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Investigation into survey techniques of large mammals: surveyor competence and camera-trapping vs. transect-sampling

Investigation into survey techniques of large mammals: surveyor competence and camera-trapping... Volume 4 † Number 1 † March 2011 10.1093/biohorizons/hzr006 Advance Access publication 23 February 2011 ......................................................................................................................................................................................................................................... Research article Investigation into survey techniques of large mammals: surveyor competence and camera-trapping vs. transect-sampling Nathan James Roberts* Centre for Wildlife Conservation, National School of Forestry, University of Cumbria, Newton Rigg, Penrith, Cumbria CA11 0AH, UK. * Corresponding author: 13 Church Road, Catsfield, Battle, East Sussex, TN33 9DP. Email: njr304@hotmail.co.uk Supervisors: Dr Owen Nevin and Dr Ian Convery, National School of Forestry, University of Cumbria, Newton Rigg, Penrith, Cumbria, CA11 0AH, UK. ........................................................................................................................................................................................................................................ Rigorous and cost-effective methods are essential to efficiently assess wildlife populations and obtain accurate data to inform conserva- tion and management decisions. In the UK, available data on terrestrial mammal species are distinctly lacking, many populations are in decline and survey methods are technically demanding and labour-intensive. There is, therefore, much need to investigate alternative methodologies to ensure that resource use is efficient and data are reliable. Camera-trapping presents a relatively new approach for surveying mammals, though in the UK, the extent to which camera traps have been used has not been quantified and their performance has not yet been compared relative to existing methods. This study uses biological parameters and economic and logistic costs to assess the efficiency and reliability of camera-trapping and transect-sampling during winter field trials. Tracks and sign surveys and sightings surveys were conducted simultaneously and where appropriate, investigated independently. In addition, a nationally-distributed questionnaire was used to investigate surveyor competence and identify temporal trends in method use in the UK. Field trials concluded that camera-trapping was the most labour-efficient method for producing a species inventory, and frequently recorded more species per sampling site than did transect-sampling. However, when the total sampling period was limited, species were encountered at a faster rate by the detection of tracks and signs than by the alternative methods investigated. The single density estimate derived from camera trap data was higher than that from transect-sampling, and no differences were observed within the three alpha diversity index estimates derived by each survey method. The questionnaire suggests that the reliability of species presence/absence data derived from tracks and signs surveys is probably compromised by surveyor confidence of species identification. A multi-evidence approach is, therefore, recommended for less-competent surveyors. Despite greater initial economic costs, it is advocated that camera-trapping may be an efficient, rigorous and cost-effective method for large-scale long-term monitoring programmes. Furthermore, data suggest that camera trap use will become increasingly frequent in the UK. More research is required to investigate the relationships between method efficiency and season, species density and habitat, and to assess the accuracy of species density estimates. Key words: camera-trapping, efficiency, mammals, reliability, transect-sampling, UK. Submitted July 2010; accepted on 20 January 2011 ........................................................................................................................................................................................................................................ Introduction However, available data on terrestrial mammalian fauna are Accurate assessments of species distributions, population distinctly lacking in the UK, and many populations are in densities and species richness are essential to effectively decline. Furthermore, surveying mammals is laborious and 1 – 4 6,9 direct conservation strategies and management practices. technically demanding. Monitoring species distributions and abundance also Numerous survey methodologies are currently practised, provides important data to evaluate whether favourable each with specific advantages and disadvantages, particu- conservation status has been achieved, and supports the larly in terms of detectability, labour and financial costs, 6 11,12 legal obligation towards species protection and conservation. and usability by surveyors. In the UK, mammal ......................................................................................................................................................................................................................................... The Author 2011. Published by Oxford University Press. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.5), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. 40 Bioscience Horizons † Volume 4 † Number 1 † March 2011 Research article ......................................................................................................................................................................................................................................... Table 1. Species considered by the field trials and questionnaire surveying is dependent on a body of full-time professionals supported by a strong foundation of volunteers. The Species Common name ability of trained volunteers is virtually comparable to that ................................................................................................................ of professionals in some instances, though the experience Cetartiodactyla and skill of the latter may compromise the relative perform- Cervidae Capreolus capreolus Roe deer ance of volunteers. It is, therefore, essential that field tech- Cervus elaphus Red deer niques can be readily implemented by people with varying Cervus nippon Sika deer levels of expertise, or else recorded species distributions Dama dama Fallow deer may rather reflect those of skilled surveyors. Hydropotes inermis Chinese water deer Transect-sampling is a widely used survey technique, and Muntiacus reevesi Muntjac considered volunteer-friendly, visual counts are the simplest Carnivora method to survey mammals. Indirect sampling techniques Canidae Vulpes vulpes Fox that rely on the detection of tracks and signs along transects Felidae Felis silvestris Wildcat may also be implemented by surveyors with limited training. Mustelidae Lutra lutra Otter Conversely, camera-trapping is a relatively new methodologi- Martes martes Pine marten cal advancement that uses specialized equipment to detect and ‘trap’ photographs of passing animals. Meles meles Badger It is recommended that new methodologies are assessed Mustela erminea Stoat relative to existing knowledge. To date, numerous field Mustela nivalis Weasel tests have been conducted to compare the efficiency, detect- Mustela putorius Polecat ability and accuracy of camera-trapping and transect- Neovison vison Mink 12,20 – 22 sampling, though none have so far been performed Eulipotyphla in the UK. Previous comparisons have concluded that Erinaceidae Erinaceus europaeus Hedgehog transect-sampling may provide a more complete species Talpidae Talpa europaea Mole inventory, and obtain a greater frequency of records than 22 Lagomorpha alternative methods. However, conflicting results have Leporidae Lepus europaeus Brown hare been reported for the efficiency of species detection in 20,23 Lepus timidus Mountain/Irish hare terms of sampling effort. Furthermore, questionnaires Oryctolagus cuniculus Rabbit indicate that field sign surveys are often considered more dif- ficult than sightings surveys, and camera-trapping has been Rodentia reported to allow for more accurate species identification Sciuridae Sciurus carolinensis Grey squirrel than can be achieved by the identification of tracks. Sciurus vulgaris Red squirrel The most appropriate method for a given survey may be determined by, inter alia, the objectives and biological ques- tions asked, characteristics and conservation status of the species density and assessing alpha diversity. Specifically, 26 26 target species and dependability of the method. the study performed field trials and used a questionnaire to Ultimately however, it is often resource availability that deter- investigate the efficiency and reliability of surveying terres- 20,21,26 mines method selection. The efficient use of resources is trial woodland mammals in the UK. Both components of paramount in conservation, and financial and labour costs the study were concerned with a target suite of species should, therefore, be key considerations in the selection of (Table 1); the majority of small mammals were not con- 16,28,29 the most feasible sampling method. Furthermore, the sidered. Field trials primarily assessed the labour and econ- application of an efficient, reliable and cost-effective method omic efficiency of each sampling technique and the 11,16,20,28 may maximize the validity of species assessments. questionnaire investigated surveyor competence. Despite escalating global popularity in the use of camera traps, no camera-trapping studies in the UK natural Materials and methods environment have been published in the literature [web of science search: TS ¼ (camera-trapping) and CU ¼ (United Field trials Kingdom or England or Scotland or Wales or Northern Study area Ireland or Great Britain or Ireland)]. However, it is antici- pated that camera traps will become of greater use by Field trials were conducted in Edenbrows Wood in Cumbria biologists as technologies and methodologies advance. (OS Reference: NY 497 498; Fig. 1), a mixed Plantation on The principal objective of the present study was to Ancient Woodland Site adjacent to the River Eden, a Special compare the rigour of camera-trapping and transect- Area of Conservation and Site of Special Scientific Interest. sampling as techniques for recording species, estimating The study area is 0.28 km and composed of mixed ......................................................................................................................................................................................................................................... 41 Research article Bioscience Horizons † Volume 4 † Number 1 † March 2011 ......................................................................................................................................................................................................................................... Figure 1. Edenbrows Wood, Cumbria (OS Reference: NY 497 498) with sampling sites defined and camera trap stations and transect locations marked. conifers and ash (Fraxinus excelsior)/oak (Quercus petraea) 2009 and Cumbria in December 2009. Three camera trap woodland. Floral composition was used to divide the study stations were assigned to each sampling site and coordinates area into six sampling sites: Grand Fir (Abies grandis); were random. Inter-camera distance ranged between 43 and Mixed Conifers; Hybrid Larch (Larix x eurolepis); Sitka 288 m. Each camera was operational for between 5 and 57 Spruce (Picea sitchensis); Mixed Broadleaves and Mixed consecutive trap nights, sampling from December 2009 to Broadleaves/Hybrid Larch. January 2010. The mean daily temperature for the period December Sixteen Reconyx (models RC55 RapidFire and PC85 2009 to February 2010—recorded at Brampton climate RapidFire Pro; Reconyx Inc., WI, USA) and two station 11 km north of the study area—was 0.78C with a CamTrakker (model MK-8; CamTrakker, GA, USA) range from 210.5 to 7.58C. The mean daily rainfall and passive infrared camera traps were used, with automatic snow depth for the same period was 2.2 mm and 3 cm, infrared flash and strobe flash, respectively. All units were respectively. programmed to capture maximum photographs per trigger, The site was selected on the basis of accessibility, size, configured to minimal latency periods between triggers and floral diversity and the high level of recreational use, which secured to trees at a height of 0.3 m to maximize capture represents the effects of disturbance associated with publicly probability. Assuming functionality, cameras were oper- accessible land, including potential equipment security ational 24 h a day, and date and time were imprinted on threats. all photographs. Traps were checked infrequently, usually Field trials were conducted from December to February as replacing memory cards. The total sampling effort was 693 field signs were less likely to be obscured by vegetation, trap nights (i.e. sum of sampling nights per camera). species observation would also, therefore, be less affected Sensor detection parameters were estimated for each 31 18 by visual background noise, and this methodology also camera model, and figures weighted by the total sampling acknowledges recommendations of the Winter Mammal effort for each model to determine the values used in analysis Monitoring (WMM) pilot study. Furthermore, the (J. Rowcliffe, personal communication). Roe deer (Capreolus sampling period was minimal to meet the assumptions of capreolus) group size (g) and average day range (v) were pro- density estimate calculations. vided by Robin Gill ( personal communication) and a primary literature source, respectively. Camera-trapping Transect-sampling The general framework of the camera-trapping survey fol- lowed a previously trialled methodology; the methodology Ten linear transects of mean length (+SD) 127.6+ 68.5 m was refined during preliminary trials in Borneo in September were established, directly connecting camera trap stations ......................................................................................................................................................................................................................................... 42 Bioscience Horizons † Volume 4 † Number 1 † March 2011 Research article ......................................................................................................................................................................................................................................... within each sampling site and extending 30 m before the where appropriate, and the three hypothetical training first station and after the last (Fig. 1). All mammals in the courses were considered theoretically feasible (A. Dunlop, target suite of species were registered according to standar- personal communication). The questionnaire was pro- dized techniques, collecting sightings and tracks and grammed with complex routing logic to automatically signs data simultaneously. Animal- and sign-observer dis- direct respondents based on individual responses, and tances were estimated without the use of equipment. piloted on nine individuals representing the five typology Transects were walked between 0820 and 1430 h, and groups (i.e. academic, mammal interest, student, etc.). sampling was conducted between January and February 2010. Each transect was walked either four or five times, achieving a total of 46 transect surveys, thereby accumulat- Data analysis ing 5.7 km of transects walked. Field trials Signs of fox (Vulpes vulpes), badger (Meles meles), mole (Talpa europaea), rabbit (Oryctolagus cuniculus), otter To evaluate the rigour of camera-trapping for surveying the (Lutra lutra) and roe deer were registered; only fox, badger target suite of species, a subset of all photographs were and otter tracks were considered. Deer faecal pellets were used, excluding domestic animals, humans, birds and small recorded according to standardized methods, and were mammals (with the exception of Sciurus spp.). Blank cap- not cleared from transects. Tracks and signs which could tures and exposures in which the species was unidentifiable not be confidently identified were photographed for ex situ were also excluded from analysis. Independent records two-way agreement. were defined as (i) consecutive photographs of the same species taken at an interval of 0.5 h or (ii) photographs Questionnaire of different species irrespective of interval length. In analyses Between February and March 2010, a seven-part web-based of transect-sampling, tracks and signs data and sightings data questionnaire was used to investigate the temporal trends in were pooled. the use of survey techniques and the reliability of species Transect-sampling data and camera-trap data were pooled identification and distance estimation by mammal surveyors to estimate total species richness by Chao Presence/Absence (see Supplementary material online). The first three parts in DIVERSITY. Species accumulation curves plot S obs investigated the respondents’ previous surveying experience, (Mao Tau) values computed in EstimateS, pooling data including reporting the period during which they first by sampling day and performing 100 randomizations implemented each technique. Respondents were then asked without replacement to eliminate bias associated with to quantify their confidence of estimating distance and iden- unequal sampling effort per day. tifying species from photograph, sight and tracks and signs. Relative efficiency of species detection was valued and The fifth part investigated the training the respondent had subsequently compared by paired t-test. Differences received and would consider in the future. In the penultimate between methods in the mean latency to first detection part, respondents were asked to quantify their anticipated (LTD) were analysed by paired t-test. future involvement in mammal surveying in the UK with Labour investments were calculated from daily records of regards to method use. Questions pertaining to demo- time expended in data collection, excluding general field graphics were included in the final part of the questionnaire time. No randomizations were performed for species for the purposes of describing the sample. accumulation plots per human hour of field investment and To achieve comprehensive sampling, the questionnaire are, therefore, presented chronologically. Economic costs was distributed to virtually all organizations collaborating included equipment and theft compensatory costs only; with the Tracking Mammals Partnership, supplemented general project costs were omitted. Cost comparisons were by additional non-governmental and governmental organiz- performed by chi-square test, incorporating Yates’ correction ations, volunteer organizations and independent ecologists. for continuity. Each unit of the sampling frame (n ¼ 134) was authorized Photographic capture rates were used to estimate species responsible questionnaire dissemination within the respective density; variance and precision were not estimated. Roe organizations and among appropriate contacts. In addition deer density was estimated from faecal pellet counts, and to direct email invitations, the questionnaire was accessible variance calculated as the SD of density estimates from via: Devon Wildlife Trust website; Lincolnshire Wildlife each sampling day. Trust newsletter, February 2010; The Mammal Society Alpha diversity indices were calculated in DIVERSITY, (TMS) website and e-bulletin, March 2010 and the public defining an individual as an independent record plus forum Wild About Britain, directing respondents to the additional animals observed in a single instance by sight or appropriate TMS web page. photograph. Previously validated questions used during the WMM All variables were tested for normality by Kolmogorov – pilot study were included to allow for direct comparisons Smirnov test and statistical comparisons performed in ......................................................................................................................................................................................................................................... 43 Research article Bioscience Horizons † Volume 4 † Number 1 † March 2011 ......................................................................................................................................................................................................................................... SPSS 15.0 (SPSS, Inc., IL, USA), measuring significance at by both camera-trapping and transect-sampling, the latter P ¼ 0.05. detected each species in fewer days (i.e. lower mean value of LTD; t ¼ 4.264, df ¼ 5, P ¼ 0.008). Specifically, species were accumulated by the detection of tracks and signs at a Questionnaire faster rate than any other detection method when sampling Statistical analyses were performed in SPSS 15.0 (SPSS, Inc., effort 5 d (Fig. 2). However, in terms of field labour invest- IL, USA), considering significance at P ¼ 0.05. All usable ments, less than 1 h was required to achieve an asymptote of data were analysed, thereby including the individual accumulative species detected by camera-trapping (Fig. 3). responses from questionnaires that were partially complete. This labour investment was significantly less than the Descriptive and statistical analyses of the survey data were amount expended for tracks and signs (x ¼ 45.15, df ¼ 1, performed. Confidence of species identification from differ- P, 0.001) and sightings (x ¼ 36.20, df ¼ 1, P, 0.001); ent forms of evidence was assessed by Kruskal – Wallis and no difference between transect-based methods was observed post-hoc analysis. Friedman tests were used to investigate (x ¼ 1, df ¼ 1, P . 0.25). Total field labour investments the frequency of method use and preference of hypothetical were equitable between methods; financial costs were signifi- training courses. Comparisons of temporal trends in cantly greater for camera-trapping (P, 0.001; Table 3). method use were performed by chi-square test, incorporating The weighted mean camera trap detection arc and distance Yates’ correction for continuity. were 0.704 u and 0.005 km, respectively. An average roe deer group size of 1.6 and average day range of 2.19 km -1 day was used to calculate density from camera-trapping Results rates. Roe deer density was estimated by transect-sampling Field trials (+SD) as 3.85+ 1.60 km , a significantly lower density than derived by camera-trapping (15.47 km ; P, 0.001). Eight target species were recorded during the field trials: badger; fox; grey squirrel (Sciurus carolinensis); mole; otter; rabbit; red squirrel (Sciurus vulgaris) and roe deer. In 117 independent records, camera traps registered all of the above species, excluding mole. A total of 142 records were obtained during transect-sampling; sightings data constituted 3 of these records. Excluding squirrels, all of the above species were detected by tracks and signs, and only rabbit and red squirrel were encountered by direct observation. Camera-trapping consistently recorded equal or more species per sampling site than did transect-sampling, yielding Figure 2. Cumulative number of species observed as a function of a greater value of relative efficiency (t ¼ 3.3, df ¼ 5, P ¼ increased sampling effort; S (Mao Tau) presented. obs 0.021; Table 2). Species richness (+SD) of the entire study site was estimated as 9+ 3.01. Of those species detected Table 2. Observed richness of sampling sites and relative efficiency of each survey method per sampling site (i.e. number of species detected by individual method/total number of species detected in each sampling site) Sampling site Camera-trapping Transect- Richness sampling ................................................................................................................ Sitka Spruce 0.8 0.4 5 Mixed Broadleaves 0.86 0.71 7 Figure 3. Cumulative number of species detected with increasing field labour investments, presented chronologically. Mixed Broadleaves/ 0.67 0.67 3 Hybrid Larch Table 3. Cost comparison of survey methods Mixed Conifers 1 0.5 6 Grand Fir 0.83 0.67 6 Method Financial (£) Time (h) ................................................................................................................ Hybrid Larch 1 0.5 4 ................................................................................................................ Camera-trapping 8423 12.23 Mean 0.86 0.57 Transect-sampling 20 14.64 SD 0.13 0.12 P ,0.001 NS ......................................................................................................................................................................................................................................... 44 Bioscience Horizons † Volume 4 † Number 1 † March 2011 Research article ......................................................................................................................................................................................................................................... Table 4. Alpha diversity indices of Edenbrows Wood, estimated by two survey methods a b c d e Method Species Individuals Diversity Abundance Richness ........................................................................................................................................................................................................................................ Camera-trapping 7 123 1.37+ 0.01 2.86 1.25 Transect-sampling 7 143 0.84+ 0.01 1.58 1.21 ........................................................................................................................................................................................................................................ P NS NS NS Observed value. Observed value (independent records plus additional animals observed in a single instance). Shannon-Wiener. Simpson’s diversity index. Margalef. Camera-trap data and transect data derived alpha diversity recorded use was during the period 1996 – 2000 (5.3%). estimates that were neither significantly different for abun- Conversely, in the period 2006 – 2009, 24.2% and 19.4% dance, richness or diversity (Table 4). of all respondents first conducted sightings surveys and tracks and signs surveys, respectively. For both transect- Questionnaire based methods, 21% of respondents first conducted each survey method pre-1990; no respondents first used either A total of 79 responses were received at a completion rate of method in 2010. 73.4% (n ¼ 58); the remaining 21 were partially complete. The frequency of respondents who stated they could con- Each region of the UK was represented by at least one fidently identify the target suite of species by photograph (i.e. respondent (except London) and the modal demographics the product of camera-trapping), sight and tracks and signs were the following: male (53.4%); aged 25 – 34 (25.9%); differed significantly between forms of evidence (Kruskal – professional country worker (27.6%) and employee or Wallis, H ¼ 29.044, df ¼ 2, P ¼ 0.000). Fewer respondents member of TMS (43.1%). The sample was comparable to were confident in the identification of species from tracks the respondents involved in the WMM pilot study, in and signs than from photographs (Mann – Whitney, U ¼ terms of typology (e.g. academic, student, etc.; t ¼ 1.49, 66.00, P ¼ 0.000) and sightings (Mann – Whitney, U ¼ df ¼ 5, P ¼ 0.197) and gender (t ¼ 4.28, df ¼ 1, P ¼ 42.50, P ¼ 0.000). Furthermore, fewer respondents were 0.146). However, respondents were typically younger in able to confidently identify species from photographs than the present study (t ¼ 3.37, df ¼ 7, P ¼ 0.012). from sight (Mann – Whitney, U ¼ 337.50, P ¼ 0.024). Questionnaire respondents indicated that camera-trapping Concerning the eight species recorded during field trials was implemented less frequently than both transect-based only, the median number of respondents who stated they sampling methods in 2009 (Friedman Test, df ¼ 2, P ¼ could confidently identify each species by photograph, sight 0.000). This relationship was also anticipated for the and tracks and signs was 54, 58 and 47, respectively; the period 2010 – 2015 (Friedman test, df ¼ 2, P ¼ 0.000). The interquartile ranges were 0, 1 and 27.75, respectively (Fig. 5). differences between 2009 and 2010 – 2015 were not signifi- Respondents were asked to quantify their confidence of cant within methods (Fig. 4). estimating animal-observer distance on a five-point scale. Of those respondents with camera-trapping experience Only 22.2% of respondents could estimate distance to the (24.1%), nearly 85% first used camera traps for wildlife highest degree of accuracy. The modal value (35.2%) of studies in the UK between 2006 and 2009, and the earliest quantified confidence was ‘4’. Figure 4. Friedman test mean rank of survey method use and anticipated future use, where integers represent the scale of annual frequency of Figure 5. Frequency of respondents able to confidently identify a range of surveys per respondent: never (0 surveys; 1); rarely (1–2 surveys; 2); mammal species (badger; fox; grey squirrel; mole; otter; rabbit; red squirrel; occasionally (3–4 surveys; 3); frequently (5þ surveys; 4). roe deer) from different forms of evidence. ......................................................................................................................................................................................................................................... 45 Research article Bioscience Horizons † Volume 4 † Number 1 † March 2011 ......................................................................................................................................................................................................................................... Of those respondents who had not been trained in the use associated costs. It is, therefore, probable that bias has of camera traps (91.5%), most (74.1%) would consider been incurred as a result of using external information. attending a camera-trapping training course. When pre- However, it is proposed that the roe deer density estimate sented with three hypothetical training courses, respondents derived from camera trap data is more accurate than that indicated that preference was varied (Friedman test, df ¼ 2, derived from faecal pellet counts, as a greater number of P ¼ 0.000). The 1-day course was most preferred and was individuals were observed by independent photographic cap- considered by 79.3% of respondents to provide adequate tures than was estimated by the latter. training to become competent in camera trap use. Density estimate comparisons are limited in the present study as transects were not conducted on consecutive days, and the age of species tracks could, therefore, not be accu- Discussion rately determined as required. Furthermore, the absence Despite the relocation of two camera traps due to accessibil- of data of animal-related parameters limited the use of ity concerns of original placement, and subsequent low camera trap data, and frequency of sightings records were sampling effort of these cameras, camera-trapping produced considered insufficient to accurately calculate species a more complete inventory than alternative methods, as con- density by distance-sampling. 23,40 cluded by other studies. In terms of sampling days, The assumption of distance-sampling that states recorded species were detected at the fastest rate by tracks and signs, distances are exact may be violated by the diverse mammal also supporting previous conclusions. However, labour surveying community, as suggested by the questionnaire efficiency of transect-sampling was comparatively limited respondents. The modal class of confidence (i.e. ‘4’) also due to the high investments required to establish transects concurs with the WMM pilot study sample. Although before sampling could commence. High variability in sur- density may be reliably calculated from inaccurate field veyor competence of species identification from field signs data, tendency to under- or over-estimate distance may bias across species and the evident inability of most mammal sur- results. veyors to confidently estimate animal – observer distance The questionnaire sample also indicates that the mammal raises concerns over the reliability of field sign data and surveying community is less able to identify species from distance-sampling-derived density estimates, respectively. tracks and signs than from sightings and photographs. This study has emphasized that failure to detect species Misidentification may result in erroneous population esti- may not be indicative of species absence, rather insufficient mates, and non-representative presence/absence data that effort or use of an inappropriate method. Due to the ambi- may misguide conservation and management initiatives, 24 14 guity of squirrel field signs, only sightings were considered potentially with severe financial implications. during field trials, for which no records of grey squirrel were Respondents further indicated that species identification obtained; this result was disputed by camera trap evidence of from photographs is more difficult than from sightings, species presence. As the grey squirrel is a direct threat to the though it should be noted that the latter is largely dependent 42 10 native red squirrel, this result also highlights the conserva- on clear observations, and is biased towards large-bodied tion significance of differences in detectability between diurnal species. Although there is also a positive relation- methods. ship between body weight and detection probability by Total field labour investments were equitable between camera traps, camera-trapping may overcome the temporal methods to ensure efficiency was directly comparable. limitations of transect-sampling by surveying at night. However, it should be noted that camera-trapping labour Furthermore, unambiguous photographs obtained by investments were probably lower than in other circumstances camera traps provide indisputable evidence of species pres- as standard detection zone checks were not performed due to ence, considerably reducing observer inaccuracies and logistical constraints. Approximately optimal positioning bias common with other methods. It is, therefore, rec- was determined during preliminary trials, which considering ommended that less-competent surveyors supplement field the above, could simulate training. The field trials, therefore, sign surveys with camera trap data, where possible. demonstrate the performance of camera-trapping when a Assuming surveyor competence, when the aim of a survey trained surveyor is limited by logistics. Alternatively, when is to produce a species inventory and the surveyor is limited the survey objectives do not include density estimation, it is by total sampling period and not human labour investments, proposed that the 9 h otherwise invested in estimating detec- it is proposed that tracks and signs surveys may offer the best tion zone parameters would probably be sufficient to approach for producing rapid faunal assessments. However, perform these checks. if the reverse limitations are applied, camera-trapping may be To estimate species density from camera trap data, it is the most efficient method as labour investments are com- 22,44 recommended that the animal-related parameters are esti- paratively minimal, unlike transect-sampling which mated simultaneously to camera-trapping; this was not required 5 h of field labour to establish transects only. logistically feasible in the present study due to the substantial Furthermore, it is proposed that camera-trapping may ......................................................................................................................................................................................................................................... 46 Bioscience Horizons † Volume 4 † Number 1 † March 2011 Research article ......................................................................................................................................................................................................................................... provide a cost-effective approach for monitoring pro- season, species density and habitat. Furthermore, density grammes at large temporal and spatial scales, as the sub- estimates derived by camera-trapping and transect-sampling 11,53 stantial equipment costs may be offset by frequent and should be validated against direct counts. repeated use. Alpha diversity estimates were not different between Supplementary data survey methods, suggesting that either method may be used to derive accurate estimates. Furthermore, it is proposed Supplementary data is available at Bioscience Horizons that Shannon-Wiener is the most appropriate index to use online. in future assessments as it recognizes the number of species and the evenness of species abundance. Acknowledgements It is suggested that transect-sampling is a well-practiced methodology historically and that the annual frequency I would like to thank my principal supervisor Dr Owen Nevin, of transect-based surveys may remain approximately co-supervisor Dr Ian Convery, and acknowledge the logistical constant in the future. Conversely, data suggest that support given by Dr Andrew Ramsey, Ellie Lindsay, Melanie camera trap use will increase, which is further supported Clapham and Robbie Hawkins. I would also like to thank by the respondents’ interest in receiving camera-trapping Dr Marcus Rowcliffe, Dr Robin Gill, Dr Mathew Crowther training. This study also provides an insight into the training and Dr Philip Stevens. I am also thankful to Marina interests of mammal surveyors and a foundation from which Pacheco, Laura Drake, Alex Dunlop, Simon Poulton, to further investigate and design future training courses. Rowena Staff and the anonymous individuals who responded to the questionnaire and assisted with distribution. Finally, I would like to thank my family and friends. Conclusion This is the first published study to compare the efficiency and Funding reliability of camera-trapping and transect-sampling as tech- niques for surveying terrestrial mammals in the UK. As Financial support was kindly received from The Clouded 20,21 reported by non-UK studies, this investigation concludes Leopard Project (USA) and Penrith Lions Club (UK). that the best balance between cost-effectiveness, labour effi- ciency and rigour can be achieved by camera-trapping. It Author biography has highlighted that despite lower initial economic costs, transect-sampling rigour may be compromised by surveyor N.J.R. studied BSc. (Hons) Animal Conservation Science at competence of identifying tracks and signs, and the compara- the Centre for Wildlife Conservation, University of tively slow rate of species accumulation per human hour of Cumbria, UK, where he acquired substantial knowledge labour investment. and expertise. Furthermore, he has received training in the This study also presents the first attempt to identify tem- use of advanced tools of modelling and analysis of spatial poral trends in survey method use in the UK. It is evident data, completing two courses in Geographic Information that camera-trapping is currently implemented less fre- Systems. Academic achievements are complemented by quently than transect-sampling, and data further suggest numerous independent and supportive research projects that the former will increase in the future, complementing and familiarity of working in temperate and tropical the global trend. environments. Independent research projects have included In a brief comparison of survey methods at a small spatial investigations of species ecology, protected area management and temporal scale, it is foolhardy to assert too much in the and animal behaviour. His principal interest is wild cat con- way of definitive conclusions. Instead, the results should be servation and research, with a specific focus on human-felid considered the inferences of a single case study only, when conflict and species ecology. As a hobbyist wildlife and land- environmental conditions were favourable for infrared scape photographer, he is also interested in the applications camera trap performance, and detectability of of camera traps in wildlife research. He aims to integrate field signs. Furthermore, it should be acknowledged that his passion for photography into future research endeavours 11,20,22,49 (i) survey efficiency may differ in space and time, as he aspires to pursue a career in wild cat conservation and (ii) capture success may vary within and between camera ecological research. 29,50,51 trap models, (iii) flash-induced trap-shy may reduce trapping rates and (iv) detection efficiency may be density dependent. References It is, therefore, advocated that further studies are con- 1. 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Biotropica 40: 211–217. ......................................................................................................................................................................................................................................... 48 Bioscience Horizons † Volume 4 † Number 1 † March 2011 Research article ......................................................................................................................................................................................................................................... 45. Cutler TL, Swann DE (1999) Using remote photography is wildlife ecology: a 50. Kelly MJ, Holub EL (2008) Camera trapping of carnivores: trap success review. Wildl Soc Bull 27: 571–581. among camera types and across species, and habitat selection by species, on salt pond mountain, Giles County, Virginia. Northeast Nat 15: 249–262. 46. 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Pollock KH, Nichols JD, Simons TR, Farnsworth GL, Bailey LL, Sauer JR (2002) to estimate densities of tigers and other cryptic mammals: a comment on Large scale wildlife monitoring studies: statistical methods for design and misleading conclusions. Anim Conserv 5: 119–120. analysis. Environmetrics 13: 105–119. ........................................................................................................................................................................................................................................ ......................................................................................................................................................................................................................................... http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Bioscience Horizons Oxford University Press

Investigation into survey techniques of large mammals: surveyor competence and camera-trapping vs. transect-sampling

Roberts, Nathan James
Bioscience Horizons , Volume 4 (1) – Mar 23, 2011
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Volume 4 † Number 1 † March 2011 10.1093/biohorizons/hzr006 Advance Access publication 23 February 2011 ......................................................................................................................................................................................................................................... Research article Investigation into survey techniques of large mammals: surveyor competence and camera-trapping vs. transect-sampling Nathan James Roberts* Centre for Wildlife Conservation, National School of Forestry, University of Cumbria, Newton Rigg, Penrith, Cumbria CA11 0AH, UK. * Corresponding author: 13 Church Road, Catsfield, Battle, East Sussex, TN33 9DP. Email: njr304@hotmail.co.uk Supervisors: Dr Owen Nevin and Dr Ian Convery, National School of Forestry, University of Cumbria, Newton Rigg, Penrith, Cumbria, CA11 0AH, UK. ........................................................................................................................................................................................................................................ Rigorous and cost-effective methods are essential to efficiently assess wildlife populations and obtain accurate data to inform conserva- tion and management decisions. In the UK, available data on terrestrial mammal species are distinctly lacking, many populations are in decline and survey methods are technically demanding and labour-intensive. There is, therefore, much need to investigate alternative methodologies to ensure that resource use is efficient and data are reliable. Camera-trapping presents a relatively new approach for surveying mammals, though in the UK, the extent to which camera traps have been used has not been quantified and their performance has not yet been compared relative to existing methods. This study uses biological parameters and economic and logistic costs to assess the efficiency and reliability of camera-trapping and transect-sampling during winter field trials. Tracks and sign surveys and sightings surveys were conducted simultaneously and where appropriate, investigated independently. In addition, a nationally-distributed questionnaire was used to investigate surveyor competence and identify temporal trends in method use in the UK. Field trials concluded that camera-trapping was the most labour-efficient method for producing a species inventory, and frequently recorded more species per sampling site than did transect-sampling. However, when the total sampling period was limited, species were encountered at a faster rate by the detection of tracks and signs than by the alternative methods investigated. The single density estimate derived from camera trap data was higher than that from transect-sampling, and no differences were observed within the three alpha diversity index estimates derived by each survey method. The questionnaire suggests that the reliability of species presence/absence data derived from tracks and signs surveys is probably compromised by surveyor confidence of species identification. A multi-evidence approach is, therefore, recommended for less-competent surveyors. Despite greater initial economic costs, it is advocated that camera-trapping may be an efficient, rigorous and cost-effective method for large-scale long-term monitoring programmes. Furthermore, data suggest that camera trap use will become increasingly frequent in the UK. More research is required to investigate the relationships between method efficiency and season, species density and habitat, and to assess the accuracy of species density estimates. Key words: camera-trapping, efficiency, mammals, reliability, transect-sampling, UK. Submitted July 2010; accepted on 20 January 2011 ........................................................................................................................................................................................................................................ Introduction However, available data on terrestrial mammalian fauna are Accurate assessments of species distributions, population distinctly lacking in the UK, and many populations are in densities and species richness are essential to effectively decline. Furthermore, surveying mammals is laborious and 1 – 4 6,9 direct conservation strategies and management practices. technically demanding. Monitoring species distributions and abundance also Numerous survey methodologies are currently practised, provides important data to evaluate whether favourable each with specific advantages and disadvantages, particu- conservation status has been achieved, and supports the larly in terms of detectability, labour and financial costs, 6 11,12 legal obligation towards species protection and conservation. and usability by surveyors. In the UK, mammal ......................................................................................................................................................................................................................................... The Author 2011. Published by Oxford University Press. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.5), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. 40 Bioscience Horizons † Volume 4 † Number 1 † March 2011 Research article ......................................................................................................................................................................................................................................... Table 1. Species considered by the field trials and questionnaire surveying is dependent on a body of full-time professionals supported by a strong foundation of volunteers. The Species Common name ability of trained volunteers is virtually comparable to that ................................................................................................................ of professionals in some instances, though the experience Cetartiodactyla and skill of the latter may compromise the relative perform- Cervidae Capreolus capreolus Roe deer ance of volunteers. It is, therefore, essential that field tech- Cervus elaphus Red deer niques can be readily implemented by people with varying Cervus nippon Sika deer levels of expertise, or else recorded species distributions Dama dama Fallow deer may rather reflect those of skilled surveyors. Hydropotes inermis Chinese water deer Transect-sampling is a widely used survey technique, and Muntiacus reevesi Muntjac considered volunteer-friendly, visual counts are the simplest Carnivora method to survey mammals. Indirect sampling techniques Canidae Vulpes vulpes Fox that rely on the detection of tracks and signs along transects Felidae Felis silvestris Wildcat may also be implemented by surveyors with limited training. Mustelidae Lutra lutra Otter Conversely, camera-trapping is a relatively new methodologi- Martes martes Pine marten cal advancement that uses specialized equipment to detect and ‘trap’ photographs of passing animals. Meles meles Badger It is recommended that new methodologies are assessed Mustela erminea Stoat relative to existing knowledge. To date, numerous field Mustela nivalis Weasel tests have been conducted to compare the efficiency, detect- Mustela putorius Polecat ability and accuracy of camera-trapping and transect- Neovison vison Mink 12,20 – 22 sampling, though none have so far been performed Eulipotyphla in the UK. Previous comparisons have concluded that Erinaceidae Erinaceus europaeus Hedgehog transect-sampling may provide a more complete species Talpidae Talpa europaea Mole inventory, and obtain a greater frequency of records than 22 Lagomorpha alternative methods. However, conflicting results have Leporidae Lepus europaeus Brown hare been reported for the efficiency of species detection in 20,23 Lepus timidus Mountain/Irish hare terms of sampling effort. Furthermore, questionnaires Oryctolagus cuniculus Rabbit indicate that field sign surveys are often considered more dif- ficult than sightings surveys, and camera-trapping has been Rodentia reported to allow for more accurate species identification Sciuridae Sciurus carolinensis Grey squirrel than can be achieved by the identification of tracks. Sciurus vulgaris Red squirrel The most appropriate method for a given survey may be determined by, inter alia, the objectives and biological ques- tions asked, characteristics and conservation status of the species density and assessing alpha diversity. Specifically, 26 26 target species and dependability of the method. the study performed field trials and used a questionnaire to Ultimately however, it is often resource availability that deter- investigate the efficiency and reliability of surveying terres- 20,21,26 mines method selection. The efficient use of resources is trial woodland mammals in the UK. Both components of paramount in conservation, and financial and labour costs the study were concerned with a target suite of species should, therefore, be key considerations in the selection of (Table 1); the majority of small mammals were not con- 16,28,29 the most feasible sampling method. Furthermore, the sidered. Field trials primarily assessed the labour and econ- application of an efficient, reliable and cost-effective method omic efficiency of each sampling technique and the 11,16,20,28 may maximize the validity of species assessments. questionnaire investigated surveyor competence. Despite escalating global popularity in the use of camera traps, no camera-trapping studies in the UK natural Materials and methods environment have been published in the literature [web of science search: TS ¼ (camera-trapping) and CU ¼ (United Field trials Kingdom or England or Scotland or Wales or Northern Study area Ireland or Great Britain or Ireland)]. However, it is antici- pated that camera traps will become of greater use by Field trials were conducted in Edenbrows Wood in Cumbria biologists as technologies and methodologies advance. (OS Reference: NY 497 498; Fig. 1), a mixed Plantation on The principal objective of the present study was to Ancient Woodland Site adjacent to the River Eden, a Special compare the rigour of camera-trapping and transect- Area of Conservation and Site of Special Scientific Interest. sampling as techniques for recording species, estimating The study area is 0.28 km and composed of mixed ......................................................................................................................................................................................................................................... 41 Research article Bioscience Horizons † Volume 4 † Number 1 † March 2011 ......................................................................................................................................................................................................................................... Figure 1. Edenbrows Wood, Cumbria (OS Reference: NY 497 498) with sampling sites defined and camera trap stations and transect locations marked. conifers and ash (Fraxinus excelsior)/oak (Quercus petraea) 2009 and Cumbria in December 2009. Three camera trap woodland. Floral composition was used to divide the study stations were assigned to each sampling site and coordinates area into six sampling sites: Grand Fir (Abies grandis); were random. Inter-camera distance ranged between 43 and Mixed Conifers; Hybrid Larch (Larix x eurolepis); Sitka 288 m. Each camera was operational for between 5 and 57 Spruce (Picea sitchensis); Mixed Broadleaves and Mixed consecutive trap nights, sampling from December 2009 to Broadleaves/Hybrid Larch. January 2010. The mean daily temperature for the period December Sixteen Reconyx (models RC55 RapidFire and PC85 2009 to February 2010—recorded at Brampton climate RapidFire Pro; Reconyx Inc., WI, USA) and two station 11 km north of the study area—was 0.78C with a CamTrakker (model MK-8; CamTrakker, GA, USA) range from 210.5 to 7.58C. The mean daily rainfall and passive infrared camera traps were used, with automatic snow depth for the same period was 2.2 mm and 3 cm, infrared flash and strobe flash, respectively. All units were respectively. programmed to capture maximum photographs per trigger, The site was selected on the basis of accessibility, size, configured to minimal latency periods between triggers and floral diversity and the high level of recreational use, which secured to trees at a height of 0.3 m to maximize capture represents the effects of disturbance associated with publicly probability. Assuming functionality, cameras were oper- accessible land, including potential equipment security ational 24 h a day, and date and time were imprinted on threats. all photographs. Traps were checked infrequently, usually Field trials were conducted from December to February as replacing memory cards. The total sampling effort was 693 field signs were less likely to be obscured by vegetation, trap nights (i.e. sum of sampling nights per camera). species observation would also, therefore, be less affected Sensor detection parameters were estimated for each 31 18 by visual background noise, and this methodology also camera model, and figures weighted by the total sampling acknowledges recommendations of the Winter Mammal effort for each model to determine the values used in analysis Monitoring (WMM) pilot study. Furthermore, the (J. Rowcliffe, personal communication). Roe deer (Capreolus sampling period was minimal to meet the assumptions of capreolus) group size (g) and average day range (v) were pro- density estimate calculations. vided by Robin Gill ( personal communication) and a primary literature source, respectively. Camera-trapping Transect-sampling The general framework of the camera-trapping survey fol- lowed a previously trialled methodology; the methodology Ten linear transects of mean length (+SD) 127.6+ 68.5 m was refined during preliminary trials in Borneo in September were established, directly connecting camera trap stations ......................................................................................................................................................................................................................................... 42 Bioscience Horizons † Volume 4 † Number 1 † March 2011 Research article ......................................................................................................................................................................................................................................... within each sampling site and extending 30 m before the where appropriate, and the three hypothetical training first station and after the last (Fig. 1). All mammals in the courses were considered theoretically feasible (A. Dunlop, target suite of species were registered according to standar- personal communication). The questionnaire was pro- dized techniques, collecting sightings and tracks and grammed with complex routing logic to automatically signs data simultaneously. Animal- and sign-observer dis- direct respondents based on individual responses, and tances were estimated without the use of equipment. piloted on nine individuals representing the five typology Transects were walked between 0820 and 1430 h, and groups (i.e. academic, mammal interest, student, etc.). sampling was conducted between January and February 2010. Each transect was walked either four or five times, achieving a total of 46 transect surveys, thereby accumulat- Data analysis ing 5.7 km of transects walked. Field trials Signs of fox (Vulpes vulpes), badger (Meles meles), mole (Talpa europaea), rabbit (Oryctolagus cuniculus), otter To evaluate the rigour of camera-trapping for surveying the (Lutra lutra) and roe deer were registered; only fox, badger target suite of species, a subset of all photographs were and otter tracks were considered. Deer faecal pellets were used, excluding domestic animals, humans, birds and small recorded according to standardized methods, and were mammals (with the exception of Sciurus spp.). Blank cap- not cleared from transects. Tracks and signs which could tures and exposures in which the species was unidentifiable not be confidently identified were photographed for ex situ were also excluded from analysis. Independent records two-way agreement. were defined as (i) consecutive photographs of the same species taken at an interval of 0.5 h or (ii) photographs Questionnaire of different species irrespective of interval length. In analyses Between February and March 2010, a seven-part web-based of transect-sampling, tracks and signs data and sightings data questionnaire was used to investigate the temporal trends in were pooled. the use of survey techniques and the reliability of species Transect-sampling data and camera-trap data were pooled identification and distance estimation by mammal surveyors to estimate total species richness by Chao Presence/Absence (see Supplementary material online). The first three parts in DIVERSITY. Species accumulation curves plot S obs investigated the respondents’ previous surveying experience, (Mao Tau) values computed in EstimateS, pooling data including reporting the period during which they first by sampling day and performing 100 randomizations implemented each technique. Respondents were then asked without replacement to eliminate bias associated with to quantify their confidence of estimating distance and iden- unequal sampling effort per day. tifying species from photograph, sight and tracks and signs. Relative efficiency of species detection was valued and The fifth part investigated the training the respondent had subsequently compared by paired t-test. Differences received and would consider in the future. In the penultimate between methods in the mean latency to first detection part, respondents were asked to quantify their anticipated (LTD) were analysed by paired t-test. future involvement in mammal surveying in the UK with Labour investments were calculated from daily records of regards to method use. Questions pertaining to demo- time expended in data collection, excluding general field graphics were included in the final part of the questionnaire time. No randomizations were performed for species for the purposes of describing the sample. accumulation plots per human hour of field investment and To achieve comprehensive sampling, the questionnaire are, therefore, presented chronologically. Economic costs was distributed to virtually all organizations collaborating included equipment and theft compensatory costs only; with the Tracking Mammals Partnership, supplemented general project costs were omitted. Cost comparisons were by additional non-governmental and governmental organiz- performed by chi-square test, incorporating Yates’ correction ations, volunteer organizations and independent ecologists. for continuity. Each unit of the sampling frame (n ¼ 134) was authorized Photographic capture rates were used to estimate species responsible questionnaire dissemination within the respective density; variance and precision were not estimated. Roe organizations and among appropriate contacts. In addition deer density was estimated from faecal pellet counts, and to direct email invitations, the questionnaire was accessible variance calculated as the SD of density estimates from via: Devon Wildlife Trust website; Lincolnshire Wildlife each sampling day. Trust newsletter, February 2010; The Mammal Society Alpha diversity indices were calculated in DIVERSITY, (TMS) website and e-bulletin, March 2010 and the public defining an individual as an independent record plus forum Wild About Britain, directing respondents to the additional animals observed in a single instance by sight or appropriate TMS web page. photograph. Previously validated questions used during the WMM All variables were tested for normality by Kolmogorov – pilot study were included to allow for direct comparisons Smirnov test and statistical comparisons performed in ......................................................................................................................................................................................................................................... 43 Research article Bioscience Horizons † Volume 4 † Number 1 † March 2011 ......................................................................................................................................................................................................................................... SPSS 15.0 (SPSS, Inc., IL, USA), measuring significance at by both camera-trapping and transect-sampling, the latter P ¼ 0.05. detected each species in fewer days (i.e. lower mean value of LTD; t ¼ 4.264, df ¼ 5, P ¼ 0.008). Specifically, species were accumulated by the detection of tracks and signs at a Questionnaire faster rate than any other detection method when sampling Statistical analyses were performed in SPSS 15.0 (SPSS, Inc., effort 5 d (Fig. 2). However, in terms of field labour invest- IL, USA), considering significance at P ¼ 0.05. All usable ments, less than 1 h was required to achieve an asymptote of data were analysed, thereby including the individual accumulative species detected by camera-trapping (Fig. 3). responses from questionnaires that were partially complete. This labour investment was significantly less than the Descriptive and statistical analyses of the survey data were amount expended for tracks and signs (x ¼ 45.15, df ¼ 1, performed. Confidence of species identification from differ- P, 0.001) and sightings (x ¼ 36.20, df ¼ 1, P, 0.001); ent forms of evidence was assessed by Kruskal – Wallis and no difference between transect-based methods was observed post-hoc analysis. Friedman tests were used to investigate (x ¼ 1, df ¼ 1, P . 0.25). Total field labour investments the frequency of method use and preference of hypothetical were equitable between methods; financial costs were signifi- training courses. Comparisons of temporal trends in cantly greater for camera-trapping (P, 0.001; Table 3). method use were performed by chi-square test, incorporating The weighted mean camera trap detection arc and distance Yates’ correction for continuity. were 0.704 u and 0.005 km, respectively. An average roe deer group size of 1.6 and average day range of 2.19 km -1 day was used to calculate density from camera-trapping Results rates. Roe deer density was estimated by transect-sampling Field trials (+SD) as 3.85+ 1.60 km , a significantly lower density than derived by camera-trapping (15.47 km ; P, 0.001). Eight target species were recorded during the field trials: badger; fox; grey squirrel (Sciurus carolinensis); mole; otter; rabbit; red squirrel (Sciurus vulgaris) and roe deer. In 117 independent records, camera traps registered all of the above species, excluding mole. A total of 142 records were obtained during transect-sampling; sightings data constituted 3 of these records. Excluding squirrels, all of the above species were detected by tracks and signs, and only rabbit and red squirrel were encountered by direct observation. Camera-trapping consistently recorded equal or more species per sampling site than did transect-sampling, yielding Figure 2. Cumulative number of species observed as a function of a greater value of relative efficiency (t ¼ 3.3, df ¼ 5, P ¼ increased sampling effort; S (Mao Tau) presented. obs 0.021; Table 2). Species richness (+SD) of the entire study site was estimated as 9+ 3.01. Of those species detected Table 2. Observed richness of sampling sites and relative efficiency of each survey method per sampling site (i.e. number of species detected by individual method/total number of species detected in each sampling site) Sampling site Camera-trapping Transect- Richness sampling ................................................................................................................ Sitka Spruce 0.8 0.4 5 Mixed Broadleaves 0.86 0.71 7 Figure 3. Cumulative number of species detected with increasing field labour investments, presented chronologically. Mixed Broadleaves/ 0.67 0.67 3 Hybrid Larch Table 3. Cost comparison of survey methods Mixed Conifers 1 0.5 6 Grand Fir 0.83 0.67 6 Method Financial (£) Time (h) ................................................................................................................ Hybrid Larch 1 0.5 4 ................................................................................................................ Camera-trapping 8423 12.23 Mean 0.86 0.57 Transect-sampling 20 14.64 SD 0.13 0.12 P ,0.001 NS ......................................................................................................................................................................................................................................... 44 Bioscience Horizons † Volume 4 † Number 1 † March 2011 Research article ......................................................................................................................................................................................................................................... Table 4. Alpha diversity indices of Edenbrows Wood, estimated by two survey methods a b c d e Method Species Individuals Diversity Abundance Richness ........................................................................................................................................................................................................................................ Camera-trapping 7 123 1.37+ 0.01 2.86 1.25 Transect-sampling 7 143 0.84+ 0.01 1.58 1.21 ........................................................................................................................................................................................................................................ P NS NS NS Observed value. Observed value (independent records plus additional animals observed in a single instance). Shannon-Wiener. Simpson’s diversity index. Margalef. Camera-trap data and transect data derived alpha diversity recorded use was during the period 1996 – 2000 (5.3%). estimates that were neither significantly different for abun- Conversely, in the period 2006 – 2009, 24.2% and 19.4% dance, richness or diversity (Table 4). of all respondents first conducted sightings surveys and tracks and signs surveys, respectively. For both transect- Questionnaire based methods, 21% of respondents first conducted each survey method pre-1990; no respondents first used either A total of 79 responses were received at a completion rate of method in 2010. 73.4% (n ¼ 58); the remaining 21 were partially complete. The frequency of respondents who stated they could con- Each region of the UK was represented by at least one fidently identify the target suite of species by photograph (i.e. respondent (except London) and the modal demographics the product of camera-trapping), sight and tracks and signs were the following: male (53.4%); aged 25 – 34 (25.9%); differed significantly between forms of evidence (Kruskal – professional country worker (27.6%) and employee or Wallis, H ¼ 29.044, df ¼ 2, P ¼ 0.000). Fewer respondents member of TMS (43.1%). The sample was comparable to were confident in the identification of species from tracks the respondents involved in the WMM pilot study, in and signs than from photographs (Mann – Whitney, U ¼ terms of typology (e.g. academic, student, etc.; t ¼ 1.49, 66.00, P ¼ 0.000) and sightings (Mann – Whitney, U ¼ df ¼ 5, P ¼ 0.197) and gender (t ¼ 4.28, df ¼ 1, P ¼ 42.50, P ¼ 0.000). Furthermore, fewer respondents were 0.146). However, respondents were typically younger in able to confidently identify species from photographs than the present study (t ¼ 3.37, df ¼ 7, P ¼ 0.012). from sight (Mann – Whitney, U ¼ 337.50, P ¼ 0.024). Questionnaire respondents indicated that camera-trapping Concerning the eight species recorded during field trials was implemented less frequently than both transect-based only, the median number of respondents who stated they sampling methods in 2009 (Friedman Test, df ¼ 2, P ¼ could confidently identify each species by photograph, sight 0.000). This relationship was also anticipated for the and tracks and signs was 54, 58 and 47, respectively; the period 2010 – 2015 (Friedman test, df ¼ 2, P ¼ 0.000). The interquartile ranges were 0, 1 and 27.75, respectively (Fig. 5). differences between 2009 and 2010 – 2015 were not signifi- Respondents were asked to quantify their confidence of cant within methods (Fig. 4). estimating animal-observer distance on a five-point scale. Of those respondents with camera-trapping experience Only 22.2% of respondents could estimate distance to the (24.1%), nearly 85% first used camera traps for wildlife highest degree of accuracy. The modal value (35.2%) of studies in the UK between 2006 and 2009, and the earliest quantified confidence was ‘4’. Figure 4. Friedman test mean rank of survey method use and anticipated future use, where integers represent the scale of annual frequency of Figure 5. Frequency of respondents able to confidently identify a range of surveys per respondent: never (0 surveys; 1); rarely (1–2 surveys; 2); mammal species (badger; fox; grey squirrel; mole; otter; rabbit; red squirrel; occasionally (3–4 surveys; 3); frequently (5þ surveys; 4). roe deer) from different forms of evidence. ......................................................................................................................................................................................................................................... 45 Research article Bioscience Horizons † Volume 4 † Number 1 † March 2011 ......................................................................................................................................................................................................................................... Of those respondents who had not been trained in the use associated costs. It is, therefore, probable that bias has of camera traps (91.5%), most (74.1%) would consider been incurred as a result of using external information. attending a camera-trapping training course. When pre- However, it is proposed that the roe deer density estimate sented with three hypothetical training courses, respondents derived from camera trap data is more accurate than that indicated that preference was varied (Friedman test, df ¼ 2, derived from faecal pellet counts, as a greater number of P ¼ 0.000). The 1-day course was most preferred and was individuals were observed by independent photographic cap- considered by 79.3% of respondents to provide adequate tures than was estimated by the latter. training to become competent in camera trap use. Density estimate comparisons are limited in the present study as transects were not conducted on consecutive days, and the age of species tracks could, therefore, not be accu- Discussion rately determined as required. Furthermore, the absence Despite the relocation of two camera traps due to accessibil- of data of animal-related parameters limited the use of ity concerns of original placement, and subsequent low camera trap data, and frequency of sightings records were sampling effort of these cameras, camera-trapping produced considered insufficient to accurately calculate species a more complete inventory than alternative methods, as con- density by distance-sampling. 23,40 cluded by other studies. In terms of sampling days, The assumption of distance-sampling that states recorded species were detected at the fastest rate by tracks and signs, distances are exact may be violated by the diverse mammal also supporting previous conclusions. However, labour surveying community, as suggested by the questionnaire efficiency of transect-sampling was comparatively limited respondents. The modal class of confidence (i.e. ‘4’) also due to the high investments required to establish transects concurs with the WMM pilot study sample. Although before sampling could commence. High variability in sur- density may be reliably calculated from inaccurate field veyor competence of species identification from field signs data, tendency to under- or over-estimate distance may bias across species and the evident inability of most mammal sur- results. veyors to confidently estimate animal – observer distance The questionnaire sample also indicates that the mammal raises concerns over the reliability of field sign data and surveying community is less able to identify species from distance-sampling-derived density estimates, respectively. tracks and signs than from sightings and photographs. This study has emphasized that failure to detect species Misidentification may result in erroneous population esti- may not be indicative of species absence, rather insufficient mates, and non-representative presence/absence data that effort or use of an inappropriate method. Due to the ambi- may misguide conservation and management initiatives, 24 14 guity of squirrel field signs, only sightings were considered potentially with severe financial implications. during field trials, for which no records of grey squirrel were Respondents further indicated that species identification obtained; this result was disputed by camera trap evidence of from photographs is more difficult than from sightings, species presence. As the grey squirrel is a direct threat to the though it should be noted that the latter is largely dependent 42 10 native red squirrel, this result also highlights the conserva- on clear observations, and is biased towards large-bodied tion significance of differences in detectability between diurnal species. Although there is also a positive relation- methods. ship between body weight and detection probability by Total field labour investments were equitable between camera traps, camera-trapping may overcome the temporal methods to ensure efficiency was directly comparable. limitations of transect-sampling by surveying at night. However, it should be noted that camera-trapping labour Furthermore, unambiguous photographs obtained by investments were probably lower than in other circumstances camera traps provide indisputable evidence of species pres- as standard detection zone checks were not performed due to ence, considerably reducing observer inaccuracies and logistical constraints. Approximately optimal positioning bias common with other methods. It is, therefore, rec- was determined during preliminary trials, which considering ommended that less-competent surveyors supplement field the above, could simulate training. The field trials, therefore, sign surveys with camera trap data, where possible. demonstrate the performance of camera-trapping when a Assuming surveyor competence, when the aim of a survey trained surveyor is limited by logistics. Alternatively, when is to produce a species inventory and the surveyor is limited the survey objectives do not include density estimation, it is by total sampling period and not human labour investments, proposed that the 9 h otherwise invested in estimating detec- it is proposed that tracks and signs surveys may offer the best tion zone parameters would probably be sufficient to approach for producing rapid faunal assessments. However, perform these checks. if the reverse limitations are applied, camera-trapping may be To estimate species density from camera trap data, it is the most efficient method as labour investments are com- 22,44 recommended that the animal-related parameters are esti- paratively minimal, unlike transect-sampling which mated simultaneously to camera-trapping; this was not required 5 h of field labour to establish transects only. logistically feasible in the present study due to the substantial Furthermore, it is proposed that camera-trapping may ......................................................................................................................................................................................................................................... 46 Bioscience Horizons † Volume 4 † Number 1 † March 2011 Research article ......................................................................................................................................................................................................................................... provide a cost-effective approach for monitoring pro- season, species density and habitat. Furthermore, density grammes at large temporal and spatial scales, as the sub- estimates derived by camera-trapping and transect-sampling 11,53 stantial equipment costs may be offset by frequent and should be validated against direct counts. repeated use. Alpha diversity estimates were not different between Supplementary data survey methods, suggesting that either method may be used to derive accurate estimates. Furthermore, it is proposed Supplementary data is available at Bioscience Horizons that Shannon-Wiener is the most appropriate index to use online. in future assessments as it recognizes the number of species and the evenness of species abundance. Acknowledgements It is suggested that transect-sampling is a well-practiced methodology historically and that the annual frequency I would like to thank my principal supervisor Dr Owen Nevin, of transect-based surveys may remain approximately co-supervisor Dr Ian Convery, and acknowledge the logistical constant in the future. Conversely, data suggest that support given by Dr Andrew Ramsey, Ellie Lindsay, Melanie camera trap use will increase, which is further supported Clapham and Robbie Hawkins. I would also like to thank by the respondents’ interest in receiving camera-trapping Dr Marcus Rowcliffe, Dr Robin Gill, Dr Mathew Crowther training. This study also provides an insight into the training and Dr Philip Stevens. I am also thankful to Marina interests of mammal surveyors and a foundation from which Pacheco, Laura Drake, Alex Dunlop, Simon Poulton, to further investigate and design future training courses. Rowena Staff and the anonymous individuals who responded to the questionnaire and assisted with distribution. Finally, I would like to thank my family and friends. Conclusion This is the first published study to compare the efficiency and Funding reliability of camera-trapping and transect-sampling as tech- niques for surveying terrestrial mammals in the UK. As Financial support was kindly received from The Clouded 20,21 reported by non-UK studies, this investigation concludes Leopard Project (USA) and Penrith Lions Club (UK). that the best balance between cost-effectiveness, labour effi- ciency and rigour can be achieved by camera-trapping. It Author biography has highlighted that despite lower initial economic costs, transect-sampling rigour may be compromised by surveyor N.J.R. studied BSc. (Hons) Animal Conservation Science at competence of identifying tracks and signs, and the compara- the Centre for Wildlife Conservation, University of tively slow rate of species accumulation per human hour of Cumbria, UK, where he acquired substantial knowledge labour investment. and expertise. Furthermore, he has received training in the This study also presents the first attempt to identify tem- use of advanced tools of modelling and analysis of spatial poral trends in survey method use in the UK. It is evident data, completing two courses in Geographic Information that camera-trapping is currently implemented less fre- Systems. Academic achievements are complemented by quently than transect-sampling, and data further suggest numerous independent and supportive research projects that the former will increase in the future, complementing and familiarity of working in temperate and tropical the global trend. environments. Independent research projects have included In a brief comparison of survey methods at a small spatial investigations of species ecology, protected area management and temporal scale, it is foolhardy to assert too much in the and animal behaviour. His principal interest is wild cat con- way of definitive conclusions. Instead, the results should be servation and research, with a specific focus on human-felid considered the inferences of a single case study only, when conflict and species ecology. As a hobbyist wildlife and land- environmental conditions were favourable for infrared scape photographer, he is also interested in the applications camera trap performance, and detectability of of camera traps in wildlife research. He aims to integrate field signs. Furthermore, it should be acknowledged that his passion for photography into future research endeavours 11,20,22,49 (i) survey efficiency may differ in space and time, as he aspires to pursue a career in wild cat conservation and (ii) capture success may vary within and between camera ecological research. 29,50,51 trap models, (iii) flash-induced trap-shy may reduce trapping rates and (iv) detection efficiency may be density dependent. References It is, therefore, advocated that further studies are con- 1. 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Journal

Bioscience Horizons – Oxford University Press

Published: Mar 23, 2011

Keywords: camera-trapping efficiency mammals reliability transect-sampling UK

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