The Use of Camera Trapping to Monitor Threatened Forest Antelope Species
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11 The Use of Camera‐Traps to Monitor Forest Antelope Species Rajan Amin1, Andrew E. Bowkett2, and Tim Wacher1 1Conservation Programmes, Zoological Society of London, United Kingdom 2Field Conservation and Research Department, Whitley Wildlife Conservation Trust, Paignton Zoo, United Kingdom Introduction Antelopes and other artiodactyl species constitute a significant component of forest and woodland ecosystems both in terms of biomass (White, 1994) and ecological services (Feer, 1995). Many species are increasingly threatened by habitat loss and hunting for bushmeat (East, 1999). Forest antelopes are primary targets for the trade in bushmeat (Wilkie & Carpenter, 1999; Fa et al., 2005) and have undergone major local and regional declines as a result (e.g., van Vliet et al., 2007). Therefore, understanding the ecology of forest antelopes and monitoring their populations are critical conservation needs. However, forest antelopes are difficult to monitor using traditional methods for forest mammals as many species are solitary and inactive during the day, while all species are shy and spend long periods concealed in dense vegetation. In addressing these challenges, biologists have started to employ modern popula- tion sampling methods. In this chapter, we provide a brief summary of conventional methods, and their limitations, for studying forest antelopes. We then discuss the use of remote photographic sampling techniques that are increasingly being employed in studies of forest antelopes. We conclude with two case studies involving camera‐traps. The first case study involves the critically endangered Aders’ duiker (Cephalophus adersi) where camera‐trapping has led directly to further research and advocacy for improved conservation of their habitats while also providing a tool for long‐term population monitoring. The second Antelope Conservation: From Diagnosis to Action, First Edition. Edited by Jakob Bro-Jørgensen and David P. Mallon. © 2016 John Wiley & Sons, Ltd. Published 2016 by John Wiley & Sons, Ltd. Camera-Trapping in Forest Antelope Management 191 case study is in a montane forest ear‐marked for mining development in West Africa. It uses camera‐traps to establish a baseline on medium-to-large mammal diversity, of which antelopes form a significant component. Sampling forest antelopes using conventional methods Standard methods for monitoring antelope populations in savanna habitats, such as aerial or road counts, are clearly not applicable in dense forests. Much useful information on forest antelope taxonomy, physiology, and feeding ecology has been obtained through examination of hunted or culled specimens (e.g., Hofman & Roth, 2003), and in cases where the number of animals removed by hunting is known, removal methods to monitor population size can be used, such as catch‐per‐unit‐effort (Lancia & Bishir, 1996). However, such informa- tion requires close cooperation with hunters, which may not be feasible or legal, and such sampling is not suitable for threatened species. Behavioural sampling of forest antelope under natural conditions is also difficult. Whereas captive studies have helped provide insights into behaviour (Bowman & Plowman, 2002) and diet (Plowman, 2002), such studies are limit ed by the constraints imposed by captivity and few forest antelope species are currently kept in viable numbers for long‐term management (Rohr & Pfefferkorn, 2003). Accurate species identification is a critical requirement for surveys, and yet even this can be difficult when sightings are rare, or typically brief, as with forest antelope. Field signs, such as spoor and faecal deposits, can provide an indirect measure of presence or relative abundance, but identification to species still needs to be reliable. Dung counts are the most commonly employed indirect measure of forest antelope abundance (e.g., Koster & Hart, 1988; Plumptre & Harris, 1995; Nielsen, 2006), but identification of dung to species has proven to be inaccurate when tested genetically (van Vliet et al., 2008; Bowkett et al., 2009; Faria et al., 2011), even when based on statistical analysis of pellet measurements (Bowkett et al., 2013). Extrapolating absolute abundance estimates from records/counts of animals or field signs requires a statistical framework to incorporate the probability of detection (Mills, 2013). Such frameworks typically require animals to be iden- tifiable as individuals, for instance, capture‐recapture methods (Nichols & Dickman, 1996), or be reliably detected when close to a sampling point, for instance, distance‐sampling (Buckland et al., 2001). As noted above, neither of these conditions is easily met for forest antelope. Documented approaches to estimating forest antelope abundance include line transect surveys (Struhsaker, 1997; Rovero & Marshall, 2004; Viquerat et al., 2012), drive counts (Bowland, 1990; Noss, 1999), territory mapping (Bowland & Perrin, 1994), and extrapo- lation from dung counts (Schmidt, 1983; Plumptre & Harris, 1995). 192 Rajan Amin et al. All these survey methods have limitations for long‐term monitoring. Line transect methods require sufficient sightings for accurate density estimates and are difficult to conduct at night when many forest antelope are most active (although see Waltert et al., 2006). Forest antelope are also likely to violate the distance‐sampling assumption that animals located at zero distance from the transect line are always detected before being disturbed (Buckland et al., 2001). Drive counts risk injury to the animals and may be expensive to conduct, as they require multiple skilled people to mind the nets. Territory mapping usually involves radio‐collaring and is therefore more applicable to research than moni- toring. Extrapolation from dung counts requires accurate faecal deposition and decomposition rates amongst other assumptions (Lunt et al., 2007). An innovative potential survey tool is the use of fake alarm calls to attract duikers, as used by traditional hunters in some areas (van Vliet et al., 2009). Validation of this method requires data on how far individuals travel to inves- tigate such calls and how consistent is their response, as has been investigated in playback survey methods for birds (e.g., Ratcliffe et al., 1998). The modern development of non‐invasive genetics, the analysis of DNA from materials such as saliva or dung (Taberlet et al., 1999), has numerous potential applications to forest antelope monitoring (see also Chapter 9). Amplification of species‐specific mitochondrial DNA fragments allows species identification from dung or bushmeat samples (Eaton et al., 2010; Ntie et al., 2010a). Such an approach is analogous to DNA barcoding (Hebert et al., 2003), although the standard universal barcoding gene (COX1) does not dif- ferentiate some duikers from their sister species (Johnston et al., 2011), so an alternative genetic marker has to be used (e.g., Ntie et al., 2010a). Genetic identification of dung allows accurate distribution mapping and validation of field identification used for abundance estimates (van Vliet et al., 2008; Bowkett et al., 2013). Identification of individual animals from faecal DNA is possible using nuclear microsatellite markers (Ntie et al., 2010b; Akomo‐Okoue et al., 2013). For forest antelope, this would allow abundance to be estimated by territory mapping or through a capture‐recapture framework wherein samples from the same individual collected in different sessions are treated as recaptures (e.g., Zhan et al., 2006). Variable genetic markers can also be used to monitor effec- tive population size (Schwartz et al., 1998) as well as to study many aspects of forest antelope biology including genetic diversity, parentage, and pedigree (Beja‐Pereira et al., 2009). Despite their many advantages, very few wildlife authorities or land managers have the resources to employ non‐invasive genetics as part of rou- tine monitoring programs. Even though the cost of genetic studies continues to fall ov erall (Hall, 2013) and there is increasing expertise in conservation genetics in Africa (Anthony et al., 2012), conservation managers are often vastly under‐resourced (Bruner et al., 2004). Therefore, while non‐invasive Camera-Trapping in Forest Antelope Management 193 genetic research on forest antelope will hopefully expand rapidly to provide new records and answer key questions, regular genetic monitoring does not appear feasible in the short term. Sampling forest antelopes using camera‐traps The use of camera‐trapping as a survey tool for medium‐to‐large terrestrial mammals has become increasingly common over recent years (Ahumada et al., 2011; O’Connell et al., 2011) and is a particularly suitable technique for longer‐term monitoring in forest habitats (Wacher & Amin, 2015; Gompper et al., 2006; Lyra‐Jorge et al., 2008; Roberts, 2011; Silveira et al., 2003). The survey method consists of remotely stationed heat‐and‐motion sensitive cameras that take photographs or videos of passing animals. Digital cameras operating 24‐hours a day are the standard (O’Connell et al., 2011). At night, infrared flash photography that is not visible to animals can be used to minimise disturbance to the animals. The strengths and also limitations of camera‐traps for sampling forest antelopes are summarised in Table 1. Table 1 Strengths and limitations of camera‐traps for sampling forest antelopes. Strengths Limitations Cost‐effective in consideration of Initial high cost of purchasing equipment effort vs. data generation (although this cost is offset over time) Operates