Distance Sampling Research Articles

Estimating forest antelope population densities using distance sampling with camera traps

AbstractTraditional transect survey methods for forest antelopes often underestimate density for common species and do not provide sufficient data for rarer species. The use of camera trapping as a survey tool for medium and large terrestrial mammals has become increasingly common, especially in forest habitats. Here, we applied the distance sampling method to images generated from camera-trap surveys in Dja Faunal Reserve, Cameroon, and used an estimate of the proportion of time animals are active to correct for negative bias in the density estimates from the 24-hour camera-trap survey datasets. We also used multiple covariate distance sampling with body weight as a covariate to estimate detection probabilities and densities of rarer species. These methods provide an effective tool for monitoring the status of individual species or a community of forest antelope species, information urgently needed for conservation planning and action.

Differential habitat use by sympatric species of mouse lemurs across a mangrove–dry forest habitat gradient

AbstractUnderstanding the mechanisms by which similar species coexist in sympatry is a major driver of ecological research. Niche partitioning and ecological plasticity can facilitate spatial and habitat use overlap between generalist and specialist species. Mouse lemurs (Microcebus spp.) are a highly speciose group of small primates that are endemic to the forests of Madagascar. In northwestern Madagascar, the relatively widespread M. murinus occurs sympatrically with the microendemic M. ravelobensis. We investigated spatial distributions and densities of these two species across a mangrove–dry forest habitat gradient in Mariarano commune. We used capture-mark-recapture techniques and nocturnal line transect surveys along six transects during June and July 2017. Spatial capture-recapture and distance sampling models were used to estimate lemur densities across habitat types. The congeners displayed differential patterns of spatial distribution and densities. Microcebus murinus was found in similar densities across all habitat types, while M. ravelobensis was found at much higher densities in dry forests compared with mangroves. This suggests that the generalist M. murinus uses a wider array of habitats more evenly than the specialist M. ravelobensis. Our study provides empirical evidence of how cryptic lemur species differ in their habitat use and distribution across an environmental gradient and provides new insights into their ecology in an understudied habitat. Lemurs are one of the most threatened groups of mammals in the world, and understanding how these species are distributed across different forest types is crucial for planning and implementing conservation measures to protect lemur habitat.

Land use influence on distribution and abundance of herbivores in Samburu-Laikipia, Kenya

The distribution and abundance of different wildlife herbivores was studied in Samburu-Laikipia landscape. The study sites included; Mpala and Oljogi, both commercial ranches in Laikipia district; Oldonyiro and Kipsing community areas in Isiolo district; West Gate Conservancy, Ngaroni Community area, Kalama Community area and Sessia-Barsalinga Community area in Samburu district; and Buffalo Spring National Reserve and Samburu National Reserve both protected areas in the landscape. The objectives of the study were: 1) Determine the influence of different land use on seasonal abundances and distribution wildlife species and 2) Examine the influence of livestock, human settlements and water on wildlife species in Samburu-Laikipia landscape. Distance sampling was used to estimate wildlife, livestock and bomas densities. Distance to nearest water was projected from GPS coordinates for both wildlife and livestock sighting using ARCGIS. Our analysis showed non-uniform distributions of wildlife groups across the Samburu-Laikipia ecosystem largely driven by seasonal rainfall patterns and land use types. Like predicted, most wildlife groups occurred in higher abundances on protected areas, Laikipia commercial ranches and community conservancies unlike in community grazing areas in both dry and wet season. However, large grazers increased substantially in community grazing areas over the wet season when livestock grazing was heavy, stimulating growth of short annuals plants of high-quality nutrients. Human activities had negative influences on all wildlife groups. Our findings indicate that the type of land -use influenced herbivore distribution and abundance in Samburu-Laikipia landscape. This suggests that human activities, including pastoralism, in conjunction with season rainfall patterns and land-use shape herbivore distribution and abundance in the area. Conservation strategies for successfully increasing survival of wildlife therefore, requires maintenance of a mixture of land-use types with well controlled and sustainable development.

Resilience of epigeal spiders (Araneae) after clear-felling for agriculture in a Central African rainforest

Epigeal spiders were collected in five lowland rainforest habitats of the Masako Reserve (Kisangani, RD Congo): primary forest (>200 y. old), old secondary forest (± 80 y.), young secondary forest (40 y.), old fallow (12 y.) and young fallow (5 y.). The density and spatial distribution of spider populations were estimated by means of nocturnal distance sampling performed in all habitats except young secondary forest, and by pitfall trapping, applied in all five habitats. The epigeal spiders of the Masako forest belong to 62 species in 25 families. The most frequent families are Ctenidae, Lycosidae, and Sparassidae in the distance samples, and Zodariidae, Salticidae, and Corinnidae in the pitfalls. The density of the Ctenidae increases in an ascending sequence from 0.007 ind. m-2 in young fallow to 0.103 ind. m-2 in primary forest. For Lycosidae the sequence is inversed. They are by far the most common in young fallow (0.028 ind. m-2) and virtually absent in primary forest. Typical forest spiders, absent from open habitats, are common in old fallow which means that after 12 years, the typical forest fauna is already re-established. Only the young fallow fauna is clearly different from that of the other habitats, which confirms the high resilience and recolonization potential of epigeal spiders.

Estimating density of mountain hares using distance sampling: a comparison of daylight visual surveys, night-time thermal imaging and camera traps

Surveying cryptic, nocturnal animals is logistically challenging. Consequently, density estimates may be imprecise and uncertain. Survey innovations mitigate ecological and observational difficulties contributing to estimation variance. Thus, comparisons of survey techniques are critical to evaluate estimates of abundance. We simultaneously compared three methods for observing mountain hare Lepus timidus using Distance sampling to estimate abundance. Daylight visual surveys achieved 41 detections, estimating density at 14.3 hares km–2 (95%CI 6.3–32.5) resulting in the lowest estimate and widest confidence interval. Night-time thermal imaging achieved 206 detections, estimating density at 12.1 hares km–2 (95%CI 7.6–19.4). Thermal imaging captured more observations at furthest distances, and detected larger group sizes. Camera traps achieved 3705 night-time detections, estimating density at 22.6 hares km–2 (95%CI 17.1–29.9). Between the methods, detections were spatially correlated, although the estimates of density varied. Our results suggest that daylight visual surveys tended to underestimate density, failing to reflect nocturnal activity. Thermal imaging captured nocturnal activity, providing a higher detection rate, but required fine weather. Camera traps captured nocturnal activity, and operated 24/7 throughout harsh weather, but needed careful consideration of empirical assumptions. We discuss the merits and limitations of each method with respect to the estimation of population density in the field.

Roadside Car Surveys: Methodological Constraints and Solutions for Estimating Parrot Abundances across the World

Parrots stand out among birds because of their poor conservation status and the lack of available information on their population sizes and trends. Estimating parrot abundance is complicated by the high mobility, gregariousness, patchy distributions, and rarity of many species. Roadside car surveys can be useful to cover large areas and increase the probability of detecting spatially aggregated species or those occurring at very low densities. However, such surveys may be biased due to their inability to handle differences in detectability among species and habitats. We conducted 98 roadside surveys, covering > 57,000 km across 20 countries and the main world biomes, recording ca. 120,000 parrots from 137 species. We found that larger and more gregarious species are more easily visually detected and at greater distances, with variations among biomes. However, raw estimates of relative parrot abundances (individuals/km) were strongly correlated (r = 0.86–0.93) with parrot densities (individuals/km2) estimated through distance sampling (DS) models, showing that variability in abundances among species (>40 orders of magnitude) overcomes any potential detectability bias. While both methods provide similar results, DS cannot be used to study parrot communities or monitor the population trends of all parrot species as it requires a minimum of encounters that are not reached for most species (64% in our case), mainly the rarest and more threatened. However, DS may be the most suitable choice for some species-specific studies of common species. We summarize the strengths and weaknesses of both methods to guide researchers in choosing the best–fitting option for their particular research hypotheses, characteristics of the species studied, and logistical constraints.

Using spatial distance sampling models to optimize survey effort and address violations of the design assumption

AbstractConventional distance sampling approaches rely on the design assumption (i.e. uniform distribution of individuals in relation to transects) to ensure unbiased inference to the population of interest. However, randomized design recommendations are not always followed or may be impractical to implement for some survey types, particularly in cases where transects must be placed perpendicular to the habitat gradient. Full‐likelihood spatial distance sampling models provide a potential solution to violations of the design assumption by jointly modelling the detection and occurrence processes using spatially indexed habitat covariates.Through simulation and an applied example based on a survey for Dall's sheep in Alaska, USA, we used a full‐likelihood distance sampling approach to investigate the potential for bias in cases where transects placed perpendicular to the habitat gradient (e.g. elevational contours) are non‐randomly sampled. We also assessed the utility of spatial approaches in cases where transects are placed along linear features, such as roads or ridgelines, where habitat may be unrepresentative of the overall study area.Our results showed that the full‐likelihood approach was generally unbiased, even in extreme scenarios where habitat was inversely related to distance from the transect. For the Dall's sheep example, our results showed that more efficient designs with reduced sampling effort in low‐quality habitats are a practical solution for reducing logistical costs when the data are analysed in a spatial modelling framework.Together, our findings confirm and extend existing work suggesting that spatial distance sampling can be a useful solution when non‐random designs are employed. Given the high cost of survey implementation in many cases, the development of valid alternatives to design‐based inference will aid in the amount of information available for a variety of species. The results of our work will be useful for practitioners in assessing alternative designs relative to particular survey applications.

Stakeholders engagement as an important step for the long‐term monitoring of wild ungulate populations

Abstract Monitoring trends in animal populations is essential for the development of appropriate wildlife management strategies. However, long‐term studies are difficult to maintain mainly due to the lack of continuous funding. In this scenario, the collaboration between local stakeholders and researchers can be a fruitful partnership to monitor game species for long periods and vast territories. We present an experimental framework with the involvement of researchers, local hunters and game managers for the continuous monitoring of wild ungulate populations. By combining vehicle‐based counts with distance sampling techniques, we implemented and validated a sampling scheme able to provide demographic information for the effective management of wild ungulate populations. Here, we used an Iberian red deer (Cervus elaphus) population as a model. The project implementation involved 30 participants including 24 stakeholders and 6 field technicians/data analysts with experience in monitoring wild ungulates. A total of eight teams covered 29 itineraries, synchronously, in two periods of ecological relevance for red deer, early summer and early autumn. Density estimates were consistent among sampling periods and characterized by acceptable coefficients of variation (approximately 20%). Our results prove that the application of the proposed framework is feasible (three to four itineraries per team), cost‐ and time‐effective (one week per sampling period) and produce population estimates fit for management. Being based on direct observations, the method would provide important demographic indicators (e.g. population density, age structure and fawn recruitment, and group size) about wild ungulate populations. Apart from engaging interested stakeholders, the success of our proposal relies on three key actions including the theoretical and field instruction of participants, the definition of timely and unbiased survey designs and the maintenance of participants’ motivation. The implementation of rigorous and standardized sampling protocols is pivotal for data integration through time and space. In the absence of continuous funding, the voluntary collaboration between entities should be fostered to study and mitigate the potential threats to wild ungulate populations resulting from disease, unregulated hunting and environmental changes.

Scaling up private land conservation to meet recovery goals for grassland birds.

Long‐term population declines have elevated recovery of grassland avifauna to among the highest conservation priorities in North America. Because most of the Great Plains is privately owned, recovery of grassland bird populations depends on voluntary conservation with strong partnerships between private landowners and resource professionals. Despite large areas enrolled in voluntary practices through U.S. Department of Agriculture's Lesser Prairie‐chicken (Tympanuchus pallidicinctus) Initiative (LPCI), the effectiveness of Farm Bill investments for meeting wildlife conservation goals remains an open question. Our objectives were to evaluate extents to which Conservation Reserve Program (CRP) and LPCI‐grazing practices influence population densities of grassland birds; estimate relative contributions of practices to regional bird populations; and evaluate percentages of populations conserved relative to vulnerability of species. We designed a large‐scale impact‐reference study and used the Integrated Monitoring in Bird Conservation Regions program to evaluate bird population targets of the Playa Lakes Joint Venture. We used point transect distance sampling to estimate density and population size for 35 species of grassland birds on private lands enrolled in native or introduced CRP plantings and LPCI‐prescribed grazing. Treatment effects indicated CRP plantings increased densities of three grassland obligates vulnerable to habitat loss, and LPCI grazing increased densities of four species requiring heterogeneity in dense, tall‐grass structure (α = 0.1). Population estimates in 2016 indicated the practices conserved breeding habitat for 4.5 million birds (90% CI: 4.0–5.1), and increased population sizes of 16 species , totaling 1.8 million birds (CI: 1.4–2.4). Conservation practices on private land benefited the most vulnerable grassland obligate species (AICc weight = 0.53). By addressing habitat loss and degradation in agricultural landscapes, conservation on private land provides a solution to declining avifauna of North America and scales up to meet population recovery goals for the most imperiled grassland birds.

Abundance and Foraging Ecology of the Black and White Colobus Monkey (Colobus guereza ssp. guereza) in Nech Sar National Park, Ethiopia

We estimated the abundance of Colobus guereza ssp. guereza in the moist evergreen riparian forest part of Nech Sar National Park, Ethiopia. The survey was conducted using the distance sampling method. Based on a preliminary study, 17 newly cut line transects were randomly aligned across the study area. The survey data were then collected for three consecutive months. Transects were walked once per month for 14-16 days. Abundance estimates were analyzed using the program 'DISTANCE'. The half-normal key function with cosine adjustment fitted our data sets best. Mean group density and mean animal density were 14 animals km-2 and 102 animals km-2, respectively, resulting in a mean estimated abundance of 2,153 animals distributed over thestudy area. The mean estimated group size was 7.24 with an estimated encounter rate of 1.72. Compared to similar studies from tropical forests in Africa, our population density estimates were intermediate between the mean values (100 to 168 animals km-2). We conclude that such intermediate density estimates reflect the fact that guerezas have suffered from human-induced reductions in habitat availability. We also suggest that the natural forest is still in a reasonable condition that likely provides them with sufficient food supply to compensate for such intermediate densities. However, a replication of this study would lead to a more comprehensive abundance estimate. We also recommend studies that would address the activity-time budget and populationdemographics of these monkeys. Nonetheless, our results provide a reference point for future studies in this area, particularly to assess population trends of C. g. guereza.

A Rapid Assessment of the Marine Megafauna Biodiversity Around South Bali, Indonesia

A low-cost, small-boat, rapid assessment survey was conducted on the waters off the southern Peninsula of Bali. The objectives were: (1) to conduct an inventory of cetacean species in the study area; (2) to map cetacean distribution to inform the design of the Badung MPA; (3) to estimate relative abundance of cetaceans and record information on presence and distribution of other marine megafauna; and (4) to train observers in the use of distance sampling methods. The survey adopted a “training while doing” approach to build local capacity for marine biodiversity monitoring, while collecting a snapshot of data to assess species richness and distribution. The survey accomplished its first two objectives, but due to violation of underlying assumptions, had mixed success with the third objective. Our survey revealed that the waters off the southern Peninsula of Bali support a rich cetacean fauna, with at least seven cetacean species, other marine megafauna, and avian species. Seven cetacean species found on our survey include: spinner dolphin (Stenella longirostris), pantropical spotted dolphin (Stenella attenuata), Fraser’s dolphin (Lagenodephis hosei), Risso’s dolphin (Grampus griseus), bottlenose dolphin (Tursiopssp.), Bryde’s whale (Balaenoptera edeni), and sperm whale (Physeter macrocephalus). Density estimates were low for all whales combined, but seem implausibly high for dolphins; likely due to violation of assumptions of distance sampling methods. Future surveys should include sufficient time for training to generate reliable abundance estimates. A dedicated bycatch study is needed to understand sustainability of bycatch mortality relative to reliable abundance estimates.

Biotic and abiotic drivers of dispersion dynamics in a large-bodied tropical vertebrate, the Western Bornean orangutan.

Understanding of animal responses to dynamic resource landscapes is based largely on research on temperate species with small body sizes and fast life histories. We studied a large, tropical mammal with an extremely slow life history, the Western Bornean orangutan (Pongo pygmaeus wurmbii), across a heterogeneous natural landscape encompassing seven distinct forest types. Our goals were to characterize fluctuations in abundance, test hypotheses regarding the relationship between dispersion dynamics and resource availability, and evaluate how movement patterns are influenced by abiotic conditions. We surveyed abundance in Gunung Palung National Park, West Kalimantan, Indonesia, for 99 consecutive months and simultaneously recorded weather data and assessed fruit availability. We developed a Bayesian hierarchical distance sampling model to estimate population dispersion and assess the roles of fruit availability, rainfall, and temperature in driving movement patterns across this heterogeneous landscape. Orangutan abundance varied dramatically over space and time. Each forest type was important in sustaining more than 40% of the total orangutans on site during at least one month, as animals moved to track asynchronies in fruiting phenology. We conclude that landscape-level movements buffer orangutans against fruit scarcity, peat swamps are crucial fallback habitats, and orangutans' use of high elevation forests is strongly dependent on abiotic conditions. Our results show that orangutans can periodically occupy putative-sink habitats and be virtually absent for extended periods from habitats that are vitally important in sustaining their population, highlighting the need for long-term studies and potential risks in interpreting occurrence or abundance measures as indicators of habitat importance.

Assessing the camera trap methodologies used to estimate density of unmarked populations

AbstractPopulation density estimations are essential for wildlife management and conservation. Camera traps have become a promising cost‐effective tool, for which several methods have been described to estimate population density when individuals are unrecognizable (i.e. unmarked populations). However, comparative tests of their applicability and performance are scarce.Here, we have compared three methods based on camera traps to estimate population density without individual recognition: Random Encounter Model (REM), Random Encounter and Staying Time (REST) and Distance Sampling with camera traps (CT‐DS). Comparisons were carried out in terms of consistency with one another, precision and cost‐effectiveness. We considered six natural populations with a wide range of densities, and three species with different behavioural traits (red deerCervus elaphus, wild boarSus scrofaand red foxVulpes vulpes). In three of these populations, we obtained independent density estimates as a reference.The densities estimated ranged from 0.23 individuals/km2(fox) to 34.87 individuals/km2(red deer). We did not find significant differences in terms of density values estimated by the three methods in five out of six populations, but REM has a tendency to generate higher average density values than REST and CT‐DS. Regarding the independents’ densities, REM results were not significantly different in any population, and REST and CT‐DS were significantly different in one population. The precision obtained was not significantly different between methods, with average coefficients of variation of 0.28 (REST), 0.36 (REM) and 0.42 (CT‐DS). The REST method required the lowest human effort.Synthesis and applications. Our results show that all of the methods examined can work well, with each having particular strengths and weaknesses. Broadly, Random Encounter and Staying Time (REST) could be recommended in scenarios of high abundance, Distance Sampling with camera traps (CT‐DS) in those of low abundance while Random Encounter Model (REM) can be recommended when camera trap performance is not optimal, as it can be applied with less risk of bias. This broadens the applicability of camera trapping for estimating densities of unmarked populations using information exclusively obtained from camera traps. This strengthens the case for scientifically based camera trapping as a cost‐effective method to provide reference estimates for wildlife managers, including within multi‐species monitoring programmes.

A comparison of three methods for estimating call densities of migrating bowhead whales using passive acoustic monitoring

Various methods for estimating animal density from visual data, including distance sampling (DS) and spatially explicit capture-recapture (SECR), have recently been adapted for estimating call density using passive acoustic monitoring (PAM) data, e.g., recordings of animal calls. Here we summarize three methods available for passive acoustic density estimation: plot sampling, DS, and SECR. The first two require distances from the sensors to calling animals (which are obtained by triangulating calls matched among sensors), but SECR only requires matching (not localizing) calls among sensors. We compare via simulation what biases can arise when assumptions underlying these methods are violated. We use insights gleaned from the simulation to compare the performance of the methods when applied to a case study: bowhead whale call data collected from arrays of directional acoustic sensors at five sites in the Beaufort Sea during the fall migration 2007–2014. Call detections were manually extracted from the recordings by human observers simultaneously scanning spectrograms of recordings from a given site. The large discrepancies between estimates derived using SECR and the other two methods were likely caused primarily by the manual detection procedure leading to non-independent detections among sensors, while errors in estimated distances between detected calls and sensors also contributed to the observed patterns. Our study is among the first to provide a direct comparison of the three methods applied to PAM data and highlights the importance that all assumptions of an analysis method need to be met for correct inference.

Living with human encroachment: Status and distribution of Green Peafowl in northern stronghold of Thailand

Green Peafowl have declined significantly across much of their historical range mostly due to habitat loss and degradation following intensive agricultural expansion, logging and infrastructure development. In Thailand, two strongholds remain, in the west and the north. While the western stronghold has been extensively investigated and is well protected, the status of the species in the northern stronghold remain unknown. This stronghold is distributed over at least four contiguous protected areas surrounded by agricultural landscapes, where conflict with farmers has recently been reported. The aims of this work are to 1) investigate the species’ status in this northern stronghold, 2) define the species’ habitat use within and outside protected areas, and 3) to provide management suggestions for the species’ long-term survival. Our results showed a high probability of species occurrence (>0.5) in the stronghold within the four protected areas. Using Distance sampling over 54 transects, 2 km long, located in the interior, edge and agriculture landscape, we estimated a density of 15.82 calling males/km2 over the whole stronghold with densities ranging from 13.55 to 19.89 calling males/km2 in the four protected areas separately. A general linear models showed that species distribution was affected positively by dry dipterocarp forest, the main species’ habitat over its range, and negatively by human settlements. A higher number of the species was predicted within the protected areas than outside, highlighting the significance of the protected contiguous forest patches in the stronghold for the long-term conservation of the species combined with the supporting agro-ecotourism through the species existence in the surrounding agricultural landscapes. Beside protected areas management, cooperation by local communities has to be included in any conservation program to avert human-wildlife conflict.

The Relationship Between GPS Sampling Interval and Estimated Daily Travel Distances in Chacma Baboons (Papio ursinus)

Modern studies of animal movement use the Global Positioning System (GPS) to estimate animals’ distance traveled. The temporal resolution of GPS fixes recorded should match those of the behavior of interest; otherwise estimates are likely to be inappropriate. Here, we investigate how different GPS sampling intervals affect estimated daily travel distances for wild chacma baboons (Papio ursinus). By subsampling GPS data collected at one fix per second for 143 daily travel distances (12 baboons over 11–12 days), we found that less frequent GPS fixes result in smaller estimated travel distances. Moving from a GPS frequency of one fix every second to one fix every 30 s resulted in a 33% reduction in estimated daily travel distance, while using hourly GPS fixes resulted in a 66% reduction. We then use the relationship we find between estimated travel distance and GPS sampling interval to recalculate published baboon daily travel distances and find that accounting for the predicted effect of sampling interval does not affect conclusions of previous comparative analyses. However, if short-interval or continuous GPS data—which are becoming more common in studies of primate movement ecology—are compared with historical (longer interval) GPS data in future work, controlling for sampling interval is necessary.

Abundance estimation for line transect sampling: A comparison of distance sampling and spatial capture-recapture models.

Accurate and precise abundance estimation is vital for informed wildlife conservation and management decision-making. Line transect surveys are a common sampling approach for abundance estimation. Distance sampling is often used to estimate abundance from line transect survey data; however, search encounter spatial capture-recapture can also be used when individuals in the population of interest are identifiable. The search encounter spatial capture-recapture model has rarely been applied, and its performance has not been compared to that of distance sampling. We analyzed simulated datasets to compare the performance of distance sampling and spatial capture-recapture abundance estimators. Additionally, we estimated the abundance of North Atlantic right whales in the southeastern United States with two formulations of each model and compared the estimates. Spatial capture-recapture abundance estimates had lower root mean squared error than distance sampling estimates. Spatial capture-recapture 95% credible intervals for abundance had nominal coverage, i.e., contained the simulating value for abundance in 95% of simulations, whereas distance sampling credible intervals had below nominal coverage. Moreover, North Atlantic right whale abundance estimates from distance sampling models were more sensitive to model specification compared to spatial capture-recapture estimates. When estimating abundance from line transect data, researchers should consider using search encounter spatial capture-recapture when individuals in the population of interest are identifiable, when line transects are surveyed over multiple occasions, when there is imperfect detection of individuals located on the line transect, and when it is safe to assume the population of interest is closed demographically. When line transects are surveyed over multiple occasions, researchers should be aware that individual space use may induce spatial autocorrelation in counts across transects. This is not accounted for in common distance sampling estimators and leads to overly precise abundance estimates.

Improving population estimates of difficult‐to‐observe species: A dung decay model for forest elephants with remotely sensed imagery

AbstractAccurate and ecologically relevant wildlife population estimates are critical for species management. One of the most common survey methods for forest mammals – line transects for animal sign with distance sampling – has assumptions regarding conversion factors that, if violated, can induce substantial bias in abundance estimates. Specifically, for sign (e.g. nests, dung) surveys, a single number representing total time for decay is used as a multiplier to convert estimated sign density into animal density. This multiplier is likely inaccurate if not derived from a study reflecting the spatiotemporal variation in decay times. Using dung decay observations from three protected areas in Gabon, and a previous study in Nouabalé‐Ndoki National Park (Congo), we developed Weibull survival models to adaptively predict forest elephant (Loxodonta cyclotis) dung decay based on environmental variables from field collected and remotely sensed data. Seasonal decay models based on remotely sensed covariates explained 86% of the variation for the wet season and 79% for the dry season. These models included canopy cover, cloud cover, humidity, vegetation complexity and slope as factors influencing dung decay. With these models, we assessed sensitivity of elephant density estimates to spatiotemporal environmental heterogeneity, showing that our methods work best for large‐scale studies >50 km2. We simulated decay studies with and without these variables in four Gabonese national parks and reanalyzed two previous surveys of elephants in Minkébé National Park, Gabon. Disregarding spatial and temporal variation in decay rate biased population estimates up to 1.6 and 6.9 times. Our reassessment of surveys in Minkébé National Park showed an expected loss of 78% of forest elephants over ten years, but the elephant abundance was 222% higher than previously estimated. Our models incorporate field or remotely sensed variables to provide an ecological context essential for accurate population estimates while reducing need for expensive decay field studies.

Giant NuthatchSitta magnadensity and habitat association in a potential stronghold in northern Thailand

SummaryPopulations of the globally endangered Giant NuthatchSitta magnahave declined significantly throughout their small world range in southern China and northern continental South-East Asia. Distance sampling and direct observations were used to estimate the density and habitat use of the Giant Nuthatch in a potential stronghold for the species, Chiang Dao Wildlife Sanctuary, Thailand. Thirteen line transects covering 6.2 km were established in open, pine-oak habitat favoured by the nuthatch, during November 2014 to December 2015. The mean density of Giant Nuthatch was 3.94±1.22 (95% CI = 2.15–7.22) individuals/km2. Hierarchical distance sampling models indicated that habitat use by Giant Nuthatch was strongly correlated with trees of large diameter. A pair of Giant Nuthatches was radio-tracked as they fed nestlings during the 2016 breeding season. The female’s home range, centred on the nest, was 7.79 ha (95% kernel home range), approximately one-fourth of that of the male, 32.01 ha. Giant Nuthatches showed a significant preference for foraging on pinesPinusspp. and used the fissured bark of mature pines in which to store acorns of deciduous tree species. Our research indicates the importance of large, mature trees in open pine-oak forest in supporting Giant Nuthatch populations.

The potential of fallow management to promote steppe bird conservation within the next EU Common Agricultural Policy reform

Abstract Agricultural intensification promoted by the European Common Agricultural Policy (CAP) has driven the decline of farmland and steppe bird populations. Policy tools to improve the environmental performance of the CAP—including Agri‐Environmental Schemes (AES) and Greening—have often failed, and the new EU agricultural reform (CAP post‐2020) offers a new opportunity to integrate effective measures addressing farmland bird declines. Fallow land and its management have proven beneficial for endangered steppe bird species by providing good quality habitat, and therefore has potential to become an effective conservation measure. We used a Hierarchical Distance Sampling community model to evaluate the ability of different conservation regimes to increase the abundance of 37 bird species including endangered steppe birds and other farmland birds in 13,309 ha of fallow land in north‐eastern Spain. The conservation regimes were based on different management prescriptions associated with AES, Greening and a local conservation measure promoting extensive fallow management targeting seven steppe bird species (Targeted Fallow Management, TFM). The positive effect of conservation measures increased as their design was more targeted to specific species. TFM increased the abundance of target and other farmland species, while AES and Greening had either no effect or negative effects on bird abundance, respectively. Effects of other Greening conservation measures related to landscape heterogeneity such as crop richness and field size were variable across the community. Policy implications. The success of Targeted Fallow Management as a conservation tool—in contrast to Agri‐Environmental Schemes and Greening—highlights the value of applying 1–2 agricultural practices just before the breeding season in fallows situated in optimal locations for target steppe bird species, to increase the abundance of these and other farmland bird species. We translate our findings into specific guidelines that we recommend including within the new eco‐schemes and AES present in the CAP post‐2020.