The Influence of Hunting on Antipredator Behavior in Central African Monkeys and Duikers

Many animals can adjust their behavioral strategies to reduce predation risk. We investigated whether rain forest monkeys and duikers alter their antipredatory behavior in response to hunting by humans in southwestern Gabon. We compared monkey and duiker responses to human observers in an area where hunting is prohibited, to those in a nearby area where hunting pressure is moderate but spatially variable. The results of our study indicate that monkeys become more secretive when hunted, commencing alarm calls only when at a certain distance (typically > 50 m) from humans. We found no difference in monkey group size between hunted and no-hunting areas. In no-hunting areas, duikers often freeze in response to approaching observers, but in hunted areas they abandon this strategy and rapidly flee from humans. Duikers also whistle more often in areas where they are hunted frequently. Our findings have at least two important implications. First, behavioral observations of monkeys and duikers may be useful in gauging local hunting intensity in African rain forests. Second, duiker densities are likely to be overestimated in hunted areas, where they more readily flee and whistle, and underestimated in no-hunting areas, where they rely on freezing behavior to avoid detection. Because behavioral adaptations to hunting vary both among species and localities, these differences should be considered when attempting to derive population-density estimates for forest wildlife.     

Ecological inferences about marine mammals from passive acoustic data

Monitoring on the basis of sound recordings, or passive acoustic monitoring, can complement or serve as an alternative to real-time visual or aural monitoring of marine mammals and other animals by human observers. Passive acoustic data can support the estimation of common, individual-level ecological metrics, such as presence, detection-weighted occupancy, abundance and density, population viability and structure, and behaviour. Passive acoustic data also can support estimation of some community-level metrics, such as species richness and composition. The feasibility of estimation and certainty of estimates is highly context dependent, and understanding the factors that affect the reliability of measurements is useful for those considering whether to use passive acoustic data. Here, we review basic concepts and methods of passive acoustic sampling in marine systems that often are applicable to marine mammal research and conservation. Our ultimate aim is to facilitate collaboration among ecologists, bioacousticians, and data analysts. Ecological applications of passive acoustics require one to make decisions about sampling design, which in turn requires consideration of sound propagation, sampling of signals, and data storage. One also must make decisions about signal detection and classification and evaluation of the performance of algorithms for these tasks. Investment in the research and development of systems that automate detection and classification, including machine learning, are increasing. Passive acoustic monitoring is more reliable for detection of species presence than for estimation of other species-level metrics. Use of passive acoustic monitoring to distinguish among individual animals remains difficult. However, information about detection probability, vocalisation or cue rate, and relations between vocalisations and the number and behaviour of animals increases the feasibility of estimating abundance or density. Most sensor deployments are fixed in space or are sporadic, making temporal turnover in species composition more tractable to estimate than spatial turnover. Collaborations between acousticians and ecologists are most likely to be successful and rewarding when all partners critically examine and share a fundamental understanding of the target variables, sampling process, and analytical methods.     

The Importance of Hunting and Habitat in Determining the Abundance of Tropical Forest Species in Equatorial Guinea

Understanding the impact of hunting on wildlife populations is crucial to achieving sustainability and requires knowledge of prey abundance responses to different levels of exploitation. While the abundance of primates has been shown to respond independently to hunting and habitat, habitat is rarely considered simultaneously when evaluating the impacts of hunting. Furthermore, the importance of these two factors in determining the abundance of other species has not been well investigated. We evaluate the independent effects of hunting and habitat on the abundance of a diverse assemblage of species, using a series of predictions and data from a study in Equatorial Guinea. Line transect surveys in sites of varying hunting intensity and habitat, and weekly interviews with hunters on current hunting effort in each site, were conducted. We also consider the role of past hunting, and discuss the interrelationships between hunting and habitat variables. We show that for primates, hunting is important in determining abundance, while for rodents and duikers, habitat is more important. Our findings show that the effects of hunting and habitat on abundance vary greatly between species, are often confounded and require an approach that isolates their independent effects to determine the true impact of hunting. Conservation managers must consider and incorporate habitat heterogeneity when managing hunting systems, taking into account the way in which the relative importance of these factors can vary between species.     

On the merits and feasibility of wildlife monitoring for conservation: a case study from Katavi National Park,Tanzania

Although long‐term monitoring is viewed as an essential part of conserving wildlife populations, it is currently carried out in surprisingly few protected areas in Africa. Here, data from a 16‐year vehicle transect monitoring programme in Katavi National Park, western Tanzania, are presented. These data provide information on large mammal densities, identify declines in populations of several large mammal species as based on encounter rates, support worrying trends observed in aerial census data and shed light on the effectiveness of recent changes in legal protection. Ground and aerial surveys confirmed that waterbuck, topi, warthog, lion and spotted hyaena populations are all in decline and that this should be a cause for concern. Counting animals by driving vehicle transects is relatively easy and inexpensive to carry out, and data here show that such counts have several pay‐offs for conservation managers especially in identifying population declines; counts should be employed more often in East Africa and elsewhere.     

Predation on primates: Ecological patterns and evolutionary consequences

It has long been thought that predation has had important ecological and evolutionary effects on primates as prey. Predation has been theorized to have been a major selective force in the evolution of hominids.¹ In modern primates, behaviors such as active defense, concealment, vigilance, flight, and alarm calls have been attributed to the selective pressures of predation, as has group living itself. It is clear that primates, like other animals, have evolved ways to minimize their risk of predation. However, the extent to which they have been able to do so, given other constraints of living such as their own need to acquire food, has not yet been resolved. Perhaps most hotly debated is whether predation has been the primary selective force favoring the evolution of group living in primates. Part of the difficulty in resolving the debate lies in a paucity of direct evidence of predation. This is regrettable yet understandable since primatologists, by definition, focus on the study of primates, not predators of primates (unless these are also primates). Systematic direct evidence of the effects of predation can best be obtained by studying predators that are as habituated to observers as are their primate prey. Until this is done, we must continue to rely on opportunistic accounts of predation and predation attempts, and on systematically obtained indirect evidence. Such data reveal several interesting patterns: (1) although smaller primates may have greater predation rates than larger primates, even the largest primates are not invulnerable to predation; (2) the use by primates of unfamiliar areas can result in higher predation rates, which might be one pressure favoring philopatry, or site fidelity; (3) arboreal primates are at greater risk of predation when they are more exposed (at forest edges and tops of canopies) than in more concealed locations; (4) predation by mammalian carnivores may often be episodic; and (5) terrestrial primates may not experience greater predation than arboreal primates.     

Primates as Predictors of Mammal Community Diversity in the Forest Ecosystems of Madagascar

The geographic distribution of species is the typical metric for identifying priority areas for conservation. Since most biodiversity remains poorly studied, a subset of charismatic species, such as primates, often stand as surrogates for total biodiversity. A central question is therefore, how effectively do primates predict the pooled species richness of other mammalian taxa? We used lemurs as indicator species to predict total non-primate mammal community richness in the forest ecosystems of Madagascar. We combine environmental and species occurrence data to ascertain the extent to which primate diversity can predict (1) non-primate mammal α-diversity (species richness), (2) non-primate complementarity, and (3) non-primate β-diversity (species turnover). Our results indicate that primates are effective predictors of non-primate mammal community diversity in the forest ecosystems of Madagascar after controlling for habitat. When individual orders of mammals are considered, lemurs effectively predict the species richness of carnivorans and rodents (but not afrosoricids), complementarity of rodents (but not carnivorans or afrosoricids), and all individual components of β-diversity. We conclude that lemurs effectively predict total non-primate community richness. However, surrogate species alone cannot achieve complete representation of biodiversity.     

Mammal distribution in a Central African logging concession area

We used data collected during a routine forest inventory to prepare a management plan for a logging concession in Gabon to identify the biophysical and human factors that better explain the distribution of mammal species within the logged-over landscape. Results of a Multiple Correspondence Analysis show that the distribution of mammals within the forest concession is more influenced by roads and hunting than by the direct effects of logging. The structure of the canopy and that of the understorey are also important factors explaining the distribution of mammals within the concession. Linear regressions and Spearman correlation tests were computed to assess the significance of the correlation between the probability of encounter for a particular species and the distance from main roads. Small diurnal monkeys were found far from the villages and between 3 and 10 km from the main roads. Elephants were equally found close or far from roads and do not seem to be affected by hunting activities. Red duikers and the yellow back duikers avoided hunted zones and were significantly more abundant far from roads. Other species like gorillas, chimpanzees or forest buffaloes show no negative relationship with distance to roads and were observed close to villages. We show also how using routinely collected data without research purposes, can be used to propose practical recommendations to managers to limit the negative impacts of logging activities within the concession.     

Automatic Round-the-Clock Detection of Whales for Mitigation from Underwater Noise Impacts

Loud hydroacoustic sources, such as naval mid-frequency sonars or airguns for marine geophysical prospecting, have been increasingly criticized for their possible negative effects on marine mammals and were implicated in several whale stranding events. Competent authorities now regularly request the implementation of mitigation measures, including the shut-down of acoustic sources when marine mammals are sighted within a predefined exclusion zone. Commonly, ship-based marine mammal observers (MMOs) are employed to visually monitor this zone. This approach is personnel-intensive and not applicable during night time, even though most hydroacoustic activities run day and night. This study describes and evaluates an automatic, ship-based, thermographic whale detection system that continuously scans the ship’s environs for whale blows. Its performance is independent of daylight and exhibits an almost uniform, omnidirectional detection probability within a radius of 5 km. It outperforms alerted observers in terms of number of detected blows and ship-whale encounters. Our results demonstrate that thermal imaging can be used for reliable and continuous marine mammal protection.     

Does climate variability influence the demography of wild primates? Evidence from long‐term life‐history data in seven species

Earth's rapidly changing climate creates a growing need to understand how demographic processes in natural populations are affected by climate variability, particularly among organisms threatened by extinction. Long‐term, large‐scale, and cross‐taxon studies of vital rate variation in relation to climate variability can be particularly valuable because they can reveal environmental drivers that affect multiple species over extensive regions. Few such data exist for animals with slow life histories, particularly in the tropics, where climate variation over large‐scale space is asynchronous. As our closest relatives, nonhuman primates are especially valuable as a resource to understand the roles of climate variability and climate change in human evolutionary history. Here, we provide the first comprehensive investigation of vital rate variation in relation to climate variability among wild primates. We ask whether primates are sensitive to global changes that are universal (e.g., higher temperature, large‐scale climate oscillations) or whether they are more sensitive to global change effects that are local (e.g., more rain in some places), which would complicate predictions of how primates in general will respond to climate change. To address these questions, we use a database of long‐term life‐history data for natural populations of seven primate species that have been studied for 29–52 years to investigate associations between vital rate variation, local climate variability, and global climate oscillations. Associations between vital rates and climate variability varied among species and depended on the time windows considered, highlighting the importance of temporal scale in detection of such effects. We found strong climate signals in the fertility rates of three species. However, survival, which has a greater impact on population growth, was little affected by climate variability. Thus, we found evidence for demographic buffering of life histories, but also evidence of mechanisms by which climate change could affect the fates of wild primates.     

Fruit and fibre: the nutritional value of figs for a small tropical ruminant,the blue duiker (Cephalophus monticola)

Tropical forests throughout the world are home to a guild of small ruminants that consume fruit as a substantial portion of their diet. Because the rumen is relatively inefficient at digesting nonstructural carbohydrates and only slowly digests cellulose, the feeding adaptations of frugivorous ruminants are enigmatic. We examined the nutritional value of wild figs to blue duikers, one of the smallest and most frugivorous ruminants, through chemical analyses and a series of digestion trials with six species of wild African figs. These figs were high in fat, protein, cell wall, lignin and Ca : P ratios, low in sugar and starch, and high in unextractable, fibre‐bound tannins when compared with many other fruits. The fibre‐bound tannins and protein caused protein digestibility and nitrogen balance to be consistently low or negative. The high fibre content of the figs allowed duikers to only digest 30–60% of energy contained in the figs. However, duikers were able to consume enough digestible energy to maintain body mass during 4‐day trials. Therefore, a ruminant digestive system is beneficial to mammals eating high fibre, high‐tannin tropical fruit like figs, especially if the mammal is small enough to harvest a sufficient amount to meet its daily energy requirements and has adaptations for reducing the effects of tannins on protein digestibility.     

Comparing motion capture cameras versus human observer monitoring of mammal movement through fence gaps: a case study from Kenya

Monitoring the movement and distribution of wildlife is a critical tool of an adaptive management framework for wildlife conservation. We installed motion‐triggered cameras to capture the movement of mammals through two purpose‐built migration gaps in an otherwise fenced conservancy in northern Kenya. We compared the results to data gathered over the same time period (1 Jan 2011–31 Dec 2012) by the human observers monitoring mammal tracks left at the same fence gaps in a sandy loam detection strip. The camera traps detected more crossing events, more species and more individuals of each species per crossing event than did the human track observers. We tested for volume detection differences between methods for the five most common species crossing each gap and found that all detection rates were heavily weighted towards the camera‐trap method. We review some of the discrepancies between the methods and conclude that although the camera traps record more data, the management of that data can be time‐consuming and ill‐suited to some time‐sensitive decision‐making. We also discuss the importance of daily track monitoring for adaptive management conservation and community security.     

Testing the importance of auditory detections in avian point counts

ABSTRACT.   Recent advances in the methods used to estimate detection probability during point counts suggest that the detection process is shaped by the types of cues available to observers. For example, models of the detection process based on distance-sampling or time-of-detection methods may yield different results for auditory versus visual cues because of differences in the factors that affect the transmission of these cues from a bird to an observer or differences in an observer's ability to localize cues. Previous studies suggest that auditory detections predominate in forested habitats, but it is not clear how often observers hear birds prior to detecting them visually. We hypothesized that auditory cues might be even more important than previously reported, so we conducted an experiment in a forested habitat in North Carolina that allowed us to better separate auditory and visual detections. Three teams of three observers each performed simultaneous 3-min unlimited-radius point counts at 30 points in a mixed-hardwood forest. One team member could see, but not hear birds, one could hear, but not see, and the third was nonhandicapped. Of the total number of birds detected, 2.9% were detected by deafened observers, 75.1% by blinded observers, and 78.2% by nonhandicapped observers. Detections by blinded and nonhandicapped observers were the same only 54% of the time. Our results suggest that the detection of birds in forest habitats is almost entirely by auditory cues. Because many factors affect the probability that observers will detect auditory cues, the accuracy and precision of avian point count estimates are likely lower than assumed by most field ornithologists.     

Selection of line-transect methods for estimating the density of group-living animals: lessons from the primates

We review the four major contemporary methods for estimating density of group-living animals from line-transect sampling: perpendicular modelling of group centers, perpendicular modelling of center of measurable individuals, strip transects and animal-observer distance. The efficacy of each method is evaluated to produce a simple selection guide. We review the literature and use field data from the Udzungwa Mountains, Tanzania. The review is relevant to all group-living animals; however, examples are drawn from the primates. Perpendicular methods have better mathematical justification than non-perpendicular methods. For perpendicular methods using detection function models, it is preferable to measure group location using center of measurable individuals, as group centers are hard to estimate. The assumptions of detection function models are often broken in poor visibility habitats or with unhabituated animals. Alternatively strip transects may be used where there are reliable data on group spread and/or visibility. Strip transects are also the most practical, along with the animal-observer method; however, the latter lacks mathematical justification. We conclude that there are arguments for continued use of all four methods. In certain situations the use of raw encounter rates may also be considered. The appropriate method is determined by minimizing bias and considering time, resources and field conditions.     

Detection of Iberian terrestrial mammals employing olfactory,visual and auditory attractants

Whereas high lure specificity for mammal monitoring is often sought, little effort has been put into identifying general-purpose attractants for multispecies mammal surveys. We examined whether the olfactory lures ‘fatty acid scent’ (FAS) and catnip oil differ in their ability to detect Iberian larger mammals (body mass >?800 g, i.e. lagomorphs, ungulates and most carnivores); whether the addition of visual and acoustic stimuli increases detection efficiency; and whether environmental variables interact with lures to influence detection. Three treatments were randomly assigned to 192 detection plots: olfactory lures only, visual lures (a combination of olfactory and visual stimuli) and auditory lures (all three types of stimuli). The design was balanced across two detection methods and three landscapes. Out of 13 target species, two were absent in the study plots and six (three common and three rare species) were detected with low frequency. The two olfactory attractants produced similar detection rates for species allowing analysis. The addition of visual and auditory stimuli did not increase detection and apparently induced repulsion for some species. Environmental variables associated with scent diffusion and lure visibility did not significantly influence mammal detection. Monitoring of mammal communities over large areas may gain efficiency by selecting lures that are simple, have a constant chemical composition, require short handling times and allow detection of all occurring species. A single olfactory attractant (FAS) could be suitable for designing large-scale monitoring programmes at least for five common mammal species, provided that passive detection methods and lure use are chosen.     

Comparison of Methods of Monitoring Wildlife Crossing-Structures on Highways

ABSTRACT Wildlife crossing-structures (e.g., underpasses and overpasses) are used to mitigate deleterious effects of highways on wildlife populations. Evaluating performance of mitigation measures depends on monitoring structures for wildlife use. We analyzed efficacy of 2 noninvasive methods commonly used to monitor crossing-structure use by large mammals: tracking and motion-activated cameras. We monitored 15 crossing-structures every other day between 29 June and 24 October 2007 along the Trans-Canada Highway in Alberta, Canada. Our objectives were to determine how species-specific detection rates are biased by the detection method used, to determine factors contributing to crossing-event detection, and to evaluate the most cost-effective approach to monitoring. We detected 3,405 crossing events by tracks and 4,430 crossings events by camera for mammals coyote-sized and larger. Coyotes (Canis latrans) and grizzly bears (Ursus arctos) were significantly more likely to be detected by track-pads, whereas elk (Cervus elaphus) and deer (Odocoileus sp.) were more likely to be detected by cameras. Crossing-event detection was affected by species, track-pad length, and number of animals using the crossing structure. At the levels of animal activity observed in our study our economic analysis indicates that cameras are more cost-effective than track-pads for study durations >1 year. Understanding the benefits and limitations of camera and track-pad methods for monitoring large mammal movement at wildlife crossing-structures will help improve the efficiency of studies designed to evaluate the effectiveness of highway mitigation measures.     

Fruit size, crop mass, and plant height explain differential fruit choice of primates and birds

Seed dispersal by animals is an important ecological process shaping plant regeneration. In general, seed dispersers are highly variable and often opportunistic in their fruit choice. Despite much research, the factors that can explain patterns of fruit consumption among different animal groups remain contentious. Here, we analysed the interactions between 81 animal species feeding on the fruits of 30 plant species in Kakamega Forest, Kenya, during 840 h of observations. Our aim was to determine whether plant characteristics, fruit morphology, fruit colours and/or fruit compounds such as water, sugar, phenols and tannins explained the relative importance of fruit consumption by the two most important consumer groups, primates and birds. We found significant differences in fruit choice between both groups. Primates fed on larger fruits and on higher trees that had larger fruit crops, whereas birds were observed feeding on smaller fruits and on smaller plants producing fewer fruits. Fruit colours did not differ between fruits consumed by primates and those consumed by birds. However, differences in the fruit choice among frugivorous birds were associated with differences in fruit colours. Smaller plants with smaller fruits produced red fruits which contrasted strongly with the background; these fruits were dispersed by a distinct set of bird species. The contents of water, sugar, phenols and tannins did not differ between fruits eaten by primates and those eaten by birds. Some phylogenetic patterns were apparent; primates fed preferentially on a phylogenetically restricted subsample of large plants with large fruits of the subclass Rosidae. We discuss why the observed primate dispersal syndrome is most likely explained by a process of ecological fitting.     

Life in a fragment: Evolution of foraging strategies of translocated collared brown lemurs,Eulemur collaris,over an 18-year period

While the drivers of primate persistence in forest fragments have been often considered at the population level, the strategies to persist in these habitats have been little investigated at the individual or group level. Considering the rapid variation of fragment characteristics over time, longitudinal data on primates living in fragmented habitats are necessary to understand the key elements for their persistence. Since translocated animals have to cope with unfamiliar areas and face unknown fluctuations in food abundance, they offer the opportunity to study the factors contributing to successful migration between fragments. Here, we illustrated the evolution of the foraging strategies of translocated collared brown lemurs (Eulemur collaris) over an 18-year period in the Mandena Conservation Zone, south-east Madagascar. Our aim was to explore the ability of these frugivorous lemurs to adjust to recently colonized fragmented forests. Although the lemurs remained mainly frugivorous throughout the study period, over the years we identified a reduction in the consumption of leaves and exotic/pioneer plant species. These adjustments were expected in frugivorous primates living in a degraded area, but we hypothesize that they may also reflect the initial need to cope with an unfamiliar environment after the translocation. Since fragmentation is often associated with the loss of large trees and native vegetation, we suggest that the availability of exotic and/or pioneer plant species can provide an easy-to-access, nonseasonal food resource and be a key factor for persistence during the initial stage of the recolonization.     

Night and day: evaluating transect methodologies to monitor duikers in the Dzanga‐Sangha Protected Areas,Central African Republic

Across the Congo Basin, human hunting pressure poses the biggest threat to small‐ and medium‐bodied forest ungulates (genus Philantomba and Cephalophus, commonly known as duikers). The exploitation of these species has cascading effects on larger ecosystem processes, as well as on human subsistence practices. This study compares encounter rates and estimated population densities of duiker species, specifically Philantomba monticola (blue duiker) in the Dzanga‐Sangha Protected Areas (APDS), Central African Republic (CAR). Data were collected using direct observations of individual animals during diurnal (135 km) and nocturnal (150 km) transects in the APDS, with abundance estimates produced using DISTANCE software. Transect data demonstrate that within hunted forests similar to APDS, nocturnal rather than diurnal transects yield more individual observations of ungulates. Despite hunting pressure in the region, estimates presented for APDS suggest some of the highest density estimates reported for blue duikers in western and central Africa (58.6 blue duikers per km²). This study directly contributes current regional data on the status of duiker populations at APDS and in the larger Sangha Trinational Landscape (TNS, UNESCO). More broadly, we highlight the potential importance of nocturnal transect data to the development of adaptive management regimes in hunted forests.     

When carnivores are “full and lazy”

Are animals usually hungry and busily looking for food, or do they often meet their energetic and other needs in the 24 h of a day? Focusing on carnivores, I provide evidence for the latter scenario. I develop a model that predicts the minimum food abundance at which a carnivore reaches satiation and is released from time constraints. Literature data from five invertebrate and vertebrate species suggest that food abundances experienced in the field often exceed this threshold. A comparison of energetic demands to kill rates also suggests that carnivores often reach satiation: for the 16 bird and mammal species analyzed, this frequency is 88% (average across species). Because pressure of time would likely lead to trade-offs in time allocation and thus to a nonsatiating food consumption, these results suggest that carnivores are often released from time constraints.     

Effect of observer experience on the monitoring of a mouflon population

Analysis of changes in population size can be severely biased when factors related to the acquisition of data, such as differences between observer experience and changes through time in the ability of individual observers to detect animals, are not controlled for. We analysed the effect of observer qualification on the number of groups and individuals observed during two census days of a mouflonOvis gmelini musimon xOvis sp. population. The difference between professional wildlife biologists and volunteers was strong during the census day one (87 groups and 410 mouflons vs 55 and 249 by experienced observers and volunteers, respectively) but decreased significantly on the second day for the number of animals detected (390 vs 292 mouflons by experienced observers and volunteers, respectively). Our result indicates that additional training will enhance reliability of data obtained from volunteers. Given the effect of observer qualification on performance during the census, we recommend to use observers of similar and adequate qualification in population counts.