Vertebrate Scavengers Research Articles

The first case of forensic entomology applied to a roadkill dog carcass in the Colombian Andes

• We report the first forensic entomology case on a roadkill animal in the neotropics. • Post mortem interval and the minimum period of insect activity are calculated based on the fly larvae collected on the dog’s liquefied brain. • The occurrence of colonizer blow flies on dry remains decomposition stage is hypothesized. • The accelerating effect of vertebrate scavengers on the duration of decomposition stages is measured based on the entomological inference. An uncommon case of forensic entomology applied to a roadkill animal is detailed; the minimum period of insect activity (PIA min : 72 h) and the postmortem interval (PMI: ≤48 h) were calculated. Inferences and possible events pre- and postmortem are related and proposed, including the possible explanation of the occurrence of colonizer carrion flies on dry remains. The accelerating effect of vertebrate scavengers on the decomposition stages of the carcass was measured (7.4 time faster). This study is the first forensic entomology case applied to a roadkill animal in the neotropics.

Effects of red imported fire ant (Solenopsis invicta) control on carrion use by vertebrate scavengers

Carrion is an important resource, and competition for carrion by microbial, invertebrate, and vertebrate scavenging communities is great. In particular, carrion is important to facultative and obligate vertebrate scavengers globally, and these species provide an irreplaceable ecological service by efficiently removing carcasses, which potentially harbor pathogens, from the environment. Although vertebrates efficiently acquire carcasses, they compete intensively with invertebrate and microbial communities, especially during warmer months when invertebrate and microbial activity peaks. The presence of invasive invertebrates may further exacerbate competition among scavenging groups; however, little is known about how invasive invertebrates can influence invertebrate scavenger dynamics and ultimately competition with vertebrate scavengers. The red imported fire ant (Solenopsis invicta; RIFA) is an invasive species of particular interest in North America, as it is a dominant predator and decomposer throughout much their range. We hypothesized that in areas where abundant, RIFA can outcompete vertebrates for carrion resources, altering nutrient cycling and food web dynamics. We tested this hypothesis by experimentally excluding RIFA from rabbit carcasses and found strong seasonal effects in our data; however, surprisingly, we found no effect of RIFA control on vertebrate scavenging efficiency, rates of carcass detection, carcass persistence, or the richness of local scavengers. Rather, we observed a highly efficient vertebrate scavenging community that assimilated 87.4% of carcasses during our study. This high rate of vertebrate scavenging efficiency was maintained in both control (93.0%) and RIFA treatment (81.8%) sites, suggesting presence of abundant RIFA populations did not limit vertebrate acquisition of carrion. Future research should focus on the interactions of RIFA with the remaining invertebrate scavenging community to further investigate whether RIFA impact the assimilation of carrion resources within invertebrate communities.

Functional traits driving species role in the structure of terrestrial vertebrate scavenger networks.

Species assemblages often have a non-random nested organization, which in vertebrate scavenger (carrion-consuming) assemblages is thought to be driven by facilitation in competitive environments. However, not all scavenger species play the same role in maintaining assemblage structure, as some species are obligate scavengers (i.e., vultures) and others are facultative, scavenging opportunistically. We used a database with 177 vertebrate scavenger species from 53 assemblages in 22 countries across five continents to identify which functional traits of scavenger species are key to maintaining the scavenging network structure. We used network analyses to relate ten traits hypothesized to affect assemblage structure with the "role" of each species in the scavenging assemblage in which it appeared. We characterized the role of a species in terms of both the proportion of monitored carcasses on which that species scavenged, or scavenging breadth (i.e., the species "normalized degree"), and the role of that species in the nested structure of the assemblage (i.e., the species "paired nested degree"), therefore identifying possible facilitative interactions among species. We found that species with high olfactory acuity, social foragers, and obligate scavengers had the widest scavenging breadth. We also found that social foragers had a large paired nested degree in scavenger assemblages, probably because their presence is easier to detect by other species to signal carcass occurrence. Our study highlights differences in the functional roles of scavenger species and can be used to identify key species for targeted conservation to maintain the ecological function of scavenger assemblages.

Reviewing the Role of Vultures at the Human-Wildlife-Livestock Disease Interface: An African Perspective

Vultures are a key component of an effective scavenger guild and have evolved a number of adaptations that allow them to locate and dispose of carcasses quickly and efficiently. The continuing decline of African vultures is threatening the stability of the African scavenger guild, which may result in increased carcass decomposition times and thus, more rapid development of pathogenic bacteria. The absence of competitive regulation by these apex scavengers may also result in changes in the composition of the vertebrate scavenger guild, with an increase in mammalian scavengers giving rise to increased contact rates at carcasses, which may increase the risk of viral disease transmission to humans, livestock, and other wildlife. Although the economic value of vultures in terms of the sanitation services they provide has been evaluated, their contribution to the economics of human health and veterinary care remains to be quantified. Efforts to do so are hampered by lack of data, as well as a number of confounding factors that may mask causality, such as improved disease prevention and surveillance systems. However, the circumstantial nature of the link between vultures and disease prevention should not deter efforts to conserve them, as their regulation of mammalian scavengers and the sanitation services they provide place them firmly within the sphere of One Health, thereby warranting their urgent protection. The restoration of vulture populations and the ecosystem services they provide will benefit the welfare of all humans, but particularly those who are most vulnerable to economic instability and the spillover of disease at the human-wildlife-livestock interface.

Megafires attract avian scavenging but carcasses still persist

AbstractAimThe effects of fires on vertebrate scavengers have not been characterized despite the importance of scavenging in shaping food web dynamics. We assessed whether the 2019/2020 megafires in Australia shifted the species richness, carcass detection and feeding times of vertebrate scavengers, and whether the fire affected carcasses persistence times.LocationBlue Mountains, south‐eastern Australia.MethodWe monitored vertebrate scavengers via remote cameras on a total of 60 experimentally placed kangaroo carcasses for 30 days in two periods before the megafire (January 2018 and 2019) and one period after the megafire (March 2020) in both open and closed canopy habitats. We compared vertebrate species richness, carcass discovery and scavenging activity before and after the fire and between the two habitats. We also assessed carcass persistence (time to carcass removal) before and after the fire and between the two habitats.ResultsWe collected more than 689,000 images of nine vertebrate scavengers including six avian, two mammal and one reptile species. We detected no decline in scavenger species richness following the fire, and rates of carcass detection for mammals and reptiles did not differ across pre‐ and post‐fire periods. On the other hand, avian scavengers detected carcasses faster in the post‐fire period and in open compared to closed canopy habitats. Overall, scavengers increased their feeding times in the post‐fire period, especially avian scavengers, but carcasses persisted longer in the post‐fire period when compared to the second pre‐fire period.Main conclusionOur study identified that a widespread fire could influence avian scavenging dynamics, but that other factors such as habitat and possibly apex scavenger presence affected carcass persistence times over the study period in addition to fire. Future monitoring of carcasses following fires should focus on the responses by both vertebrate and insect scavengers to fully elucidate the effects of these major disturbance events on critical ecosystem processes linked to decomposition.

Vertebrate scavenging dynamics differ between carnivore and herbivore carcasses in the northern boreal forest

AbstractVertebrate scavenging can impact food web dynamics, but our understanding of this process stems predominantly from monitoring herbivore carrion and extrapolating results across carcass types. Recent evidence suggests carnivores may avoid intraguild scavenging to reduce parasite transmission. If this behavior is widespread across diverse ecosystems, estimation of nutrient cycling and community scavenging rates are likely biased to a currently unknown degree. We examined whether the time to initiate scavenging, carcass persistence, or the richness of species scavenging in the boreal forest of Yukon, Canada, differed between carnivore and herbivore carcasses. Vertebrates took longer to initiate scavenging on carnivore carcasses (3.2 d) relative to herbivore carcasses (1.1 d), and carnivore carcasses persisted on the landscape for over a month longer (48.4 d and 5.5 d, respectively). The longer persistence times were due to the reduction in scavenging by carnivores such as Canada lynx (Lynx canadensis). Decreased scavenging was caused by changes in the propensity to consume carnivore carrion, as the number of species detecting a carcass within the first week did not differ between carnivore and herbivore carcasses. These results have ramifications for our understanding of nutrient cycling and food web dynamics in the boreal forest and provide further support that carcass type should be included in future studies.

Uncovering the vertebrate scavenger guild composition and functioning in the Cerrado biodiversity hotspot

AbstractScavenging is widespread among vertebrates, being very important for maintaining certain ecosystem functions. Despite this, the scavenger communities remain poorly known in some biomes, especially in the Neotropics. Our main objective was to describe for the first time the scavenger community and identify the factors affecting scavenging efficiency in the Brazilian Cerrado. We analyzed the effects of vegetation cover, time of carcass placement and carcass weight, on scavenger species richness, individual abundances, carcass detection and consumption times, and carcass consumption rate. We monitored 11 large and 45 small carcasses using automatic cameras. We documented a total of 19 vertebrate scavenging species, four species of vultures and 15 facultative scavengers. We found that carcass size was the most important factor affecting the scavenger assemblage and consumption patterns. Large carcasses were dominated by vultures, whereas small carcasses were consumed mainly by facultative scavengers. We also found differences between large and small carcasses in all carcass consumption variables except for detection time. However, we did not find an effect of vegetation cover or time of carcass placement on scavenging patterns. The negligible role of mammals and non‐raptor birds in large carcasses is also noteworthy, probably due to the consumption and foraging efficiency of the vultures, and the more frugivorous habits of the mesocarnivores. Our results show a highly diverse and efficient scavenging vertebrate community in the Brazilian Cerrado, and the need to preserve them in the face of the significant habitat transformations suffered by this biodiversity hotspot.Abstract in Portuguese is available with online material.

Resource concealment and the evolution of parental care in burying beetles

AbstractComparative experimental study of species can provide insight into behavioral transitions in evolution. The insects offer many such examples for the analysis of parental care. We examined three distantly related species of Nicrophorus and two non‐Nicrophorus silphid beetles for their ability to conceal odors from a carcass that cue competitors that attempt to usurp the resource. We predicted that species with well‐developed parental care would exhibit a heightened ability to conceal a resource from competitors, even when differences in burying behavior and direct defense were experimentally eliminated. Carcasses were provided to male–female pairs in the laboratory for 3 days and then experimentally buried in the field, without parents, to assess discovery by Nicrophorus and vertebrate scavengers. The burying beetles Ni. orbicollis, Ni. sayi and Ni. pustulatus were far more successful in hiding a prepared resource (>76%) from free‐flying Nicrophorus than the less parental Ptomascopus morio or Necrophila americana (<25%). Carcasses provided to P. morio and Ne. americana were also more likely to be discovered by Nicrophorus than non‐prepared control carcasses, suggesting that microbially derived odor cues available to competitors were increased by non‐Nicrophorus interaction with carcasses. In the absence of burial, carcass preparation had no effect on vertebrate scavenging. We hypothesize that the evolution of burying and carcass modification to conceal a discovered resource from diverse competitors, more so than control of microbial decay, was a critical step in the evolutionary transition to monopolization of a small carcass, nesting and extended parental care in the Silphidae.

Scavenging beetles control the temporal response of soil communities to carrion decomposition

Abstract Carrion is a frequent but overlooked source of nutrients to the soil. The decomposition of carrion is accelerated by invertebrate scavengers, but the impact of the scavengers on below‐ground biota and its functions is scarcely known. We conducted a laboratory experiment to investigate the effects of the burying beetle Nicrophorus vespilloides on the soil community of a temperate broadleaved forest. We assembled microcosms from soil collected from an oak woodland and treated them with mouse Mus musculus carcasses and mating pairs of burying beetles (♀+♂) in a factorial design with control soils. We sampled independent replicates over time to investigate how the beetles affect soil microarthropods and microbial biomass (bacteria and fungi) in relation to soil pH and organic matter content. The beetle treatment initially reduced the total microbial biomass and abundance of major groups of microarthropods relative to the control soil. At the same time, organic matter increased in the beetle treatment and then dropped to the pre‐beetle level (i.e. soil baseline) at the end of the beetle breeding cycle (2 weeks). The rapid temporal changes in organic matter were mimicked by the relative abundances of the dominant microarthropod groups, with Oribatida relatively more abundant than Collembola and predaceous mites in the beetle treatment. The overall final effect of the beetle (relative to the laboratory control) on microarthropods was negative but the beetle kept these variables within the levels observed for freshly collected soil (baseline), while the final effect on pH was positive, and most likely driven by the surplus of nutrients from the carcass and biochemical changes triggered by the decomposition process. In nature, scavenging invertebrates are widespread. Our study demonstrates that beetles breeding in carcasses regulate the dynamics of key components of the soil food web, including microbial biomass, changes in the relative abundances of dominant microarthropods and soil organic matter and pH. Given the abundance of these beetles in nature, the study implies that the distribution of these beetles is a key driver of variation in soil nutrient cycling in woodlands. A free Plain Language Summary can be found within the Supporting Information of this article.

Predicted climate-induced reductions in scavenging in eastern North America.

Scavenging is an important function within ecosystems where scavengers remove organic matter, reduce disease, stabilize food webs, and generally make ecosystems more resilient to environmental changes. Global change (i.e., changing climate and increasing human impact) is currently influencing scavenger communities. Thus, understanding what promotes species richness in scavenger communities can help prioritize management actions. Using a long-term dataset from camera traps deployed with animal carcasses as bait along a 1881 km latitudinal gradient in the Appalachian Mountains of eastern USA, we investigated the relative impact of climate and humans on the species richness and diversity of vertebrate scavengers. Our most supported models for both mammalian and avian scavengers included climatic, but not human, variables. The richness of mammalian and avian scavengers detected was highest during relatively warm (5-10°C) and dry (100-150 mm precipitation) winters, when food was likely limited and both reliance on and detection of carrion was high. The diversity of mammalian and avian scavengers detected was highest under drier conditions. We then used these results to project the future species richness of scavengers that would be detected within our sampling area and under the climate scenario of 2070 (emissions level RCP8.5). Our predictions suggest up to 80% and 67% reductions, respectively, in the richness of avian and mammalian scavengers that would be detected at baited sites. Climate-induced shifts in behavior (i.e., reduction in scavenging, even if present) at this scale could have cascading implications for ecosystem function, resilience, and human health. Further, our study highlights the importance of conducting studies of scavenger community dynamics within ecosystems across wide spatial gradients within temperate environments. More broadly, these findings build upon our understanding of the impacts of climate-induced adjustments in behavior that can likely have negative impacts on systems at a large scale.

Carcasses at Fixed Locations Host a Higher Diversity of Necrophilous Beetles.

Simple SummaryWhereas vertebrate scavengers have a higher diversity reported at randomly placed carcasses, the drivers of insect diversity on carrion, such as the exposure type (fixed versus random) or the carrion species, are still incompletely understood. We analyzed beetle diversity at differently exposed carcasses in the low-range mountain forest of the Bavarian Forest National Park in Germany. We tested if scavenging beetles, similarly to vertebrate scavengers, show a higher diversity at randomly placed carcasses compared to easily manageable fixed places. Ninety-two beetle species at 29 exposed wildlife carcasses (roe, red deer, and red foxes) were detected. Beetle diversity was higher at fixed locations possessing extended highly nutrient-rich cadaver decomposition islands as important refuges for threatened red-listed species, such as Necrobia violacea (Coleoptera: Cleridae). Particularly noticeable in our insect traps were the following two rare species, the “primitive” carrion beetle Necrophilus subterraneus (Coleoptera: Agyrtidae) and the false clown beetle Sphaerites glabratus (Coleoptera: Sphaeritidae). In Europe, only the species S. glabratus out of the genus Sphaerites is present. This emphasizes the importance of carrion for biodiversity conservation. We clearly show the relevance of leaving and additional providing wildlife carcasses in a dedicated place in protected forests for preserving very rare and threatened beetle species as essential members of the decomposing community.In contrast to other necromass, such as leaves, deadwood, or dung, the drivers of insect biodiversity on carcasses are still incompletely understood. For vertebrate scavengers, a richer community was shown for randomly placed carcasses, due to lower competition. Here we tested if scavenging beetles similarly show a higher diversity at randomly placed carcasses compared to easily manageable fixed places. We sampled 12,879 individuals and 92 species of scavenging beetles attracted to 17 randomly and 12 at fixed places exposed and decomposing carcasses of red deer, roe deer, and red foxes compared to control sites in a low range mountain forest. We used rarefaction-extrapolation curves along the Hill-series to weight diversity from rare to dominant species and indicator species analysis to identify differences between placement types, the decay stage, and carrion species. Beetle diversity decreased from fixed to random locations, becoming increasingly pronounced with weighting of dominant species. In addition, we found only two indicator species for exposure location type, both representative of fixed placement locations and both red listed species, namely Omosita depressa and Necrobia violacea. Furthermore, we identified three indicator species of Staphylinidae (Philonthus marginatus and Oxytelus laqueatus) and Scarabaeidae (Melinopterus prodromus) for larger carrion and one geotrupid species Anoplotrupes stercorosus for advanced decomposition stages. Our study shows that necrophilous insect diversity patterns on carcasses over decomposition follow different mechanisms than those of vertebrate scavengers with permanently established carrion islands as important habitats for a diverse and threatened insect fauna.

Unravelling the vertebrate scavenger assemblage in the Gobi Desert, Mongolia

Despite the essential role that vertebrate scavengers play in ecosystems, most studies have been conducted in Europe and North America, and there is a lack of information on vertebrate scavengers in vast regions of the world. Our aim was to describe the functioning and composition of the unknown vertebrate scavenger assemblage in the Gobi Desert, Mongolia, and determine how carcass size and habitat type affect species composition and carrion use. We monitored carcasses with camera traps and we also conducted observation points to survey the raptor community and identify the proportion of raptor species making use of the carcasses. We recorded eight vertebrate scavenger species (five birds and three mammals) by camera trap and seven raptors at observation points. Over half of the raptor species recorded at the observation points were also found feeding on carrion. The two most threatened species were only recorded in the mountain habitat. Furthermore, scavenger abundance and consumption rates were higher at large carcasses. This study highlights the importance of scavenging by raptors and other vertebrate scavengers for carrion elimination in ecosystems with extreme climatic conditions.

Dingoes dining with death

Dingoes (Canis dingo) are known for hunting and killing animals to meet their energetic requirements, but like almost all predators they also scavenge animal remains. To improve our understanding of dingo scavenging ecology, we investigated the role of abiotic and biotic factors in shaping carcass utilisation by dingoes and further determined whether dingo scavenging influenced carcass persistence in the landscape. To do so, we monitored visitation and scavenging by dingoes using remote cameras positioned on 119 kangaroo carcasses in open and closed canopy habitats and in warm and cool seasons. The carcasses were monitored across multiple study sites, which incorporated forest, alpine and desert ecoregions in Australia. We found that season played an important role in shaping carcass utilisation by dingoes, as well as carcass persistence. Warmer seasons increased the rate of carcass discovery 6.3-fold in the Forest study site and 4.8-fold in the Alpine study site, and also increased the time dingoes spent feeding on carcasses in the Alpine study site. Further, across all study sites, carcasses persisted at least 4.7 times longer in cool compared with warm seasons. On the other hand, carcass utilisation by dingoes was not influenced by habitat, although carcasses were more likely to persist in open compared with closed canopy habitats in the Alpine study site. Finally, our study showed that dingo scavenging may contribute to substantial carcass removal in certain contexts. Indeed, decreased carcass persistence in the Forest study site was evident in the cool season, when dingo scavenging occurred during the first two weeks of monitoring. The variability in results highlights the complexity of patterns in dingo scavenging and, more broadly, of vertebrate scavenging. It emphasises the need to consider multiple abiotic and biotic factors to properly understand the functional roles of different scavenger species. Longer-term studies with additional seasonal replicates may also yield a more detailed picture of the role of dingoes as apex scavengers.

Changes in the Microbiome at the Onset and End of Decomposition

Decomposition is a rapidly evolving process that is dependent on various environmental factors such as climate, temperature, insect activity, large vertebrate scavenging, and microbial activity. Although other factors such as body weight and time have been evaluated, microbial activity should be considered as another major component in the decomposition process. This study was designed to investigate the microbiome and potential bacterial succession using two different DNA extraction methods, classic microbiologic techniques and 16S ribosomal sequencing at the onset and end of decomposition. Differences were observed between the bacterial phyla found on Day 1 versus Day 6. Among the various phyla, several different bacterial species were observed such as Kurthia gibsonii, K. sibirica, Staphylococcus sciuri, S. lentus, and Serratia marcescens. An interesting change in the phyla present was observed for Day 6. None of the bacterial samples collected on any of the anatomical sites were identified in the phylum Firmicutes. In fact, most of the bacteria collected from the mouth, nose, and genitals were identified in the phyla Actinobacteria and Proteobacteria. Two different bacterial species, Myroides odoratus and Leucobacter aridicollis were present in the two phyla at Day 6 that were not observed at the onset of decomposition. Likewise, many of the bacterial species present at Day 1 were not observed in Day 6. The difference in bacterial diversity observed at the onset and end of decomposition suggest that a timeline or bacterial succession could be developed that could support post-mortem interval determinations

Terrestrial and semi-aquatic scavengers on invasive Pacific pink salmon (Oncorhynchus gorbuscha) carcasses in a riparian ecosystem in northern Norway

Pacific pink salmon (Oncorhynchus gorbuscha) invasions, thought to originate from populations introduced and established in Russia, occurred along the Norwegian coast in 2017 and 2019. Despite several thousand pink salmon entering and establishing in northern Norwegian rivers, current understanding of the ecological effect of the species in northern Europe is limited. Scavengers feeding on pacific salmon carcasses are important vectors for the transport of marine derived energy and nutrients to terrestrial ecosystems in the Pacific Northwest, North America, where the salmon naturally occur. However the role of terrestrial and aquatic scavengers in the consumption and removal of pink salmon beyond the salmon’s native range is unknown. This study has identified terrestrial and sub-aquatic vertebrate scavengers on pink salmon carcasses in a sub-arctic river in northern Norway. Avian scavengers filmed by a camera placed near sites baited with pink salmon carcasses included the Eurasian magpie (Pica pica), hooded crow (Corvus cornix), common raven (Corvus corax), the European herring gull (Larus argentatus), redwing (Turdus iliacus) and goosander (Mergus merganser). However, the largest carcass weight was removed by red foxes (Vulpes vulpes). Carcasses entering Vesterelv River in 2019 were estimated to provide energy and nutrients to the river ecosystem an order of magnitude lower than in the Pacific Northwest. This study provides some of the first information in northern Europe on the mechanisms and quantification of energy and nutrient transfer from the ocean to riparian environments via introduced Pacific pink salmon. Results help to begin to determine the ecological effect of pink salmon and the development of appropriate management strategies.

Interspecific interactions among functionally diverse frugivores and their outcomes for plant reproduction: A new approach based on camera-trap data and tailored null models.

The study of plant-frugivore interactions is essential to understand the ecology and evolution of many plant communities. However, very little is known about how interactions among frugivores indirectly affect plant reproductive success. In this study, we examined direct interactions among vertebrate frugivores sharing the same fruit resources. Then, we inferred how the revealed direct interspecific interactions could lead to indirect (positive or negative) effects on reproductive success of fleshy fruited plants. To do so, we developed a new analytical approach that combines camera trap data (spatial location, visitor species, date and time, activity) and tailored null models that allowed us to infer spatial-temporal interactions (attraction, avoidance or indifference) between pairs of frugivore species. To illustrate our approach, we chose to study the system composed by the Mediterranean dwarf palm, Chamaerops humilis, the Iberian pear tree, Pyrus bourgaeana, and their shared functionally diverse assemblages of vertebrate frugivores in a Mediterranean area of SW Spain. We first assessed the extent to which different pairs of frugivore species tend to visit the same or different fruiting individual plants. Then, for pairs of species that used the same individual plants, we evaluated their spatial-temporal relationship. Our first step showed, for instance, that some prey frugivore species (e.g. lagomorphs) tend to avoid those C. humilis individuals that were most visited by their predators (e.g. red foxes). Also, the second step revealed temporal attraction between large wild and domestic frugivore ungulates (e.g. red deer, cows) and medium-sized frugivores (e.g. red foxes) suggesting that large mammals could facilitate the C. humilis and P. bourgaeana exploitation to other smaller frugivores by making fruits more easily accessible. Finally, our results allowed us to identify direct interaction pathways, that revealed how the mutualistic and antagonistic relations between animal associates derived into indirect effects on both plants seed dispersal success. For instance, we found that large-sized seed predators (e.g. ungulates) had a direct positive effect on the likelihood of visits by legitimate seed dispersers (e.g. red foxes) to both fleshy fruited plants. Then, seed predators showed an indirect positive effect on the plants' reproductive success. Our new analytical approach provides a widely applicable framework for further studies on multispecies interactions in different systems beyond plant-frugivore interactions, including plant-pollinator interactions, the exploitation of plants by herbivores, and the use of carcasses by vertebrate scavengers.

The fate of small-mammal carrion is affected by carcass size and visual conspicuousness in a Neotropical rainforest

Scavenging of carrion is essential to terrestrial ecosystems and can shape food webs and behavior. The prevalence and importance of scavenging has often been underestimated and overlooked in food web studies. Small-mammal carrion is even less studied and difficult to estimate, especially in the Neotropics. This project explored small-mammal carcass scavenging in a Neotropical, mid-elevation rainforest, and specifically studied the rate of carcass removal by scavengers, how the conspicuousness and weight of carcasses affect scavenging, and what vertebrate scavengers utilize this carrion resource. I deployed 194 mouse carcasses of various weights, above and below the leaf litter, and surveyed them daily until disappearance. I paired each carcass with a trail camera to help identify vertebrate scavengers. A general linear model analysis showed that most mouse carcasses disappeared within 1 to 2 days. Carcasses above the leaf litter were removed quicker and larger mice generally lasted longer. Only 6.25 % of the carcasses were removed by vertebrates. Most carcasses were removed by something too small to trigger the trail cameras, likely scarab beetles. The results of this study show that small-mammal carcasses are a sought-after resource in Neotropical forests, and that invertebrates are able to quickly hoard and secure small carrion more efficiently than vertebrate scavengers. A better understanding of scavenging ecology in Neotropical forests will help in developing a broader framework of the trophic interactions within and across ecosystems.

Response of vertebrate scavengers to power line and road rights-of-way and its implications for bird fatality estimates

Linear infrastructures, such as power lines and roads, are an important source of bird mortality. However, little is known on the potential effect of these infrastructures on local scavenger guilds, their foraging activity and the resulting bird carcass removal patterns. This is an important source of bias in studies aiming to quantify bird fatalities due to linear infrastructures. We used camera-traps to record scavenger identity and persistence patterns of bird carcasses placed close to linear infrastructure and nearby controls in two Mediterranean agricultural regions. We found that linear infrastructure influence on scavenger identity varied depending on the region. Contrary to expectations, linear infrastructure presence had either none or a positive effect on carcass persistence, meaning that carcasses placed within power line or road rights-of-way were not removed faster than the ones placed in controls. We conclude that linear infrastructure effect on vertebrate scavenging patterns is likely to be region-specific, and that reliable correction factors for carcass removal-bias in bird fatality estimates require site-specific experiments to characterize local scavenging processes.

Caching Behavior of Large Prey by Eurasian Lynx: Quantifying the Anti-Scavenging Benefits

Large solitary felids often kill large prey items that can provide multiple meals. However, being able to utilize these multiple meals requires that they can cache the meat in a manner that delays its discovery by vertebrate and invertebrate scavengers. Covering the kill with vegetation and snow is a commonly observed strategy among felids. This study investigates the utility of this strategy using observational data from Eurasian lynx (Lynx lynx)-killed roe deer (Capreolus capreolus) carcasses, and a set of two experiments focused on vertebrate and invertebrate scavengers, respectively. Lynx-killed roe deer that were covered by snow or vegetation were less likely to have been visited by scavengers. Experimentally-deployed video-monitored roe deer carcasses had significantly longer time prior to discovery by avian scavengers when covered with vegetation. Carcass parts placed in cages that excluded vertebrate scavengers had delayed invertebrate activity when covered with vegetation. All three datasets indicated that covering a kill was a successful caching/anti-scavenger strategy. These results can help explain why lynx functional responses reach plateaus at relatively low kill rates. The success of this anti-scavenging behavior therefore has clear effects on the dynamics of a predator–prey system.

Competition and Co-existence of Two Photorhabdus Symbionts with a Nematode Host

Photorhabdus spp. (Enterobacteriales: Morganellaceae) occur exclusively as symbionts of Heterorhabditis nematodes for which they provide numerous services, including killing insects and providing nutrition and defence within the cadavers. Unusually, two species (Photorhabdus cinerea and Photorhabdus temperata) associate with a single population of Heterorhabditis downesi at a dune grassland site. Building on previous work, we investigated competition between these two Photorhabdus species both at the regional (between insects) and local (within insect) level by trait comparison and co-culture experiments. There was no difference between the species with respect to supporting nematode reproduction and protection of cadavers against invertebrate scavengers, but P. cinerea was superior to P. temperata in several traits: faster growth rate, greater antibacterial and antifungal activity and colonisation of a higher proportion of nematodes in co-culture. Moreover, where both bacterial symbionts colonised single nematode infective juveniles, P. cinerea tended to dominate in numbers. Differences between Photorhabdus species were detected in the suite of secondary metabolites produced: P. temperata produced several compounds not produced by P. cinerea including anthraquinone pigments. Bioluminescence emitted by P. temperata also tended to be brighter than that from P. cinerea. Bioluminescence and pigmentation may protect cadavers against scavengers that rely on sight. We conclude that while P. cinerea may show greater local level (within-cadaver) competitive success, co-existence of the two Photorhabdus species in the spatially heterogeneous environment of the dunes is favoured by differing specialisations in defence of the cadaver against differing locally important threats.