Evaluation of line-transect sampling for estimating koala abundance in the Pine Rivers Shire, south-east Queensland

Abstract

Distance sampling using line transects has not been previously used or tested for estimating koala abundance. In July 2001, a pilot survey was conducted to compare the use of line transects with strip transects for estimating koala abundance. Both methods provided a similar estimate of density. On the basis of the results of the pilot survey, the distribution and abundance of koalas in the Pine Rivers Shire, south-east Queensland, was determined using line-transect sampling. In total, 134 lines (length 64 km) were used to sample bushland areas. Eighty-two independent koalas were sighted. Analysis of the frequency distribution of sighting distances using the software program DISTANCE enabled a global detection function to be estimated for survey sites in bushland areas across the Shire. Abundance in urban parts of the Shire was estimated from densities obtained from total counts at eight urban sites that ranged from 26 to 51 ha in size. Koala abundance in the Pine Rivers Shire was estimated at 4584 (95% confidence interval, 4040–5247). Line-transect sampling is a useful method for estimating koala abundance provided experienced koala observers are used when conducting surveys.

The Distribution and Abundance of an Island Population of Koalas (Phascolarctos cinereus) in the Far North of Their Geographic Range

“…These results fall within the range of koala densities from other Queensland area studies using various methods including the FSCM (0–2.51 koalas ha −1 ) [25]; distance sampling (0–0.76 koalas ha −1 ) [8]; and direct counts (0.1–2.0 koalas ha −1 ) [16], 0.4 koalas ha −1 [28], (0.02–0.4 koalas ha −1 ) [29]. Although the density from this study is broadly consistent with other studies from Queensland, it is much lower than abundances on southern islands [41].…”

“…Dique et al [8] estimated koala density in the urban habitats of the Pine Rivers Shire, Queensland, to be between 0.06 and 0.42 ha −1 , or 25% of the regional population. Urban areas account for 548 hectares, or 11%, of the total area of Magnetic Island [42].…”

“…Due to their sedentary nature [3], koalas can be difficult to detect. This combination of factors makes estimating koala abundance difficult and costly [6]–[8], and has resulted in a limited number of estimates at regional, state and national levels [6], [9], [10].…”

“…Abundance and density estimations have primarily been obtained from transect counts, with fixed boundaries [20], [23], [26]–[30]. Inference from community surveys [11], [14]; distance sampling [8]; mark-resight [19], [22], [31] and fecal pellet surveys [25], [17] have also been used. However, abundance surveys of low density, patchy koala populations, scattered over large regions, such as those typical of Queensland, have been challenging for conventional methods, such as direct counts, where even extensive efforts can lead to limited data or overlooked animals and inaccurate results [6].…”

Faecal particle size and tooth wear of the koala (Phascolarctos cinereus)

“…Non-invasive methods of evaluating koala distribution, such as mapping faecal pellet distributions, are important tools for conserving such cryptic species because they produce an unequivocal record of presence with minimal effort Ellis et al 2013). The analysis of faecal pellet distributions has been particularly useful for studying koala population trends (Seabrook et al 2011) because they can have large home ranges of up to 100 ha (Ellis et al 2002) and are often difficult to observe during surveys of their habitat (Dique et al 2003;Phillips and Callaghan 2011;Woosnam-Merchez et al 2012). In addition to information about which trees koalas use and eat, recent work suggests that fresh pellets may be analysed to produce information on endocrine profiles (Davies et al 2013;Narayan et al 2013) and genetic information for free-ranging koalas (Wedrowicz et al 2013).…”