Anthropogenic habitat disturbance and food availability affect the abundance of an endangered primate: a regional approach

Assessing the effects of survey-inherent disturbance on primate detectability: Recommendations for line transect distance sampling

Habitat destruction and over-hunting are increasingly threatening the arboreal primates of Central Africa. To establish effective conservation strategies, accurate assessments of primate density, abundance, and spatial distribution are required. To date, the method of choice for primate density estimation is line transect distance sampling. However, primates fleeing human observers violate methodological assumptions, biasing the accuracy of resulting estimates. In this study, we used line transect distance sampling to study five primate species along 378 km of transects in Salonga National Park, Democratic Republic of the Congo. We tested the effect of different levels of survey-inherent disturbance (i.e., cutting) on the number of observed (i) primate groups, and (ii) individuals within groups, by counting groups at three different time lags after disturbance of the transect, (i) a minimum of 3 h, (ii) 24 h, (iii) a minimum of 3 days. We found that survey-inherent disturbance led to underestimated densities, affecting both the number of encountered groups and of observed individuals. However, the response varied between species due to species-specific ecological and behavioral features. Piliocolobus tholloni and Colobus angolenis resumed an unaltered behavior only 24 h after disturbance, while Lophocebus aterrimus, Cercopithecus ascanius, and Cercopithecus wolfi required a minimum of 10 days. To minimize bias in density estimates, future surveys using line transect distance sampling should be designed considering survey-inherent disturbance. We recommend evaluating the factors driving primate response, including habitat type, niche occupation, and hunting pressure, peculiar to the survey-specific area and primate community under study.

Forest maturity has a stronger influence on the prevalence of spider monkeys than howler monkeys in an anthropogenically impacted rainforest landscape

The transformation and depletion of primary forest over the past few decades have placed almost half of the world’s primate species under the threat of extinction. Developing any successful conservation program for primates requires distribution and demography data, as well as an understanding of the relationships between these factors and their habitat. Between March and June 2010 and 2011 we collected data on the presence and demographic parameters of howler and spider monkeys by carrying out surveys, and validated our findings using local knowledge. We then examined the relationship between forest type and the presence of these primates at 54 sites in the northern area of the Selva Zoque Corridor, Mexico. We detected 86 spider monkey groups across 31 plots and censused 391 individuals (mean ± SD = 5.9 ± 3.0 individuals per sub-group, n = 67 sub-groups). We also detected 69 howler monkey groups across 30 plots and censused 117 individuals (mean ± SD = 5.3 ± 2.4 individuals per group, n = 22 groups). Howler monkey presence was not related to any specific vegetation type, while spider monkeys were present in areas with a higher percentage of tall forest (trees > 25 m high). Overall, spider monkeys were more prevalent than howler monkeys in our sampling sites and showed demographic characteristics similar to those in better protected areas, suggesting that the landscape features in the Uxpanapa Valley are suitable for their needs. Conversely, howler monkey presence was found to be more limited than in other regions, possibly due to the extended presence of spider monkeys.

Effect of Anthropogenic Activities on the Population of Moor Macaques (Macaca maura) in South Sulawesi, Indonesia

Forest loss due to anthropogenic activities is one of the main causes of plant and animal species decline. Studying the species’ population status (i.e., density, abundance, and geographic distribution) on a regular basis is one of the main tools to assess the effect of anthropogenic activities on wildlife, to monitor population dynamics and to intervene with effective conservation strategies when the population of an endangered species declines. On Sulawesi Island, Indonesia, anthropogenic activities, such as agriculture, are decreasing the remaining natural habitats available for several endemic and endangered species. The effect of this forest loss on the threatened moor macaques (Macaca maura) in South Sulawesi is unknown, and data on the population status of this species are needed to design effective conservation strategies. To assess the population status of the moor macaques, we walked linear transects (N = 29, survey effort = 114 km) at six sites between November 2019 and March 2020 to estimate macaque population density and encounter rate. We tested the effect of anthropogenic activities on macaque encounter rate. Our global density estimate (24 individuals/km2) was lower than the overall estimate from the most detailed survey conducted on this species, which covered its whole geographic distribution (36.1 individuals/km2). However, these results should be interpreted with caution because the previous density estimate falls within the confidence intervals of our estimate. Furthermore, we found regional declines in moor macaque encounter rates in at least two sites compared with previous studies. We found a high presence of anthropogenic activity in the forests inhabited by macaques. Moor macaques were less abundant in open areas with no forest (i.e., clear cuttings) than in forested areas, and in the presence of nonspecies-specific hunting traps (i.e., wire-loop traps). Moreover, moor macaques were more abundant in areas with a higher presence of humans and domestic animals. Overall, our data suggest that the population of this species may be declining in certain regions but further surveys are needed to corroborate whether this is occurring across the entire geographic distribution.

Spider monkey use of natural and artificial terrestrial water sources in Calakmul, Mexico

Geoffroy’s spider monkeys (Ateles geoffroyi) satisfy their need for water mainly from food items and arboreal water sources, but climate change and other anthropogenic impacts can drive a more frequent use of ground water by this arboreal species. Here, we report 25 events of use of natural and artificial terrestrial water bodies by spider monkeys recorded using camera-trapping in the Calakmul region, Mexico. Interestingly, these events occurred during the rainy season in locations where we did not record large predators and in most cases involved adult male individuals. These records suggest that habitat disruptions such as those associated with changing weather patterns and selective logging of large trees holding water reservoirs can lead to a greater use of terrestrial water sources by spider monkeys.

Line-transect versus point-transect sampling: the effects of survey area and survey effort on method efficiency for Geoffroy’s spider monkeys

Abstract ContextLine-transect sampling is considered to be a more efficient survey method than point-transect sampling to estimate population densities and abundance of many animal species. AimsIn the present study, we tested whether this claim holds true when surveying arboreal fast-moving primate species occurring at low densities, and whether the potential difference in efficiency can be explained by the difference in the size of the survey area between the methods. We further examined the impact of survey effort for point-transect sampling. MethodsWe conducted line- and point-transect sampling for Geoffroy’s spider monkeys (Ateles geoffroyi) in the same locations and compared the numbers of detected individual monkeys and the probability of their occurrence per survey between the two methods. We further compared the data from point-transect sampling gathered within three different waiting periods. Key resultsWe found a higher probability to detect monkeys and a higher number of monkeys during line-transect sampling than during point-transect sampling, but more spider monkeys were detected at point transects when controlling for the size of the survey area. More monkey detections were made during the first 10 min than during the second and third 10-min periods of point-transect surveys. ConclusionsWe showed that line-transect sampling is more efficient than point-transect sampling when surveying Geoffroy’s spider monkeys in a flat landscape of tropical forest with homogenous visibility. We discuss factors influencing survey results and recommend 20 min as the maximum waiting time at point transects when surveying arboreal mammals. ImplicationsOur study has provided a quantitative approach to compare efficiency across survey methods for fast-moving arboreal animals that occur at low densities, and supports the use of point-transect sampling in sites where line-transect sampling is not feasible, such as in human-modified landscapes.