically consist of aerial or on‐foot surveys (Sumner , Udevitz et al , Liu et al , Schmidt et al ). However, remotely activated cameras or camera traps are an increasingly used tool in the evaluation of wildlife presence and habitat use (Nichols et al ) and may be advantageous in situations where conventional techniques are restricted or too expensive.…”

Pairing call‐response surveys and distance sampling for a mammalian carnivore

“…Distance sampling yields robust population estimates for rare species (Focardi et al 2002, Ellis and Bernard 2005, Zylstra et al 2010), high survey efficiency over both small and large sampling regions (e.g., Andriolo et al 2005, Durant et al 2011, and population estimates from a single sampling event. As a result, distance sampling has broader applicability than CMR for monitoring populations of large and wide-ranging mammals (Samuel et al 1987, Jathanna et al 2003, Liu et al 2008, Schmidt et al 2012.…”