Density and population estimate of gibbons (Hylobates albibarbis) in the Sabangau catchment, Central Kalimantan, Indonesia

Abstract

We demonstrate that although auditory sampling is a useful tool, this method alone will not provide a truly accurate indication of population size, density and distribution of gibbons in an area. If auditory sampling alone is employed, we show that data collection must take place over a sufficient period to account for variation in calling patterns across seasons. The population of Hylobates albibarbis in the Sabangau catchment, Central Kalimantan, Indonesia, was surveyed from July to December 2005 using methods established previously. In addition, auditory sampling was complemented by detailed behavioural data on six habituated groups within the study area. Here we compare results from this study to those of a 1-month study conducted in 2004. The total population of the Sabangau catchment is estimated to be about in the tens of thousands, though numbers, distribution and density for the different forest subtypes vary considerably. We propose that future density surveys of gibbons must include data from all forest subtypes where gibbons are found and that extrapolating from one forest subtype is likely to yield inaccurate density and population estimates. We also propose that auditory census be carried out by using at least three listening posts (LP) in order to increase the area sampled and the chances of hearing groups. Our results suggest that the Sabangau catchment contains one of the largest remaining contiguous populations of Bornean agile gibbon.

First estimates of population ecology and threats to Sunda clouded leopards Neofelis diardi in a peat-swamp forest, Indonesia

“…Sabangau is a peat swamp forest, a habitat in which Sunda clouded leopards have not previously been studied, and which it was predicted that they would inhabit at low density, if at all, in accordance with the low productivity of this type of ecosystem , Cheyne et al 2008. We found an estimated density range of 0.72 to 4.41 individuals per 100 km 2 using data from Blocks 6, 9 and 15 and from the M 0 and M h models.…”

Population mapping of gibbons in Kalimantan, Indonesia: correlates of gibbon density and vegetation across the species’ range

“…Gibbon density was estimated using fixed-point counts, as described by Brockelman & Ali (1987) and following the protocol described by Buckley et al (2006), Cheyne et al (2008) and Hamard et al (2010). therland 2000).…”

A Comparison of Hylobatid Survey Methods Using Triangulation on Müller’s Gibbon (Hylobates muelleri) in Sungai Wain Protection Forest, East Kalimantan, Indonesia

“…Without data on the mean gibbon home range size in each forest type in Sungai Wain Protection Forest it is difficult to conclude which of the density estimates is the most accurate. If the distance generated estimate for the pristine forest was indeed the more accurate of the two, the resulting value of 5.1 groups/km 2 would be the highest value reported for any Bornean gibbon species (Buckley et al 2006;Cheyne et al 2008Cheyne et al , 2012Chivers 1984;Hamard et al 2010;Leighton 1987;Marshall 2009;Mitani 1990;Nijman and Menken 2005;Robbins et al 1991;Rodman 1978;Suzuki 1992;Wilson and Wilson 1975). It is possible that the presence of the surrounding regenerating forest has had a compression effect on the pristine area, resulting in higher than average densities of Müller's gibbons.…”

“…where n represents the total number of groups heard from a set of listing posts, p(m) is the anticipated proportion of groups expected to sing over a period of m days, and E is the total effective listening area (Brockelman and Ali 1987;Cheyne et al 2008). Independent data from this site were not available; we therefore calculated the correction factor p(m) using calling data from the present study with the formula…”

“…In addition, gibbons may not call every day even if no adverse climatic conditions are in effect (Brockelman and Srikosamatara 1993). Therefore, locations should be surveyed for a minimum of 4 d to ensure that all groups in the area are recorded (Brockelman and Ali 1987;Brockelman and Srikosamatara 1993;Cheyne et al 2008;Hamard et al 2010;O'Brien et al 2004). We surveyed 9 of the 10 sites for 4 d, and the last for only 2 d because of time constraints.…”