The formerly widespread but now Vulnerable dorcas gazelle Gazella dorcas has declined markedly during the last 2 decades. The semi-captive population in M'Sabih Talaa Reserve, west-central Morocco, is genetically distinct and may be the last remnant of the Moroccan dorcas gazelle G. dorcas massaesyla. The last estimate of the size of this population was c. 200, in 1996. To assess the current population we used line-transect distance sampling to survey this population over five seasons from April 2008 to August 2009. The estimated population declined from 113 to 87 individuals from April to November 2008, increased to 111 in February 2009 (primarily because of recruitment), declined to 99 from February to April 2009, and to 95 by August 2009. These results indicate a decline of nearly 50% in < 15 years. The main conservation actions required for this subspecies are the suppression of poaching and feral dogs, the creation of other reserves to receive dorcas gazelles from M'Sabih Talaa (to avoid loss of the single population from a catastrophic event), and the implementation of a genetic management programme.

Data about breeding populations of birds in the Antarctica are rare and fragmented. Thus, information about the status of the breeding populations of Antarctic birds is crucial given the current scenario of climate change, which is particularly acute in Antarctica. This paper presents new information about the populations of the Antarctic tern Sterna vittata, the kelp gull Larus dominicanus, the southern giant petrel Macronectes giganteus, the Antarctic skua Catharacta antarctica lonnbergi, the chinstrap penguin Pygoscelis antarctica and the gentoo penguin Pygoscelis papua on Byers Peninsula (Livingston Island, South Shetland Islands). We used line transects counts to estimate both densities and numbers of nests of the different species. We estimate that there are 398.96 birds km-2 of southern giant petrels (2793 individuals), 62.4 birds km-2 of Antarctic tern (3746 individuals) and 269.1 birds km-2 of kelp gull (1884 individuals). Furthermore, we found 15 nests of Antarctic skua in 25 km2, from which we can estimate that 60–91 birds must breed on Byers Peninsula. We also censused two colonies of gentoo penguins (3000 and 1200 pairs) and 50 pairs of chinstrap. Compared to previous estimates, gentoo penguins seem to have increased whereas chinstrap penguin have decreased. Finally, the populations of Antarctic tern, southern giant petrel and kelp gull have stabilized or slightly increased.

The banteng Bos javanicus is a globally threatened species of wild cattle restricted to South-East Asia. We report the first robust estimate of banteng density and population size from anywhere in the species' global range, using distance-based line transect sampling within two protected areas, Mondulkiri Protected Forest and Phnom Prich Wildlife Sanctuary, which form part of the Eastern Plains Landscape, Cambodia. We surveyed 110 line transects multiple times during the dry seasons of 2009–2010 and 2010–2011. In a total survey effort of 1,310 km there were 63 encounters with banteng. The mean estimate of the population across the 3,406 km2 study area is 3,200 (95% confidence interval 1,980–5,170). This suggests that the protected area complex of the Eastern Plains Landscape supports the majority of the global population of banteng. Stronger protection, both in the form of increased anti-hunting and poaching patrols and integrated land-use planning to prevent habitat loss within protected areas, is essential for securing wild cattle populations in the Eastern Plains Landscape.

Locating activity hotspots – areas of higher density, more intense use, or distinct social units – is a prerequisite for answering many questions in animal ecology. However, for many species, carrying out such research from direct observations in tropical habitat is time-consuming and unrealistic for non-habituated animals. This study aimed to locate chimpanzee home ranges from transect nest counts. For validation purposes, 233 line transects were sampled within the home ranges of four habituated social groups of chimpanzees in Taï National Park, Côte d'Ivoire. In total, 373 km of transects were surveyed over 188 days and 683 nests of chimpanzee were recorded. First, we characterized heterogeneity of nest distribution patterns, including variation in density and group size within the area. Second, we used scan statistics, a likelihood-based cluster technique to locate chimpanzee social groups and compared them with the known home range boundaries. Chimpanzee nest distribution was characterized by a positive density and group-size gradient away from the range periphery. Furthermore, nest distribution clusters corresponding to the four groups could be successfully identified, although additional clusters for, for example, low-density areas between social groups seem to be an unavoidable by-product. The approach taken can be extended to a wide spectrum of data stemming from direct observations, camera traps, acoustic or genetic sampling to derive information about structure and patchiness of wild animal populations.

The global population of saiga Saiga tatarica, categorized as Critically Endangered on the IUCN Red List, declined by > 95% at the end of the 20th century, resulting in several conservation initiatives to protect the species. Previously used methods to monitor population trends were inadequate to assess numbers of saiga properly. We report findings from the first survey for Mongolian saiga S. tatarica mongolica to utilize statistically rigorous methodology, using line transect distance sampling in 2006 and 2007 to obtain population estimates in and around the Sharga Nature Reserve, the southern part of the species' current range. We estimate a density of 0.54 and 0.78 saiga km-2 in 2006 and 2007, respectively. Our best models suggest that 4,938 (95% confidence interval, CI = 2,762–8,828) saiga occupied the 4,524-km2 study area in 2006 and 7,221 (95% CI = 4,380–11,903) occupied the 4,678-km2 study area in 2007. Although these estimates, with their large confidence intervals, preclude an assessment of the impacts of conservation initiatives on population trends, they suggest that the Mongolian saiga population is larger than previous reports based on minimum counts, and adequate to support in situ population recovery. Modifications to the survey protocol hold promise for improving the precision of future estimates. Distance sampling may be a useful, scientifically defensible method for monitoring saiga population trends and assessing the effectiveness of conservation efforts to stabilize and recover populations.

Despite a ≥75% reduction in the geographic range of Mongolian gazelles Procapra gutturosa over the past 50 years, the species is still recognized as the most numerous large grassland herbivore in Asia. Its actual population size, however, is still disputed, and we therefore estimated its numbers in an 80,000 km2 area in the eastern steppe of Mongolia by driving long-distance (1,200–1,400 km) transect surveys during spring and autumn 2000–2002. Quantitative estimates of gazelle numbers are essential for understanding the causes of changes in the population, and thus devising conservation strategies to assure its long-term viability. Observed herds ranged in size from 1–4,000; among surveys, median herd sizes varied from 14–42. Density estimates varied from 10.7 gazelles km−2 in spring to 11.5 gazelles km−2 in autumn, with total population estimates of 803,820 (483,790–1,330,100 95% confidence interval) and 870,625 (499,432–1,491,278 95% confidence interval), respectively. Confidence limits were wide, and to obtain a coefficient of variation of 20%, transect lengths would need to be extended three- to four-fold. Until more efficient means for conducting population surveys can be implemented, driving long-distance transects, combined with distance analysis, seem to provide the best quantitative estimate of Mongolian gazelle populations.

Ecological densities of large herbivores were estimated using the line transect method in the tropical moist forests of Bhadra Tiger Reserve, southern India, during November 2000. The species of interest were chital Axis axis, sambar Cervus unicolor, muntjac Muntiacus muntjak, gaur Bos gaurus and Hanuman langur Presbytes entellus. Six permanent transects, ranging from 2.6 to 3.6 km (totalling 18.2 km) were each walked 26 times. A total of 473 km were walked during the surveys. Numbers of detections were generally low (51, 25, 68, 17 and 302 for chital, sambar, muntjac, gaur and langur, respectively). Mean estimated densities of different species were [${\smash{\raise6pt\hbox{\gary}}{\hspace*{-6pt}{D}}}$ (${\pm}\,$SE)]: 4.51 (${\pm}\,$1.05) chital km−2, 0.89 (${\pm}\,$0.23) sambar km−2, 3.64 (${\pm}\,$0.63) muntjac km−2, 1.48 (${\pm}\,$0.63) gaur km−2 and 22.62 (${\pm}\,$2.64) langur km−2. Possible shortcomings of our estimates are considered and suggestions made for improving future surveys. A comparison with densities estimated for these species in other well-protected parks showed that the chital, gaur and sambar densities in Bhadra were extremely low. The main causal factors for these low densities seem to be poaching and livestock grazing.

Our aim is to estimate the volume-weighted mean of the volumes of three-dimensional ‘particles’ (compact, not-necessarily-convex subsets) from plane sections of the particle population. The standard stereological technique is to place test lines in the plane section, and measure cubed intercept lengths with the two-dimensional particle profiles. This paper discusses more efficient estimators obtained by integrating over all possible placements of the test line. We prove that these estimators have smaller variance than the line transect estimators, and indeed are related to them by the Rao-Blackwell process. In the improved estimators, the cubed intercept length is replaced by a moment of the distance between two points in the section profile. This can be computed as a moment of the set covariance function, which in turn is computable using the fast Fourier transform. We also derive an isoperimetric-type inequality between the improved estimator and the area-weighted 3/2th moment of the profile areas. Finally, we present two practical applications to particles of silicon carbide and to synaptic boutons in brain tissue. We estimate the variance of the technique and the gain in efficiency over line transect techniques; the efficiency improvement appears to be as much as one order of magnitude.