Vertebrate Scavengers Research Articles

Large home range scavengers support higher rates of carcass removal

Abstract Vertebrate scavenger communities vary in species composition across the globe. They include a wide array of species with diverse ecological strategies and life histories that support essential ecosystem functions, such as carrion removal. While previous studies have mostly focussed on how community aspects such as species richness and composition affect carrion consumption rates, it remains unclear whether this important function of scavengers is better explained by the dominance of key functional traits or niche complementarity as a result of a diverse functional representation. Here, we test three competitive hypotheses to assess if carrion consumption in vertebrate scavenger communities depends on: (a) the presence of key dominant traits (functional identity hypothesis), (b) functional diversity that promotes niche complementarity (functional diversity hypothesis) or (c) the accumulation of individuals and species, irrespective of their trait representation (functional equivalence). To explore these hypotheses, we used five study areas in Spain and South Africa, which represent a gradient of scavenger biodiversity, that is, ranging from communities dominated by facultative scavengers, such as generalists and meso‐predators, to those including vultures and large carnivores. Within study areas, traits that characterize obligate scavengers or large carnivores (e.g. mean home range, proportion of social foragers) were positively linked to rapid carrion consumption, while the biomass of functional groups including facultative scavengers were either weakly or negatively associated with carrion consumption. When combining all study areas, higher rates of carrion consumption were related to scavenger communities dominated by species with large home ranges (e.g. Gyps vultures), which was found to be a key trait. In contrast, metrics describing functional diversity (functional dispersion) and functional equivalence (species richness and abundance) had lower predictive power in explaining carrion consumption patterns. Our data support the functional identity hypothesis as a better framework for explaining carrion consumption rates than functional diversity or equivalence. Our findings contribute to understanding the mechanisms sustaining ecosystem functioning in vertebrate communities and reinforce the role of obligate scavengers and large carnivores as keystone species in terrestrial ecosystems.

Preservation of latest Cretaceous (Maastrichtian)-Paleocene frogs (Eorubeta nevadensis) of the Sheep Pass Formation of east-central Nevada and implications for paleogeography of the Nevadaplano.

Here we report on exceptional preservation of remains of the frog Eorubeta nevadensis in deposits of the Sheep Pass Formation, ranging from Late Cretaceous to Eocene, in the south Egan Range, Nevada. This formation represents a lacustrine basin within the Sevier retroarc hinterland. The formation is subdivided into six members (A–F); of interest here are members B and C. The base of member B is ?uppermost Cretaceous-Paleocene, while member C is Paleocene. Member B frogs are preserved in three taphonomic modes. Mode 1 frogs are nearly complete and accumulated under attritional processes, with frogs settling on microbial mats, as evidenced by crenulated fabric of entombing limestone. Mode 2 involves accumulation of frogs as a result of attritional processes. These frogs are mostly complete with some showing evidence of invertebrate scavenging. Possible scavengers are gastropods, ostracods, and decapods. Mode 3 is represented by isolated, reworked remains of frogs as a result of storm activity, supported by the association of elements with disarticulated bivalves and mud rip-up clasts. Member C preserves frogs in two taphonomic modes. Mode 4 are nearly complete frogs that accumulated during discrete mass mortality events. Numerous individuals are preserved along bedding planes in identical preservational states. Mode 5 is beds of frog bone hash, which represent increased energy to the depositional system (likely tempestites) and reworking of previously buried frog remains. Taphonomy of the frogs, along with the associated fauna and flora, are consistent with preservation in a cool, temperate lake basin, supporting previous interpretations that the Nevadaplano was an elevated plateau during the late Cretaceous through the Eocene. This is a period of time coincident with a climatic thermal optimum, thus the most parsimonious explanation for a temperate lake at the latitude of east-central Nevada is to invoke high elevation, which is consistent with independent structural and clumped stable isotope studies.

Succession of bacterial communities on carrion is independent of vertebrate scavengers.

The decomposition of carrion is carried out by a suite of macro- and micro-organisms who interact with each other in a variety of ecological contexts. The ultimate result of carrion decomposition is the recycling of carbon and nutrients from the carrion back into the ecosystem. Exploring these ecological interactions among animals and microbes is a critical aspect of understanding the nutrient cycling of an ecosystem. Here we investigate the potential impacts that vertebrate scavenging may have on the microbial community of carrion. In this study, we placed seven juvenile domestic cow carcasses in the Grassy Mountain region of Utah, USA and collected tissue samples at periodic intervals. Using high-depth environmental sequencing of the 16S rRNA gene and camera trap data, we documented the microbial community shifts associated with decomposition and with vertebrate scavenger visitation. The remarkable scarcity of animals at our study site enabled us to examine natural carrion decomposition in the near absence of animal scavengers. Our results indicate that the microbial communities of carcasses that experienced large amounts of scavenging activity were not significantly different than those carcasses that observed very little scavenging activity. Rather, the microbial community shifts reflected changes in the stage of decomposition similar to other studies documenting the successional changes of carrion microbial communities. Our study suggests that microbial community succession on carrion follows consistent patterns that are largely unaffected by vertebrate scavenging.

Fine spatial-scale variation in scavenger activity influences avian mortality assessments on a boreal island.

Bird-window collisions are the second leading cause of human-related avian mortality for songbirds in Canada. Our ability to accurately estimate the number of fatalities caused by window collisions is affected by several biases, including the removal of carcasses by scavengers prior to those carcasses being detected during surveys. We investigated the role of scavenger behavior in modifying perceived carcass removal rate while describing habitat-specific differences for the scavengers present in a relatively scavenger-depauperate island ecosystem. We used motion activated cameras to monitor the fate of hatchling chicken carcasses placed at building (under both windows and windowless walls) and forest (open and closed canopy) sites in western Newfoundland, Canada. We recorded the identity of scavengers, timing of events, and frequency of repeat scavenging at sites. Using 2 treatments, we also assessed how scavenging varied with 2 levels of carcass availability (daily versus every third day). Scavenger activities differed substantially between forest and building sites. Only common ravens (Corvus corax) removed carcasses at building sites, with 25 of 26 removals occurring under windows. Burying beetles (Nicrophorus spp.) dominated scavenging at forest sites (14 of 18 removals), completely removing carcasses from sight in under 24 hours. Availability had no effect on removal rate. These findings suggest that ravens look for carcasses near building windows, where bird-window collision fatalities create predictable food sources, but that this learning preceded the study. Such behavior resulted in highly heterogeneous scavenging rates at fine spatial scales indicating the need for careful consideration of carcass and camera placement when monitoring scavenger activity. Our observations of burying beetle activity indicate that future studies investigating bird collision mortality near forested habitats and with infrequent surveys, should consider local invertebrate community composition during survey design. The high incidence of invertebrate scavenging may compensate for the reduced vertebrate scavenger community of insular Newfoundland.

Network structure of vertebrate scavenger assemblages at the global scale: drivers and ecosystem functioning implications

The organization of ecological assemblages has important implications for ecosystem functioning, but little is known about how scavenger communities organize at the global scale. Here, we test four hypotheses on the factors affecting the network structure of terrestrial vertebrate scavenger assemblages and its implications on ecosystem functioning. We expect scavenger assemblages to be more nested (i.e. structured): 1) in species‐rich and productive regions, as nestedness has been linked to high competition for carrion resources, and 2) regions with low human impact, because the most efficient carrion consumers that promote nestedness are large vertebrate scavengers, which are especially sensitive to human persecution. 3) We also expect climatic conditions to affect assemblage structure, because some scavenger assemblages have been shown to be more nested in colder months. Finally, 4) we expect more organized assemblages to be more efficient in the consumption of the resource. We first analyzed the relationship between the nestedness of the scavenger assemblages and climatic variables (i.e. temperature, precipitation, temperature variability and precipitation variability), ecosystem productivity and biomass (i.e. NDVI) and degree of human impact (i.e. human footprint) using 53 study sites in 22 countries across five continents. Then, we related structure (i.e. nestedness) with its function (i.e. carrion consumption rate). We found a more nested structure for scavenger assemblages in regions with higher NDVI values and lower human footprint. Moreover, more organized assemblages were more efficient in the consumption of carrion. However, our results did not support the prediction that the structure of the scavenger assemblages is directly related to climate. Our findings suggest that the nested structure of vertebrate scavenger assemblages affects its functionality and is driven by anthropogenic disturbance and ecosystem productivity worldwide. Disarray of scavenger assemblage structure by anthropogenic disturbance may lead to decreases in functionality of the terrestrial ecosystems via loss of key species and trophic facilitation processes.

Invasive European wasps alter scavenging dynamics around carrion

European wasps (Vespula germanica) have invaded parts of North and South America, Australia and New Zealand. They are opportunistic predators and scavengers that can disrupt food webs and species interactions, but their role in food webs associated with carrion is poorly understood. In this study we examined wasp abundance at 20 vertebrate carcasses in south-eastern Australia. We also collected data on the abundance of blowflies and the occurrence and behavior of vertebrate scavengers at the same carcasses. Wasps arrived within minutes of deploying fresh carcasses and were approximately 4.3 times more abundant in forest compared with grassland habitats. Wasps killed and mutilated native blowflies and may have prevented them from ovipositing on carcasses, as we subsequently found that these carcasses were devoid of fly larvae. European wasps also appeared to interfere with dingoes (Canis dingo) feeding on carcasses, based on observations from cameras showing dingoes snapping their heads in the air and then retreating from the carcasses suddenly. The other major vertebrate scavenger in the system, feral pigs (Sus scrofa), did not show similar behavioral responses. Although we observed European wasps feeding on carcasses, carcass mass loss was slow. This could be a direct result of European wasps suppressing flies and potentially excluding dingoes from accessing carcasses. We conclude that European wasps may alter the way energy flows through scavenging food webs, which could have cascading impacts on ecosystem dynamics and services, although manipulative experiments would help to further evaluate these possibilities.

Effect of mammalian mesopredator exclusion on vertebrate scavenging communities

Carrion is a valuable resource used by facultative scavengers across the globe. Due to conflicts with humans, many vertebrate scavengers have experienced population declines due to direct persecution or indirect effects of human activities. However, little is known about the implications of altered scavenger community composition on the fate and efficiency of carrion removal within ecosystems. In particular, mammalian mesopredators are efficient scavengers that are often subjected to control, thus, it is important to understand how the reduction of this scavenger guild influences the fate of carrion resources and efficiency of carrion removal within ecosystems. We evaluated the influence of the absence of mammalian mesopredators on vertebrate scavenging dynamics by comparing the efficiency of carrion removal and species composition at carrion between sites where we experimentally manipulated mesopredator abundance and paired control sites. Overall scavenging rates were high, even within our mesopredator exclusion sites (79% of carcasses). Despite the exclusion of an entire guild of dominant scavengers, we saw little effect on scavenging dynamics due to the extensive acquisition of carrion by avian scavengers. However, we observed a slight reduction in vertebrate scavenging efficiency in sites where mesopredators were excluded. Our results suggest vertebrate communities are highly efficient at carrion removal, as we saw a functional response by avian scavengers to increased carrion availability. These data provide insights into the impact of mesopredator control on food web dynamics, and build upon the growing body of knowledge investigating the role of vertebrate scavengers on ecosystem services provided through carrion removal.

The effect of clothing on decomposition and vertebrate scavengers in cooler months of the temperate southwestern Cape, South Africa

With research providing conflicting results from different habitats across the globe, the effect of clothing on decomposition is unclear; some studies indicate clothing increases decomposition rate by facilitating increased insect activity, and others conclude clothing prolongs the decay process. In South Africa, such research is lacking, with no data for the Western Cape Province, which suffers from a high murder rate with many unclaimed, unidentified bodies. Improving post-mortem interval (PMI) estimates will increase chances of correct forensic identification of decedents by narrowing the search window for police. Since no current PMI estimation method accounts for the possible influence of clothing, this study was designed to examine the effect of seasonally appropriate common clothing on decomposition rate in the thicketed Cape Flats Dune Strandveld, Cape Town, a forensically significant region. Four ∼60 kg domestic pig carcasses (Sus scrofa domesticus) were used as proxies for human decomposition, two were clothed and two unclothed. The clothing, altered by a seamstress to ensure an appropriate fit, caused a notable decrease in decay rate in this initial sample. Daily weight loss was used as a quantitative measure of decomposition progression, as the clothing prevented the use of visual decomposition scoring systems. Weight loss was closely associated with scavenging activity by the Cape grey mongoose (Galerella pulverulenta), with a clear scavenger preference for unclothed carcasses. This suggests that the effect of clothing on decomposition may be better assessed in this environment by examining how scavengers interact with only a single clothed carcass.

Seasonal Difference in Carcass Persistence Rates at Wind Farms with Snow, Hokkaido, Japan

Carcass persistence rates strongly affect estimation of avian fatalities resulting from collisions with wind turbines. Our aim was to compare bird carcass persistence rates based on trials during different seasons at wind farms where the ground was snow covered in winter. Carcass persistence was found to be considerably shorter during late winter than during summer/autumn, and was considered to result from food shortages for terrestrial vertebrate scavengers during winter, and the higher visibility of carcasses resting on snow-covered ground in late winter. It is critical to represent carcass persistence rates in different seasons at wind farms.

Vertebrate scavenger guild composition and utilization of carrion in an East Asian temperate forest.

Scavenging is a common feeding behavior by many species that plays an important role in ecosystem stability and function while also providing ecosystem services. Despite its importance, facultative scavenging on large animal carcasses has generally been overlooked in Asian temperate forest ecosystems. The aim of this study was to determine the composition and feeding behavior of the facultative scavenger guild as it relates to sika deer (Cervus nippon) carcasses in Japanese forests. There are no obligate scavengers or large predators that kill adult ungulates, but humans fill the role of large predators by culling deer for population management. We documented nine vertebrate species scavenging on deer carcasses and found that mammals were more frequent scavengers than birds and also fed for longer durations. This result suggests that there is a facultative scavenger guild composed mainly of mammals in our forest ecosystem and that carcass utilization by birds was restricted to only forest species. Raccoon dogs (Nyctereutes procyonoides) and Asian black bears (Ursus thibetanus) were the most frequent scavenger species and also fed for longer durations than other scavengers. There were significant seasonal differences in scavenging by Asian black bear, Japanese marten (Martes melampus), and mountain hawk‐eagle (Nisaetus nipalensis), suggesting the availability of other food resources may alter facultative scavenging by each species. Our results support that scavenging is widespread in this system and likely has important functions including building links in the food web.

Vertebrate Scavengers Control Abundance of Diarrhea-causing Bacteria in Tropical Plantations.

Scavenging is a common phenomenon, particularly amongst carnivorous vertebrates. By consuming carrion, vertebrate scavengers reduce resource availability for both pathogenic bacteria and their insect vectors. We investigated the ability of wild vertebrate scavengers to control agents of human diarrheal diseases (specifically Salmonella spp. and Shiga toxin-producing Escherichia coli [STEC]) in oil palm plantations in Sabah (East Malaysia), and the existence of spillover effect whereby additional vertebrate scavengers from adjacent forest patches result in greater disease control in plantation sections near these forest edges. Experimental carcasses were removed by common scavengers (Varanus salvator, Canis lupus familiaris, and Viverra tangalunga) at different time points, and this determined the length of time that the carcasses persisted in the environment. The amount of pathogenic bacteria on the surfaces of filth flies collected above the experimental carcasses was positively correlated to the duration of carcass persistence, and reduction in pathogenic bacterial abundances was largely due to carcass consumption by these vertebrate scavengers. Instead of a predicted positive spillover effect (greater scavenger activity near forest edges, hence reduced pathogen abundance), we detected a weak inverse spillover effect in which STEC counts were marginally higher in plantation sections near forest patches, and human hunting along the forest-plantation boundaries could explain this. We propose that making oil palm plantations scavenger-friendly could yield great human health benefits for the millions of workers employed in this rapidly-expanding industry, without drastically changing current management practices.

Integrative microbial-zoological assessment of the postmortem period in forensic medical examination

Is a complex microbial-zoological characterization of the post-mortal period and ways of its determination during forensic examination. The heterotrophic component of the microflora of the corpse and its bed were studied using standard methods of microbiological research and PCR analysis, necrophilic insects - entomological method, and damages from some vertebrate animals - traditional methods of their analysis. We studied 125 corpses of humans, pigs, chickens, mice and some other representatives of mammal class weighing from 100 g to 100 kg at different times of decomposition. We isolated and studied more than 1000 isolates of microorganisms, more than 32 000 insects and more than 100 damages caused by rodents, dogs, cats and birds. We determined the main trends in microbial decomposition of dead bodies. The general characteristics of the corpse decomposition by insects are given and anatomical-topographical and morphological features of the corpse damage by some vertebrates are established. Significant The heterotrophic component of the microflora of the corpse and its bed were studied using standard methods of microbiological research and PCR analysis, necrophilic insects - entomological method, and damages from some vertebrate animals - traditional methods of their analysis. We studied 125 corpses of humans, pigs, chickens, mice and some other representatives of mammal class weighing from 100 g to 100 kg at different times of decomposition. We isolated and studied more than 1000 isolates of microorganisms, more than 32 000 insects and more than 100 damages caused by rodents, dogs, cats and birds. We determined the main trends in microbial decomposition of dead bodies. The general characteristics of the corpse decomposition by insects are given and anatomical-topographical and morphological features of the corpse damage by some vertebrates are established. Significant microbial and zoological characteristics of the post-mortem period have been identified, and ways of its establishment have been determined and confirmed by practical testing during forensic examination. A set of practical recommendations has been developed for forensic experts on the collection of necrophilous insects during the examination of the corpse at the scene and the tactics of the examination with the involvement of entomologists. The results obtained prove that there is a close correlation between the impact of vertebrate scavengers, necrophilic insects and the enzymatic activity of a specific community of heterotrophic microorganisms on the corpse.

Rewilding traditional grazing areas affects scavenger assemblages and carcass consumption patterns

The abandonment of traditional livestock farming systems in Mediterranean countries is triggering a large-scale habitat transformation, which, in general, consists of the replacement of open grazing areas by woodlands through non-managed regeneration. As a consequence, wild ungulates are occupying rapidly the empty niche left by domestic ungulates. Both types of ungulates represent the main trophic resource for large vertebrate scavengers. However, a comparison of how vertebrate scavengers consume ungulate carcasses in different habitats with different ungulate species composition is lacking. This knowledge is essential to forecast the possible consequences of the current farmland abandonment on scavenger species. Here, we compared the scavenging patterns of 24 wild and 24 domestic ungulate carcasses in a mountainous region of southern Spain monitored through camera trapping. Our results show that carcasses of domestic ungulates, which concentrate in large numbers in open pasturelands, were detected and consumed earlier than those of wild ungulate carcasses, which frequently occur in much lower densities at more heterogenous habitats such as shrublands and forest. Richness and abundance of scavengers were also higher at domestic ungulate carcasses in open habitats. Vultures, mainly griffons (Gyps fulvus), consumed most of the carcasses, although mammalian facultative scavengers, mainly wild boar (Sus scrofa) and red fox (Vulpes vulpes), also contributed importantly to the consumption of wild ungulate carcasses in areas with higher vegetation cover. Our findings evidence that the abandonment of traditional grazing may entail consequences for the scavenger community, which should be considered by ecologists and wildlife managers.

Nestling carcasses from colonially breeding wading birds: patterns of access and energetic relevance for a vertebrate scavenger community

Energy transfer is fundamental to ecosystem processes, affecting productivity and community structure. Large aggregations of colonially breeding birds are known as nutrient sources through deposition of feces, but also may deposit large quantities of energy in the form of dead nestlings. The magnitude and ecological relevance of this process to the scavenger community is poorly understood. We used trail cameras to monitor the fates of size-appropriate chicken carcasses in heron colonies in order to quantify the proportion of available fallen nestlings that were consumed by scavengers in the Everglades of Florida, USA. Overall, 85% of 160 carcasses were consumed, with Turkey Vultures (Cathartes aura, 47%) and American Alligators (Alligator mississippiensis, 29%) being the primary consumers. Probability of consumption by alligators or vultures was related to distance from nest to water, local nesting density, and colony type. Consumption probabilities of both scavengers in relation to habitat covariates suggested clear resource partitioning promoting coexistence. We estimate fallen nestlings throughout this ecosystem could support 16% of the alligator population and 147 adult Turkey Vultures during a nesting season. This work indicates that fallen nestlings can serve as an important source of energy for scavengers at colonial breeding aggregations, particularly in oligotrophic systems.

Key Ecological Function Peaks at the Land–Ocean Transition Zone When Vertebrate Scavengers Concentrate on Ocean Beaches

Ecotones can form hot spots of biodiversity by containing species from multiple ecosystems. Because biodiversity is often linked to ecological function, we posit that rates of key ecological functions are highest at ecotones and decline away from them. Here we test this hypothesis by measuring spatial decays in the function of carrion scavenging on a gradient ranging from ocean beaches upland into abutting coastal dunes. A large field experiment in Eastern Australia, at the ecotone formed by ocean beaches, employed multiple carrion placements and motion-triggered cameras to identify the animals consuming carcasses and the removal rates of necromass. Significantly more carrion was consumed by vertebrate scavengers at the beach interface (50–80% of total necromass removed) and declined significantly with distance (max. 350 m) into the abutting coastal dunes (20–25%). This marked cline was due to the consumption of carrion by both dune-dwelling and beach-dwelling animals at the beach–dune interface and a decline in scavenging activity by both groups farther upland. These spatial effects were consistent between sites, but the lower carrion removal away from the beach became less pronounced as the carcasses putrefied, suggesting that microbial actions can modify carrion suitability for vertebrate scavengers and hence change spatial patterns in ecological function. Our findings provide quantitative support for the widespread notion that ecological transition zones are hot spots of ecological functions and highlight the importance of managing functionally important species at ecotones.

Avoidance of carnivore carcasses by vertebrate scavengers enables colonization by a diverse community of carrion insects.

Carrion resources sustain a complex and diverse community of both vertebrate and invertebrate scavengers, either obligate or facultative. However, although carrion ecology has received increasing scientific attention in recent years, our understanding of carrion partitioning in natural conditions is severely limited as most studies are restricted either to the vertebrate or the insect scavenger communities. Moreover, carnivore carcasses have been traditionally neglected as study model. Here, we provide the first data on the partitioning between vertebrate and invertebrate scavengers of medium-sized carnivore carcasses, red fox (Vulpes vulpes (Linnaeus)), in two mountainous Mediterranean areas of south-eastern Spain. Carcasses were visited by several mammalian and avian scavengers, but only one carcass was partially consumed by golden eagle Aquila chrysaetos (Linnaeus). These results provide additional support to the carnivore carrion-avoidance hypothesis, which suggests that mammalian carnivores avoid the consumption of carnivore carcasses to prevent disease transmission risk. In turn, the absence of vertebrate scavengers at carnivore carcasses enabled a diverse and well-structured successional community of insects to colonise the carcasses. The observed richness and abundance of the most frequent families was more influenced by the decomposition time than by the study area. Overall, our study encourages further research on carrion resource partitioning in natural conditions.

Scavenging in the Anthropocene: Human impact drives vertebrate scavenger species richness at a global scale

Understanding the distribution of biodiversity across the Earth is one of the most challenging questions in biology. Much research has been directed at explaining the species latitudinal pattern showing that communities are richer in tropical areas; however, despite decades of research, a general consensus has not yet emerged. In addition, global biodiversity patterns are being rapidly altered by human activities. Here, we aim to describe large-scale patterns of species richness and diversity in terrestrial vertebrate scavenger (carrion-consuming) assemblages, which provide key ecosystem functions and services. We used a worldwide dataset comprising 43 sites, where vertebrate scavenger assemblages were identified using 2,485 carcasses monitored between 1991 and 2018. First, we evaluated how scavenger richness (number of species) and diversity (Shannon diversity index) varied among seasons (cold vs. warm, wet vs. dry). Then, we studied the potential effects of human impact and a set of macroecological variables related to climatic conditions on the scavenger assemblages. Vertebrate scavenger richness ranged from species-poor to species rich assemblages (4-30 species). Both scavenger richness and diversity also showed some seasonal variation. However, in general, climatic variables did not drive latitudinal patterns, as scavenger richness and diversity were not affected by temperature or rainfall. Rainfall seasonality slightly increased the number of species in the community, but its effect was weak. Instead, the human impact index included in our study was the main predictor of scavenger richness. Scavenger assemblages in highly human-impacted areas sustained the smallest number of scavenger species, suggesting human activity may be overriding other macroecological processes in shaping scavenger communities. Our results highlight the effect of human impact at a global scale. As species-rich assemblages tend to be more functional, we warn about possible reductions in ecosystem functions and the services provided by scavengers in human-dominated landscapes in the Anthropocene.

Do scavengers prevent or promote disease transmission? The effect of invertebrate scavenging on Ranavirus transmission

Abstract Host–parasite interactions are shaped by the broader web of community interactions, from interspecific competition to predator–prey dynamics. Heterospecific scavengers might also affect parasite transmission from infectious carcasses, which can be an important source of infections for some wildlife diseases. A robust scavenger community can quickly remove carcasses and tissue and thus prevent secondary transmission by necrophagy or contact with infectious carcasses. Alternatively, by spreading infectious particles and tissues throughout the environment, scavengers may increase rates of casual contact with pathogens and thus overall transmission. However, there has been little empirical consideration of the contrasting roles that scavengers might play in infectious disease dynamics. We carried out a series of studies to determine the efficiency with which scavenging invertebrates remove carcasses of Long‐toed Salamander (Ambystoma macrodactylum) larvae and their role in the transmission of frog virus 3 (Genus: Ranavirus, Family: Iridoviridae) from carcasses. We then estimated the functional response of one efficient invertebrate scavenger (Family: Dytiscidae) to increasing carcass densities in field conditions in order to determine the capacity of scavenging invertebrates to consume large amounts of carcass tissue, as may be present at high prevalence sites. We found that removal of infectious carcasses by scavengers strongly reduced transmission to naïve larvae. Scavengers were as effective at reducing transmission from a carcass as a physical barrier preventing contact with the carcass. There was little evidence that scavenging released sufficient infectious tissues into the water column to rival direct contact as a route of infection. Moreover, while scavenging rates saturated at increasing carcass densities, consistent with a type II functional response, there were sufficient densities of dytiscid larvae, not to mention other scavenging invertebrates, in a surveyed pond to theoretically prevent transmission from carcasses. Our results suggest that at least in systems in which conspecific necrophagy is common, the scavenger community can play an important role in reducing transmission. A plain language summary is available for this article.

Vertebrate Scavenger Species Composition on Nantucket Island, Massachusetts and Implications for Nicrophorus americanus Olivier (American Burying Beetle) Reintroduction

We surveyed scavenger species on Nantucket Island, MA, using motion-activated wildlife cameras baited with carcasses of either a Mus musculus domesticus (House Mouse) or Colinus virginianus (Bobwhite Quail) in the summer of 2016. We aimed to identify vertebrate scavenger species, measure how long carcasses remained available, and examine differences in carrion consumption between grassland and shrubland vegetation types. This information is important for management decisions concerning a reintroduced population of a federally endangered obligate scavenger, Nicrophorus americanus (American Burying Beetle), on Nantucket Island. Carcasses were removed or consumed within 2.7 ± 1.8 d, and vertebrates removed the carcass in 74% of trials. Carcasses persisted for similar lengths of time between the 2 vegetation types, but avian scavengers were significantly more common on Bobwhite Quail carcasses in grassland, and mammalian scavengers were significantly more common on House Mouse carcasses in shrubland habitats. Avian species appear to be significant competitors for carrion appropriate for American Burying Beetle reproduction.

Bacteria defend carrion from scavengers

AbstractCarrion in the form of dead seal pups and algal mats placed on soft bottom habitats at Explorers Cove and Salmon Bay, McMurdo Sound, attract scavenging invertebrates that are driven away by hydrogen sulphide produced by sulphate-reducing bacteria sequestered below a layer of Beggiatoa/Thioploca-like filamentous bacteria. This system is usually found for lipid-rich marine mammal carrion, but also occurred with natural algal mats.