GENERAL GUIDELINES FOR STANDARDIZING LINE TRANSECT SURVEYS OF TROPICAL FOREST PRIMATES1 (original) (raw)
Related papers
Design and Analysis of Line Transect Surveys for Primates
International Journal of Primatology, 2010
Line transect surveys are widely used for estimating abundance of primate populations. The method relies on a small number of key assumptions, and if these are not met, substantial bias may occur. For a variety of reasons, primate surveys often do not follow what is generally considered to be best practice, either in survey design or in analysis. The design often comprises too few lines (sometimes just one), subjectively placed or placed along trails, so lacks both randomization and adequate replication.
Line transect surveying is a relatively rapid and efficient procedure for the assessment of primate populations; although the reliability of the resulting density estimates is affected by a number of factors, including habitat configuration. In this study, primate populations were surveyed at a highly fragmented site in northeastern Brazil, where the resident species include the endangered Coimbra-Filho's titi, Callicebus coimbrai, and the critically endangered yellow-breasted capuchin, Cebus xanthosternos. In addition to standard line transect surveys, data were collected on the composition and distribution of resident groups during playback surveys and ecological monitoring. During surveys, a 5.3-km trail system was walked regularly over a 7-month period, accumulating a total transect length of 476 km and 104 sightings of Callicebus and 41 of Cebus (as well as 19 records of a third primate, Callithrix jacchus). Data were analyzed using the DISTANCE program and the Kelker method, using the perpendicular distances to first animal sighted. Estimates of group density were highly discrepant from known values for both species; although in the case of Cebus, this seemed to reflect grouping patterns at the site. For Callicebus, population density was overestimated considerably when known group counts were used. Overall, there seems to be a need for a much more rigorous standardization of procedures, and the analysis and presentation of results, in order to guarantee the most reliable interpretation possible of the data. These considerations are especially important in the case of endangered species, such as those studied here. Am.
Monitoring mammal populations with line transect techniques in African forests
1. Line transect survey techniques have been used to estimate population density for a variety of mammal species in tropical forests. In many cases indirect methods, surveying signs of animals such as counts of dung or nests, have been used because of the poor visibility in these forests. The estimates of the production and decomposition rates of these signs each have their associated errors; however, for the majority of published studies these errors have not been incorporated into the estimate of the standard errors or con®dence limits of the density estimate. An equation is given showing how this should be done.
Line Transect Sampling of Primates: Can Animal-to-Observer Distance Methods Work?
International Journal of Primatology, 2010
Line transect sampling is widely used for estimating abundance of primate populations. Animal-to-observer distances (AODs) are commonly used in analysis, in preference to perpendicular distances from the line. This is in marked contrast with standard practice for other applications of line transect sampling. We formalize the mathematical shortcomings of approaches based on AODs, and show that they are likely to give strongly biased estimates of density. We review papers that claim good performance for the method, and explore this performance through simulations. These confirm strong bias in estimates of density using AODs. We conclude that AOD methods are conceptually flawed, and that they cannot in general provide valid estimates of density.
Primates in Fragments, 2013
Understanding the strategies that primates use to survive in fragmented forest landscapes is vital for constructing informed management plans for specific regions and to enable researchers to start to make generalizations. In a 15-month study, we investigated factors that influenced the status of red-tailed monkeys (Cercopithecus ascanius) and their plant food resources in 20 of the few remaining privately owned forest fragments in Central Uganda. We employed transect methods for vegetation assessments and censuses with a short stop upon sighting redtails to establish demographics and food plants consumed. While the sample involved forests of very different successional stages, forest size was the most important factor influencing both red-tail population size and the number of groups per fragment. Number of food tree species influenced only the number of red-tail groups per fragment. Basal area of food tree species and food tree abundance per fragment were not related to red-tail population size or the number of groups per fragment. Food tree species richness, total number of trees, and basal area of food trees increased significantly with fragment size. Availability of food resources was Chapter 15
International Journal of Primatology, 2013
Monitoring populations of endangered species over time is necessary to guide and evaluate conservation efforts. This is particularly important for nonprotected areas that ensure connectivity between protected populations but are prone to uncontrolled hunting pressure. We investigated whether use of transects by local people and transect reuse for repeated surveys influence great ape nesting and bias results. We conducted simultaneous marked nest count surveys over 12 mo on established and newly opened transects in a nonprotected area subject to traditional heavy use by local people and recorded forest composition and signs of human activity. Chimpanzee and gorilla density estimates and encounter rates per kilometer were lower on established transects than on new ones. A generalized linear model indicated that hunting activity, distance to a regularly used forest trail, and transect type (old or new) predicted chimpanzee nest abundance, and distance to the trail and transect type predicted gorilla nest abundance, with no effect of habitat type (percentage suitable habitat) for either species. We, therefore, suggest that the difference in great ape nesting is a result of high levels of hunting by local people on established transects and forest trails. Our results support the use of repeated line transect surveys for monitoring great ape populations in many circumstances, although we advocate taking precautions in nonprotected areas, to avoid the bias imposed by use of established transects for hunting.
Acta Scientiarum. Biological Sciences, 2020
Human activities result in the formation of a mosaic of forest patches within a non-habitat matrix. The response of the local biodiversity to changes in land-use may occur at different scales. It is important to evaluate the effects of the attributes of both the patches and the surrounding landscape on the occupancy of forest patches by animal populations. Here, we assessed the predictive potential of local (basal area, tree density), patch (size, shape) and landscape scale (total area of forest, number of patches, matrix permeability, patch proximity) variables on the occupancy of forest patches by the syntopic primates Alouatta caraya, Sapajus libidinosus and Callithrix penicillata in the city of Goiânia in the Cerrado region of central Brazil. We used playback to survey primate populations in 22 focal patches and assessed the landscape within a 1000 m buffer zone around each site. In A. caraya, occupancy was influenced by the shape of the focal patches, the amount of forest and f...
Conservation Science and Practice, 2019
Knowledge about distribution of primate species and their densities is crucial for conservation and management. However, such information is often lacking or anecdotal, even for seemingly abundant species. Long-tailed macaques (Macaca fascicularis) are distributed across southeast Asia and recognized by the International Union for Conservation of Nature Species Survival Commission Primate Specialist Group (IUCN SSC PSG) as both widespread and rapidly declining. Precise local density and abundance data are scarce across their range. To provide density and abundance estimates for a long-tailed macaque population we conducted line transect distance sampling throughout Baluran National Park (250 km 2), East Java, Indonesia covering all habitats. Long-tailed macaque density was 41.4 ind/km 2 (95% confidence interval, CI: 23.04-74.39), with an estimated abundance of 10,350 individuals (95% CI: 5,760-18,598). A density of 41.4 ind/km 2 is lower than previous estimates for other sites in Java. Species distribution and habitat suitability analysis revealed a macaque preference for areas close to or on roads and trails, invasive acacia and/or native savannah. Long-tailed macaques were provisioned with human food by commuters and tourists along roads and trails, probably structuring their distribution/habitat use. To evaluate if long-tailed-macaques have been overestimated for years, we also conducted a nonrandom point distance sampling survey according to macaque presence restricted to roads and trails. This survey provided density and abundance results much higher than the line transect distance sampling survey. Our study provides much needed baseline data for this species. Baluran National Park management and management in other areas can use these results to create informed management decisions regarding long-tailed macaques. We recommend conducting systematic surveys of long-tailed macaques throughout their range, and possibly reassessing conservation status, and conservation and management measures for long-tailed macaques.
Landscape Ecology, 2017
Context: Primates are an important component of biodiversity in tropical regions. However, many studies on the effects of habitat change on primates ignore the relative influence of landscape composition and configuration. Objectives: This study addresses the question: how important are landscape-scale forest area and composition relative to patch-scale (1-1080 ha) and site-scale (transect of 1 km) habitat variables for the occupancy and abundance of four primate species in the Colombian Llanos. Methods: Using a randomly stratified survey design, 81 fragments were surveyed for primate occupancy and abundance. We used zero-inflated models to test the relative influence of landscape-scale, patch-scale and site-scale variables on occupancy and abundance for each species. A 95% confidence set of models was constructed using the cumulative Akaike weight for each model and the relative importance of each set of variables calculated for each primate species. Results: Occupancy was determined by a combination of site-scale, patch-scale and landscape-scale variables but this varied substantially among the primate species. Conclusion: Our study highlights the importance of managing primates at a range of scales that considers the relative importance of site-, patch-and landscape-scale variables.