Dominant Prey Research Articles

Differential exploitation of a single dominant prey species by migratory shorebirds – a preliminary observation from the vulnerable sandy beaches of the southwest coast of India

Observations on the food resources of migratory shore birds in selected sandy shores of Kerala on the southwest coast of India revealed that their main prey resource is a single species of sand crab (mole crab), Emerita holthuisi Sankolli, 1965, the major crustacean resource in the narrow stretches of sandy shores of central Kerala. Three sandy beaches flanking tidal estuaries, abundant in shore crabs, were selected as the representative sites to study in detail the feeding of shorebirds on the sand crabs. We observed the presence of mole crabs for a year and noted that they are found almost year round on these shores. The shore birds were found to exploit them during their wintering months from October to February. The variations in adaptations of 8 species of predatory shore birds in preying on E. holthuisi were also noted. The same predator-prey relationship was observed in similar small stretches of sandy shores in other parts of central Kerala also.

Consumption of mesopelagic prey in the Strait of Messina, an upwelling area of the central Mediterranean Sea: feeding behaviour of the blue jack mackerel Trachurus picturatus (Bowdich, 1825)

This study describes for the first time the feeding behaviour and mesopelagic food consumption of adult Trachurus picturatus in the Strait of Messina (central Mediterranean Sea), where the distinctive hydrodynamic regime and the lunar cycle influence food availability for this predator. Indeed, the Strait of Messina is characterized by the upwelling of colder, saltier and nutrient-rich Levantine Intermediate Water, supporting the congregation and abundance of the mesopelagic community. Despite the commercial importance of T. picturatus in the Mediterranean and Atlantic fisheries, its trophic ecology is almost unknown. Overall, 262 specimens of T. picturatus were collected from small-scale fisheries of the Strait of Messina (September 2016–August 2017) and their stomach content was examined to investigate dietary composition and feeding strategy. Although the absence of a dominant prey item ruled out specialized predatory behaviour in T. picturatus, mesopelagic prey dominated the diet of this species and a significant fraction of food (more than 80% in terms of Index of Relative Importance) was represented by euphausiids and mesopelagic fish. The predator exploitation of mesopelagic prey resources was analysed, considering the ecological implications of the hydrodynamic regime of the study area, which is strongly influenced by upwelling processes linked to the lunar cycle. For this reason, we tested and confirmed the hypothesis that moon phases could influence the food intake of T. picturatus and seasonal variations in the diet as well as size-related dietary shift were also observed.

Physiology and behaviour of juvenile snowshoe hares at the start of the 10-year cycle

Snowshoe hares, Lepus americanus, are the dominant prey species in the boreal forest and they undergo regular, predator-driven population cycles every 8–11 years. Previous research has found that hare stress physiology is highly sensitive to both within-year (seasonal/litter group) and across-year (cycle phase) variation in predation risk and that maternal–offspring stress profiles are tightly correlated. Thus, both pre- and postnatal environments may interact to shape offspring physiological phenotype. If changes in the function and reactivity of the maternal stress axis are associated with variation in offspring behaviours that increase survival during periods of high predation risk, then the maternal effects on offspring physiology seen previously could represent a mechanistic route of adaptive maternal programming. To examine the relationship between physiology and behaviour in snowshoe hares, we monitored free-ranging adult and juvenile stress hormone levels in the first and second litters of the breeding season and assessed open field exploratory behaviour in weaning-age and independent juveniles in the southwestern Yukon (Canada) during 2013–2015, when predator density was low but increasing. Thus, our study spanned the late low phase (2013) and the early increase phase (2014–2015) of the hare population cycle. We found that increased concentrations of faecal cortisol metabolites (FCMs) were associated with aspects of risk avoidance in weaning-age hares. Juveniles with higher stress hormone levels spent more time under cover and were less active during open field trials, highlighting a potential mechanistic route to allow individuals to sensitively cope with a changing environment. Although average FCM levels of breeding females and juveniles were not correlated with one another and litter-based differences in physiology and behaviour were not present during these low-risk phases of the cycle, the association between stress hormone levels and behaviour sets the stage for adaptive maternal effects on offspring behaviour and survival as the cycle progresses and predation risk intensifies.

Status of an alien turtle in city park waters and its potential threats to local biodiversity: the red-eared slider in Beijing

Invasive alien species pose a serious threat to native biodiversity and the ecosystem structure through predation or competition, and this threat is especially severe in China. Red-eared sliders (Trachemys scripta elegans) were introduced to mainland China to meet demands for food, traditional Chinese medicine, and the pet trade. However, there has been a lack of field surveys to assess the population, behavior and ecological impacts of introduced red-eared sliders in urban aquatic ecosystems in northern China. We conducted such research in 33 urban parks in Beijing from April to November 2016. The alien sliders were recorded on 514 occasions at 19 parks, and 45 individuals were captured from 4 parks to evaluate their diet composition and reproductive status. The observations showed that red-eared sliders accounted for 95% of the recorded turtles in the parks. The male to female ratio was 1.0:3.5, and the ratio of adults to juveniles was 1.0:3.1. According to stomach content analysis, the sliders fed mainly on animals: the dominant prey were Gastropoda, Osteichthyes, Crustacea, Hexapoda, Bivalvia, Reptilia and Aves in descending order. The high frequency (83%) of follicles and oviduct development in adult females suggested a strong reproductive capacity, which was further supported by one case of early female maturity. Bacteriological examinations demonstrated that the carrying rate of Salmonella bacteria was up to 17.6%. This study demonstrated that red-eared sliders have successfully colonized the waters of urban parks in Beijing and potentially threaten native aquatic biodiversity.

Diel schedules of locomotor, reproductive and feeding activity in wild populations of African annual killifish

Abstract Diel patterns of different activities arise from adaptations to periodic cycling of environmental parameters and may involve trade-offs between acquiring benefits and minimizing associated costs. In this study, we provide fundamental baseline data on diel activity of natural populations of Nothobranchius fishes, model organisms in laboratory studies, including links between diurnal rhythms and ageing. Initially, we quantified the diel change in activity in wild populations of three African killifish species (Nothobranchius furzeri, Nothobranchius orthonotus and Nothobranchius pienaari) and compared average activity between sexes. In all species, males were more active than females, probably as a result of their active pursuit of females. Swimming activity peaked at midday. In N. furzeri, the only species occurring at all sites, oocytes were ovulated in the early morning, and most spawning events had occurred by the early afternoon. Gut fullness and diet richness increased before spawning activity and peaked in the morning. Daytime diet was dominated by chironomid larvae, whereas notonectid bugs were the dominant prey at night, perhaps as a result of different prey detectability over the diel cycle. Finally, no loyalty to any particular pool section was detected in N. furzeri. Collectively, these data provide the first empirical description of diel activity in three wild populations of African killifish.

Diet of <i> Odorrana chapaensis </i> (Bourret, 1937) from Son La Province, Vietnam

Since there is currently a lack of data on the natural history and feeding ecology of Odorrana chapaensis, which was listed in the IUCN Red List (2019), we herein provided the feeding ecology of this amphibian species is virtually lacking. We herein provide data about the diet of O. chapaensis based on the results of our field work in Ngoc Chien Commune, Muong La District and Xim Vang Commune, Bac Yen District, Son La Province, Vietnam. We used the stomach-flushing method to obtain the stomach contents of 85 individuals at two survey sites. A total of 20 prey categories with 334 items, comprising 299 items of invertebrates and 35 unidentified items, were found in the stomachs of O. chapaensis. The dominant prey items of O. chapaensis were Araneae, Polydesmida, insect larvae, Blattodea, Coleoptera, Dermaptera, Lepidoptera, Hymenoptera, and Orthoptera. The importance index for these categories ranged from 3.5% to 32.5%. Coleoptera was the category with the highest frequency of prey items; its representatives were found in 45 stomaches.

Diet of <i> Odorrana chapaensis </i> (Bourret, 1937) from Son La Province, Vietnam

Since there is currently a lack of data on the natural history and feeding ecology of Odorrana chapaensis, which was listed in the IUCN Red List (2019), we herein provided the feeding ecology of this amphibian species is virtually lacking. We herein provide data about the diet of O. chapaensis based on the results of our field work in Ngoc Chien Commune, Muong La District and Xim Vang Commune, Bac Yen District, Son La Province, Vietnam. We used the stomach-flushing method to obtain the stomach contents of 85 individuals at two survey sites. A total of 20 prey categories with 334 items, comprising 299 items of invertebrates and 35 unidentified items, were found in the stomachs of O. chapaensis. The dominant prey items of O. chapaensis were Araneae, Polydesmida, insect larvae, Blattodea, Coleoptera, Dermaptera, Lepidoptera, Hymenoptera, and Orthoptera. The importance index for these categories ranged from 3.5% to 32.5%. Coleoptera was the category with the highest frequency of prey items; its representatives were found in 45 stomaches.

South American sea lions Otaria byronia as biological samplers of local cephalopod fauna in the Patagonian shelf marine ecosystem

AbstractCephalopods are important prey in the diet of top predators, such as marine mammals and seabirds. However, detailed information on their trophic relationships in the Patagonian marine ecosystem is scarce, including those cephalopod species with commercial interest. The aims of this study were to evaluate the composition of the cephalopod component in the diet of Otaria byronia and determine the habitat use and trophic levels of their main cephalopod prey by measuring the stable isotopic signature of cephalopod beaks. Between May 2005 and February 2009, fresh faecal samples were collected from two sea lions rookeries in San Matias Gulf. Cephalopods occurred in 39.4% of the 1112 samples collected during the whole period of study. The dominant prey species was Octopus tehuelchus, which occurred in 45.8% of scats containing cephalopod remains, and represented 58.7% in terms of numerical abundance and 52.0% in mass of cephalopods consumed. The second species most consumed was the myopsid Doryteuthis gahi. The significant higher δ15N values of O. tehuelchus beaks in comparison with those of D. gahi showed that these two species have different trophic levels while occupying similar habitat (δ13C values) in neritic waters of the Patagonian shelf.

A comparison of diet estimates of captive beluga whales using fatty acid mixing models with their true diets

Beluga whales (Delphinapterus leucas) are sentinel species for Arctic environmental change; however, whether belugas are resilient to anticipated changes in prey dynamics remains uncertain, partly due to a lack of dietary information. Mixing models are promising tools to evaluate the diets of marine mammals, using dietary tracers such as fatty acid signatures. Additionally, captive feeding trials are useful to test the effectiveness of these tools for application to wild populations. In our study, we compared the ability of two models, quantitative fatty acid signature analysis in R (QFASAR) and Fatty Acid Source Tracking Algorithm in R (FASTAR) to reconstruct the diets of captive beluga whales that had been fed a long-term diet consisting mostly of Pacific herring (Clupea harengus pallasi), and in smaller proportions, capelin (Mallotus villosus) and squid (Doryteuthis opalescens). To account for fatty acid metabolism, we compared a suite of calibration coefficients derived from captive feeding trials of American mink (Mustela vison), harp seal (Pagophilus groenlandicus), harbour seal (Phoca vitulina richardsi), and grey seal (Halichoerus grypus) fed monotypic diets. For both methods, diets estimated using calibration coefficients derived from feeding trials of mink fed herring and/or seal oil were able to correctly identify herring as the dominant prey source of belugas. In addition, there was higher precision among diet estimates using these calibration coefficients in comparison to those generated using calibration coefficients derived from feeding trials of pinnipeds or mink fed poultry. QFASAR more accurately approximated the diet proportions of the whales than FASTAR, possibly because of the greater robustness to errors in the calibration coefficients. Based on QFASAR, diet estimates best reflect the whales' true dietary proportions consumed approximately two weeks to one month prior to sampling, similar to timeframes seen in previous studies of harbour seals. We recommend caution when using these models with prey that have high within-species variability in fatty acid signatures or small sample sizes, as well as prey with similar fatty acid signatures. The application of mixing models is promising to identify the prey of wild beluga whales and other marine mammals.

Stable isotope analyses of ancient and modern Adélie Penguin (Pygoscelis adeliae) mummies from the Ross Sea Region, Antarctica

We performed stable carbon (δ13C) and nitrogen (δ15N) isotope analyses of 12 ancient Adelie penguin (Pygoscelis adeliae) chick mummies recovered from abandoned colonies in the Ross Sea region, Antarctica, to investigate isotopic variation and fractionation over time. We also examined latitudinal variation in penguin diet to address if the modern dietary pattern (an increase in krill as dominant prey to the north) in this region has existed in the past or if this is a recent phenomenon. The ancient mummies range in age from > 48,000 14C years before present (BP) to ~ 500 calendar years BP. Feather, skin, bone, and toenail samples were analyzed from each individual where available. Identical analyses were performed on five modern mummified Adelie penguin chick carcasses and breast feathers of ten recently dead chicks from each of two active colonies, Cape Hallett and Adelie Cove. We found significantly lower δ15N values in Cape Hallett modern chicks as compared to those from Adelie Cove, indicating an entire trophic-level difference in modern diet that agrees with other studies in this region. The ancient mummies exhibited consistent isotopic fractionation of δ13C among the four different tissues through time. Variation in δ15N and δ13C values was greater in bone and skin than in feather or toenail, but δ15N in all four tissues indicated similar dietary trends with latitude as occurs in this region today. These results provide insight into the dietary variability of Adelie penguins across the Ross Sea region and a framework for similar analyses with other avian species.

Feeding Habits of the Mediterranean Horse Mackerel

Feeding habits of the horse mackarel, Trachurus mediterraneus in Bandırma Bay, the Sea of Marmara were investigated in the years of 2013-2015. Stomach contents of 90 specimens collected by commercial vessels were analysed. The stomach contents were determined to consist of 2 major systematic groups: Crustacea (Copepoda, Cladocera, Mysidacea, Ampipoda, Decapoda), and Pisces. The predominant and preferred prey category was Crustaceans. Besides, Crustaceans were identified as the most important food items considering the index of relative importance (IRI). Howver, teleost eggs were occasional foods. Euphausiacea, was food category with especially abundant in spring while Copepoda was the most in autumn. Feeding intensity varied throughout 3 seasons (winter, spring, and autumn). The lowest and highest feeding intensities were recorded in winter and autumn, respectively. Euphausiids were observed to be dominant prey during winter and spring. The lowest and highest feeding intensities were recorded in winter and autumn, respectively. T. mediterraneus revealed carnivorous feeding habit and. Euphausiacea food item with highest occurrence.

Biotic factors influencing the unexpected distribution of a Humboldt marten (Martes caurina humboldtensis) population in a young coastal forest.

Pacific martens (Martes caurina) are often associated with mature forests with complex structure for denning, resting, and efficient hunting. Nonetheless, a small isolated population of the Humboldt subspecies of Pacific martens (Martes caurina humboldtensis) occupies a narrow strip of young, coastal forest (< 70 years old) but not inland mature forest in the central Oregon Coast Range. We examined factors contributing to this unexpected distribution of martens by 1) analyzing marten diets using DNA metabarcoding to assess 90 scats, 2) using camera traps to assess differences in the relative abundances of prey, competitors, and predators across a coastal to inland gradient of vegetation types, and 3) quantifying differences in extent of fruit-producing shrubs and vegetation structure within vegetation types. Diets of martens were diverse (12, 10, and 3 species of birds, mammals, and amphibians respectively), and most fall and winter scats contained fruit. Voles, mice, and varied thrushes (Ixoreus naevius) were dominant prey items. Voles, mice, and most birds, but not varied thrushes, were more commonly observed in the coastal shrub-dominated forest than in inland forest. The coastal shrub-dominated forest had the highest diversity of vertebrates and potential prey overall. Bobcats (Lynx rufus), a key potential predator, were more commonly detected in inland forest. Of potential competitors, western spotted skunks (Spilogale gracilis) were more commonly detected in inland forest, with gray foxes (Urocyon cinereoargenteus) and raccoons (Procyon lotor) detected almost exclusively in coastal forests. Vegetation in coastal forests appears to provide, at least seasonally, more prey and fruit, and more overhead shrub cover compared with inland forest. Remaining plausible hypotheses for the restricted distribution of marten to coastal forests include increased prey, fruit, and overhead cover, and reduced predation risk from bobcats.

Implementation of an end-to-end model of the Gulf of Lions ecosystem (NW Mediterranean Sea). I. Parameterization, calibration and evaluation

An end-to-end model named OSMOSE-GoL has been built for the Gulf of Lions, the main French Mediterranean fishing area. This spatialized dynamic model links the coupled hydrodynamic and biogeochemical model Eco3M-S/SYMPHONIE (LTL – low trophic level model) to OSMOSE (HTL – high trophic level model). It includes 15 compartments of living organisms, five from the LTL model (i.e. nanophytoplankton, microphytoplankton, nanozooplankton, microzooplankton and mesozooplankton) and ten from the HTL model (northern krill, southern shortfin squid, European pilchard, European anchovy, European sprat, Atlantic horse mackerel, Atlantic mackerel, blue whiting, European hake and Atlantic bluefin tuna). With the exception of northern krill and European sprat, all HTL species are commercially exploited and undergo fisheries mortality pressure. The modeled species represent more than 70% of annual catches in this area. This paper presents the parameterization, calibration and evaluation of this model with satellite data for phytoplankton and with biomass, landings, diet and trophic level data for HTL groups. For most species, the diets in output of OSMOSE-GoL are similar to field and literature data in terms of dominant prey groups and species. However, some differences were observed. Various reasons may explain the mismatch between the modeled diet and field data. Benthic prey sometimes observed in the stomach content of the HTL predators were not modeled in OSMOSE-GoL. Field studies were carried out at specific periods and locations, while our data concern the period 2001–2004 and the entire modeled domain. Inter- and intra-annual variations in spatial distribution and density of prey may also explain these differences. The model estimates trophic level values similar to those cited in the literature for all the HTL compartments. These values are also close to the trophic levels estimated by a previous Ecopath model for the same area and period. Even though some improvements are still possible, this model may already be of use to explore fishery or Marine Protected Areas scenarios for socio-ecosystem management issues.

Mechanisms of radiocesium depuration in Sebastes cheni derived by simulation analysis of measured 137Cs concentrations off southern Fukushima 2014–2016

The cesium depuration mechanisms were studied in Japanese rockfish Sebastes cheni off Fukushima, in which the radiocesium level remains higher than in other teleost. Samples were collected approximately 5 km south from the nuclear power plant during 2014–2016, and the 137Cs concentrations in fish, stomach content and prey species were measured. The stable cesium content in fish was also analyzed and compared with fish age which was determined by annual ring analysis in otoliths. The 137Cs concentrations in the dominant prey species, mysids and brown shrimp, were several Bq kg-w.w.−1; indicating that transfer via the food chain was substantial compared to that from seawater during the study period. The 137Cs concentrations in S. cheni decreased from 2014 to 2016 due to the metabolic excretion and the rate of decrease in its diet. Biokinetic model analyses confirmed the slower turnover of stable cesium in S. cheni, represented as a biological half-life (Tb1/2) of 140–215 d, and was associated with stable Cs levels in food of 5–7 ng g-w.w.−1. The 137Cs levels in S. cheni were also simulated, which showed that the 137Cs depuration in fish exposed to the initial contaminated plume in 2011 resulted from slower metabolic excretion, while the 137Cs levels in fish born after 2012 could be regarded as equilibrated with the environmental levels of 137Cs. Furthermore, the simulation results suggest that 137Cs depuration in S. cheni population was also caused by the alternation of generation, which can be substantial by the addition of new year class population hatched after 2012 that were not contaminated by the initial contaminated plume from the 2011 accident.

The Common Buzzard Buteo buteo Population in a Changing Environment, Central Poland as a Case Study

Common buzzard is the most abundant bird of prey in Europe, and its population has undergone serious changes. In this study, we focused on a population in Central Poland (study area 105 km2, forests around 24 km2, seven forest complexes) to analyze how certain environmental factors influenced population abundance, breeding parameters, and diet composition. The study was undertaken from 2011 to 2018, and the results were compared with data from two study periods (1982–1992; 2001–2003). Current population density was 3.5 pairs/10 km2 of total area and 14.3 pairs/10 km2 of forested area, it was negatively correlated to the abundance of northern goshawk, and it grew in the last few decades. Mammals were dominant prey (72.6% prey items, 38.6% of biomass), but their share in diet changed following rodent availability. A decrease in the share of voles was recorded, reflecting drop in their abundance and dampening of abundance cycles. Breeding parameters were similar to those in the past, and the number of offspring depended on small rodent availability. Buzzards adapted to changes in the stand structure, i.e., when share of Scots pine decreased, they chose it as their nesting tree less frequently. All this showed that buzzard is a very adaptable species.

Intraspecific variation in a dominant prey species can bias marine predator dietary estimates derived from stable isotope analysis

AbstractIt is often assumed that variation in consumer stable isotope values (δ15N and δ13C) reflect shifts in diet between isotopically distinct prey species. However, an alternate hypothesis is that such variation could be as a result of spatial, temporal, or ontogenetic variation in the stable isotope values of a key prey species that propagate up marine food chains. In the Southern Ocean, Antarctic krill (Euphausia superba) occupy a key position, linking primary production to secondary consumers including fish, squid, seabirds, and marine mammals. As such Antarctic krill represent an ideal prey species to test the critical assumptions behind what has become a common method of dietary analysis in marine predators. Similar to previous studies, we found that stable isotope values of Antarctic krill exhibit significant intraspecific variation associated with both ontogenetic (size) and oceanographic factors (chlorophyll a concentration). Our modeling results showed that intraspecific variation in the stable isotope values of Antarctic krill has the potential to force mean isotope values of krill predators by as much as 2.4‰, independent of changes in the species composition of diet. Our findings indicate that intraspecific variation in the stable isotope values of a single, dominate prey species, such as Antarctic krill, has the potential to bias both absolute and relative estimates of marine predator diets using stable isotope mixing models. Therefore, caution is warranted to avoid spatial, temporal, and ontogenetic mismatches between the stable isotope values of prey sources used in mixing models and the actual stable isotope values of prey consumed by marine predators.

Prey fish communities of the Laurentian Great Lakes: A cross-basin overview of status and trends based on bottom trawl surveys, 1978-2016

Annual bottom trawl surveys were initiated in the 1970s in Laurentian Great Lakes Superior, Huron, Michigan and Ontario and in 1990 in Erie to provide annual assessments of the status and trends of prey fish communities. Native Cisco Coregonus artedi and Bloater C. hoyi dominated the prey fish community of Lake Superior. Prey fish communities in lakes Huron and Michigan were dominated by nonnative Rainbow Smelt Osmerus mordax and Alewife Alosa pseudoharengus for much of 1978-2016, but Bloater was an important species during the 1980-1990s and more recently has become the dominant prey species in these lakes. Alewife dominated the prey fish community of Lake Ontario during all 1978-2016. While nonnatives dominated the prey fish community in Lake Erie, native Emerald Shiner Notropis atherinoides was an important species and occasionally the dominant prey fish after the establishment of Round Goby Neogobius melanostomus in the late 1990s. During the 1980s-1990s Bythotrephes cederstroemi, Dreissena polymorpha, and Dreissena bugensis caused profound changes in Laurentian Great Lakes ecosystems and likely contributed to declines in fish community biomass in lakes Michigan and Huron. The impacts of these invaders were more muted in lakes Erie and Ontario. Lake Superior stands out as the Laurentian Great Lakes success story: Lake Trout Salvelinus namaycush was restored, and native prey fishes dominate and support a viable fishery. Although the abundance of Bloater has increased recently in lakes Huron and Michigan, recovery of native prey fishes remains uncertain. The absence of native species among the principal prey fish in Lake Ontario indicates a lack of progress in native fish recovery. Recovery of native prey fishes remains unclear in Lake Erie. The ever-changing state of the Laurentian Great Lakes caused by the impacts of invasive species and ongoing climate and ecosystem change will continue to challenge restoration of native fish communities in the 21st Century.

A review: poisoning by anticoagulant rodenticides in non-target animals globally.

Worldwide use of anticoagulant rodenticides (ARs) for rodents control has frequently led to secondary poisoning of non-target animals, especially raptors. In spite of the occurrence of many incidents of primary or secondary AR-exposure and poisoning of non-target animals, these incidents have been reported only for individual countries, and there has been no comprehensive worldwide study or review. Furthermore, the AR exposure pathway in raptors has not yet been clearly identified. The aim of this review is therefore to comprehensively analyze the global incidence of primary and secondary AR-exposure in non-target animals, and to explore the exposure pathways. We reviewed the published literature, which reported AR residues in the non-target animals between 1998 and 2015, indicated that various raptor species had over 60% AR- detection rate and have a risk of AR poisoning. According to several papers studied on diets of raptor species, although rodents are the most common diets of raptors, some raptor species prey mainly on non-rodents. Therefore, preying on targeted rodents does not necessarily explain all causes of secondary AR-exposure of raptors. Since AR residue-detection was also reported in non-target mammals, birds, reptiles and invertebrates, which are the dominant prey of some raptors, AR residues in these animals, as well as in target rodents, could be the exposure source of ARs to raptors.

Dietary analysis reveals the vulnerability of the endangered Maugean skate (Zearaja maugeana) to benthic changes in Macquarie Harbour

Species occupying high trophic positions with a small population size, limited diet and restricted range are vulnerable to extinction. The endangered Maugean skate (Zearaja maugeana) in Macquarie Harbour is potentially threatened by changing benthic environmental conditions (declining dissolved oxygen concentrations and decreased macrofaunal diversity). To inform investigations on potential indirect impacts of benthic environmental changes on the Maugean skate and its prey, non-lethal techniques were used to identify dietary composition and trophic position of the species. The Maugean skate occupies a high trophic position (3.70) in the food web, with both stable-isotope (median 86% contribution to isotopic signatures, credible interval (CI)=44–100%) and stomach-content analysis showing crustaceans, particularly brachyuran crabs (58.5% index of relative importance), as the dominant prey type. Aquaculture feed from salmonid fish farms operating in the harbour was not found to be important in skate diet. This study showed that the Maugean skate consumes a small number of benthic prey species, highlighting its vulnerability to changing environmental conditions in the harbour.

Density and spatial partitioning of endangered sympatric Javan leopard (Felidae) and dholes (Canidae) in a tropical forest landscape

This study explores two large carnivores, Javan leopard (Panthera pardus melas) and dhole (Cuon alpinus) that are known to have an overlapping diet and are sympatric in the south-western part of West Java. We characterised their spatiotemporal habitat together with four medium-sized prey species. We used photographs collected along 39.420 night-traps from 108 camera-traps installed on the peninsula of Ujung Kulon National Park (UKNP). We are using maximum entropy modelling (MaxEnt) to investigate seasonal environmental factors. Concerning the dominant prey species, our results showed that distances to secondary forest edge were highly significant for both Javan leopard and dhole in wet and dry seasons. Javan leopard is mostly active at dawn and dusk, whereas spatially correlated with Javan mousedeer and red muntjac. Dhole exhibited diurnal activity and were avoiding Javan leopard to a certain extent. Its spatial use is overlapping with red muntjac, wild boar, and banteng. Using Spatially Explicit Capture-Recapture (SECR) methods, the density estimation for Javan leopard were 10.91 and 11.54 individuals/100 km2 in wet and dry seasons, respectively. We confirmed UKNP as one of Indonesia's biodiversity hotspots and a critical area to preserve Javan leopard and dholes.