Statistically rigorous surveys of primate and ungulate populations were conducted in the Seima Protection Forest (SPF) in 2008, at a much higher level of survey effort than in previous years. These surveys reinforced the importance of the site for Black-shanked Douc and Yellow-cheeked Crested Gibbon with no decline in primate numbers detectable at the site, despite their high overall global threat status.
The primary methodology employed in this regard is distance sampling, using visual detections of target species on line transects. Fourteen transects 3-5km in length are located within a 1086 km2 survey area. This area represents the most important habitat for wildlife within the site, as identified in the 2002 preliminary surveys. Transects were placed randomly, with stratification by broad forest type (evergreen forest, semi-evergreen forest, deciduous dipterocarp forest) and location (approximately southern, central and northern SPF). This ensured that transects are representative of the forest types, topography and varying human pressures within the SPF.
The transects are walked once (2005-2007) or twice (2008) a day in the two hours just after sunrise and those preceding sunset, when animals are most active and easy to observe. Survey teams consist of two people only. For each animal (or animal group) encountered the following information is recorded: co-ordinate (recorded using a GPS unit), number of animals, distance between the animal or centre of a group of animals and the observers on the line (with a laser rangefinder), compass bearing to the animal or to the centre of a group of animals, and compass bearing of the transect line. The total effort walked on line transects in 2008 was 1344km, which represents an eight-fold increase from that invested in previous years.
Observations of both primate species were restricted to evergreen, semi-evergreen and riverine habitat, in accordance with their habitat preferences.