Key Prey Species Research Articles

Gut microbiota dynamics of adult and sub‐adult sika deer during reintroduction

AbstractPrey populations significantly influence the distribution of top predators. The sika deer (Cervus nippon), a key prey species for the Amur tiger in Northeast China, plays a critical role in the recovery and dispersal of Amur tiger populations. Reintroduction is a pivotal strategy for restoring prey populations, but it presents challenges, especially in terms of adaptation to the natural environment during the natural training process before animals are released. In this study, we sampled six adult and six sub‐adult sika deer and employed high‐throughput sequencing of the 16S ribosomal RNA gene to investigate changes in gut microbial diversity, composition, and function during natural training. The results showed that adult sika deer had higher gut microbiota diversity compared to sub‐adults. However, as natural training progressed, the gut microbial diversity in sub‐adults approached that of adults. Additionally, beneficial, fiber‐digesting bacteria associated with adaptation to the natural environment tended to increase during nature training in both adult and sub‐adult sika deer, while pathogenic bacteria tended to decrease. We also compared the metabolic function of the gut microbiota in adult and sub‐adult sika deer, which showed that the carbohydrate metabolic function of both adults and sub‐adults decreased significantly with natural training, declining more rapidly in sub‐adults. Conversely, the lipid metabolic function in sub‐adults increased significantly with natural training. Overall, a period of nature training is necessary before reintroducing animals to their natural habitats, and sub‐adult sika deer, in particular, exhibit greater adaptability to environmental changes as reflected by their gut microbiota dynamics. These findings offer valuable insights for the reintroduction of sika deer and other ungulates. We recommend incorporating natural training in reintroduction programs and prioritizing sub‐adult animals for reintroduction.

Predicting the Impact of Climate Change on the Selection of Reintroduction Sites for the South China Tiger (Panthera tigris amoyensis) in China.

The South China tiger (Panthera tigris amoyensis) is a tiger subspecies unique to China and one of the top ten endangered species in the world. It used to play an important role in the overall function of the ecosystem. This study rationally screened out key prey species of the South China tiger-the Chinese serow, Chinese goral, tufted deer, water deer, Chinese muntjac, red muntjac, sambar deer, and wild boar. Candidate sites for the rewilding and reintroduction of the South China tiger were derived by exploring changes in suitable habitats for the prey using the MaxEnt model. The results show that: (1) by 2070, except for the high-suitability areas of water deer and Chinese muntjac, the areas of suitable habitats for the other six prey species would all have decreased significantly; (2) the location of the high-suitability area of the South China tiger obtained by superimposing the suitable areas of the eight prey species would be almost stable in 2050 and 2070, but the habitat index of some high- and medium-suitability areas would decrease and turn into low-suitability areas; (3) the core candidate sites were 83,415 km2 in total, of which 25,630 km2 overlapped with existing protected areas, accounting for 30.7% of the core candidate sites, and the remaining 69.3% of the core candidate sites were mostly distributed around the protected areas; (4) the maximum core candidate site area was projected to be 10,000 km2 by 2070, which could support a small population of 23 male tigers and 66 female tigers to survive and reproduce in the wild. This study revealed the core candidate sites for the rewilding of South China tigers and estimated the number of tigers that could be reintroduced to these areas, providing a preliminary research basis for promoting the rewilding of South China tigers in China.

Environmental DNA reveals fine‐scale spatial and temporal variation of marine mammals and their prey species in a Scottish marine protected area

AbstractMarine mammal foraging grounds are popular focal points for marine protected area (MPA) implementation, despite being temporally dynamic, requiring continuous monitoring to infer prey availability and abundance. Marine mammal distributions are assumed to be driven by their prey in foraging areas, but limited understanding of prey distributions often prevents us from exploring how shifting prey availability impacts both seasonal and long‐term marine mammal distributions. Environmental DNA (eDNA) metabarcoding could enhance the understanding of marine mammal habitat use in relation to their prey through simultaneous monitoring of both. However, eDNA applications focused on marine mammals or predator–prey dynamics have been limited to date. In this study, we assess spatiotemporal changes in the distribution and abundance of cetaceans, minke whales (Balaenoptera acutorostrata), bottlenose dolphins (Tursiops truncatus) and harbor porpoises (Phocoena phocoena) in relation to key prey species in a newly established MPA, employing eDNA metabarcoding. We recovered 105 molecular operational taxonomic units (OTUs) from marine vertebrates using two primer sets targeting 12S and 16S genes, along with 112 OTUs from a broader eukaryotic primer set targeting 18S rRNA. Overall, key forage fish prey species, sandeels and clupeids, were the most abundant teleost fishes detected, although their availability varied temporally and with distance from shore. We also found clear spatial partitioning between coastal bottlenose dolphins and the more pelagic minke whales and harbor porpoises, paralleling availability of their main prey species. Other species of conservation interest were also detected including the critically endangered European eel (Anguilla anguilla), Atlantic bluefin tuna (Thunnus thynnus), and the invasive pink salmon (Oncorhynchus gorbuscha). This study demonstrates the application of eDNA to detect spatiotemporal trends in the occurrence and abundance of cetacean predators and their prey, furthering our understanding of fine‐scale habitat use within MPAs. Future long‐term monitoring of predator–prey dynamics with eDNA could improve our ability to predict climate‐induced shifts in foraging grounds and enhance rapid responses with appropriate management actions.

Is the Iberian lynx a hunters’ ally? a case study from a reintroduced population in Portugal

The Iberian lynx (Lynx pardinus) is one of the most endangered felids in the world, and a high proportion of its populations occur in hunting grounds managed for red-legged partridge (Alectoris rufa) and wild rabbit (Oryctolagus cuniculus), both game species of high socio-economic value and the latter a key prey species for the lynx. In this case study from south-eastern Portugal, we evaluated the game management practices, the abundance of partridges and rabbits (expressed as Kilometric Abundance Index), and the occurrence of mesocarnivores in four hunting grounds, two with and two without breeding lynx. In all grounds game management was conducted but in those where lynx occurred, full-time gamekeepers were employed and hunting was the major source of income. The results showed that grounds with breeding lynx had higher KAI values for partridges and rabbits, together with reduced mesocarnivores occurrence (particularly red fox Vulpes vulpes and stone marten Martes foina), compared to those without breeding lynx. Our results confirm that lynx occurrence fits within the management traits of those hunting grounds in Iberia aiming to increase partridges and rabbits for sustainable hunting, as they act as ‘natural’ gamekeepers. This could be considered as a ‘win-win’ situation; successful for lynx’s establishment and small game conservation.

Ecosystem structure and function of the North Water Polynya

The North Water Polynya is one of the most productive Arctic regions on Earth, sustaining the world's northernmost Inuit communities for millennia. The polynya is a large and persistent region of open water surrounded by sea ice and exhibits high primary productivity, is a biodiversity hotspot, and is a key habitat and migration corridor for Arctic species. Many aspects of the ecosystem structure and the role of resident species in the North Water Polynya remain uncertain. To shed light on these, we developed the first representation of the North Water Polynya food web using the Ecopath modelling framework. Modelled trophic flows indicated that pelagic and benthic communities were primarily connected by Age 1+ Arctic cod ( Boreogadus saida), walrus ( Odobenus rosmarus), and ringed seal ( Pusa hispida). Large copepods, Age 1+ Arctic cod, and bivalves were key prey species. Overall productivity in the North Water Polynya was higher compared to Western Baffin Bay and Western Greenland, corroborating expectations of relatively high productivity within the polynya. This model provides a baseline description of the North Water Polynya ecosystem structure and function prior to future climate-driven food web changes and the emergence of large-scale commercial fisheries.

Energy densities of key prey species in the California Current Ecosystem

The energetic content of primary and secondary consumers is central to understanding ecosystem functioning, community assembly, and trophodynamics. However, these foundational data are often limited, especially for marine ecosystems. Here we report the energy densities of important prey species in the California Current Ecosystem. We investigated variation in energy density within and between species and explored potential underlying causes of these differences. Northern anchovy (Engraulis mordax) is the most energy dense of the species analyzed with a median value nearly twice as high as was found in krill (Euphausia pacifica and Thysanoessa spinifera). Relationships with body size varied among species; krill energy density increased, with both length and wet weight. In addition, we find that anchovy, sardine (Sardinops sagax), and market squid (Doryteuthis opalescens) have higher energy content in the summer and fall as compared to the spring. This aligns with the ecosystem phenology of strong upwelling during spring (March – May) driving high primary productivity, followed by widespread predator presence through the summer and fall (June – October). Our results inform food web studies in the California Current and suggest new avenues for investigating differences in species and ecosystem energetics in an era of rapid global change.

Relative abundance of Roe deer (Capreolus pygargus) related to overstory structure and understory food resources in Northeast China

Large herbivores are particularly susceptible to changes in quantity and quality of forage resources, in turn constraining populations of large and threatened carnivores. Key prey species for Amur tigers (Panthera tigris altaica) and leopards (P. pardus orientalis), Siberian roe deer (Capreolus pygargus) have a spatial distribution which is greatly influenced by habitat quality across topographic regions. In this study, we used 138 camera-trap stations to record the abundance and distribution of Siberian roe deer in the mountains (n=88) and valleys (n=50) of the Northeast China Tiger and Leopard National Park, and we examined the impact of overstory structure and understory food resources on the relative abundance index (RAI) of the deer. We use generalized linear mixed models (GLMM) with negative binomial distributions, with the response variable of RAI of either of deer on the mountain or in the valley. We included canopy cover (CC), tree richness (TR) and basal area (BA) from overstory structure and mass of shrub layer (SM), mass of grasses and sedges (GM), forbs mass (FoM), ferns mass (FeM) and understory mass (UM) from understory food as fixed effects. We found that RAI of roe deer was significantly higher for the mountain than the valley. For the mountain, BA, TR and FoM were found to have a significant positive effect on roe deer, while CC showed a negative effect. In the valley, BA had a significant positive effect on roe deer, while SM showed a negative effect. Roe deer appeared to trade-off overstory structure with understory food resources, especially BA and FoM, which may lead them to prefer mountains over valleys in the national park. These findings will assist in understanding the distribution of roe deer populations in Northeast China Tiger and Leopard National Park, and may suggest more effective conservation and management strategies for the forest ecosystems of Northeast China.

Foraging movements of humpback whales relate to the lateral and vertical distribution of capelin in the Barents Sea

Understanding how individual animals modulate their behaviour and movement patterns in response to environmental variability plays a central role in behavioural ecology. Marine mammal tracking studies typically use physical environmental characteristics that vary, and/or proxies of prey distribution, to explain predator movements. Studies linking predator movements and the actual distributions of prey are rare. Here we analysed satellite tag data from ten humpback whales in the Barents Sea (north-east Atlantic) to examine how their spatial movement and dive patterns are influenced by the geographic and vertical distribution of capelin, which is a key prey species for humpback whales. We used capelin density estimates based on direct observations from a trawl-acoustic survey and sun elevation to explore the drivers of changes in movement patterns. We found that the humpback whales’ exhibited characteristic area restricted search movement where capelin density was the highest. While horizontal movements showed both positive and negative individual relationships with sun elevation, humpback whale dive depth was positively correlated with diurnal variations in the vertical distribution of capelin. This suggests that in addition to whales foraging in regions of high capelin density, they also target the densest shoals of capelin at a range of depths, throughout the day and night. Overall, our findings suggest that regions of high capelin density are important foraging grounds for humpback whales, highlighting the central role capelin plays in the Barents Sea marine ecosystem.

Quantifying the impacts of an invasive weed on habitat quality and prey availability for tiger snakes (Notechis scutatus) in urban wetlands

Invasive plants are a threat to natural ecosystems worldwide, with urban wetlands being some of the most susceptible and highly modified environments of all. The tiger snake (Notechis scutatus) is a top predator that persists in urban wetlands of south-western Australia, many of which have been degraded by introduced kikuyu grass (Cenchrus clandestinus). To evaluate the potential impact of kikuyu grass on habitat quality for tiger snakes we quantified the structural features of habitats within wetlands degraded by kikuyu grass and compared them to wetlands with native vegetation. We also examined tiger snake prey availability, assessed predation risk for juvenile snakes using clay models, and measured the thermal quality of the vegetation. Proliferation of kikuyu grass has reduced habitat structural heterogeneity by reducing available bare ground and increasing vegetation density. This homogenisation of habitat structure had little effect on the predation risk for juveniles or the thermal properties of tiger snake shelter sites; however, one key prey species, the motorbike frog, had significantly lower abundance in the most impacted habitat. Habitat types with more structural complexity also offered tiger snakes more stable thermal regimes and lower predation risk. These findings indicate that the current extent of kikuyu grass invasion offers overall similar habitat quality for tiger snakes to native vegetation and may contribute to their persistence in urban wetlands; however, both tiger snakes and their anuran prey may benefit from increased habitat structural complexity.

Using head, pectoral girdle bones and otoliths to estimate length and weight of Argentine anchovy (Engraulis anchoita), a key species in Patagonian marine ecosystem

The Argentine anchovy, Engraulis anchoita, plays a vital role as a key prey species for several marine predators in the north Patagonian marine ecosystem of the Atlantic Ocean. Reconstructing the length and weight of each consumed specimen is essential to provide a detailed description of the trophic ecology of top marine predators. Predictive linear regression equations were calculated for the Patagonian stock of Argentine anchovy to estimate parameters of length-weight relationships using measurements of whole individuals and diagnostic elements such as otoliths, head bones and pectoral fin bones. Among the diagnostic elements analyzed, the cleithrum and dentary exhibited the best fit. This study validates the use of head and pectoral girdle bones as reliable indicators for predicting the weight and length of Argentine anchovy across a wide size range, which corresponds to the target range of various predators. These relationships can contribute to the determination of body condition, estimation of consumed biomass, and calculation of energy density, providing valuable insights into the trophic ecology of predators in the southern Atlantic Ocean.

Risks, resources, and refugia: Spatial overlap between yellow-eyed penguin foraging distribution and prey, commercial fisheries, and marine protected areas

Conservation of the endangered yellow-eyed penguin (Megadyptes antipodes) in New Zealand has principally sought to manage terrestrial threats, while relatively little has been done to understand or address marine threats, such as reduced prey availability, commercial fisheries interactions, and habitat destruction. We assessed spatial similarities between mainland yellow-eyed penguin marine distribution and resources (prey), risks (fisheries interactions), and areas of refugia (marine protected areas, MPAs). We determined if suitable penguin foraging habitat, based on environmental predictors using a Maxent species distribution model (SDM), also supports a high diversity of key prey species identified using a stacked SDM. We also created a novel index to predict areas of potential commercial fisheries interactions and mapped the overlap of penguin distribution and MPAs. Areas along the middle of the continental shelf had the highest prey diversity and probability of penguin presence, which overlapped with gillnet fisheries in these regions. Suitable penguin habitat also overlaps with trawl fisheries inshore along much of the South Island coast. <1 % of the penguin range overlaps with current MPAs, and the proposed South-East Marine Protected Areas network would protect only 3.6 % of the current penguin foraging distribution. This study takes an ecosystem approach to assess complex interactions between commercial fisheries, marine ecosystems, and MPAs, which is urgently required for marine spatial planning and adaptive ecosystem management of not only this endangered seabird but for southeast New Zealand coastal habitat and biota also.

Population estimate and conservation status of the Persian Leopard, Panthera pardus tulliana, in the Bamo and Khoshk Mountains in Kurdistan Region, northern Iraq

In Iraq, the endangered Persian Leopard (Panthera pardus tulliana) is distributed in the northern part (Kurdistan Region) along the Zagros mountain steppe ecoregion, which includes the Bamo and Khoshk Mountains, where we carried out a field survey between October 2020 and November 2022 including camera trapping and interviews with local communities. At least five individuals were recorded during this study, including males, a female, and a family, given a population density of 1.25 indivuduals/100 km2. Bezoar Goat and Wild Boar are their key prey species in the area. Poaching and wildlife trafficking, decreasing natural water sources, overgrazing, minefields, and forest fires are identified as key threats facing the Persian Leopard population, their prey species, and their natural habitats in the Bamo and Khoshk Mountains. It is suggested to designate the study area as a national protected area or a transboundary conservation area between Iraq and Iran.

Influencing factors of predation on five keystone prey species in Haizhou Bay based on Delta-GAMMs.

Trophic dynamics is one of the major regulators of fishery production in marine ecosystems, which is important for the implementation of ecosystem-based fisheries management. Based on data collected form bottom trawl surveys in Haizhou Bay and adjacent waters during autumn of 2011 and 2018, Delta-GAMMs (Delta-generalized additive mixed models) were constructed to evaluate the effects of biotic and abiotic factors on the predation of five key prey species (including Leptochela gracilis, Alpheus japonicus, Loligo spp., Larimichthys polyactis, and Oratosquilla oratoria) in the Haizhou Bay. Percent frequency of occurrence and predation pressure index were used to identify their major predators. Variance inflation factor and full subsets regression were analyzed to quantify the degree of multicollinearity between these factors. The results showed that the occurrence frequency of keystone prey species in the stomach of predators ranged from 8.5% to 42.2%, and the weight percentage ranged from 4.2% to 40.9%. The average deviance explanation rate of the "binomial" model was 16.1%, and the average deviance explanation rate of the "positive" model was 23.8%. Body length of predator, predator population density, and sea bottom temperature were important factors influencing prey-predator trophic interactions. Predator length was the most important factor, with feeding probability and weight percentage of keystone prey species all increasing with body length of predator. Feeding probability and weight percentage of key prey species decreased with predator population density. The effects of environmental factors such as sea bottom temperature, depth of water, latitude, and sea bottom salinity showed different trends, depending on the prey-predator assemblage. This study showed that the Delta-GAMMs was an effective method to explore the trophic interactions between prey and predators in marine ecosystems, and could provide a theoretical basis for the conservation and sustainable use of fisheries resources.

Environmental DNA survey of the Winter Salmonosphere in the Gulf of Alaska

AbstractPacific salmon (Oncorhynchus spp.) are a foundation species around the north Pacific, yet many wild populations have experienced steep declines over the last decades associated with decreased marine survival. Due to limited sampling, our understanding of the dynamic North Pacific Ocean ecosystem remains poor and factors impacting marine survival of salmon remain largely unknown, specifically in the winter when salmon face limited resources. Here, we present a late winter ecosystem‐wide environmental DNA (eDNA) survey performed in 2019 and 2020 in the Gulf of Alaska. Our eDNA data refines the ocean distribution and relative abundance of Pacific salmon, as well as their prey such as copepods. Vertical diurnal migrators like myctophids and squid that are prey and/or competitors of salmon and represent the bulk of the open ocean biomass in the Gulf of Alaska. We detected these species irrespective of time of day in the eDNA data, resolving the nighttime bias associated with trawl catches. Furthermore, eDNA uncovered cryptic predators of salmon such as salmon sharks (Lamna ditropis) and beaked whales (Ziphiidae) not evident from catch or observer data. Open‐ocean communities of the central Gulf of Alaska were characterized by low species richness in contrast to hotspots of biological activity associated with oceanographic features such as eddies and the continental shelf. Network analysis revealed the ecological interactions that salmon navigate in the open‐ocean ecosystem by identifying key prey species, competitors, and predators and revealed the negative impact of the northern sea nettle (Chrysaora melanaster) on salmon that was associated with a marine heatwave in 2019. Finally, we highlight the utility of eDNA for open ocean ecosystem research and provide recommendations for further surveys. This dataset, complementing traditional survey methods, illustrates the winter salmonosphere in the North Pacific Ocean at improved resolution and provides a baseline for future research.

EDNA Metabarcoding Analyses of Diet in Yellow-Billed Loons of Northern Alaska

Environmental DNA is a burgeoning tool used to address wide-ranging scientific questions, including determining diets of difficult-to-sample predators. Loons are large piscivorous diving birds that capture and consume prey underwater, making it nearly impossible to visually determine their diet via observation alone. Identifying species' diets is important for understanding basic life history traits, and revealing key prey species can clarify species' roles in complex trophic webs, aid in understanding population and community dynamics, and help identify critical habitat for protection. Current information about loon diet is largely anecdotal, and traditional non-observational methods for quantifying loon diet have limitations. Analysis of eDNA from loon feces may provide biologists with a non-invasive technique for determining diet without negative sampling effects, and with increased resolution as compared to other techniques. We surveyed lakes in two areas of northern Alaska for Yellow-billed Loons (Gavia adamsii). Loon fecal samples were collected opportunistically from latrine sites without disturbing any animals and analyzed using novel marker sets to determine loon species and diet. Fish species were detected in all fecal samples, the most common being Alaska blackfish (Dallia pectoralis), and ninespine stickleback (Pungitius pungitius). This research demonstrates that eDNA metabarcoding analyses of loon fecal samples can determine the specific loon species that deposited the feces and characterize the piscine portion of their diet with limited disturbance to the animals.

Long‐term patterns in ecosystem phenology near Palmer Station, Antarctica, from the perspective of the Adélie penguin

AbstractClimate change is leading to phenological shifts across a wide range of species globally. Polar oceans are hotspots of rapid climate change where sea ice dynamics structure ecosystems and organismal life cycles are attuned to ice seasonality. To anticipate climate change impacts on populations and ecosystem services, it is critical to understand ecosystem phenology to determine species activity patterns, optimal environmental windows for processes like reproduction, and the ramifications of ecological mismatches. Since 1991, the Palmer Antarctica Long‐Term Ecological Research (LTER) program has monitored seasonal dynamics near Palmer Station. Here, we review the species that occupy this region as year‐round residents, seasonal breeders, or periodic visitors. We show that sea ice retreat and increasing photoperiod in the spring trigger a sequence of events from mid‐November to mid‐February, including Adélie penguin clutch initiation, snow melt, calm conditions (low winds and warm air/sea temperature), phytoplankton blooms, shallow mixed layer depths, particulate organic carbon flux, peak humpback whale abundances, nutrient drawdown, and bacterial accumulation. Subsequently, from May to June, snow accumulates, zooplankton indicator species appear, and sea ice advances. The standard deviation in the timing of most events ranged from ~20 to 45 days, which was striking compared with Adélie penguin clutch initiation that varied &lt;1 week. In general, during late sea ice retreat years, events happened later (~5 to &gt;30 days) than mean dates and the variability in timing was low (&lt;20%) compared with early ice retreat years. Statistical models showed the timing of some events were informative predictors (but not sole drivers) of other events. From an Adélie penguin perspective, earlier sea ice retreat and shifts in the timing of suitable conditions or prey characteristics could lead to mismatches, or asynchronies, that ultimately influence chick survival via their mass at fledging. However, more work is needed to understand how phenological shifts affect chick thermoregulatory costs and the abundance, availability, and energy content of key prey species, which support chick growth and survival. While we did not detect many long‐term phenological trends, we expect that when sea ice trends become significant within our LTER time series, phenological trends and negative effects from ecological mismatches will follow.

Recovery of a marine keystone predator transforms terrestrial predator–prey dynamics

Sea otters (Enhydra lutris) and wolves (Canis lupus) are two apex predators with strong and cascading effects on ecosystem structure and function. After decades of recovery from near extirpation, their ranges now overlap, allowing sea otters and wolves to interact for the first time in the scientific record. We intensively studied wolves during 2015 to 2021 in an island system colonized by sea otters in the 2000s and by wolves in 2013. After wolf colonization, we quantified shifts in foraging behavior with DNA metabarcoding of 689 wolf scats and stable isotope analyses, both revealing a dietary switch from Sitka black-tailed deer (Odocoileus hemionus), the terrestrial insitu primary prey, to sea otters. Here we show an unexpected result of the reintroduction and restoration of sea otters, which became an abundant marine subsidy for wolves following population recovery. The availability of sea otters allowed wolves to persist and continue to reproduce, subsequently nearly eliminating deer. Genotypes from 390 wolf scats and telemetry data from 13 wolves confirmed island fidelity constituting one of the highest known wolf population densities and upending standardly accepted wolf density predictions based on ungulate abundance. Whereas marine subsidies in other systems are generally derived from lower trophic levels, here an apex nearshore predator became a key prey species and linked nearshore and terrestrial food webs in a recently deglaciated and rapidly changing ecosystem. These results underscore that species restoration may serve as an unanticipated nutrient pathway for recipient ecosystems even resulting in cross-boundary subsidy cascades.

Effects of Inhabiting and Life Patterns on the UV Spectral Properties of Small Mammalian Herbivores’ Urine

It is well known that avian predators can use prey excretions such as urine and feces to track their prey, and the urine and feces of small mammalian herbivores can reflect ultraviolet (UV) light and emit fluorescent light. There are still some debates as to whether UV visibility of small mammalian herbivores’ urine is used as a hunting cue by avian raptors. Some studies in Europe have demonstrated that diurnal raptors are capable of utilizing these cues to target key prey species. However, researchers in Australia have argued that raptors do not use the UV visibility of urine while hunting. To our knowledge, there are no reports from Asia concerning the ultraviolet spectral characteristics of small mammal herbivores’ urine. This study examined the UV spectral properties of urine from 6 small mammal herbivores species by comparing the UV reflectance and fluorescence spectra of urine from small mammalian herbivores living in plateau meadows, plateau shrubs, open marshland, farmland, and semi-desert grassland in China. In addition, we compared the UV spectral properties of urine from ground-dwelling species of rodents and subterranean species to determine whether ultraviolet visibility of small mammal herbivores’ urine could be used as a visual signal by Asian vole-eating raptors. The results showed that: 1) the SC370 values of urine from four small mammal herbivores species were ordered as plateau pika (plateau meadow) > root voles (plateau bush) > reed voles (swampland) > Brandt’s vole (desert grassland); and 2) UV fluorescence peak intensity and the wavelengths of urine from ground-dwelling species (such as the root vole, plateau pika, or Brandt’s vole) were significantly higher than those of subterranean-dwelling species (mandarin vole and plateau zokor). These results indicate that UV visibility of small mammal herbivores’ urine may act as a visual cue for raptors.

Stomach content and stable isotopes illustrate large spatial similarity in the Wadden Sea fish food-web structure

Spatial variability in the Wadden Sea fish food-web structure was studied by comparing stomach content and bulk stable isotopes of fish species caught simultaneously in the Ems and Marsdiep basins during 2012-2014. Almost all 31 fish species caught were generalist feeders. In both basins, similar predator-prey relationships were found in which a few key prey species fuelled the fish food web. Copepods and brown shrimp were the most important prey species in both basins, mysid shrimp were more important as prey in the Ems basin, while shore crab and herring were more important prey species in the Marsdiep basin. The observed spatial variability in prey preferences was most likely the result of local differences in predator and prey abundances. Published absolute trophic positions based on compound-specific stable isotopes were available for some fish species and indicated low variability between the basins. Estimated absolute trophic positions based on stomach content and on bulk stable isotopes could not be used for the analysis of spatial variability due to sensitivity to sampling procedure (stomach content) and sampling size and baseline (bulk stable isotopes). Although estimates based on bulk stable isotopes underestimated absolute trophic levels in both basins, they can be used for the analysis of relative trophic positions of fish species. Relative trophic positions showed a significant correlation for most fish between the Ems and Marsdiep basins, also indicating a large spatial similarity in trophic structure.

Using web-sourced photographs to examine temporal patterns in sex-specific diet of a highly sexually dimorphic raptor.

Traditional methods to study raptor diet are usually limited temporally, e.g. prey remains at nesting sites, and are unsuitable to examine dietary changes throughout the year. Using web-sourced photography, we explore temporal patterns in prey size and key prey species between sexes of the sexually dimorphic Eurasian sparrowhawk (Accipiter nisus) throughout the United Kingdom. We examined 666 photographs of sparrowhawk on prey and identified the prey species involved, together with sparrowhawk sex. Changes in prey size and proportions of key prey species over time (seasonally and monthly) were explored for each sex. Prey weight was substantially higher for females than males. However, on average, prey size for both sexes declined during the summer period (May–June) being the lowest in June, which is the main nestling-rearing month for both sparrowhawks and their prey. Compared with summer, rock doves (Columba livia) were more important prey for female sparrowhawk in winter. Whereas, for males, Eurasian blackbirds (Turdus merula) were more important in spring compared with autumn. Web-sourced photography can overcome several limitations of previous methods used to study raptor diet including the ability to quantify diet between the sexes throughout the entire year, however, may also introduce a prey-size bias toward larger prey items.