Comparison of point transect distance and traditional acoustic point‐count sampling of hoolock gibbons in Htamanthi Wildlife Sanctuary, Myanmar

Abstract

Effective conservation demands more accurate and reliable methods of survey and monitoring of populations. Surveys of gibbon populations have relied mostly on mapping of groups in "listening areas" using acoustical point-count data. Traditional methods of estimating density in have usually used counts of gibbon groups within fixed-radius areas or areas bounded by terrain barriers to sound transmission, and have not accounted for possible decline in detectability with distance. In this study we sampled the eastern hoolock gibbon (Hoolock leucogenys) population in Htamanthi Wildlife Sanctuary (WS), Myanmar, using two methods: the traditional pointcount method with fixed-radius listening areas, and a newer method using pointtransect Distance analysis from a sample point established in the center of each listening point array. The basic data were obtained by triangulating on singing groups from four LPs for 4 days, in 10 randomly selected sample areas within the sanctuary. The point transect method gave an average density of 3.13 groups km −2 , higher than the estimates of group density within fixed-radius areas without correction for detectability. A new method of analysis of singing probability per day (p[1]) gave an estimate of 0.547. Htamanthi WS is an important conservation area containing an estimated 7000 (95% confidence interval: 5000-10,000) hoolock groups. Surveys at Htamanthi WS and locations in the Hukaung Valley suggest that the extensive evergreen forests in northern Myanmar have the capacity to support 2-4 (average about 3) groups of hoolock gibbons per km 2 , but most forests in its range have yet to be surveyed.

Density and population size estimates of the endangered northern yellow-cheeked crested gibbon Nomascus annamensis in selectively logged Veun Sai-Siem Pang National Park in Cambodia using acoustic spatial capture-recapture methods

“…As we were unable to access the same listening post locations in one site towards the northern VSSP boundary, we selected listening posts as close as possible, 1.3 km south-west from those used in the previous study. Since gibbon groups do not duet every day [72][73][74], gibbon auditory surveys are commonly conducted over three [8,27,75,76] or four consecutive days in each site [23,24,44,72]. We surveyed each site for three days to increase the number of gibbon groups heard, while maximising the overlap of survey dates with the previous study, which surveyed each site for one day during February and March in 2010 [46].…”

Performance of autonomous recorders to detect a cryptic and endangered primate species, the black lion‐tamarin (Leontopithecus chrysopygus)

“…When it comes to arboreal animals, recognizing the species by ear can be easier than looking for it visually. In this case, other methods are widely used, such as acoustical point‐count data, which consists in registering animal vocalizations within fixed radius listening areas (Brockelman et al, 2020) and sound playback. The latter seeks the response of an animal to a conspecific sound, evidencing its presence (Johnson et al, 1981), a method commonly used in primate studies (Coelho et al, 2020; Gestich et al, 2017; Ruiz‐Miranda et al, 2019; Savage et al, 2010).…”