Size Of Animal Populations Research Articles

Assessing the effectiveness of acoustic signals in mark-recapture studies to estimate dolphins’ population size

Abstract Accurate estimations of animal population size are pivotal for implementing management strategies properly. Recapture technique based on sounds as a specimen identification mark has barely been used for marine mammals. However, inferring abundance estimates from acoustic methods could enhance the accuracy and precision of population size assessments. Here, we tested the possibility of using signature whistles as individual marks for estimating the size of common bottlenose dolphin (Tursiops truncatus) populations. Data were continuously collected for 326 days in 2015-2016, by using a fixed acoustic device located in the Sicily Strait (Italy). The SIGID method was applied to identify Signature Whistles Types (SWTs) over 7000 hours of recordings. 80 SWTs were detected as long as their stereotyped fundamental frequency contours were repeated in bout of at least 6 renditions. The mean SWTs monthly recording rate resulted in 0.19 (sd = 0.16), with 20 SWTs recorded over 5 or more different encounters (until a maximum of 30 encounters). The Jolly–Seber model (with POPAN formulation) was run in Mark software to estimate the population size. The estimated population size resulted in 171 bottlenose dolphins (95% CI = 137-215). Even if the detection and identification of signature whistles required crucial precautions, and animals could be detected differently from visual techniques, the population size estimate obtained was comparable with previous results based on physical marks data. These outcomes demonstrated that signature whistles can be considered a strongly effective tool for integrating traditional mark-recapture techniques with finely estimated dolphins’ population abundances.

Ecosystem of game animals is the economic and mathematical model for optimizing the size and structure of game animal populations in the ecosystem

Methodology of economic and mathematical modeling involves the formation of a system from subsystems and elements united by logical relationships. The size and structure of subsystems and elements can be optimized in the system for diff erent optimality criteria. According to this algorithm, mathematical models of ecosystems with diff erent content bases are formed. Biological subsystems and elements can serve as a basis for an ecosystem that is solved for economic optimality criteria, or economic indicators can act as relationships in the ecosystem. In this way, the content base of the mathematical model is represented by biological subsystems and elements, and the optimality criteria are formed on the basis of economic indicators. This process is refl ected in the economic and mathematical model of a specifi c ecosystem. An original economic and mathematical model (EMM) for optimizing the size and structure of game animal populations in a given ecosystem has been proposed in the paper. The presented EMM is based on optimizing the size and structure of populations of both predators and preys in hunting areas, taking into account the boundaries of their range. The EMM “Ecosystem of Game Animals” is based on the EMM “Predator-Prey” and has a block-diagonal structure, where the main blocks are the “Prey” and “Predator” blocks, and the feeding and habitat blocks of game animals act as connecting ones. The optimality criteria of the EMM “Ecosystem of Game Animals” can be expressed by objective functions that implement diff erent scenarios for the implementation of the model. The described model allows us to create a mathematical representation of the ecosystem and study the biological characteristics of game animal populations, which ultimately contributes to more rational resource management in the hunting areas of our country.

The weak association between hypoxia tolerance and thermal tolerance increases the susceptibility of abalone to climate change

The simultaneous occurrence of high temperatures and hypoxia events caused mass die-offs of aquatic animals. It is crucial to investigate the relationship between hypoxia tolerance and thermal tolerance of aquatic animals to predict the biological and ecological outcomes under global climate change scenarios. In this study, the hypoxia tolerance and thermal tolerance of Pacific abalone, Haliotis discus hannai, were measured by methods based on adhesion capacity (hypoxia adhesion duration and heat adhesion duration) and heart rate fluctuations (breakpoint of dissolved oxygen and Arrhenius breakpoint temperature). Weak correlations were found between hypoxia tolerance and thermal tolerance (Spearman correlation, r = −0.09, P = 0.2069; Pearson correlation, r = −0.04, P = 0.3313). Furthermore, a total of 21 significant SNPs and 19 candidate genes (such as cubn, lrp6, gria2, rft2, and casp8) were identified to be associated with hypoxia tolerance of Pacific abalone by conducting whole genome resequencing and genome-wide association study (GWAS). But there was no overlap between candidate genes associated with hypoxia tolerance and candidate genes associated with thermal tolerance, validating the weak correlation between hypoxia tolerance and thermal tolerance. This study highlights that individuals with greater hypoxia tolerance do not necessarily have greater thermal tolerance. Global warming and hypoxia may pose a greater threat to population size and genetic diversity of some aquatic animals than previously believed.

Similarity learning networks uniquely identify individuals of four marine and terrestrial species

AbstractEstimating the size of animal populations plays an important role in evidence‐based conservation and management. Some methods for estimating population size rely on animals being individually identifiable. Traditionally, this has been done by marking physically captured animals, but increasingly, animals with distinctive natural markings are surveyed noninvasively using cameras. Animal reidentification from photographs is usually done manually, which is expensive, laborious, and requires considerable skill. An alternative is to develop computer vision methods that can support or replace the manual identification task. We developed an automated approach using deep learning to identify whether a pair of photographs is of the same individual or not. The core of the approach is a similarity learning network that uses paired convolutional neural networks with a triplet loss function to summarize image pairs and decide whether they are from the same individual. Prior to the main matching step, two additional convolutional neural networks perform image segmentation, cropping the animal object within the image, and orientation prediction, deciding which side of the animal was photographed. We applied the approach to four species, with images of the same individual often spanning several years: systematic surveys of bottlenose dolphins (Tursiops truncatus, 2008–2019) and harbor seals (Phoca vitulina, 2015–2019), a citizen science dataset of western leopard toads (Sclerophrys pantherina, unknown dates), and a publicly available repository of humpback whale images (Megaptera novaeangliae, unknown dates). For these species, our best‐performing models were able to identify whether a pair of images were from the same individual or different individuals in 95.8%, 94.6%, 88.2%, and 83.8% of the cases, respectively. We found that triplet loss functions outperformed binary cross‐entropy loss functions and that data augmentation and additional manual curation of training data provided small but consistent improvements in performance. These results demonstrate the potential of deep learning to replace or, more likely, support and facilitate manual individual identification efforts.

Food security and the value of game animals—a study of Sweden

The food security value of wild meat is calculated by combining proxy methods for quantifying game animal abundance with shadow pricing techniques for assessing the unit values of food security. This study calculated the food security values of moose, roe deer, wild boar, and fallow deer for Sweden overall and for individual counties. The results showed that meat from these animal populations accounts for approximately 9% of meat consumption in Sweden and for 1.2% of the minimum energy food consumption during periods of crisis for the whole of Sweden, while in some counties it can be as much as 8%. The calculated unit value, or shadow price, of the minimum energy requirement ranged between € 0.1 and € 4.2/mcal, depending on the magnitude of the crisis scenario. At most, the total food security value of actual animal population sizes amounted to 0.50 billion euros, but this was unevenly distributed, with high values in counties that have an abundance of moose and wild boar.

Integrating Species Distribution Models to Estimate the Population Size of Forest Musk Deer (Moschus berezovskii) in the Central Qinling Mountains of Shaanxi

Understanding the population size of animals is crucial for formulating scientific management policies, especially for endangered species. The central area of the Qinling Mountains in Shaanxi is a vital area for forest musk deer, but research is insufficient and estimates of its population size are lacking. In this study, we constructed a species distribution model for the forest musk deer in the central Qinling Mountains in Shaanxi using topography, land-use, and bioclimatic variables alongside forest musk deer occurrence data. The Time-to-Event (TTE) model was employed to estimate the population density of forest musk deer in the selected survey area. By utilizing the suitable habitat area provided by the species distribution model, the population density in the central Qinling Mountains of Shaanxi was estimated by extrapolating from the survey area. Our estimate of the population size of forest musk deer in the central Qinling Mountains of Shaanxi is approximately 2722 ± 788. Similar population estimation methods could be more widely applied, especially in areas with limited survey resources.

An Authentic Demonstration of the Mark–Recapture Technique Using Ant Colonies

The mark–recapture technique paired with the Lincoln–Peterson index is a commonly used method of estimating the size of animal populations in ecological research. However, this technique is difficult to emulate in an educational setting due to the logistical constraints inherent to the process of capturing and marking live animals. As a result, most lessons on mark–recapture use captive animals or inanimate objects as the focal population. This approach may give students an inaccurate understanding of the potential applications and limitations of the mark–recapture technique. Here, we describe an authentic application of the mark–recapture technique that allows students to gain hands-on experience with the method on naturally occurring ant colonies, a ubiquitous animal system. By participating in this lesson, students will directly engage with the mark–recapture technique to estimate the number of individuals within ant colonies and will learn about the natural history of ants in the process.

Reproductive Phenology and Climatic Drivers of Plant Species Used as Food by the Hainan Gibbon, Nomascus hainanus (Primates: Hylobatidae)

The timing of flowering and fruiting plays a critical role in the reproduction, population size, and range of fruit-eating animals. The Hainan Tropical Rainforest National Park, China, hosts one of the world’s most endangered primate species, the Hainan gibbon (Nomascus hainanus). Understanding the phenological patterns of the principal food sources of the Hainan gibbon is crucial for the effective management of their habitats and the conservation of this threatened population. To that end, we conducted a regression analysis to better understand how climate may impact the timing and availability of fruits known to support the Hainan gibbon. We observed significant seasonal and inter-annual variations in the reproductive phenology of these fruiting species, with most species flowering from March to June and fruiting from August to December. Importantly, we found that Hainan gibbons face severe food scarcity between January and April. We show that sunshine exerts a significant effect on the flowering time, while fruiting phenology is most sensitive to temperature. We suggest that the restoration of the Hainan gibbon habitat should include planting more tree species which that produce fruit in the time of low food availability between January-April, including the species Memecylon ligustrifolium, Wrightia pubescens, Sarcosperma laurinum, Eurya ciliata, and Pouteria annamensis.

Meta-analysis reveals impacts of disturbance on reptile and amphibian body condition.

Ecosystem disturbance is increasing in extent, severity and frequency across the globe. To date, research has largely focussed on the impacts of disturbance on animal population size, extinction risk and species richness. However, individual responses, such as changes in body condition, can act as more sensitive metrics and may provide early warning signs of reduced fitness and population declines. We conducted the first global systematic review and meta-analysis investigating the impacts of ecosystem disturbance on reptile and amphibian body condition. We collated 384 effect sizes representing 137 species from 133 studies. We tested how disturbance type, species traits, biome and taxon moderate the impacts of disturbance on body condition. We found an overall negative effect of disturbance on herpetofauna body condition (Hedges' g = -0.37, 95% CI: -0.57, -0.18). Disturbance type was an influential predictor of body condition response and all disturbance types had a negative mean effect. Drought, invasive species and agriculture had the largest effects. The impact of disturbance varied in strength and direction across biomes, with the largest negative effects found within Mediterranean and temperate biomes. In contrast, taxon, body size, habitat specialisation and conservation status were not influential predictors of disturbance effects. Our findings reveal the widespread effects of disturbance on herpetofauna body condition and highlight the potential role of individual-level response metrics in enhancing wildlife monitoring. The use of individual response metrics alongside population and community metrics would deepen our understanding of disturbance impacts by revealing both early impacts and chronic effects within affected populations. This could enable early and more informed conservation management.

A review of N‐mixture models

AbstractN‐mixture models were born in 2004 of the necessity to model animal population size from point counts with imperfect detection of individuals, where capture‐recapture methods are infeasible. Initially developed for applications where population size was assumed constant, N‐mixture models were extended in 2011 to include population dynamics, allowing application to populations whose size fluctuates during the study. A further extension in 2014 accommodates populations with multiple “states” such as age class or sex. More recent extensions model spatial movement of animals among habitat patches or the spatial spread of infectious disease in a human population. The core idea underlying this class of models is a hierarchical structure, where the observation model is defined conditional on the model for true abundance. This hierarchy allows researchers to incorporate information about observation and abundance processes, while permitting distinct inferences about elements affecting detection and those affecting abundance. Another benefit of the hierarchical approach is the ability to accommodate many existing sampling protocols such as removal sampling and distance sampling. One drawback to N‐mixture models is that since they estimate both abundance and detection from replicated but unmarked counts, model parameters may not be clearly identifiable. A second drawback is that when observed counts are large, calculating the N‐mixture likelihood is computationally infeasible. This difficulty motivated an approximate likelihood based on the normal approximation to the binomial. The normal approximation provides a diagnostic of parameter estimability based on the closed‐form expression of the Fisher information matrix for a multivariate normal likelihood.This article is categorized under:Data: Types and Structure > Image and Spatial DataStatistical Learning and Exploratory Methods of the Data Sciences > Modeling Methods

Spatio-temporal changes in chimpanzee density and abundance in the Greater Mahale Ecosystem, Tanzania.

Species conservation and management require reliable information about animal distribution and population size. Better management actions within a species' range can be achieved by identifying the location and timing of population changes. In the Greater Mahale Ecosystem (GME), western Tanzania, deforestation due to the expansion of human settlements and agriculture, annual burning, and logging are known threats to wildlife. For one of the most charismatic species, the endangered eastern chimpanzee (Pan troglodytes schweinfurthii), approximately 75% of the individuals are distributed outside national park boundaries, requiring monitoring and protection efforts over a vast landscape of various protection statuses. These efforts are especially challenging when we lack data on trends in density and population size. To predict spatio-temporal chimpanzee density and abundance across the GME, we used density surface modeling, fitting a generalized additive model to a 10-year time-series data set of nest counts based on line-transect surveys. The chimpanzee population declined at an annual rate of 2.41%, including declines of 1.72% in riparian forests (from this point forward, forests), 2.05% in miombo woodlands (from this point forward, woodlands) and 3.45% in nonforests. These population declines were accompanied by ecosystem-wide declines in vegetation types of 1.36% and 0.32% per year for forests and woodlands, respectively; we estimated an annual increase of 1.35% for nonforests. Our model predicted the highest chimpanzee density in forests (0.86 chimpanzees/km2 , 95% confidence intervals (CIs) 0.60-1.23; as of 2020), followed by woodlands (0.19, 95% CI 0.12-0.30) and nonforests (0.18, 95% CI 0.10-1.33). Although forests represent only 6% of the landscape, they support nearly one-quarter of the chimpanzee population (769 chimpanzees, 95% CI 536-1103). Woodlands dominate the landscape (71%) and therefore support more than a half of the chimpanzee population (2294; 95% CI 1420-3707). The remaining quarter of the landscape is represented by nonforests and supports another quarter of the chimpanzee population (750; 95% CI 408-1381). Given the pressures on the remaining suitable habitat in Tanzania, and the need of chimpanzees to access both forest and woodland vegetation to survive, we urge future management actions to increase resources and expand the efforts to protect critical forest and woodland habitat and promote strategies and policies that more effectively prevent irreversible losses. We suggest that regular monitoring programs implement a systematic random design to effectively inform and allocate conservation actions and facilitate interannual comparisons for trend monitoring, measuring conservation success, and guiding adaptive management.

Population assessment without individual identification using camera-traps: A comparison of four methods

The use of camera traps to estimate population size when animals are not individually recognizable is gaining traction in the ecological literature, because of its applicability in population conservation and management.We estimated population size of synthetic animals with four camera trap sampling-based statistical models that do not rely on individual recognition. Using a realistic model of animal movement to generate synthetic data, we compared the random encounter model, the random encounter and staying time model, the association model and the time-to-event-model and we investigated the impact of violation of assumptions on the population size estimates.While under ideal conditions these models provide reliable population estimates, when synthetic animal movements were characterised by differences in speed (due to diverse behaviours such as locomotion, grazing and resting) none of the model provided both unbiased and precise density estimates. The random encounter model and the time-to-event-model provided precise results but tended to overestimate population size, while the random encounter and staying time model was less precise and tended to underestimate population size. Lastly, the association model was unable to provide precise results. We found that each tested model was very sensitive to the method used to estimate the range of the field-of-view of camera traps. Density estimates from both random encounter model and time-to-event-model were also very sensitive to biases in the estimate of animals’ speed. We provide guidelines on how to use these statistical models to get population size estimates that could be useful to wildlife managers and practitioners.

Історична пам’ять і некрополітика у прозі Олександра Ірванця

This article is focused on the literary representation of the historical memory about totalitarian past of Ukraine in dystopias by Olexandr Irvanets. The aim of the research is to analyze how phenomenon of necropolitics, substantiatiated in theory by Cameroonian scholar Achille Mbembe as a sovereignty’s right to decide who can live and who must die, is artistically reflected in Irvanets’s works “Rivne / Rovno (The Wall)”, “Ochamymria”, “Libenkraft’s Disease”, and “Kharkiv 1938”. Achievement of this aim presupposes completion of such tasks: to specify content of the phenomenon of necropolitics in Achille Mbembe’s theory, make clear genre of the above-mentioned works by Olexandr Irvanets, outline nuances of interpretation of Ukraine’s colonial past in the above works, and analyze in which way representation of nectopolitics in these texts is overlapped with the material of Ukrainians’ historical memory. The offered article is particularly relevant, since its key concept, necropolitics, despite its prevalence in social sciences, was utilized in the literary criticism very rarely, and was never used by the moment in the Ukrainian literary studies. Therefore, the analysis of the contemporary Ukrainian writer’s works from the position of the considered theory broadens a range of multidisciplinary approaches to the literary work. Division of the fictional space into open and closed zones, alienation of the shown states from other countries, unlimited power of the state over citizens’ lives and deaths, and display of characters’ corporeality as permanently threatened are the main ways of necropolitics realization in the dystopian worlds of Irvanets’s prose. Social unification, stigmatization of the characters, different from others, their deprivation of unique individuality are considered a symbolical equivalent of physical extermination. In all analyzed works, symbolical, moral destruction is shown as deindividualization of unique personalities, transformation them into obedient faceless mass. Means of this transformation include technological inventions (“thoughts unifying radial aggregate” in the novel “Rivne / Rovno (The Wall)”), common exhausting senseless labor (in the tale “Ochamymria”), political repressions against dissidents (in the novel “Kharkiv 1938”), mysterious and very dangerous disease (in the novel “Libenkraft’s Disease”). The most complete and detailed picture of necropolitical society is artistically represented in the novel “Libenkraft’s Disease” that contains a very high number of scenes of violence. Characteristically, the author puts regulation of the question “who can live and who must die” within human population in one row with the regulation of population size of animals – the impressive scene of dog’s extermination on pages of the work proves it. Like many classical dystopias, the novel has no happy end, moreover, the protagonist who, due to infecting by the Libenkraft’s disease, gains shrewd all-seeing eyes, sees that necropower complete and final victory over individuality.

Estimating red fox density using non-invasive genetic sampling and spatial capture\u2013recapture modelling

Spatial capture–recapture modelling (SCR) is a powerful tool for estimating density, population size, and space use of elusive animals. Here, we applied SCR modelling to non-invasive genetic sampling (NGS) data to estimate red fox (Vulpes vulpes) densities in two areas of boreal forest in central (2016–2018) and southern Norway (2017–2018). Estimated densities were overall lower in the central study area (mean = 0.04 foxes per km2 in 2016, 0.10 in 2017, and 0.06 in 2018) compared to the southern study area (0.16 in 2017 and 0.09 in 2018). We found a positive effect of forest cover on density in the central, but not the southern study area. The absence of an effect in the southern area may reflect a paucity of evidence caused by low variation in forest cover. Estimated mean home-range size in the central study area was 45 km2 [95%CI 34–60] for females and 88 km2 [69–113] for males. Mean home-range sizes were smaller in the southern study area (26 km2 [16–42] for females and 56 km2 [35–91] for males). In both study areas, detection probability was session-dependent and affected by sampling effort. This study highlights how SCR modelling in combination with NGS can be used to efficiently monitor red fox populations, and simultaneously incorporate ecological factors and estimate their effects on population density and space use.

The population genetics of urban and rural amphibians in North America.

Human land transformation is one of the leading causes of vertebrate population declines. These declines are thought to be partly due to decreased connectivity and habitat loss reducing animal population sizes in disturbed habitats. With time, this can lead to declines in effective population size and genetic diversity which restrict the ability of wildlife to efficiently cope with environmental change through genetic adaptation. However, it is not well understood whether these effects generally hold across taxa. We address this question by repurposing and synthesizing raw microsatellite data from online repositories for 19 amphibian species sampled at 554georeferenced sites in North America. For each site, we estimated gene diversity, allelic richness, effective population size, and population differentiation. Using binary urban-rural census designations, and continuous measures of human population density, the Human Footprint Index, and impervious surface cover, we tested for generalizable effects of human land use on amphibian genetic diversity. We found minimal evidence, either positive or negative, for relationships between genetic metrics and urbanization. Together with previous work on focal species that also found varying effects of urbanization on genetic composition, it seems likely that the consequences of urbanization are not easily generalizable within or across amphibian species. Questions about the genetic consequences of urbanization for amphibians should be addressed on a case-by-case basis. This contrasts with general negative effects of urbanization in mammals and consistent, but species-specific, positive and negative effects in birds.

How Size and Condition Influence Survival and Cause‐Specific Mortality of Female Elk

ABSTRACTThe size of animal populations fluctuates with number of births, rate of immigration, rate of emigration, and number of deaths. For many ungulate populations, adult female survival is the most important factor influencing population growth. Therefore, increased understanding of survival and causes of mortality for adult females is fundamental for conservation and management. The objectives of our study were to quantify survival rates of female elk (Cervus canadensis) and determine cause‐specific mortality. We predicted that hunter harvest would be the leading cause of mortality. Further, we predicted that hunters would harvest animals that were in prime age (2–9 yr) and in better condition than elk predated by mountain lions (Puma concolor). From 2015 to 2017, we captured 376 female elk in central Utah, USA. We assessed body size and condition of captured elk, fitted each animal with a global positioning system‐collar, and determined cause of death when we received mortality signals. We estimated survival using Kaplan‐Meier estimates and Cox proportional hazard models within an Akaike's Information Criterion model selection framework to identify covariates that influenced survival. We analyzed differences in size and condition measurements between harvested elk and predated elk using analysis of variance tests. Our best model indicated consistent survival across years; mean survival was 78.3 ± 3.5% (SE) including hunter harvest and 95.5 ± 1.7% without hunter harvest. In decreasing order of importance, elk mortality occurred from hunter harvest (21.2%), mountain lion predation (3.7%), depredation removal (0.5%), automobile collision (0.3%), disease (0.3%), complications during calving (0.3%), and those characterized as undetermined (1.3%). Neck circumference and body length were negatively associated with survival, suggesting that larger animals in good condition had lower survival as a result of hunter harvest. Individuals that died because of cougar predation were smaller and had less loin muscle than the average animal. Hunters removed large, healthy, prime‐aged females, individuals that likely have a greater effect on population growth than elk lost to other predators. If the proportion of larger, healthy females in the population begins to decline, hunting practices may require adjustment because hunters may be removing individuals with the greatest reproductive value. © 2021 The Wildlife Society.

Predation pressure of the grey wolf (Canis lupus L. 1758) on wild, domestic and companion animals in Poland

The aim of this study was to determine the predation pressure of the grey wolf (Canis lupus) on wild ungulate populations and the relationship between the size of the grey wolf population and the number of confirmed kills of livestock and companion animals in Poland over eight hunting seasons from 2011/2012 to 2018/2019. There is a positive and complete relationship between the increasing wolf population and the number of confirmed deer kills. The size of the wolf population in Poland was compared to the size of domestic and companion animal population and the number of specimens that fell prey to the grey wolf. It was demonstrated that as the wolf population in Poland increases, the number of confirmed kills of farm and companion animals rises. It seems rational to take steps aimed at mitigating this problem as soon as possible. It is necessary to consider implementation of an integrated protection system that involves culling and employing available methods to deter wolves from attacking grazing herds.

Estimating and validating koala

Context It is notoriously difficult to estimate the size of animal populations, especially for cryptic or threatened species that occur in low numbers. Recent advances with acoustic sensors make the detection of animal populations cost effective when coupled with software that can recognise species-specific calls. Aims We assess the potential for acoustic sensors to estimate koala, Phascolarctos cinereus, density, when individuals are not identified, using spatial count models. Sites were selected where previous independent estimates of density were available. Methods We established acoustic arrays at each of five sites representing different environments and densities of koalas in New South Wales. To assess reliability, we compared male koala density estimates derived from spatial count modelling to independently derived estimates for each site. Key results A total 11 312 koala bellows were verified across our five arrays. Koalas were detected at most of our sample locations (96–100% of sensors; n = 130), compared with low detection rates from rapid scat searches at trees near each sensor (scats at <2% of trees searched, n = 889, except one site where scats were present at 69% of trees, n = 129). Independent estimates of koala density at our study areas varied from a minimum of 0.02 male koalas ha−1 to 0.32 ha−1. Acoustic arrays and the spatial count method yielded plausible estimates of male koala density, which, when converted to total koalas (assuming 1:1 sex ratio), were mostly equivalent to independent estimates previously derived for each site. The greatest discrepancy occurred where the acoustic estimate was larger (although within the bounds of uncertainty) than the independent mark–recapture estimate at a fragmented, high koala-density site. Conclusions Spatial count modelling of acoustic data from arrays provides plausible and reliable estimates of koala density and, importantly, associated measures of uncertainty as well as an ability to model spatial variations in density across an array. Caution is needed when applying models to higher-density populations where home ranges overlap extensively and calls are evenly spread across the array. Implications The results add to the opportunities of acoustic methods for wildlife, especially where monitoring of density requires cost-effective repeat surveys.

Is harvest size a valid indirect measure of abundance for evaluating the population size of game animals using harvest‐based estimation?

Indirect measures of abundance are essential for evaluating temporal and spatial trends in animal populations under hunting pressure and hence for evaluating the impact of hunting on the population stock. Recently, harvest‐based estimation has received attention due to its capacity to estimate population size, hunting mortality and population growth parameters based on the responses of indirect measures to hunting pressure. Although harvest size is a widely used statistic for game animals and its validity as an indirect measure of abundance has been intensively investigated, its applicability to harvest‐based estimation has rarely been studied. In this study, we applied a simulation approach to examine the accuracy of harvest‐based estimation when harvest size is used as an indirect measure under different temporal patterns of capture effort (constant, increasing and decreasing). We simulated a dataset using a Poisson‐binomial surplus‐production model that explicitly considers the effect of capture effort on harvest size and tested the estimation accuracy and model identifiability (i.e. whether there is sufficient statistical information in a dataset to specify model parameters) when harvest size is used as an indirect measure. We then compared the estimates with those of the original Poisson‐binomial surplus‐production model. We found that estimates of the population size and intrinsic growth rate were severely biased when the temporal heterogeneity in capture effort was large. When capture effort was constant and harvest size was thus proportional to the population size, on average, only 10% of iterations were identifiable. The use of harvest size as a population index in harvest‐based estimation can result in seriously biased estimates of population size and growth rate or low identifiability of parameters. Our results highlight the importance of monitoring capture effort and unbiased population indices, in addition to harvest sizes, to evaluate the population status of game animals by harvest‐based estimation.

Estimating animal population size with very high-resolution satellite imagery.

Very high-resolution (VHR) satellite sensors can be used to estimate the size of animal populations, a critical factor in wildlife management, and acquire animal spatial distributions in an economical, easy, and precise way. We developed a method for satellite population size estimation that includes a noninvasive photogrammetry, from which the animal's average orthographic area is calculated, and an imagery interpretation method that estimates population size based on the ratio of an observed animal population area to the average individual area. As a proof of concept, we used this method to estimate the population size of Whooper Swans (Cygnus cygnus) in a national nature reserve in China. To reduce errors, the reserve was subdivided into regions of interest based on locations of Whooper Swan and background brightness. Estimates from the satellite pixels were compared with manual counts made over 2 years, at 3 locations, and in 3 land-cover types. Our results showed 1124 Whooper Swans occupied a national nature reserve on 15 February 2013, and the average percent error was 3.16% (SE = 1.37). These results demonstrate that our method produced robust data for population size estimation that were indistinguishable from manual count data. Our method may be used generally to estimate population sizes of visible and gregarious animals that exhibit high contrast relative to their environments and may inform estimations of populations in complex backgrounds.