Long-term monitoring of primate, bird, and ungulate populations 2010-2020 for protected area management, Keo Seima Wildlife Sanctuary, Cambodia

Study Extent

The study area is the former core zone, an area of 1,880 km2.

Sampling

Data were collected jointly by the Wildlife Conservation Society (WCS) and the Forestry Administration of the Royal Government of Cambodia (RGC) between 2010 and 2016, and by WCS and the Ministry of Environment of the RGC in 2018 and 2020. Square line transects of 4 km length were arranged throughout KSWS in a systematic grid with a random start point, and field teams conducted distance sampling surveys along the 40 line transects in 2010, 2011, 2013, 2014, 2016, 2018, and 2020. Field teams recorded visual observations of 11 species that were listed as threatened on the IUCN Red List, or were easily detected on line transects, or both (see Table 1 for species and name abbreviations). Laser rangefinders and compasses were used to measure distances and angles from the line transect to detected objects, which constituted either isolated individuals or spatially aggregated individuals (clusters), and cluster sizes were recorded. Distances were measured to the geometric center of clusters. Perpendicular distances from detected objects to the line transect were calculated prior to analysis. Field protocols followed standard line transect methodology outlined in Buckland et al. (2001) and were consistent between years. For further details of field protocols see Supporting Information, O’Kelly et al. (2012), and Nuttall et al. (2017).

Quality Control

Square line transects can potentially cause detection bias around the corners, as animals on the inner side of the corner could be detected twice. Although double-counting does not in itself violate distance-sampling assumptions, bias may arise if the two sightings are non-independent, for example if the second sighting occurs because animals are still present at the location of the first sighting. To assess whether there was evidence of corner-bias in our data, we tested for differences in density of observations between corner areas and non-corner areas. The corner samples were obtained from all transect sections within 50 m of a corner, and the non-corner samples were obtained by two methods: firstly as all transect sections not within 50 m of a corner; and secondly by using 50 m transect sections around each of 1000 randomly-selected points, discarding any that overlapped with corner areas. For either method, observation density was calculated for the corner and non-corner samples and compared using a t-test. Neither method resulted in a significant difference in observation density between corner areas and non-corner areas, so no further action was taken to address corner effects. For 2010 and 2011 data, the time was not collected for observations, so linking observations to morning or evening events was not possible. Instead, the two events on a single date (morning and evening) were grouped, giving a higher total effort, and all observations for that date were assigned to the single event. This makes not difference to distance sampling analysis, but is noted to explain the apparent higher effort per event from those years. In fact, daily effort is generally equal across all years, but subdivided from 2013 onwards.

Method steps

1. Anon during peer-review

Black-shanked douc (Pygathrix nigripes), southern yellow-cheeked crested gibbon (Nomascus gabriellae), Germain's silver langur (Trachypithecus germaini), long-tailed macaque (Macaca fascicularis), northern pig-tailed macaque (Macaca leonina), stump-tailed macaque (Macaca arctoides), green peafowl (Pavo muticus), wild pig (Sus scrofa), northern red muntjac (Muntiacus vaginalis), banteng (Bos javanicus), gaur (Bos gaurus), Eld's deer (Rucervus eldii), sambar (Rusa unicolor). Records for banteng, gaur, Eld's deer, and sambar are not published here due to risk of poaching, but are available on request where appropriate.

1. Sus scrofa
   common name: Wild pig rank: species
2. Muntiacus vaginalis
   common name: Northern red muntjac rank: species
3. Pygathrix nigripes
   common name: Black-shanked douc rank: species
4. Pavo muticus
   common name: Green peafowl rank: species
5. Trachypithecus germaini
   common name: Germain's silver langur rank: species
6. Macaca leonina
   common name: northern pig-tailed macaque rank: species
7. Nomascus gabriellae
   common name: Southern yellow-cheeked crested gibbon rank: species
8. Macaca fascicularis
   common name: Long-tailed macaque rank: species
9. Rusa unicolor
   common name: Sambar rank: species
10. Macaca arctoides
    common name: Stump-tailed macaque rank: species
11. Rucervus eldii
    common name: Eld's deer rank: species
12. Bos gaurus
    common name: Gaur rank: species
13. Bos javanicus
    common name: Banteng rank: species

Observations of species within the central area of Keo Seima Wildlife Sanctuary, Cambodia.