Comparing the Use of Camera Traps and Farmer Reports to Study Crop Feeding Behavior of Moor Macaques (Macaca maura)
Investigating crop feeding patterns by primates is an increasingly important objective for primatologists and conservation practitioners alike. Although camera trap technology is used to study primates and other wildlife in numerous ways, i.e., activity patterns, social structure, species richness, abundance, density, diet, and demography, it is comparatively underused in the study of human–primate interactions. We compare photographic (N = 210) and video (N = 141) data of crop feeding moor macaques (Macaca maura) from remote sensor cameras, functioning for 231 trap days, with ethnographic data generated from semistructured interviews with local farmers. Our results indicate that camera traps can provide data on the following aspects of crop feeding behavior: species, crop type and phase targeted, harvesting technique used, and daily and seasonal patterns of crop feeding activity. We found camera traps less useful, however, in providing information on the individual identification and age/sex class of crop feeders, exact group size, and amount of crops consumed by the moor macaques. While farmer reports match camera trap data regarding crop feeding species and how wildlife access the gardens, they differ when addressing crop feeding event frequency and timing. Understanding the mismatches between camera trap data and farmer reports is valuable to conservation efforts that aim to mitigate the conflict between crop feeding wildlife and human livelihoods. For example, such information can influence changes in the way certain methods are used to deter crop feeding animals from damaging crops. Ultimately, we recommend using remote-sensing camera technology in conjunction with other methods to study crop feeding behavior.
KeywordsBehavioral flexibility Crop raiding Ethnoprimatology Human–wildlife conflict Macaca maura Methods
Across many areas of the world, agricultural areas continue to expand, often eliminating or encroaching on wildlife habitat and resulting in considerable human–wildlife conflict (Woodroffe et al. 2005). Some wildlife, such as primates, can flexibly adapt to such alterations in their habitat by incorporating agricultural crops into their dietary repertoire, a behavior commonly referred to as crop raiding, or more recently, crop foraging or crop feeding (Hockings et al.2015; see also Hill 2015). Multiple primate species are well-known crop feeders, e.g., capuchins (Cebus spp.: McKinney 2011), macaques (Macaca spp.: Riley 2007), baboons (Papio spp.: Strum 2010), and chimpanzees (Pan troglodytes: Hockings et al. 2009). In many cases, primates’ intelligence and agility help them gain access to agricultural areas, while large group size and diurnal activity make certain species more conspicuous crop feeders than other wildlife (Riley 2007).
Because of the detrimental impact crop feeding behavior can have on human livelihoods and the likelihood of local support for conservation efforts, this flexible behavior has become an impediment to primate conservation. Understanding the underlying causes of crop feeding and the factors that might lead to effective mitigation programs has therefore become an important concern for primatologists and conservation practitioners (Hockings and Humle 2009; Strum 2010; Woodroffe et al. 2005). To do so requires the documentation of patterns of crop feeding, thereby making the methodology behind the study of human–wildlife conflict worthy of investigation in and of itself.
To date, primate crop feeding behavior has been studied using various data collection methods, including direct observation (Priston et al. 2012); feeding traces, i.e., inspecting food remains for evidence of species-specific harvesting and consumption techniques such as ripped stems and bite marks (Riley 2007), fecal analysis (Bessa et al. 2015; McLennan 2013), and ethnographic interviews (Hill 1997; Linkie et al. 2007). Direct observation is advantageous because it can generate more accurate measures of the timing, frequency, and amount of damage caused by crop feeding, and it enables researchers to collect demographic information on participating crop feeding individuals (Hockings et al. 2009). However, it can be difficult to conduct direct observations on crop feeding primates, particularly if they are unhabituated. There are also important ethical concerns to consider when choosing direct observation as the primary strategy, namely, that habituation (which direct observation typically necessitates) may lead to increased rates of crop feeding (Fedigan 2010; Seiler and Robbins 2016), and rapport with farmers may be compromised by the fact that researchers allow crop feeding to happen during observations, thereby negatively impacting farmers’ livelihoods. For these reasons, indirect methods tend to be more frequently used. For example, Riley (2007) measured the amount and seasonality of feeding on cacao pods by unhabituated Tonkean macaques (Macaca tonkeana) and other wildlife by quantifying feeding traces. To study the foraging strategies of chimpanzees living in matrix habitat in Bulindi, Uganda, McLennan (2013) examined feeding traces and collected fecal samples, which identified four important cultivated fruits (cacao, guava, mango, and papaya) in the chimpanzee diet. The farmers themselves who suffer from crop feeding are also sources of information regarding the timing, frequency, and severity of the damage along with the species responsible for the damage (Hill 1997). However, farmer reports may conflict with data from other sources, resulting in varying information on the extent of crop damage (Naughton-Treves 1997; Riley 2007) and identification of the species responsible for the most damage (Linkie et al. 2007; Siex and Struhsaker 1999). Another potential tool for indirect measurement that is becoming increasingly popular to study human–wildlife conflict, including crop feeding behavior, are remote sensor cameras, or camera traps (Krief et al. 2014).
Camera traps are increasingly being used by primatologists, primarily because they allow researchers to conduct noninvasive observations, eliminate the need to habituate, and collect data in a variety of locations, time periods, and conditions (O’Connell et al. 2011; Pebsworth and LaFleur 2014). Accordingly, researchers have used this method to examine a suite of variables, including activity patterns, species richness, abundance, density, demography, and interactions among predators, prey, and competitors (Farris et al. 2014; Galvis et al. 2014). For example, camera traps revealed nocturnal activity patterns in the Guizhou snub-nosed monkey (Rhinopithecus brelichi), a species long assumed to be diurnal (Tan et al. 2013). They have also been useful in documenting the presence, demography, and social behavior of unhabituated primate groups (Bezerra et al.2014; Boyer-Ontl and Pruetz 2014). Camera traps may therefore be an alternative method for studying crop feeding, particularly when direct behavioral observation is difficult and/or ethically problematic because of concerns regarding increased likelihood of crop feeding and increased risk of injury or death for habituated, crop feeding primates.
Human–primate conflict due to crop feeding is particularly salient in Indonesia given that it supports the richest nonhuman primate fauna of any Asian country, i.e., ca. 44 species, 84% of which are listed as threatened with extinction (IUCN 2008). In the last 50 years, >40% of the country’s forests have been cleared, primarily for agricultural development (Barber et al. 2002), and >60% of the human population lives in rural areas relying on agriculture as a primary source of income (ILO 2012). Macaques are especially problematic because they are highly adaptable and often thrive in secondary forests, disturbed habitats, buffer zones, and along forest–agricultural edges (Brotcorne et al. 2014; Richard et al. 1989). Human–macaque interactions in Sulawesi occur predominantly at the forest–farm interface (Priston et al. 2012; Riley 2007), where crop feeding is a common behavior exhibited by all species of Sulawesi macaques (Riley 2010).
The moor macaque (Macaca maura) is one of the seven macaque species that inhabit Sulawesi (Fooden 1969). They live in the southwest region of the island in multimale–multifemale, female philopatric social groups that range in size from ca. 15–40 individuals (Okamoto et al. 2000; Watanabe and Matsumura 1996). Moor macaques in this region of South Sulawesi inhabit dipterocarp forest with limestone formations in addition to forests adjacent to agricultural areas (Supriatna et al. 1992). They are primarily frugivorous but also eat leaves, flowers, shoots, and stems from trees, shrubs, and herbaceous vegetation, with figs (Ficus spp.) comprising a large part of their diet, as well as insects (Matsumura 1991; Sagnotti 2013). Many macaque species also feed on cultivated foods. Supriatna et al. (1992) reported that moor macaques feed on the following crops: corn, banana, tomato, coconut, long bean, soybean, peanut, bushbean, eggplant, cassava, sweet potato, jackfruit, cacao, orange, cashew, guava, and mango.
We here evaluate two methods used to assess crop feeding behavior by moor macaques in South Sulawesi, Indonesia: observations via remote sensor cameras and local farmers’ reports. We collected these data as part of a broader ethnoprimatological, i.e., the study of the human–primate interface, project examining the ecological and nutritional correlates of crop feeding by moor macaques and farmers’ perceptions of and reactions to this behavior. Our objective here is twofold. First, we evaluate the effectiveness of camera traps in studying crop feeding behavior by unhabituated moor macaques. Specifically, we ask: What elements of crop feeding behavior can be measured using camera traps? What can camera traps tell us about crop feeding as a flexible behavioral strategy? Because camera traps are best suited for detecting gregarious, relatively large-bodied, ground-dwelling species (Tobler et al. 2008; Treves et al. 2010), we predicted that this method would be suitable for examining crop feeding by moor macaques, a species known for being both arboreal and terrestrial (Sagnotti 2013). Second, we examine how camera trap data compare with local farmers’ perceptions of the conflict derived from ethnographic research. Given that previous studies have found that farmers’ reports may contrast with findings from other methods (Linkie et al. 2007; Riley 2007), we predicted that farmers’ reports would deviate from camera trap results on the frequency and timing of crop feeding events, and the species most responsible.
Study Site and Study Species
We defined a crop feeding event (CFE) as a situation in which one or more macaques were present in a garden. A CFE was considered independent if >1 h had passed between captured images. We chose the time designation of 1 h based on camera trap recorded CFE durations. Macaque CFEs were broken down further into two categories. A potential CFE occurred when one or more individuals were simply present in the garden. An actual CFE occurred if the photo/video indicated physical manipulation and/or consumption of human-cultivated food items. We installed three cameras in the mixed-crop garden, which is maintained by only one farmer and his family, and where cacao, coffee, bananas, ginger, chilies, short beans, and other fruits are grown. We installed two cameras along the edge of the cacao stand, facing the majority of the trees. We placed another camera within the garden, and moved it depending on the location of fruiting trees. Crops were available at this location throughout the study period. We installed five cameras along the edge of or within the monocrop garden where watermelon (available August–September), corn (available September–October), and wet rice (not available during the study period) are planted depending on the season. This garden is managed by several farmers depending on the current crop type. At the time of this project, there were zero to five farmers working at this location at any given time. We installed multiple cameras that monitored the same general area to have a better view of the areas macaques were known to access repeatedly because of the larger and more open nature of this garden. We installed and took down individual camera traps on different days, resulting in varying numbers of trap days for each unit. We moved one camera in the mixed-crop garden on two separate occasions depending on the presence/absence of macaque crop feeding activity in the area and location of fruiting trees, and we removed one camera in the monocrop garden because it was damaged. We based our decisions for camera trap location on the willingness of the farmers to participate in the project, farmer knowledge about how macaques access the gardens, and other practical considerations, e.g., wind, vegetation obstruction, desired camera height, equipment security, and so forth. We used a 32 GB Class 4 SDHC memory card in each camera and monitored the equipment monthly to ensure proper camera function and maintain memory storage.
When a camera was installed, we collected the following information: camera ID, GPS location, date, and height. We downloaded photos and videos in the field onto a laptop. We then inspected each photograph/video for presence of crop feeding wildlife or other relevant information, e.g., presence of people, dogs, and so on. Photos containing potentially crop feeding wildlife were assigned a number and placed in a digital folder based on the date downloaded. We catalogued all saved photographs/videos in a spreadsheet containing the following information: camera ID, date downloaded, photo ID, date, time, species, and number of individuals. We opportunistically collected data on human crop guarding from the camera traps in the mixed-crop garden. This was possible because of the smaller size of the garden, and therefore the increased likelihood that human presence would also be recorded by the camera traps. Guarding occurs when one or more humans are present in or near the garden and able to chase away animals that may attempt to enter.
Semistructured interview questions conducted with farmers in Bengo, South Sulawesi, Indonesia
Year of birth
How long have you lived here?
How big is your garden?
How long have you been farming here?
What types of food do you grow?
How far is your garden from the village?
What kinds of animals, if any, raid your garden?
How often do monkeys raid your garden?
What time of day do the monkeys raid?
Where did the monkeys come from?
How long have monkeys been raiding your garden/raiding in this area?
How many groups of monkeys live nearby?
What food items have monkeys eaten/damaged on your property?
How do you deter the monkeys from raiding your garden?
How often do you employ these deterrence methods?
How well do these deterrence methods work?
Does raiding occur more frequently now than in the past?
How does raiding affect your livelihood?
Do you think people should chase monkeys? Why or why not?
We sorted and interpreted photographs and videos from the camera traps to reveal the frequency and timing of CFEs. We analyzed crop feeding data primarily using descriptive statistics. Using SPSS v. 22, we conducted chi-squared goodness of fit tests to evaluate differences in the number of crop feeding events across different time periods: 05:00–09:00, 10:00–14:00, and 15:00–18:00 h, and morning vs. afternoon. We considered results significant at P < 0.05. We transcribed and qualitatively analyzed interview responses through coding and identification of major themes (LeCompte and Schensul 1999).
Farmers who agreed to have cameras installed on their property were instructed to react to CFEs as they normally would. If photographs/videos of people contained relevant information about wildlife crop feeding or guarding behavior, we made note of the event but deleted the image file to protect the privacy of the farmers. The research complied with protocols approved by the SDSU Institutional Animal Care and Use Committee, IACUC (APF #14-03-007R) and Institutional Review Board for Human Subjects (vIRB approval #1721094), and adhered to the legal requirements for foreigners conducting research in Indonesia.
CFEs Captured by Camera Traps
Image data of moor macaques from eight camera traps located inside the mixed-crop and monocrop gardens from July 2014 through March 2015
Total no. of saved photos and videos
Photos of macaques
Videos of macaques
Crop Feeding Species and Crop Type Affected: Farmers’ Reports and Camera Trap Data Align
Comparison of farmer response frequency and CFE frequency of crop feeding species from July 2014–March 2015
Wildlife speciesa (Indonesian name)
Total number of farmer responsesb (N = 6)
Frequency of CFEsc
Wild pig (babi hutan)
CFE Frequency and Timing: Farmers’ Reports and Camera Trap Data Do Not Align
Farmers reported that macaques feed on crops any time of day, whenever there is an opportunity, e.g., the garden is unguarded, because the “food is delicious and easy to access.” Farmers did not report the occurrence of crop feeding by macaques at night. Farmers also joked about when macaques crop feed: “If we are tired and want to nap, then the monkeys come!” or “If I think it has been a while since I have seen monkeys and they must be far away, that’s when they come!” While farmers reported that many CFEs occur in the morning (06:00–11:00 h), in contrast to the camera trap data, the most frequently reported time of day was dusk (17:00–18:00 h). Farmers typically leave their gardens or have already gone home for the day by dusk. Two farmers reported that monkeys will hide nearby a garden and wait for the farmers to leave before crop feeding.
Entire Groups or Single Individuals? Farmers’ Reports and Camera Traps Align
Farmers (N = 4) report that entire groups and individuals may crop feed, depending on human presence. They report that entire groups crop feed successfully and cause more damage when crops are unguarded, but that single individuals may successfully crop feed while people are present in the garden and still cause damage. The camera traps recorded 27 individual CFEs and 30 group CFEs in the mixed-crop garden. There were seven individual CFEs and three group CFEs in the monocrop garden. There were 1–13 individuals captured in a single photograph or video.
Our results indicate that with proper attention to camera location and placement, camera traps can provide data on crop feeding species, crop type and phase targeted, daily and seasonal patterns of crop feeding activity, and whether groups and/or single individuals crop feed. Video data from camera traps can also provide critical information on the different harvesting techniques used by feeding wildlife, which could in turn inform subsequent studies that use the feeding traces method (see ESM Video 2). However, our study also revealed the limitations of this method. Although camera traps may allow for individual identification of large, solitary animals with distinct markings (see Wegge et al. 2004), we found identifying individual primates to be difficult and unreliable. We attempted to identify active crop feeders (individuals actively manipulating a food item in a garden) by age and sex class but quickly found that our identifications were likely biased toward individuals that are more conspicuous and therefore easier to identify, i.e., adult males. As has been noted in other camera trap studies, the detection probability of individuals is lower than large social groups (Treves et al. 2010), meaning that camera traps are also more likely to capture group vs. individual CFEs. For this reason, sample frequencies of group CFEs are likely to be more representative than individual CFEs. Although camera traps will likely capture evidence of a primate group’s presence in a garden, they cannot be relied on to provide consistent photographic evidence regarding actual manipulation and/or consumption of crop items. Therefore, it is likely that many of the potential CFEs in this study are actual CFEs. Finally, camera traps are not effective in helping to assess the severity of crop feeding damage. Additional methods such as examining food traces (Riley 2007) and talking directly with the farmers (Hill 1997; Linkie et al. 2007) are needed to assess post-crop feeding damage.
Previous research in Sumatra, Indonesia, and Uganda has found that farmer reports regarding crop feeding do not always coincide with results from other methods and farmers’ perceived risk of crop loss is often greater than observed crop damage (Linkie et al. 2007; Webber and Hill 2014). In our study, the fact that the placement of cameras, which was suggested by participating farmers, was successful in capturing CFEs indicates that farmers’ reports and camera trap data coincide. Farmers’ reports of specific crops targeted, the species that crop feed, and the most frequent and destructive crop feeding species, i.e., macaques and wild pigs, also coincide with camera trap data. However, we found that farmer reports differ from photographic data in identifying the timing of crop feeding events. According to farmers, macaques will raid any time of day, whenever there is an opportunity, suggesting that CFEs are more likely to occur when a garden is unguarded. Although farmers report that many CFEs occur in the morning, the most frequently reported time of day was dusk, when farmers are typically leaving their gardens. Our camera trap data show that the most actual CFEs occurred in the early afternoon, a time when most farmers reported being present in their gardens. This discrepancy might be explained by farmers’ beliefs that simply being present in the garden is an effective deterrence method. In contrast, guarding was found to be more effective for certain species when practiced by an actively patrolling, armed male (Hill and Wallace 2012), in combination with other active threats (Osborn and Hill 2005).
Our results also indicate a mismatch between farmers’ reports and camera trap data on the frequency of macaque CFEs. Although most farmers reported CFEs occurring multiple times per week, camera traps captured far fewer CFEs than would be expected based on this report. Farmers may associate more destructive crop feeding behavior with a conspicuous, large-bodied, diurnal species such as macaques simply because they encounter them more frequently (Linkie et al. 2007). During interviews, farmers shared stories about entire crops being destroyed in a single CFE. One farmer explained that he feels lucky when he harvests anything at all. In contrast, two interviewees reported that only two and three of their watermelons were damaged by macaques during the study period. Such variation in farmer reports may be due to changes in crop feeding patterns (Hockings et al. 2015) and timing of the interviews. Because primates negotiate the immediate decision to crop feed based on multiple, constantly changing factors, farmer perceptions of crop feeding are likely influenced accordingly (McLennan and Hill 2012). General differences in overall CFE frequencies at the two locations can be explained by the frequency and consistency of human guarding behavior and the varying size and amount of vegetation cover in the two gardens. The fact that these camera trap data are for a particular range of months while the participating farmers are likely integrating information from their experiences across a longer time period may help to explain some of the mismatches.
Evaluating the discrepancies between camera trap data and farmers’ reports is important to gain a broader understanding of the impact crop feeding has on human livelihoods in Sulawesi, Indonesia, and beyond. Adesina et al. (1994), for example, found that rice farmers in the Ivory Coast could not identify diseases on their plants, thus leading to a potentially serious misunderstanding about the cause of a diminished harvest. Comparative studies such as ours do not aim to prove farmers “wrong” or “right” about what is happening; rather, human perceptions of wildlife are important from a conservation perspective regardless of whether or not they align with evidence from other sources. If farmers perceive that primates are the biggest threat to their crops and their livelihood, they will act on that belief, potentially affecting the status of endangered populations through the use of lethal deterrence methods. It is therefore important to communicate the results of crop feeding research back to farmers (cf. Riley 2007). Sharing research results can help farmers have a better understanding of the effectiveness of their guarding techniques, and how they may need to alter them for the future. For example, our results suggest that farmers dealing with macaque crop feeding need to be more vigilant throughout the day and that passive guarding is an insufficient deterrent. Although it is not practical to expect one individual to actively guard for the entire day, as farmers often must attend to other tasks that may take them away from the garden, farmers may choose to coordinate active guarding responsibilities with other farmers or family members. This collaborative effort was demonstrated to be effective at the monocrop garden in this study, which experienced far fewer CFEs than the mixed-crop garden that was protected by only one farmer. Our camera traps also provided evidence that macaques consume unripe crops, e.g., cacao pods, indicating that certain crops may need to be guarded throughout their life cycle.
Comparisons of ethnographic and camera trap data are useful to researchers trying to protect endangered species and farmers trying to protect their harvest. Each method can provide new insight that may not have been previously considered. Camera traps provide information about crop feeding animal behavior, which cannot be observed directly, that may influence the use of certain deterrence methods. For example, if a farmer has never closely observed the harvesting techniques of various crop feeding species, videos from camera traps may provide detailed information about how different animals use different strategies while crop feeding. Farmers may choose to alter crop guarding techniques in light of this new information. In addition, camera traps can be used to systematically assess deterrence method success, a method that we suggest using in conjunction with discussions with farmers. In addition to the methodological and applied contributions of this study, our results contribute to our understanding of crop feeding as a flexible foraging behavior. Our findings show that macaques exhibit flexibility in the diurnal patterning of crop feeding, i.e., assessing risk on a day-to-day basis to determine what is palatable and available in the garden, whether farmers are present and guarding, and so forth, and crop phase consumed, i.e., consuming crops at various stages of maturity.
Lessons Learned and Conclusions
To help inform future studies of human–primate conflict, we offer the following recommendations. In all ethnographic interviews it is important to consider carefully the terms used in the interview schedule and how, if applicable, they will be translated into the local language. Terminology should be neutral, reflect no biases of the researcher, and should not influence farmer responses. For example, in future studies we would simply use the word eat instead of translating the already biased term crop raiding, reflecting the more recent use of foraging and feeding instead of raiding in the literature (Hill 2015). It is also extremely important to establish a trusting relationship with participants of the study and the larger community in which one works, prior to camera trap installment. If camera traps are hastily installed and/or poorly explained, conflicts between researchers and farmers may arise. For example, we had to remove a camera trap after only a couple of days when a farmer concluded that the camera we installed was attracting macaques to his watermelon garden. When a positive, collaborative relationship is established, farmers may be more likely to provide invaluable information on the past occurrence of crop feeding events within their gardens, including knowledge about where, how, and when wildlife most often enter. It is key to consult farmers about camera trap placement. Generally, it is also important to consider body size, i.e., smaller animals require cameras placed closer to the ground, and behavior of the target species, i.e., if certain areas of the habitat are frequented such as mineral licks, when deciding on camera trap height and placement (Acrenaz et al.2012).
We recommend using multiple camera traps to survey every hectare of agricultural area, installing them both along the edge of and within agricultural areas depending on surrounding vegetation and crop type targeted by crop feeding species. Cameras must be placed in areas fairly clear of surrounding vegetation to ensure clarity of the photographs and the ease and time with which data are catalogued (Acrenaz et al.2012). For example, a branch located too close to the camera unit that moves with the wind can result in thousands of photographs that must still be examined. The security boxes and locks used to secure the cameras to the substrates were effective and we had no issues with camera security, although this is a concern when using expensive equipment.
Our results demonstrate that camera traps represent a useful tool for studying many aspects of primate crop feeding behavior. However, this method is limited in what information it can provide about crop feeding when used alone. We suggest using camera traps in addition to other methods including ethnography, direct observation (if ethical and practical), fecal analyses, and feeding traces. Because both camera traps and local reports by farmers have limitations, we stress the importance of using multiple methods to triangulate results (see also Bessa et al. 2015; McLennan 2013).
We thank the Kementerian Negara Riset dan Teknologi Republik Indonesia (RISTEK) for permission to conduct research in Indonesia, and Universitas Hasanuddin (UNHAS) for permission to work in the Education Forest. We are grateful for financial support provided by a Henry Luce Award from the American Institute for Indonesian Studies (PI: E. P. Riley) and San Diego State University’s University Grant Program (PI: E. P. Riley). We are indebted to Dr. Ngakan Putu Oka and Pak Muhammad Restu for their sponsorship, and the UNHAS Forestry Faculty for providing GIS data for the Education Forest. We also thank Joanna Setchell, the guest editors, Kimberley Hockings, Matthew McLennan, Noemi Spagnoletti, and two anonymous reviewers for their helpful comments on the manuscript. Finally, we offer many thanks to our field assistants (Amir, Paisal, and Pak Pado), Cristina Sagnotti, and the farmers whose assistance and participation made this research possible.
Compliance with Ethical Standards
Conflict of Interest
The authors have no conflict of interest or competing financial interest to declare.
Shows an adult moor macaque consuming an unripe cacao pod (MPG 22138 kb)
Demonstrates the cacao harvesting technique used by an adult male vmoor macaque. (MPG 23690 kb)
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