In this study, we sequenced a partial segment of the mitochondrial control region from 21 proboscis monkeys of the Klias peninsula, the last large population remaining on the west coast of Sabah, Malaysia. Our results showed that this population retains substantial genetic variation, and subpopulations from different river systems in the central and southern portions of the Klias share multiple haplotypes. We also compared our data with previously generated sequences from 2 eastern populations of proboscis monkeys in Sabah and found little evidence of regional genetic structure. Based on these results, we argue that conservation efforts should focus on restoring connectivity between central and southern Klias peninsula proboscis monkeys and discuss future analyses needed to better understand the mitochondrial structure of proboscis monkeys in Sabah.
This is the first report on inter-individual relationships within a one-male group of proboscis monkeys (Nasalis larvatus) based on detailed identification of individuals. From May 2005 to 2006, focal and ad libitum data of agonistic and grooming behaviour were collected in a forest along the Menanggul River, Sabah, Malaysia. During the study period, we collected over 1,968 h of focal data on the adult male and 1,539 h of focal data on the six females. Their social interactions, including agonistic and grooming behaviour, appeared to follow typical patterns reported for other colobines: the incidence of social interaction within groups is low. Of 39 agonistic events, 26 were displacement from sleeping places along the river, 6 were the α male threatening other monkeys to mediate quarrels between females and between females and juveniles, and 7 were displacement from feeding places. Although the agonistic behaviour matrix based on the 33 intra-group agonistic events (excluding events between adults and juveniles and between adults and infants) was indicative of non-significant linearity, there were some specific dominated individuals within the group of proboscis monkeys. Nonetheless, grooming behaviour among adult females within a group were not affected by the dominance hierarchy. This study also conducted initial comparisons of grooming patterns among proboscis monkeys and other primate species. On the basis of comparison of their grooming networks, similar grooming patterns among both-sex-disperse and male-philopatric/female-disperse species were detected. Because adult females in these species migrate to groups repeatedly, it may be difficult to establish the firm grooming exchange relationship for particular individuals within groups, unlike in female-philopatric/male-disperse species. However, grooming distribution patterns within groups among primate species were difficult to explain solely on the basis of their dispersal patterns. Newly immigrated females in some species including proboscis monkeys are eager to have social interactions with senior group members to improve their social position.
Animals can have both positive (e.g. via seed dispersal) and negative (e.g. via herbivory) impacts on plants. The net effects of these interactions remain difficult to predict and may be affected by overhunting and habitat disturbance, two widespread threats to tropical forests. Recent studies have documented their separate effects on plant recruitment but our understanding of how defaunation and logging interact to influence tropical tree communities is limited. From 2013 to 2016, we followed the fate of marked tree seedlings (n = 1489) from 81 genera in and outside experimental plots. Our plots differentially excluded small, medium and large-bodied mammal herbivores in logged and unlogged forest in Malaysian Borneo. We assessed the effects of experimental defaunation and logging on taxonomic diversity and plant trait (wood density, specific leaf area, fruit size) composition of seedling communities. Although seedling mortality was highest in the presence of all mammal herbivores (44%), defaunation alone did not alter taxonomic diversity nor plant trait composition. However, herbivores (across all body sizes) significantly reduced mean fruit size across the seedling community over time (95% confidence interval (CI): -0.09 to -0.01), particularly in logged forest (95% CI: -0.12 to -0.003). Our findings suggest that impacts of mammal herbivores on plant communities may be greater in forests with a history of disturbance and could subsequently affect plant functional traits and ecological processes associated with forest regeneration.
Human land use is continuously altering the natural environment, yet the greater ecological implications of this change for many groups that are key to healthy ecosystem functioning remains uncharacterised in the tropics. Terrestrial scavenging vertebrates are one such group, providing integral ecosystem services through the removal of carrion which is a crucial component of both nutrient cycling and disease dynamics. To explore how anthropogenic processes may affect forest scavengers, we investigated the changes in the relative occupancy of two important terrestrial scavengers along a gradient of land use intensity, ranging from protected forest to oil palm plantation in Borneo. We found the Malay civet (Viverra tangalunga) had highest, albeit variable, occupancy in areas of low land use intensity and the Southeast Asian water monitor (Varanus salvator macromaculatus) had highest occupancy in areas of high land use intensity. Land use had no effect on the combined occupancy of the two species. In high land use intensity sites, individual water monitors were larger and had better body condition, but at population level had a highly biased sex ratio with more males than females and increased signs of intraspecific conflict. We did not assess scavenging rate or efficiency as a process, but the high occupancy rates and apparent health of the scavengers in high land use intensity landscapes suggests this ecological process is robust to land use change.
Periods of extreme food abundance, such as irregular masting events, can dramatically affect animal populations and communities, but the extent to which anthropogenic disturbances alter animal responses to mast events is not clear. In South-East Asia, dipterocarp trees reproduce in mast fruiting events every 2-10 years in some of the largest masting events on the planet. These trees, however, are targeted for selective logging, reducing the intensity of fruit production and potentially affecting multiple trophic levels. Moreover, animal responses to resource pulse events have largely been studied in systems where the major mast consumers have been extirpated. We sought to evaluate the influence of human-induced habitat disturbance on animal responses to masting in a system where key mast consumers remain extant. We used motion-triggered camera traps to quantify terrestrial mammal and bird occurrences in Sabah, Malaysian Borneo, relative to variation in fruit biomass from 69 plant families during a major (2014) and minor (2015) masting event and a non-mast year (2013), in both logged and unlogged forests. Bearded pigs (Sus barbatus) showed the clearest responses to masting and occurrence rates were highest in unlogged forest in the year following the major mast, suggesting that the pulse in fruit availability increased immigration or reproduction. We also detected local-scale spatial tracking of dipterocarp fruits in bearded pigs in unlogged forest, while this was equivocal in other species. In contrast, pigs and other vertebrate taxa in our study showed limited response to spatial or temporal variation in fruit availability in logged forest. Our findings suggest that vertebrates, namely bearded pigs, may respond to masting via movement and increased reproduction, but that these responses may be attenuated by habitat disturbance.
In non-human primates, the daily feeding rhythm, i.e., temporal fluctuation in feeding activity across the day, has been described but has rarely received much analytical interpretation, though it may play a crucial part in understanding the adaptive significance of primate foraging strategies. This study is the first to describe the detailed daily feeding rhythm in proboscis monkeys (Nasalis larvatus) based on data collected from both riverbank and inland habitats. From May 2005 to May 2006, data on feeding behavior in a group of proboscis monkeys consisting of an alpha-male, six adult females and immatures was collected via continuous focal animal sampling technique in a forest along the Menanggul River, Sabah, Malaysia. In both the male and females, the highest peak of feeding activity was in the late afternoon at 15:00-17:00, i.e., shortly before sleeping. The differences in the feeding rhythm among the seasons appeared to reflect the time spent eating fruit and/or the availability of fruit; clearer feeding peaks were detected when the monkeys spent a relevant amount of time eating fruit, but no clear peak was detected when fruit eating was less frequent. The daily feeding rhythm was not strongly influenced by daily temperature fluctuations. When comparing the daily feeding rhythm of proboscis monkeys to that of other primates, one of the most common temporal patterns detected across primates was a feeding peak in the late afternoon, although it was impossible to demonstrate this statistically because of methodological differences among studies.
Reports of wild great ape fatalities have been very limited, and only two have described wild orangutan deaths. We found a wounded juvenile female Bornean orangutan on 7 October 2006 in the Danum Valley, Sabah, Malaysia, and observed the individual's behavior for 7 days until her death on 13 October 2006. The 5-6-year-old orangutan, which we had observed since 2004, was wounded in the left brachium, back, and right hand. The individual's behavior changed after injury; the mean nest-nest active time became significantly shorter than before injury (from 12 h 3 min to 9 h 33 min), the mean waking time became significantly later (0552-0629 hours) and the mean bedtime became significantly earlier (from 1747 to 1603 hours). In the activity budget, resting increased significantly from 28.0 to 53.3%. Traveling and feeding decreased significantly from 23.5 to 12.7% and from 45.6 to 32.8%, respectively. The rate of brachiation during traveling and nest making decreased, whereas ground activity increased from 0 to 9%. We observed one vomiting incident and four occurrences of watery diarrhea during the 7 days before the individual died. The results of an autopsy performed by a local veterinarian suggested that the cause of death was septicemia because of Pseudomonas aeruginosa infection of the severely contaminated wounds. The morphology and distribution of the wounds suggested they had been incurred during an attack by a large animal with fangs and/or claws. This juvenile female became independent of its mother at ~4-5 years of age, slightly earlier than average. This individual might have been vulnerable to predatory attack because of her small body size (~5 kg at death) and lack of the mother's protection.
We observed the diet and activity of Bornean orangutans (Pongo pygmaeus morio) in the primary lowland dipterocarp forests of Danum Valley, Sabah, Malaysia, during 2005-2007, including two mast fruitings. We collected 1,785 hr of focal data on 26 orangutans. We identified 1,466 samples of their food plants and conducted a fallen fruit census to monitor fruit availability in the study area. Their activity budget was 47.2% feeding, 34.4% resting, and 16.9% traveling. Fruits accounted for the largest part (60.9%) of feeding time, especially during mast fruiting periods (64.0-100%), although the percentages of leaves (22.2%) and bark (12.3%) were higher than those reported for P. abelii and P. pygmaeus wurmbii. Although 119 genera and 160 plant species were consumed by focal animals, only 9 genera accounted for more than 3% of feeding time (total: 67.8% for 9 genera). In particular, the focal orangutans fed intensively on Ficus and Spatholobus during most of the study period, especially in periods of fruit shortage. The percentage of fruit feeding changed markedly from 11.7 to 100% across different months of the year, and was positively correlated with the amount of fallen fruit. When fruit feeding and availability decreased, orangutans fed primarily on leaves of Spatholobus and Ficus, and the bark of Spatholobus and dipterocarp. The percentage of time devoted to feeding during mast fruitings, when the orangutans foraged almost exclusively on fruits, was lower than during seasons when the orangutan diet included leaves and bark as well as fruits. Resting increased as feeding decreased in the late stage of each fruiting season, suggesting that the orangutans adopted an energy-minimizing strategy to survive the periods of fruit shortage by using energy stored during the fruit season.
Agricultural expansion is the largest threat to global biodiversity. In particular, the rapid spread of tree plantations is a primary driver of deforestation in hyperdiverse tropical regions. Plantations tend to support considerably lower biodiversity than native forest, but it remains unclear whether plantation traits affect their ability to sustain native wildlife populations, particularly for threatened taxa. If animal diversity varies across plantations with different characteristics, these traits could be manipulated to make plantations more "wildlife friendly." The degree to which plantations create edge effects that degrade habitat quality in adjacent forest also remains unclear, limiting our ability to predict wildlife persistence in mixed-use landscapes. We used systematic camera trapping to investigate mammal occurrence and diversity in oil palm plantations and adjacent forest in Sabah, Malaysian Borneo. Mammals within plantations were largely constrained to locations near native forest; the occurrence of most species and overall species richness declined abruptly with decreasing forest proximity from an estimated 14 species at the forest ecotone to -1 species 2 km into the plantation. Neither tree height nor canopy cover within plantations strongly affected mammal diversity or occurrence, suggesting that manipulating tree spacing or planting cycles might not make plantations more wildlife friendly. Plantations did not appear to generate strong edge effects; mammal richness within forest remained high and consistent up to the plantation ecotone. Our results suggest that land-sparing strategies, as opposed to efforts to make plantations more wildlife-friendly, are required for regional wildlife conservation in biodiverse tropical ecosystems.
We investigated the population density of Bornean orangutans (Pongo pygmaeus morio) and fruit availability for 10 years (2005-2014), in primary lowland dipterocarp forests in the Danum Valley, Sabah, Malaysia. During the research period, two mast fruitings and three other peak fruiting events of different scales occurred in the study area. The orangutan population density, estimated every 2 months by the marked nest count method, changed between 0.3 and 4.4 ind/km(2) and the mean population density was 1.3 ind/km(2) ± SE 0.1 (n = 56). The population density increased markedly during mast and peak fruiting periods. A significant positive correlation was observed between the population density and fruit availability in the study period (Spearman, R = 0.3, P
Vertebrate granivores destroy plant seeds, but whether animal-induced seed mortality alters plant recruitment varies with habitat context, seed traits, and among granivore species. An incomplete understanding of seed predation makes it difficult to predict how widespread extirpations of vertebrate granivores in tropical forests might affect tree communities, especially in the face of habitat disturbance. Many tropical forests are simultaneously affected by animal loss as well as habitat disturbance, but the consequences of each for forest regeneration are often studied separately or additively, and usually on a single plant demographic stage. The combined impacts of these threats could affect plant recruitment in ways that are not apparent when studied in isolation. We used wire cages to exclude large (elephants), medium, (sambar deer, bearded pigs, muntjac deer), and small (porcupines, chevrotains) ground-dwelling mammalian granivores and herbivores in logged and unlogged forests in Malaysian Borneo. We assessed the interaction between habitat disturbance (selective logging) and experimental defaunation on seed survival, germination, and seedling establishment in five dominant dipterocarp tree species spanning a 21-fold gradient in seed size. Granivore-induced seed mortality was consistently higher in logged forest. Germination of unpredated seeds was reduced in logged forest and in the absence of small to large-bodied mammals. Experimental defaunation increased germination and reduced seed removal but had little effect on seed survival. Seedling recruitment however, was more likely where logging and animal loss occurred together. The interacting effects of logging and hunting could therefore, actually increase seedling establishment, suggesting that the loss of mammals in disturbed forest could have important consequences for forest regeneration and composition.
Knowledge of niche partitioning with respect to habitat is indispensable to understand the mechanism of coexistence of multiple species. Among primates, however, data are still deficient because repeated survey for a sufficiently long time, covering seasonal changes over a large area, is the only way to clarify habitat segregation within a seasonally fluctuating environment. Southeast Asia is particularly interesting because of the supra-annual, highly unpredictable seasonality in fruiting known as mast fruiting. We conducted repeated route census, habitat monitoring, and group tracking for 25 months in two study sites (ca. 10 km apart) in the largely primary lowland dipterocarp forest of the Danum Valley Conservation Area, eastern Sabah, northern Borneo, Malaysia. The five species of diurnal primates (Bornean orangutan Pongo pygmaeus, Müeller's gibbon Hylobates muelleri, red leaf monkey Presbytis rubicunda, long-tailed macaque Macaca fascicularis, and southern pig-tailed macaque M. nemestrina) did not show horizontal spatial segregation. Red leaf monkeys showed preferences for places with short tree height, but their distribution was not confined to such places. In response to the fruiting peak observed once during the study period, orangutans increased their numbers simultaneously in the two study sites. The average tree height used by the five species was different, but their range overlapped substantially. Compared with other primate communities, the lack of horizontal spatial segregation and the suggested long-distance movement of orangutans seem to be unique characteristics in Borneo, although the use of different forest strata is a widespread phenomenon among primate communities throughout the world.
Tropical forest degradation is a global environmental issue. In degraded forests, seedling recruitment of canopy trees is vital for forest regeneration and recovery. We investigated how selective logging, a pervasive driver of tropical forest degradation, impacts canopy tree seedling recruitment, focusing on an endemic dipterocarp Dryobalanops lanceolata in Sabah, Borneo. During a mast-fruiting event in intensively logged and nearby unlogged forest, we examined four stages of the seedling recruitment process: seed production, seed predation, and negative density-dependent germination and seedling survival. Our results suggest that each stage of the seedling recruitment process is altered in logged forest. The seed crop of D. lanceolata trees in logged forest was one-third smaller than that produced by trees in unlogged forest. The functional role of vertebrates in seed predation increased in logged forest while that of non-vertebrates declined. Seeds in logged forest were less likely to germinate than those in unlogged forest. Germination increased with local-scale conspecific seed density in unlogged forest, but seedling survival tended to decline. However, both germination and seedling survival increased with local-scale conspecific seed density in logged forest. Notably, seed crop size, germination, and seedling survival tended to increase for larger trees in both unlogged and logged forests, suggesting that sustainable timber extraction and silvicultural practices designed to minimize damage to the residual stand are important to prevent seedling recruitment failure. Overall, these impacts sustained by several aspects of seedling recruitment in a mast-fruiting year suggest that intensive selective logging may affect long-term population dynamics of D. lanceolata. It is necessary to establish if other dipterocarp species, many of which are threatened by the timber trade, are similarly affected in tropical forests degraded by intensive selective logging.
Pollution with pesticides is a widespread global problem and biomonitoring of the environment and human populations is necessary to assess potential harmful biological effects. One of the pesticides that are showing up in vegetables and fruit is chlorpyrifos (CPS). CPS is a nerve-poisoning organophosphorus insecticide, which is in up to 1/3 of all conventionally produced citrus fruits. Our review shows that CPS is a hazardous material that poses risks to human health and also pollutes the environment. There is numerous risk assessment of CPS reported, however, the assessment is easily affected by factors such as climate change, exposure period and CPS concentration. Therefore, rigorous update of the hazardous level of CPS is needed to determine the threshold level safe for humans and animals. There is a need for remediation using for example photoreactive nanoparticle methods and microbial degeneration possessing high degradation efficiency (73-97%). In addition, stringent biomonitoring of food, environment and human exposure should occur to avoid exposure to chemicals via citrus fruits and vegetables. This is necessary to assess health risks and socioeconomic impacts which also require collaboration between private and public sectors to facilitate the growth, sale and manufacturing of biopesticides.
Global warming is reducing the Arctic sea-ice and causing energetic stress to marine key predatory species such as polar bears and narwhals contributing to the ongoing pollution already threatening the biodiversity and indigenous people of the vulnerable region. Now, the opening of the Arctic gateway and in particular the increase in shipping activities causes further stress to marine mammals in the region. These shipping activities are foreseen to happen in the Northwest and Northeast Passage, Northern Sea Route and Transpolar Sea Route in the Arctic Ocean, which could be yet another step towards a crucial tipping point destabilizing global climate, including weathering systems and sea-level rise. This calls for international governance through the establishment of Arctic International National Parks and more Marine Protected Areas through the Arctic Council and UN's Law of the Sea to ensure sustainable use of the Arctic Ocean and adjacent waters.
Humans influence tropical rainforest animals directly via exploitation and indirectly via habitat disturbance. Bushmeat hunting and logging occur extensively in tropical forests and have large effects on particular species. But how they alter animal diversity across landscape scales and whether their impacts are correlated across species remain less known. We used spatially widespread measurements of mammal occurrence across Malaysian Borneo and recently developed multispecies hierarchical models to assess the species richness of medium- to large-bodied terrestrial mammals while accounting for imperfect detection of all species. Hunting was associated with 31% lower species richness. Moreover, hunting remained high even where richness was very low, highlighting that hunting pressure persisted even in chronically overhunted areas. Newly logged sites had 11% lower species richness than unlogged sites, but sites logged >10 years previously had richness levels similar to those in old-growth forest. Hunting was a more serious long-term threat than logging for 91% of primate and ungulate species. Hunting and logging impacts across species were not correlated across taxa. Negative impacts of hunting were the greatest for common mammalian species, but commonness versus rarity was not related to species-specific impacts of logging. Direct human impacts appeared highly persistent and lead to defaunation of certain areas. These impacts were particularly severe for species of ecological importance as seed dispersers and herbivores. Indirect impacts were also strong but appeared to attenuate more rapidly than previously thought. The lack of correlation between direct and indirect impacts across species highlights that multifaceted conservation strategies may be needed for mammal conservation in tropical rainforests, Earth's most biodiverse ecosystems.
Habitat corridors are important tools for maintaining connectivity in increasingly fragmented landscapes, but generally they have been considered in single-species approaches. Corridors intended to facilitate the movement of multiple species could increase persistence of entire communities, but at the likely cost of being less efficient for any given species than a corridor intended specifically for that species. There have been few tests of the trade-offs between single- and multispecies corridor approaches. We assessed single-species and multispecies habitat corridors for 5 threatened mammal species in tropical forests of Borneo. We generated maps of the cost of movement across the landscape for each species based on the species' local abundance as estimated through hierarchical modeling of camera-trap data with biophysical and anthropogenic covariates. Elevation influenced local abundance of banded civets (Hemigalus derbyanus) and sun bears (Helarctos malayanus). Increased road density was associated with lower local abundance of Sunda clouded leopards (Neofelis diardi) and higher local abundance of sambar deer (Rusa unicolor). Pig-tailed macaque (Macaca nemestrina) local abundance was lower in recently logged areas. An all-species-combined connectivity scenario with least-cost paths and 1 km buffers generated total movement costs that were 27% and 23% higher for banded civets and clouded leopards, respectively, than the connectivity scenarios for those species individually. A carnivore multispecies connectivity scenario, however, increased movement cost by 2% for banded civets and clouded leopards. Likewise, an herbivore multispecies scenario provided more effective connectivity than the all-species-combined scenario for sambar and macaques. We suggest that multispecies habitat connectivity plans be tailored to groups of ecologically similar, disturbance-sensitive species to maximize their effectiveness.
Although the role of primates in seed dispersal is generally well recognized, this is not the case for colobines, which are widely distributed in Asian and African tropical forests. Colobines consume leaves, seeds and fruits, usually unripe. A group of proboscis monkeys (Colobinae, Nasalis larvatus) consisting of 1 alpha-male, 6 adult females and several immatures, was observed from May 2005 to May 2006. A total of 400 fecal samples from focal group members covering 13 months were examined, with over 3500 h of focal observation data on the group members in a forest along the Menanggul River, Sabah, Malaysia. Intact small seeds were only found in 23 of 71 samples in Nov 2005, 15 of 38 in Dec 2005 and 5 of 21 in Mar 2006. Seeds of Ficus (all <1.5 mm in length) were found in all 3 months and seeds from Antidesma thwaitesianum (all <3 mm) and Nauclea subdita (all <2 mm) only in Nov and Dec, which was consistent with members of the study group consuming fruits of these species mostly at these times. To our knowledge, these are the first records of seeds in the fecal samples of colobines. Even if colobines pass relatively few seeds intact, their high abundance and biomass could make them quantitatively significant in seed dispersal. The potential role of colobines as seed dispersers should be considered by colobine researchers.
The proliferation of camera-trapping studies has led to a spate of extensions in the known distributions of many wild cat species, not least in Borneo. However, we still do not have a clear picture of the spatial patterns of felid abundance in Southeast Asia, particularly with respect to the large areas of highly-disturbed habitat. An important obstacle to increasing the usefulness of camera trap data is the widespread practice of setting cameras at non-random locations. Non-random deployment interacts with non-random space-use by animals, causing biases in our inferences about relative abundance from detection frequencies alone. This may be a particular problem if surveys do not adequately sample the full range of habitat features present in a study region. Using camera-trapping records and incidental sightings from the Kalabakan Forest Reserve, Sabah, Malaysian Borneo, we aimed to assess the relative abundance of felid species in highly-disturbed forest, as well as investigate felid space-use and the potential for biases resulting from non-random sampling. Although the area has been intensively logged over three decades, it was found to still retain the full complement of Bornean felids, including the bay cat Pardofelis badia, a poorly known Bornean endemic. Camera-trapping using strictly random locations detected four of the five Bornean felid species and revealed inter- and intra-specific differences in space-use. We compare our results with an extensive dataset of >1,200 felid records from previous camera-trapping studies and show that the relative abundance of the bay cat, in particular, may have previously been underestimated due to the use of non-random survey locations. Further surveys for this species using random locations will be crucial in determining its conservation status. We advocate the more wide-spread use of random survey locations in future camera-trapping surveys in order to increase the robustness and generality of inferences that can be made.
We analysed the reproductive parameters of free-ranging female orangutans at Sepilok Orangutan Rehabilitation Centre (SORC) on Borneo Island, Sabah, Malaysia. Fourteen adult females produced 28 offspring in total between 1967 and 2004. The average censored interbirth interval (IBI) (i.e. offspring was still alive when mother produced a next offspring) was 6 years. This was shorter than censored IBIs reported in the wild but similar to IBIs reported for those in captivity. The nonparametric survival analysis (Kaplan-Meier method) revealed a significantly shorter IBI at SORC compared with wild orangutans in Tanjung Putting. The infant (0-3 years) mortality rate at SORC of 57% was much higher than rates reported both in the wild and captivity. The birth sex-ratio was significantly biassed toward females: 24 of the 27 sex-identified infants were females. The average age at first reproduction was 11.6 years, which is younger than the age in the wild and in captivity. The high infant mortality rate might be caused by human rearing and increased transmission of disease due to frequent proximal encounters with conspecifics around the feeding platforms (FPs). This young age of first reproduction could be because of the uncertainty regarding estimated ages of the female orangutans at SORC. It may also be affected by association with other conspecifics around FPs, which increased the number of encounters of the females with males compared with the number of encounters that would take place in the wild. Provision of FPs, which improves the nutritional condition of the females, caused the shorter IBI. The female-biassed birth sex-ratio can be explained by the Trivers and Willard hypothesis. The female-biassed sex ratio could be caused by the mothers being in poor health, parasite prevalence and/or high social stress (but not food scarcity) due to the frequent encounters with conspecifics around FPs.