762 B. Buuveibaatar et al. Population surveys in Russia


We surveyed the gazelle population in five Russian sites covering 10,089 km2 (Fig. 1; Supplementary Table 1). We did not survey the remainder of the Russian gazelle range (19,611 km2) as gazelles use this area exclusively in the winter and would have been absent during the summer survey months. The surveys in the Daursky and Dzeren Valley protected areas (the core range of the species in Russia) used total counts within 1,643 grid cells (each 2 × 2 km) systematically placed across an area of 6,572 km2. Eight experienced teams carried out the survey sim- ultaneously during 10–12 June 2020 to minimize double counting of groups. The teams counted gazelle groups from vantage points as they covered the entire area of each grid cell by car. When they encountered gazelles, the teams photographed the large herds using a quadcop- ter for subsequent accurate estimation of group size. In addition, to determine the accuracy of the method, the teams repeated the surveys twice (within the same day or the next day) in the same control zone, determining the number, sex and age of gazelles in each group. We also conducted transect surveys for the west Krasnokamensk (766 km2) and north Onon River (1,320 km2)areas during 12–20 June 2020.Itwas notfeasible todrive along a systematic array of transects in these areas because of the rugged landscape, and thus vehicles mainly followed existing dirt tracks. We surveyed along six road transect lines for each area (527 km for west Krasnokamensk and 451 km for north Onon River). Finally, we sought expert opinion to estimate the population size of gazelles around the Sokhondinsky Nature Reserve (962 km2) and north Daursky areas (469 km2).


Data analysis for the surveys in Mongolia


Weanalysed distance data as exact distances and in distance intervals, the latter to address the challenges associated with locating the centre of a group that is not uniform with re- spect to both the distribution of individuals within the group and the shape of the group (Buckland et al., 2001, 2015). We examined the data to check that the assumptions of the method were met (i.e. distances had been recorded accurately and all groups on or close to the centrelines had been observed). We modelled detection probability of gazelles using a hazard rate function (without and with sim- ple polynomial adjustment terms for the 2019 and 2020 data, respectively) to account for any potential evasive movement (Supplementary Figs 1 & 2). We binned the 2019 and 2020 perpendicular distance data into four and seven equal intervals of up to 350 m(24% right truncation to improve model fit) and 1,221 m(5% right truncation), re- spectively, to account for the difficulty of locating the centre


of groups when taking the radial distance and compass bear- ing measurements. To address any bias that may have occurred during the


estimation of group size, we used the expected rather than mean group size when the regression line fit to the natural logarithm of group size vs detectability was significant at the 15% α-level. During the 2020 survey, we classed group sizes as either ‘counted’ (observers attempted to count all individuals in the group) or ‘estimated’ (observers estimated group sizes, mostly for larger groups). To limit the error introduced by the estimated group sizes, we aimed for at least 95%ofthe groupsizedatausedinthe analysis to be from counted groups. To achieve this, we re- placed estimated group sizes recorded for sightings fur- thest from the observers (which were likely to be the least accurate) falling within the right truncation distance with the closest counted group sizes recorded for sightings beyond the truncation distance. We post-stratified the 2020 survey data into five strata (Fig. 2) to facilitate com- parison of our results with those from previous surveys (Olson et al., 2011). To obtain a comprehensive estimate of the gazelle


population in Mongolia, we extrapolated the density esti- mates obtained from distance sampling surveys to the un- surveyed region of south-westernMongolia. This involved calculating the mean gazelle density for the southern Gobi and west survey strata within the central and eastern Mongolia survey region, which border the south-western Mongolia survey region. By multiplying the area of the south-western Mongolia survey region by themean gazelle density derived from the two surveyed regions, we ob- tained an approximate estimate of the gazelle population in the target area.


Data analysis for the surveys in Russia


To improve the accuracy of the counts for the Daursky and Dzeren Valley protected areas, we eliminated duplicate ob- servations by excluding groups that had been previously counted and subsequently moved to an adjacent survey plot and were counted again; such duplicates were identified based on group size and composition. We assessed the ac- curacy of group size estimates through repeated counting of individuals in larger herds (usually .100–200 individuals) as well as control counting based on photographs of the lar- gest herds obtained from the quadcopter. In the final calcu- lations, we accounted for missed observations by increasing the mean by the proportion of groups missed and adjusting the group size estimate. The population assessment for the remainder of the Russian surveys in west Krasnokamensk, north Onon River, Sokhondinsky Nature Reserve and north Daursky assumed 100% detectability of gazelles dur- ing the counts.


Oryx, 2024, 58(6), 759–768 © The Author(s), 2024. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605323001515


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