The effect of camera-trap viewshed obstruction on wildlife detection: implications for inference

2020 ◽  
Vol 47 (2) ◽  
pp. 158 ◽  
Author(s):  
Remington J. Moll ◽  
Waldemar Ortiz-Calo ◽  
Jonathon D. Cepek ◽  
Patrick D. Lorch ◽  
Patricia M. Dennis ◽  
...  
Keyword(s):  
Image Data ◽  
Camera Trap ◽  
Camera Traps ◽  
Mammal Species ◽  
Ecological Processes ◽  
Detection Rates ◽  
Management Application ◽  
Efficiency And Effectiveness ◽  
Steep Slopes ◽  
Wildlife Detection

Abstract ContextCamera traps are one of the most popular tools used to study wildlife worldwide. Numerous recent studies have evaluated the efficiency and effectiveness of camera traps as a research tool. Nonetheless, important aspects of camera-trap methodology remain in need of critical investigation. One such issue relates to camera-trap viewshed visibility, which is often compromised in the field by physical obstructions (e.g. trees) or topography (e.g. steep slopes). The loss of visibility due to these obstructions could affect wildlife detection rates, with associated implications for study inference and management application. AimsWe aimed to determine the effect of camera-trap viewshed obstruction on wildlife detection rates for a suite of eight North American species that vary in terms of ecology, commonness and body size. MethodsWe deployed camera traps at 204 sites throughout an extensive semi-urban park system in Cleveland, Ohio, USA, from June to September 2016. At each site, we quantified camera-trap viewshed obstruction by using a cover-board design. We then modelled the effects of obstruction on wildlife detection rates for the eight focal species. Key resultsWe found that detection rates significantly decreased with an increasing viewshed obstruction for five of the eight species, including both larger and smaller mammal species (white-tailed deer, Odocoileus virginianus, and squirrels, Sciurus sp., respectively). The number of detections per week per camera decreased two- to three-fold as visibility at a camera site decreased from completely free of obstruction to mostly obstructed. ConclusionsThese results imply that wildlife detection rates are influenced by site-level viewshed obstruction for a variety of species, and sometimes considerably so. ImplicationsResearchers using camera traps should address the potential for this effect to ensure robust inference from wildlife image data. Accounting for viewshed obstruction is critical when interpreting detection rates as indices of abundance or habitat use because variation in detection rate could be an artefact of site-level viewshed obstruction rather than due to underlying ecological processes.

scholarly journals Long-term monitoring of margays (Leopardus wiedii): Implications for understanding low detection rates

PLoS ONE ◽  
2021 ◽  
Vol 16 (3) ◽  
pp. e0247536
Author(s):  
Bart J. Harmsen ◽  
Nicola Saville ◽  
Rebecca J. Foster
Keyword(s):  
Detection Rate ◽  
Camera Trap ◽  
Wide Distribution ◽  
Camera Traps ◽  
Detection Rates ◽  
Terrestrial Mammals ◽  
Exclusive Territories ◽  
Carnivore Species ◽  
Density Population

Population assessments of wide-ranging, cryptic, terrestrial mammals rely on camera trap surveys. While camera trapping is a powerful method of detecting presence, it is difficult distinguishing rarity from low detection rate. The margay (Leopardus wiedii) is an example of a species considered rare based on its low detection rates across its range. Although margays have a wide distribution, detection rates with camera traps are universally low; consequently, the species is listed as Near Threatened. Our 12-year camera trap study of margays in protected broadleaf forest in Belize suggests that while margays have low detection rate, they do not seem to be rare, rather that they are difficult to detect with camera traps. We detected a maximum of 187 individuals, all with few or no recaptures over the years (mean = 2.0 captures/individual ± SD 2.1), with two-thirds of individuals detected only once. The few individuals that were recaptured across years exhibited long tenures up to 9 years and were at least 10 years old at their final detection. We detected multiple individuals of both sexes at the same locations during the same survey, suggesting overlapping ranges with non-exclusive territories, providing further evidence of a high-density population. By studying the sparse annual datasets across multiple years, we found evidence of an abundant margay population in the forest of the Cockscomb Basin, which might have been deemed low density and rare, if studied in the short term. We encourage more long-term camera trap studies to assess population status of semi-arboreal carnivore species that have hitherto been considered rare based on low detection rates.

Spot on: using camera traps to individually monitor one of the world’s largest lizards

2020 ◽  
Vol 47 (4) ◽  
pp. 326 ◽  
Author(s):  
Harry A. Moore ◽  
Jacob L. Champney ◽  
Judy A. Dunlop ◽  
Leonie E. Valentine ◽  
Dale G. Nimmo
Keyword(s):  
Activity Patterns ◽  
Image Data ◽  
Dorsal Surface ◽  
Camera Trap ◽  
Camera Traps ◽  
Identification Accuracy ◽  
Individual Identification ◽  
Lizard Species ◽  
Late Afternoon ◽  
Large Animals

Abstract ContextEstimating animal abundance often relies on being able to identify individuals; however, this can be challenging, especially when applied to large animals that are difficult to trap and handle. Camera traps have provided a non-invasive alternative by using natural markings to individually identify animals within image data. Although camera traps have been used to individually identify mammals, they are yet to be widely applied to other taxa, such as reptiles. AimsWe assessed the capacity of camera traps to provide images that allow for individual identification of the world’s fourth-largest lizard species, the perentie (Varanus giganteus), and demonstrate other basic morphological and behavioural data that can be gleaned from camera-trap images. MethodsVertically orientated cameras were deployed at 115 sites across a 10000km2 area in north-western Australia for an average of 216 days. We used spot patterning located on the dorsal surface of perenties to identify individuals from camera-trap imagery, with the assistance of freely available spot ID software. We also measured snout-to-vent length (SVL) by using image-analysis software, and collected image time-stamp data to analyse temporal activity patterns. ResultsNinety-two individuals were identified, and individuals were recorded moving distances of up to 1975m. Confidence in identification accuracy was generally high (91%), and estimated SVL measurements varied by an average of 6.7% (min=1.8%, max=21.3%) of individual SVL averages. Larger perenties (SVL of >45cm) were detected mostly between dawn and noon, and in the late afternoon and early evening, whereas small perenties (SVL of <30cm) were rarely recorded in the evening. ConclusionsCamera traps can be used to individually identify large reptiles with unique markings, and can also provide data on movement, morphology and temporal activity. Accounting for uneven substrates under cameras could improve the accuracy of morphological estimates. Given that camera traps struggle to detect small, nocturnal reptiles, further research is required to examine whether cameras miss smaller individuals in the late afternoon and evening. ImplicationsCamera traps are increasingly being used to monitor reptile species. The ability to individually identify animals provides another tool for herpetological research worldwide.

Effects of different attractants and human scent on mesocarnivore detection at camera traps

2020 ◽  
Vol 47 (4) ◽  
pp. 338
Author(s):  
Bracy W. Heinlein ◽  
Rachael E. Urbanek ◽  
Colleen Olfenbuttel ◽  
Casey G. Dukes
Keyword(s):  
Fatty Acid ◽  
Castor Oil ◽  
Camera Trap ◽  
Camera Traps ◽  
Individual Species ◽  
Detection Rates ◽  
Capture Success ◽  
Affect Detection ◽  
Species Specific

Abstract ContextCamera traps paired with baits and scented lures can be used to monitor mesocarnivore populations, but not all attractants are equally effective. Several studies have investigated the efficacy of different attractants on the success of luring mesocarnivores to camera traps; fewer studies have examined the effect of human scent at camera traps. AimsWe sought to determine the effects of human scent, four attractants and the interaction between attractants and human scent in luring mesocarnivores to camera traps. Methods We compared the success of synthetic fermented egg (SFE), fatty acid scent (FAS) tablets, castor oil, and sardines against a control of no attractant in luring mesocarnivores to camera traps. We deployed each attractant and the control with either no regard to masking human scent or attempting to restrict human scent for a total of 10 treatments, and replicated treatments eight to nine times in two different phases. We investigated whether: (1) any attractants increased the probability of capturing a mesocarnivore at a camera trap; (2) not masking human scent affected the probability of capturing a mesocarnivore at a camera trap; and (3) any attractants increased the probability of repeat detections at a given camera trap. We also analysed the behaviour (i.e. speed and distance to attractant) of each mesocarnivore in relation to the attractants. Key resultsSardines improved capture success compared with the control treatments, whereas SFE, castor oil, and FAS tablets had no effect when all mesocarnivores were included in the analyses. Masking human scent did not affect detection rates in the multispecies analyses. Individually, the detection of some species depended on the interactions between masking (or not masking) human scent and some attractants. ConclusionsSardines were the most effective as a broad-based attractant for mesocarnivores. Mesocarnivores approached traps baited with sardines at slower rates, which allows for a higher success of capturing an image of the animal. ImplicationsHuman scent may not need to be masked when deploying camera traps for multispecies mesocarnivore studies, but researchers should be aware that individual species respond differently to attractants and may have higher capture success with species-specific attractants.

scholarly journals Mammal diversity among vertical strata and the evaluation of a survey technique in a central Amazonian forest

2021 ◽  
Vol 61 ◽  
pp. e20216133
Author(s):  
Alexander Roldán Arévalo-Sandi ◽  
André Luis Sousa Gonçalves ◽  
Kota Onizawa ◽  
Tsuneaki Yabe ◽  
Wilson Roberto Spironello
Keyword(s):  
Camera Trap ◽  
Camera Traps ◽  
Sampling Effort ◽  
Mammal Species ◽  
Lowland Forest ◽  
Survey Technique ◽  
Terrestrial Habitats ◽  
Common Technique ◽  
The Difference ◽  
Mammal Diversity

Mammal groups have a vast variety of habitats, which include aquatic, aerial, arboreal, and terrestrial. For terrestrial habitats, camera traps are used as a common technique to record mammals and other vertebrates and have been recently utilized to observe arboreal animals as well. Here, we compare the difference in mammal diversity between floor and canopy strata and evaluate the use of camera trapping in a lowland forest in central Amazon. We installed nine paired camera traps, one in the canopy stratum and other in the floor stratum, in the Alto Cuieiras Biological Reserve (Brazilian Amazon). With a sampling effort of 720 camera-days, we recorded 30 mammal species: nine in canopy strata, 14 in floor strata, and seven in scansorial strata (sharing both strata). On the forest floor, the species with the greatest abundance was Myoprocta acouchy; in the canopy, Isothrix paguros had the greatest abundance; and among the scansorial species, Proechymis sp. was the most abundant. Our results show the differences in mammal diversity between floor and canopy strata; canopy strata contained more small and frugivorous mammals. Although we obtained a relatively low sampling effort with the camera-trap method compared with other studies utilizing different techniques, our results were especially similar to those of previous studies that worked with canopy and floor strata. Thus, camera trap can be very effective for recording short periods of time, and this method is less physically exhaustive and expensive for researchers to study vertical strata.

First photographic records of bush dogs (Speothos venaticus) from camera-traps in Guyana

Mammalia ◽  
2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Matthew T. Hallett ◽  
Anthony Roberts ◽  
Ashley P. Holland ◽  
Angus Jackman
Keyword(s):  
Camera Trap ◽  
Camera Traps ◽  
Individual Study ◽  
Detection Rates ◽  
Detailed Measurement ◽  
Scale Modelling ◽  
In The Wild ◽  
Bush Dog ◽  
Speothos Venaticus ◽  
Photographic Records

AbstractThe bush dog (Speothos venaticus) is rare, elusive, and difficult to study in the wild. Guyana contains a wealth of intact tropical forest (∼18.4 million ha) and savanna (1.6 million ha) habitats, but management of this species is hindered by a lack of data. We present two photographic records (consisting of nine individuals) of bush dogs from camera-traps set in the Kanuku Mountains Protected Area (KMPA) – the first of this species in Guyana. These records highlight the importance of Guiana Shield forests and Guyana’s expanding protected areas system to the conservation of these wide-ranging carnivores. Additionally, we recommend that detailed measurement and reporting of site variables become standard, as it will improve the efficacy of camera-trap studies of bush dogs and allow for broad-scale modelling of space use not otherwise possible due to the low detection rates at the scale of each individual study.

scholarly journals Influence of camera-trap sampling design on mammal species capture rates and community structures in southeastern Brazil

2013 ◽  
Vol 13 (2) ◽  
pp. 51-62 ◽  
Author(s):  
Ana Carolina Srbek-Araujo ◽  
Adriano Garcia Chiarello
Keyword(s):  
Activity Patterns ◽  
Camera Trap ◽  
Camera Traps ◽  
Southeastern Brazil ◽  
Sampling Point ◽  
Community Structures ◽  
Mammal Species ◽  
Forest Interior ◽  
Trap Location ◽  
Capture Rates

The distribution of species and population attributes are critical data for biodiversity conservation. As a tool for obtaining such data, camera traps have become increasingly common throughout the world. However, there are disagreements on how camera-trap records should be used due to imperfect species detectability and limitations regarding the use of capture rates as surrogates for abundance. We evaluated variations in the capture rates and community structures of mammals in camera-trap surveys using four different sampling designs. The camera traps were installed on internal roads (in the first and fourth years of the study), at 100-200 m from roads (internal edges; second year) and at 500 m from the nearest internal road (forest interior; third year). The mammal communities sampled in the internal edges and forest interior were similar to each other but differed significantly from those sampled on the roads. Furthermore, for most species, the number of records and the capture success varied widely among the four sampling designs. A further experiment showed that camera traps placed on the same tree trunk but facing in opposing directions also recorded few species in common. Our results demonstrated that presence or non-detection and capture rates vary among the different sampling designs. These differences resulted mostly from the habitat use and behavioral attributes of species in association with differences in sampling surveys, which resulted in differential detectability. We also recorded variations in the distribution of records per sampling point and at the same spot, evidencing the stochasticity associated with the camera-trap location and orientation. These findings reinforce that for species whose specimens cannot be individually identified, the capture rates should be best used as inputs for presence and detection analyses and for behavior inferences (regarding the preferential use of habitats and activity patterns, for example). Comparisons between capture rates or among relative abundance indices, even for the same species, should be made cautiously.

High variation in camera trap-model sensitivity for surveying mammal species in northern Australia

2018 ◽  
Vol 45 (7) ◽  
pp. 578 ◽  
Author(s):  
Jaime Heiniger ◽  
Graeme Gillespie
Keyword(s):  
Detection Probability ◽  
High Sensitivity ◽  
Camera Trap ◽  
Camera Traps ◽  
Northern Australia ◽  
Mammal Species ◽  
Survey Tool ◽  
Significant Difference ◽  
Event Trigger ◽  
The Difference

Context The use of camera traps as a wildlife survey tool has rapidly increased, and understanding the strengths and weaknesses of the technology is imperative to assess the degree to which research objectives are met. Aims We evaluated the differences in performance among three Reconyx camera-trap models, namely, a custom-modified high-sensitivity PC850, and unmodified PC850 and HC550. Methods We undertook a controlled field trial to compare the performance of the three models on Groote Eylandt, Northern Territory, by observing the ability of each model to detect the removal of a bait by native mammals. We compared variation in detecting the known event, trigger numbers, proportion of false triggers and the difference in detection probability of small to medium-sized mammals. Key results The high-sensitivity PC850 model detected bait take 75% of the time, as opposed to 33.3% and 20% for the respective unmodified models. The high-sensitivity model also increased the detection probability of the smallest mammal species from 0.09 to 0.34. However, there was no significant difference in detection probability for medium-sized mammals. Conclusions Despite the three Reconyx camera models having similar manufacturer-listed specifications, they varied substantially in their performance. The high-sensitivity model vastly improved the detection of known events and the detection probability of small mammals in northern Australia. Implications Failure to consider variation in camera-trap performance can lead to inaccurate conclusions when multiple camera models are used. Consequently, researchers should carefully consider the parameters and capabilities of camera models in study designs. Camera models and their configurations should be reported in methods, and variation in detection probabilities among different models and configurations should be incorporated into analyses.

Quantifying imperfect camera-trap detection probabilities: implications for density modelling

2020 ◽  
Vol 47 (2) ◽  
pp. 177 ◽  
Author(s):  
T. McIntyre ◽  
T. L. Majelantle ◽  
D. J. Slip ◽  
R. G. Harcourt
Keyword(s):  
Population Density ◽  
Surface Temperature ◽  
Ambient Temperature ◽  
Population Level ◽  
Camera Trap ◽  
Camera Traps ◽  
Imperfect Detection ◽  
Detection Rates ◽  
Detection Probabilities ◽  
Density Modelling

Abstract ContextData obtained from camera traps are increasingly used to inform various population-level models. Although acknowledged, imperfect detection probabilities within camera-trap detection zones are rarely taken into account when modelling animal densities. AimsWe aimed to identify parameters influencing camera-trap detection probabilities, and quantify their relative impacts, as well as explore the downstream implications of imperfect detection probabilities on population-density modelling. MethodsWe modelled the relationships between the detection probabilities of a standard camera-trap model (n=35) on a remotely operated animal-shaped soft toy and a series of parameters likely to influence it. These included the distance of animals from camera traps, animal speed, camera-trap deployment height, ambient temperature (as a proxy for background surface temperatures) and animal surface temperature. We then used this detection-probability model to quantify the likely influence of imperfect detection rates on subsequent population-level models, being, in this case, estimates from random encounter density models on a known density simulation. Key resultsDetection probabilities mostly varied predictably in relation to measured parameters, and decreased with an increasing distance from the camera traps and speeds of movement, as well as heights of camera-trap deployments. Increased differences between ambient temperature and animal surface temperature were associated with increased detection probabilities. Importantly, our results showed substantial inter-camera (of the same model) variability in detection probabilities. Resulting model outputs suggested consistent and systematic underestimation of true population densities when not taking imperfect detection probabilities into account. ConclusionsImperfect, and individually variable, detection probabilities inside the detection zones of camera traps can compromise resulting population-density estimates. ImplicationsWe propose a simple calibration approach for individual camera traps before field deployment and encourage researchers to actively estimate individual camera-trap detection performance for inclusion in subsequent modelling approaches.

Searching for rare and secretive snakes: are camera-trap and box-trap methods interchangeable?

2020 ◽  
Vol 47 (6) ◽  
pp. 476 ◽  
Author(s):  
Dalton B. Neuharth ◽  
Wade A. Ryberg ◽  
Connor S. Adams ◽  
Toby J. Hibbitts ◽  
Danielle K. Walkup ◽  
...  
Keyword(s):  
Life Histories ◽  
Detection Rate ◽  
Temporal Trends ◽  
Habitat Type ◽  
Camera Trap ◽  
Camera Traps ◽  
Similar Data ◽  
Detection Rates ◽  
Snake Species ◽  
Snake Detection

Abstract ContextAdvancements in camera-trap technology have provided wildlife researchers with a new technique to better understand their study species. This improved method may be especially useful for many conservation-reliant snake species that can be difficult to detect because of rarity and life histories with secretive behaviours. AimsHere, we report the results of a 6-month camera-trapping study using time lapse-triggered camera traps to detect snakes, in particular the federally listed Louisiana pinesnake (Pituophis ruthveni) in eastern Texas upland forests in the USA. MethodsSo as to evaluate the efficacy of this method of snake detection, we compared camera-trap data with traditional box-trapping data collected over the same time period across a similar habitat type, and with the same goal of detecting P. ruthveni. Key resultsNo differences in focal snake species richness were detected across the trap methods, although the snake-detection rate was nearly three times higher with camera traps than with the box traps. Detection rates of individual snake species varied with the trapping method for all but two species, but temporal trends in detection rates were similar across the trap methods for all but two species. Neither trap method detected P. ruthveni in the present study, but the species has been detected with both trap methods at other sites. ConclusionsThe higher snake-detection rate of the camera-trap method suggests that pairing this method with traditional box traps could increase the detection of P. ruthveni where it occurs. For future monitoring and research on P. ruthveni, and other similarly rare and secretive species of conservation concern, we believe these methods could be used interchangeably by saturating potentially occupied habitats with camera traps initially and then replacing cameras with box traps when the target species is detected. ImplicationsThere are financial and logistical limits to monitoring and researching rare and secretive species with box traps, and those limits are far less restrictive with camera traps. The ability to use camera-trap technologies interchangeably with box-trap methods to collect similar data more efficiently and effectively will have a significant impact on snake conservation.

scholarly journals Environmental DNA for tracking waterhole visitation in savanna ecosystems

2020 ◽  
Author(s):  
Maxwell J. Farrell ◽  
Danny Govender ◽  
Mehrdad Hajibabaei ◽  
Michelle van der Bank ◽  
T. Jonathan Davies
Keyword(s):  
Large Scale ◽  
Environmental Dna ◽  
Camera Traps ◽  
Specific Reference ◽  
Arid Environments ◽  
Reference Library ◽  
Mammal Species ◽  
Biodiversity Indicator ◽  
Detection Rates

AbstractThe analysis of waterborne environmental DNA (eDNA) is effective for detecting invasive species and conducting large-scale biodiversity assessments, making it a potentially powerful tool for documenting diversity at sites where large numbers of species aggregate. We explore the utility of eDNA from waterholes for describing local mammal communities, quantifying patterns of species co-occurrences, and monitoring of rare or threatened species. In savanna ecosystems water can be a scarce resource during dry seasons and in periods of drought, promoting the aggregation of medium to large mammals. To explore the reliability of eDNA as a biodiversity indicator in these arid and semi-arid environments, we compare eDNA metabarcoding and camera traps for documenting waterhole use by mammals in the Kruger National Park, South Africa. We find that eDNA metabarcoding can recover the majority of mammal species detected in camera traps, but the DNA signatures of mammal visitation are temporally limited. Detection rates varied across sites, sampling time, species, and choice of reference library, with the best performance for water-dependent large bodied mammals visiting within two days of sampling, and matched to a curated system-specific reference library. Our results demonstrate that eDNA-based approaches can be used to track mammals of conservation concern, and reflect patterns of recent waterhole use and co-occurrence across water-dependent species, but also highlight limitations including the lack of long-term eDNA persistence in small and highly utilized waterholes and variability in detection rates among species. Sequencing of eDNA is a valuable tool for next-generation biodiversity sampling and has many exciting applications, but it is not sufficient to capture long-term waterhole visitation patterns or reliably detect rare and small-bodied species.

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