Distance Sampling Research Articles

Population study of long-tailed macaque (Macaca fascicularis) on Deli Island, Banten, Indonesia

Abstract. Fitriana YS, Sulistyadi E, Tohir RK, Hasibuan MM, Rifaie F, Maryanto I, Lubis AM, Rifqi MF. 2024. Population study of long-tailed macaque (Macaca fascicularis) on Deli Island, Banten, Indonesia. Biodiversitas 25: 144-150. Understanding the distribution and population dynamics of primate species is essential for practical conservation efforts. However, such information is often unavailable, even for species whose populations appear abundant. The long-tailed macaque (Macaca fascicularis Raffles, 1821) is a species with a wide range in Southeast Asia, including Sumatra, Java, Kalimantan, Bali, Lombok, and Lesser Sunda in Indonesia. However, comprehensive data on population density across its Indonesian distribution area still needs to be improved. To address this knowledge gap, we conducted a thorough survey and study to estimate the population density of long-tailed macaques on Deli Island, located in Banten Province. Long-tailed macaques were introduced to Deli Island between 1989 and 1990 with a total of 1000 males and 10,000 females. To date, a total of 9,500 individuals have been harvested from this island in the period 1991-2010. We employed the line transect distance sampling (LTDS) method with a perpendicular distance approach that covered all habitat types throughout the island. Our findings revealed that the population density of long-tailed macaques on Deli Island is approximately five individuals per hectare, with an estimated total population of 4,860. The data pertaining to age structure and sex ratio is notably limited, primarily due to challenges in identification caused by dense vegetation. To address these limitations and acquire a more comprehensive understanding, additional research is essential for the accurate determination of the age structure and sex ratio on the island. Our study provides crucial baseline data for conserving this species. We recommend implementing a systematic survey encompassing the entire distribution range of the long-tailed macaque across Indonesia. Such an initiative will be instrumental in assessing its threat status and laying out a comprehensive plan for conservation efforts.

Acoustic estimates of sperm whale abundance in the Mediterranean Sea as part of the ACCOBAMS Survey Initiative

Acoustic surveys for sperm whales (Physeter macrocephalus) were conducted in the Mediterranean Sea in summer 2018 as part of the vessel-based component of the ACCOBAMS Survey Initiative (ASI). Equal-spaced zigzag transects provided uniform coverage of key sperm whale habitats and were surveyed using a towed hydrophone array deployed from a research vessel at speeds of 5-8 knots. A total of 14,039 km of tracklines were surveyed in the western basin, Hellenic Trench and Libyan waters, with an acoustic coverage of 10% realised for sperm whales. During these surveys, 254 individual sperm whales were detected on the trackline, with an additional 66 individuals off-track. Sperm whales were only seen ten times on-track, with an additional 16 off-track sightings. Estimates of slant range to echolocating whales were used to derive density estimates through both design- and model-based distance sampling methodologies. An acoustic availability of 0.912 (sd = 0.036) was derived from via published models. When correcting for availability bias, a design-based abundance estimates of 2,673 individuals (95% CI 1,739-4,105; CV = 0.21) was derived for the surveyed blocks, which incorporated most known sperm whale habitat in the Mediterranean Sea. The equivalent model-based estimate was 2,825 whales (2,053-3,888; CV = 0.16). Over 97% of detected whales were in the western basin, with highest densities in the Algerian and Liguro-Provencal Basins between Algeria and Spain/France. In the eastern basin, detections were sparse and concentrated along the Hellenic Trench. A density surface modelling (DSM) exercise identified location and benthic aspect as being the most instructive covariates for predicting whale abundance. Distance sampling results were used in a power analysis to quantify the survey effort required to identify population trends. In the most extreme scenario modelled (10% per annum decline with decennial surveys), the population could have dropped by 90% before the decline was identified with high statistical power. Increasing the regularity of surveys would allow population trends to be detected more expediently. Mediterranean sperm whales are listed as Endangered on the IUCN’s Red List and the need for urgent conservation measures to reduce injury and mortality remains paramount for this unique sub-population.

Assessment of wild prey of mammalian carnivores in Barda Wildlife Sanctuary, Gujarat, India

The Barda Wildlife Sanctuary (Barda WLS) is a semi-arid ecosystem that plays an important role in the conservation of mammalian carnivores. It is essential to evaluate the population of important wild prey species in Barda, which has conservation implications for mammalian predators and themselves. We assessed the density, biomass, and population structure of wild prey species by surveying road (n = 10) and trail (n = 8) transects using the distance sampling framework method. We used male-to-female sex ratios and the percent contribution of each age class to assess population structure. Mean group size (MGS), median group size (Mdgs), and mean crowding (Mc) were calculated to analyze group size. Of the species studied, Indian peafowl had the highest density (51.61 ± 7.08 individuals/km2), followed by wild pig (10.77 ± 4.59), blue bull (3.50 ± 0.51), Indian hare (3.03 ± 0.73), and spotted deer (0.62 ± 0.04). The male-to-adult female sex ratio was biased towards females, except for Indian peafowl. All species had small group sizes except wild pigs. The results of this study can aid in its development as one of the important protected areas in Gujarat for the conservation of mammalian predators, along with framing conservation strategies for Barda WLS.

PelaSIG, a QGIS plugin for marine megafauna census: application to the aerial ACCOBAMS Survey Initiative dataset

The distribution of wild animals and their monitoring over large areas raises many logistical and technical difficulties that hinder the collection of observation data. The use of Geographic Information Systems (GIS) has increased significantly in recent years. QGIS, an open-source GIS software dedicated to the processing of geospatial data, enables the development of dedicated plugins for specific workflows. The open-source PelaSIG plugin has been developed in Python for QGIS 3 to facilitate and standardise the different steps before and after distance sampling surveys. It brings together a set of tools for survey preparation, automatic data checking, visualisation and presentation of survey effort and sightings to provide an adapted workflow. This plugin is currently designed to process dedicated aerial datasets collected with the SAMMOA software during marine megafauna surveys (i.e., marine mammals, seabirds, elasmobranchs, sea turtles, etc.). Here, we first describe the different tools already available, and then, we present an application with the dataset from the aerial survey of the ACCOBAMS Survey Initiative (ASI) conducted in 2018 over the Mediterranean Sea and using a multi-target protocol.

Using fusion effects to decrease uncertainty in distance sampling models when collating data from different surveys

AbstractEstimates of population abundance are required to study the impacts of human activities on populations and assess their conservation status. Despite considerable effort to improve data collection, uncertainty around estimates of cetacean densities can remain large. A fundamental concept underlying distance sampling is the detection function. Here we focus on reducing the uncertainty in the estimation of detection function parameters in analyses combining data sets from multiple surveys, with known effects on the precision of density estimates. We developed detection functions using infinite mixture models that can be applied on data collating multiple species and/or surveys. These models enable automatic clustering by fusing the species and surveys with similar detection functions. We present a simulation analysis of a multisurvey data set in a Bayesian framework where we demonstrated that distance sampling models including fusion effects showed lower uncertainty than classical distance sampling models. We illustrated the benefits of this new model using data of line transect surveys from the Bay of Biscay and Iberian Coast. Future estimates of abundance using conventional distance sampling models on large multispecies surveys or on data sets combining multiple surveys could benefit from this new model to provide more precise density estimates.

Species composition, relative abundance, and habitat association of birds in Dodola dry evergreen afro-montane forest and sub-afro-alpine scrubland vegetation, southeast Ethiopia.

Birds' functional groups are useful for maintaining fundamental ecological processes, ecosystem services, and economic benefits. Negative consequences of loss of functional groups are substantial. Birds are usually found at a high trophic level in food webs and are relatively sensitive to environmental change. The first surveillance bird study was carried out southeast of Ethiopia adjacent to Bale Mountain National Park aimed at investigating the composition, relative abundance, and distribution of Aves. Using regular systematic point transact sampling, the density and species composition were analyzed through the mark recapture distance sampling engine assisted by R statistical software. This study recorded a total of seventy-eight bird species over two distinct seasons. Among these, fifteen species were exclusive to Erica habitats, twenty-six were found in natural forest habitats, and three were specific to plantation forest habitats. The study also discovered three endemic species. Based on the 2018 IUCN Red List categories, six of the species are globally threatened, three are near threatened, and the remaining sixty-nine are classified as least concern. The relative abundance of birds did not significantly differ across habitats and seasons, but variations were observed among blocks. Bird density was found to fluctuate across the three habitats and two seasons; however, these habitat differences were not influenced by seasonal changes. The findings of this study reveal that the differences in composition and relative abundance are not merely seasonal changes in the forest and Erica habitats. Instead, these habitats create microclimates that cater to specific bird species. However, this localized endemism also presents challenges. The concentration of endemic species and potential resource constraints could pose a threat to these habitat-specialist birds.

Population decline of the Black-bellied Sandgrouse Pterocles orientalis in continental Spain, a main western Palearctic stronghold

Summary Many European farmland bird populations are rapidly declining because of agricultural intensification and land-use changes. Robust estimates of population sizes and trends, habitat use, and protected area coverage within the distribution range are crucial to inform the conservation and management of threatened species. Here we report on the results of the 2019 Black-bellied Sandgrouse Pterocles orientalis (BBS) survey promoted and coordinated by SEO/BirdLife to update its breeding distribution, population size, and trends in continental Spain. A total of 660 grid cells, 10 × 10 km, Universal Transverse Mercator (UTM), were surveyed (81% of the distribution area), with 2,257 visits to 1,750 walked transects (7,001 km in total; 10.6 km per UTM). BBS was detected in 43% of sampled UTMs. At transect level, occupancy was 11% higher inside protected areas. At UTM level, occupancy was estimated at 0.58 (Bayesian credible interval [BCI] 95%: 0.55–0.61), revealing that BBS occupied about half of its previous breeding range (2003–2005). Using hierarchical distance sampling modelling, we estimated an average density of 1.33 individuals/km2 in occupied areas, and a population of 4,025 individuals (confidence interval: 1,840–7,609) within sampled areas, with an additional 697 individuals (confidence interval 461–1,075) in areas that were not surveyed. Further, the relative abundance of BBS (Kilometric Abundance Index) declined by 63% between 2005 and 2019 (annual decline rate of 4.5%). BBS used agricultural habitats (73%) and unprotected areas (54%) despite a higher occupancy within protected areas. Given the recent decline rate and persistent threats, the BBS conservation status should be upgraded to “Endangered” in peninsular Spain. Its future depends on land-use changes and agricultural practices, in particular the maintenance of fallows, semi-natural habitats, and pastures for extensive grazing. Better protection of important areas and targeted conservation initiatives should be promoted to halt and reverse the population decline in this key western Palearctic stronghold.

Riverine forest as a significant habitat to harbor a wide range of bird species.

Riverine forests are unique and highly significant ecosystems that are globally important for diverse and threatened avian species. Apart from being a cradle of life, it also serves as a gene pool that harbors a variety of flora and fauna species (repeated below). Despite the fact, this fragile ecosystem harbored avian assemblages; it is now disappearing daily as a result of human activity. Determining habitat productivity using bird species is critical for conservation and better management in the future. Multiple surveys were conducted over a 15-month period, from January to March 2019, using the distance sampling point count method. A total of 250 point count stations were fixed systematically at 300 m intervals. In total, 9929 bird individuals were recorded, representing 57 species and 34 families. Out of 57 bird species, two were vulnerable, one was data deficient, one was nearly threatened, and the remaining 53 species were of least concern. The Eurasian Collard Dove - Streptopelia decaocto (14.641 ± 2.532/ha), White-eared Bulbul - Pycnonotus leucotis (13.398 ± 4.342/ha) and Common Babbler - Turdoides caudata (10.244 ± 2.345/ha) were the three first plenteous species having higher densities. However, the densities of three species, i.e., Lesser Whitethroat - Sylvia curruca, Gray Heron - Ardea cinerea and Pallas Fish Eagle - Haliaeetus leucoryphus, were not analyzed due to the small sample size. The findings of diversity indices revealed that riverine forest has harbored the diverse avian species that are uniformly dispersed across the forest. Moreover, recording the ten foraging guilds indicated that riverine forest is rich in food resources. In addition, the floristic structure importance value index results indicated that riverine forest is diverse and rich in flora, i.e. trees, shrubs, weeds and grass, making it an attractive and productive habitat for bird species.

How abundant is a species at the limit of its distribution range? Crested porcupine Hystrix cristata and its northern population.

The crested porcupine (Hystrix cristata) is a rodent present in Africa and southern Europe (Italy exclusively). The Italian population is expanding from the centre to the north and south, but little is known about the species' abundance. Reliable population density estimates are important for monitoring trends in wildlife populations and for developing effective conservation and management strategies. In this context, we aimed to first report crested porcupine population density on the northern limit of its current distribution range using a non-invasive approach. Specifically, we randomly placed 38 camera traps in an area of 242 km2 in north Italy (Lombardy region), and we applied camera trap distance sampling. We estimated a porcupine density of 0.49 ind·km-2 (±0.33, standard error). The results presented here are the first crested porcupine density estimate accounting for imperfect detection (i.e. species present but not detected). The abundance estimate reported here is fundamental for a better understanding of the species status in Europe and for implementing conservation and management plans.

Succession and climatic stochasticity induce long-term decline of a forest browser.

Removal of predators and creation of early seral habitat have, in many systems, caused substantial population growth of herbivores. Hyperabundant herbivores, in turn, induce cascading ecosystem effects, but few studies have investigated long-term browser density trends in relation to succession and stochastic climate events. Here, we use annual, empirical population estimates of a forest browser to relate forest succession to long-term decline of an herbivore that prefers early seral habitat. From 2007-2021, concurrent with reduced timber harvest, we used line-transect distance sampling to document annual changes in Columbian black-tailed deer (Odocoileus hemionus columbianus) density on a mid-sized (17.3km2) predator-free island. We documented successional changes associated with forest aggradation and decreased forage quality for deer: early successional shrub/scrub habitat declined 3.8%/year; timber volume increased 4.5%/year; and canopy coverage increased 2.5%. In 2007-2008, deer densities were the greatest observed (~44/km2), but then an historic snowstorm reduced deer density by 39%. From 2010-2021, as forests continued to mature, deer density decreased 4.0%/year, declining to 20 deer/km2. Using a multivariate approach to combine habitat variables (i.e., early seral coverage, timber volume, and canopy closure) into a measure of forest maturation, we found a significant negative relationship between deer density and forest aggradation. Thus, consistent with predictions for bottom-up limited browsers, we observed significant annual declines in a deer population throughout an extended period of forest regrowth. Despite declines, deer density on the island exceeds mainland densities, and overbrowsing likely continues to disrupt ecosystem processes.

Efficient data collection for camera trap‐based density estimation: A preliminary assessment

Abstract Camera traps have great potential for generating wildlife insights by providing high resolution site‐specific data. Methods of data collection and analysis reliant on these tools for population density estimation can be relatively resource intensive, hindering their mainstream adoption. Here, we explore the potential of population density estimates derived from a distance sampling method based on optics theory, which greatly simplifies the process of setting up camera sites and analysing data. Specifically, we (1) tested the method on human subjects in an artificial environment, (2) compared it to another method relying on virtual grids on images using wild populations of black‐backed jackal (Canis mesomelas) and African civet (Civettictis civetta) in South Africa and (3) deployed it to estimate wild boar (Sus scrofa) population densities in Hungary. The initial human trials resulted in an estimate that was extremely close to true population density. When compared to the virtual grid method, results suggest that our distance sampling method can deliver accurate estimates with increased convenience and robustness against disruptions of the camera sites. The wild boar study resulted in a realistic density estimate, which can be used as a baseline when assessing future fluctuations in population density. As this new approach does not have special requirements for setting up camera sites, it is efficient and widely applicable across other density estimation methods requiring an estimate for effective detection distance. Additionally, the method can be applied in the retrospective analysis of existing datasets.

Unveiling the Diverse Mammalian Species of a Tropical Rainforest in Northeast Bangladesh

Tropical rainforest supports an incredible diversity of mammalian species. The forest patches of northeast Bangladesh are considered hotspots for a range of threatened mammals. However, the transboundary Lathitila reserve forest in Moulvibazar district of northeast Bangladesh remained largely unexplored. We assessed the diversity of medium- and small-sized mammals using camera-trapping, and distance sampling, which was supplemented by sign survey and interviews. We recorded a total of 38 species of mammals belonging to 9 orders and 22 families. The Carnivora (34%) contained the highest number of mammals followed by Rodentia (21%), Primates (18%), Chiroptera (10%), and Artiodactyla (5%). Thirty seven percent of the recorded species were rare, followed by very common (26%), occasional (24%) and common (13%). Of these, 45% were categorized as threatened in the updated national Red List of IUCN Bangladesh. The remarkable species that we recorded are the Critically Endangered Asian elephant (Elephas maximus), Western hoolock gibbon (Hoolock hoolock), Chinese pangolin (Manis pentadactyla), Phayre’s leaf monkey (Trachypithecus phayrei), Northern pig-tailed macaque (Macaca leonina), and Bengal slow loris (Nycticebus bengalensis). The Endangered Fishing cat (Prionailurus viverrinus), and Asian small-clawed otter (Aonyx cinerea) were also recorded. The principal threats to the Lathitila forest are the habitat degradation, habitat fragmentation, human disturbance, illegal wood extraction, and wildlife poaching. This study highlights the conservation importance of this least-known forest, thereby protection measures are urgently needed to conserve its diverse mammalian fauna. Bangladesh J. Zool. 51(2): 135-154, 2023

Estimating abundance of a small population of Bryde's whales: a comparison between aerial surveys and boat‐based platforms of opportunity

AbstractAccurate abundance estimates are essential for the development of effective conservation management strategies, yet they are difficult to produce for small populations that are elusive and sparsely distributed throughout their range. For such populations it is challenging to collect a representative dataset sufficient for robust estimation of detectability and abundance. Over a one‐year study, we used two methods to estimate abundance of a Nationally Critical, widely dispersed Bryde's whale population in the Hauraki Gulf, Aotearoa/New Zealand; (i) distance sampling from systematic line‐transect aerial surveys (n = 22 surveys, 9,944 km, total sightings 21–24 whales), and (ii) mark‐recapture (MR) using photo‐identification images collected from a platform‐of‐opportunity and small‐boat surveys (218 sampling occasions, 27 whales). From the aerial surveys, we estimated an average of 15 whales (95% CI = 6, 30; CV = 37%) at the sea‐surface at any time. For the boat‐based surveys, we developed a custom MR model to address seasonal and individual heterogeneity in capture probabilities and obtained an estimate of 72 distinct whales (95% CI = 38, 106; CV = 24%) in the population. These two approaches provide different perspectives on the abundance and dynamics of Bryde's whales. The aerial surveys estimate the average number of individuals present at any one time, whereas the MR model estimates the total number of animals that used the Gulf during the study. Although neither sampling method is optimal for estimating the abundance of this small, dispersed population, the use of two complementary approaches informs conservation managers about patterns of abundance and distribution over different temporal and spatial scales. It is common to have limited resources for marine research where model assumptions cannot be met. Here, we highlight pragmatic strategies showing how models can be customized to the population of interest to assist with monitoring species of conservation concern.

Population Density of Wild Animals and Their Conflict in Konasa_Pulasa Community Conserved Forest, Omo Valley, Southern Ethiopia

Human-wildlife conflict presents an increasing challenge to conservation, particularly in densely populated parts of low-income countries. An investigation on wild animal population density and its conflict was carried out from December 2019 to May 2020 in the Konasa_Pulasa Community Conserved Forest, Omo Valley, Southern Ethiopia: implications for wildlife conservation. The distance sampling method was used to estimate the population status of wild animals in an area of 187.57 km2. Human-wild animal conflict was quantified using a questionnaire survey with 290 randomly selected household heads from five villages. In addition, focus group discussions were conducted to obtain additional information. The mean density of the Anubis baboons was 4.51 ± 0.76, that of the grivet monkeys was 3.24 ± 0.51, that of the porcupines was 0.89 ± 0.17, that of the spotted hyenas was 0.58 ± 0.15, and that of the black-backed jackals was 0.65 ± 0.12 individuals/km2. The result shows that crop damage and livestock predation were common problems in the study area. The most damaged cereal crops were maize (26.5%). The Anubis baboon was the most common crop raiding species (34.9%). An estimated average loss of different crop types was US$15.01 per year per household. Regarding livestock, sheep (36.2%) and poultry (44.3%) were the animals most attacked. The predator responsible for livestock depredation reported most frequently was the spotted hyena (35%), followed by the black-backed jackal (24%) and the leopard (16%), and it was responsible for the loss of 271 domestic animals with an estimated economic loss of US $24,395.92 in five villages. Guarding (47.4%) was the main means of mitigation methods. Most farmers’ (47.4%) attitude towards wild animal conservation was positive. The extent of the damage varied between villages and with the distance from the forest boundary. Local people close to the forest boundaries were highly vulnerable to wild animal conflict. Our results show that livestock predation and crop damage were common problems caused by Anubis baboon, verves monkeys, porcupines, spotted hyenas, and black-backed jackals. The increase in the population of wild animals and the proximity to the forest are the causes of HWC. Guarding is the dominant traditional method used to reduce HWC in the study area. Using effective methods to reduce livestock damage and loss to crops, including improved livestock husbandry, cultivating unpalatable crops near the forest and raising local community awareness could make local residents aware of conservation.

Population size and conservation status of large terrestrial mammals in a West African protected area

AbstractTerrestrial large mammals are threatened in West and Central Africa due to trade and consumption. The species population size was estimated using diurnal distance sampling in Old Oyo National Park, Nigeria. Mean species abundance and density ranged from 631 ± 281 to 3320 ± 1163 individuals and 2.0661 ± 1.356 to 6.7525 ± 3.0376 individuals km−2 between sub‐habitat types, and from 258 ± 125 to 2671 ± 867 individuals and 0.9526 ± 0.6801 to 5.1377 ± 1.8988 individual km−2 between the ranges. Based on IUCN guidelines for local assessment, we classified 1 species as Vulnerable, 10 Near Threatened and 1 Least Concern. Long‐term population monitoring and education programmes are crucial.

Distribution patterns of marine megafauna density in the Mediterranean Sea assessed through the ACCOBAMS Survey Initiative (ASI)

The ACCOBAMS Survey Initiative (ASI) is the first synoptic large-scale survey of the entire ACCOBAMS Area and as such it plays a key role in filling the current gaps in our biological and ecological knowledge of large vertebrate species occurring in the region. Data gathered during the ASI were analyzed in a distance sampling surface-modelling framework to assess the summer distribution, densities and patterns, as well as to investigate the correlates of these parameters, for large vertebrate species and taxa in the Mediterranean Basin. Static and dynamic explanatory variables, including water depth (m), distance to depth contours (km), distance to canyons and seabed slope (km), sea surface temperature (°C), mixed layer depth (m) and levels of chlorophyll-a (mg/l), were considered to predict density and compute its variance spatially at a resolution of 10x10 km. A strong longitudinal gradient from low densities in the east to high densities in the west is shared by most taxa. In addition, several taxa also showed a less marked latitudinal gradient varying in direction according to species, and finally, a few of them exhibited patchy distributions.

Simulation Modeling to Assess Line Transect Distance Sampling Under a Range of Translocation Scenarios

Abstract The accuracy of posttranslocation population monitoring methods is critical to assessing long-term success in translocation programs. Translocation can produce unique challenges to monitoring efforts; therefore, it is important to understand the flexibility and robustness of commonly used monitoring methods. In Florida, USA, thousands of gopher tortoises Gopherus polyphemus have been, and continue to be, translocated from development sites to permitted recipient sites. These recipient sites create a broad range of potential monitoring scenarios due to variability in soft-release strategies, habitat conditions, and population demographics. Line transect distance sampling is an effective method for monitoring natural tortoise populations, but it is currently untested for translocated populations. We therefore produced 3,024 individual-based, spatially explicit scenarios of translocated tortoise populations that differed in recipient site and tortoise population properties, based on real-world examples, literature review, and expert opinion. We virtually sampled simulated tortoise populations by using line transect distance sampling methods and built a Bayesian hierarchical model to estimate the population density for each simulation, which incorporated individual-level covariates (i.e., burrow width and burrow occupancy). Line transect distance sampling was largely appropriate for the conditions that typify gopher tortoise recipient sites, particularly when detection probability on the transect lines was greater than or equal to 0.85. Designing the layout of transects relative to the orientation of soft-release pens, to avoid possible sampling biases that lead to extreme outliers in estimates of tortoise densities, resulted in more accurate population estimates. We also suggest that use of individual-level covariates, applied using a Bayesian framework as demonstrated in our study, may improve the applicability of line transect distance sampling surveys in a variety of contexts and that simulation can be a powerful tool for assessing survey design in complex sampling situations.

Clark's nutcracker forest community visitation: Whitebark pine maintains a keystone seed disperser.

Clark's nutcrackers (Nucifraga columbiana) are obligate seed dispersers for whitebark pine (Pinus albicaulis), but they frequently use other conifer seed resources because of annual variability in cone production or geographic variation in whitebark pine availability. Whitebark pine is declining from several threats including white pine blister rust, leading to potential population declines in the nutcracker and the pine. We hypothesize that where there are few additional seed resources, whitebark pine becomes the key and limiting resource supporting nutcracker populations. We investigated how nutcrackers use coniferous forest community types within Yellowstone National Park to determine potential seed resources and the importance of whitebark pine. We established sites representing five forest community types, including whitebark pine, lodgepole pine (P. contorta), Engelmann spruce (Picea engelmannii), limber pine (P. flexilis), and Douglas-fir (Pseudotsuga menziesii). Each transect annually generated nutcracker point counts, conifer cone production indices, community composition data, and seed resource use observations. We compared hierarchical distance sampling models, estimating nutcracker density and its relationship to forest community type, seed harvesting time-period, year, study site, and cone seed energy. We found cone production varied across years indicating annual variability in energy availability. Nutcracker density was best predicted by forest community type and survey time-period and was highest in whitebark pine stands during the mid-harvesting season. Nutcracker density was comparatively low for all other forest community types. This finding underscores the importance of whitebark pine as a key seed resource for Clark's nutcracker in Yellowstone National Park. The decline of whitebark pine potentially leads to a downward spiral in nutcrackers and whitebark pine, arguing for continued monitoring of nutcrackers and implementation of restoration treatments for whitebark pine.

Reducing bias in density estimates for unmarked populations that exhibit reactive behaviour towards camera traps

Abstract Density estimates guide wildlife management, and camera traps are commonly used to estimate sizes of unmarked populations. Unfortunately, animals often alter their natural behaviour in the presence of camera traps, which may bias subsequent density estimates. We simulated 100 populations of known density to test several new and existing methods that aimed to reduce bias in density estimates from camera trap distance sampling (CTDS) and the random encounter model (REM). Within our simulated populations, we introduced different behavioural reactions including attraction towards cameras, freezing when near cameras and fleeing from cameras. CTDS and REM provided density estimates with decent coverage of confidence intervals (CTDS = 94%, REM = 87%), mean coefficient of variation (CTDS = 0.121, REM = 0.071) and minimal bias (root‐mean squared error: CTDS = 1.336, REM = 0.913) for simulated populations with no reactive behaviour. However, failure to implement a method to account for reactive behaviour resulted in low coverage, large bias and potentially imprecise density estimates when 30% of the simulated population potentially reacted by attraction to or fleeing from camera traps. We identified a corrective strategy that enhanced confidence interval coverage, increased precision and reduced bias for every behavioural reaction except when individuals potentially fled from cameras. Synthesis and applications. We provide empirically tested methods for reducing bias of density estimates. Wildlife managers requiring population estimates of animals that exhibit reactive behaviour can use our methods to reduce inaccuracy. We encourage future studies to quantify behavioural responses to camera traps and to implement, test and possibly extend our methods to reduce bias through simulation.

Acoustic scattering properties of a seagrass, Cymodocea nodosa: in-situ measurements

Abstract Marine prairies play various crucial roles in marine ecosystems. The seagrasses that compose them are one of the most important components engineering the marine coastal system, providing significant spatial niches. Some of the seagrasses found in marine prairies are protected, and it is not recommended to sample them with destructive methods. Non-destructive methods such as remote sensing have been proposed as important means of studying these protected species. In the present study, the acoustic scattering properties of Cymodocea nodosa were studied with two different in/ex situ experiments conducted on a Turkish Mediterranean coast using a scientific echosounder (206 kHz split beam transducer) in different months over the years 2011 and 2012. After a series of acoustic processes, correlations and regression equations were established between different acoustic parameters of the Elementary Distance Sampling Units and biometric traits of below/above ground parts of the seagrass. The relationships were logarithmically established producing first a Rayleigh zone, followed by a geometrical zone that occurred with increased biometrics. No seasonal difference occurred in the relationships for the above-ground parts. Unlike the leaves, seagrass sheaths demonstrated unstable echo energy, inconsistent relationships, and unexplained acoustic responses over the span of several months. Regarding leaf density changing in time, significant relationships were explained as a function of the acoustic zones. Four points were highlighted to explain the differences in the estimations between the two experiments; i) the backscattering strengths depended on strength of biomass and its fractions (leaf area, shoot density and volume) between the two experiments, ii) the first experiment measured backscattering strength from individual specimens, but the second experiment was performed on the total biomass of seagrass per unit area, iii) different frequency response to the biometrics occurred in the two experiments, and iv) the non-linear effect of the sheath could not be separated from that of the leaf during the second experiment. The present study was the first attempt to characterize relationships between the biometric and acoustic backscattering properties of C. nodosa, and will guide researchers in future use of non-destructive methods.