Food searching in griffon vultures

Observations are presented on food searching in griffon vultures. To locate food directly, griffon vultures do not use a sense of smell but rely on vision. However, most birds locate carcasses indirectly—by watching the activities of neighbouring birds. The method of food searching is described and the number of birds which arrive at a carcass is shown to depend on the amount of food that is available. Birds do not hold feeding ranges, but travel widely during food searching, one bird travelling 180 km in 6 days. The density of searching birds varies greatly according to the density of ungulates in an area, birds being most numerous over high ungulate concentrations. The altitude at which birds search also varies, birds flying at higher altitudes over areas of low ungulate density and at lower altitudes over ungulate concentrations. These variations in searching density and height are shown to affect the efficiency of food searching. Carcasses are located rapidly and the food consumed quickly in high ungulate density areas, while in low ungulate density conditions carcasses can take a long time to be located. It is concluded that griffon vultures are more likely to find food and are better able to compete with mammalian competitors by searching over migratory ungulate herds than over areas containing resident ungulate species. Their adaptations for gliding flight enable these birds to follow these migratory ungulates throughout the year.     

Rate of decline of the Oriental white-backed vulture population in India estimated from a survey of diclofenac residues in carcasses of ungulates

The non-steroidal anti-inflammatory drug diclofenac is a major cause of the rapid declines in the Indian subcontinent of three species of vultures endemic to South Asia. The drug causes kidney failure and death in vultures. Exposure probably arises through vultures feeding on carcasses of domesticated ungulates treated with the drug. However, before the study reported here, it had not been established from field surveys of ungulate carcasses that a sufficient proportion was contaminated to cause the observed declines. We surveyed diclofenac concentrations in samples of liver from carcasses of domesticated ungulates in India in 2004-2005. We estimated the concentration of diclofenac in tissues available to vultures, relative to that in liver, and the proportion of vultures killed after feeding on a carcass with a known level of contamination. We assessed the impact of this mortality on vulture population trend with a population model. We expected levels of diclofenac found in ungulate carcasses in 2004-2005 to cause oriental white-backed vulture population declines of 80-99% per year, depending upon the assumptions used in the model. This compares with an observed rate of decline, from road transect counts, of 48% per year in 2000-2003. The precision of the estimate based upon carcass surveys is low and the two types of estimate were not significantly different. Our analyses indicate that the level of diclofenac contamination found in carcasses of domesticated ungulates in 2004-2005 was sufficient to account for the observed rapid decline of the oriental white-backed vulture in India. The methods we describe could be used again to assess changes in the effect on vulture population trend of diclofenac and similar drugs. In this way, the effectiveness of the recent ban in India on the manufacture and importation of diclofenac for veterinary use could be monitored.     

Patterns of scavenger arrival at cheetah kills in Serengeti National Park Tanzania

Scavenging by large‐bodied vertebrates is observed in many ecosystems but has rarely been quantified. Here we document the timing and order of scavenger arrival at 639 cheetah kills in Serengeti National Park, Tanzania, focusing on ecological and heterospecific factors that may impact detectability of carcasses. We found that small‐, medium‐ and large‐sized vultures, jackals, spotted hyaenas and lions were more likely to be present at the carcasses of large‐bodied than small‐bodied prey. Lions and spotted hyaenas were less likely to locate kills in tall grass; medium‐sized vultures were likely to arrive before both large‐ and small‐sized vultures. Spotted hyaenas and vultures were likely to be present at kills simultaneously. Despite numerous anecdotal accounts, we did not find that hyaenas use alighting vultures as a means of locating food. Our findings show that environmental variables and other scavenger species strongly influence scavenger arrival at carcasses in this ecosystem.     

Toxicity of non-steroidal anti-inflammatory drugs to Gyps vultures: a new threat from ketoprofen

Three Gyps vulture species are on the brink of extinction in South Asia owing to the veterinary non-steroidal anti-inflammatory drug (NSAID) diclofenac. Carcasses of domesticated ungulates are the main food source for Asia''s vultures and birds die from kidney failure after consuming diclofenac-contaminated tissues. Here, we report on the safety testing of the NSAID ketoprofen, which was not reported to cause mortality in clinical treatment of scavenging birds and is rapidly eliminated from livestock tissues. Safety testing was undertaken using captive non-releasable Cape griffon vultures (Gyps coprotheres) and wild-caught African white-backed vultures (G. africanus), both previously identified as susceptible to diclofenac and suitable surrogates. Ketoprofen doses ranged from 0.5 to 5 mg kg⁻¹ vulture body weight, based upon recommended veterinary guidelines and maximum levels of exposure for wild vultures (estimated as 1.54 mg kg⁻¹). Doses were administered by oral gavage or through feeding tissues from cattle dosed with ketoprofen at 6 mg kg⁻¹ cattle body weight, before slaughter. Mortalities occurred at dose levels of 1.5 and 5 mg kg⁻¹ vulture body weight (within the range recommended for clinical treatment) with the same clinical signs as observed for diclofenac. Surveys of livestock carcasses in India indicate that toxic levels of residual ketoprofen are already present in vulture food supplies. Consequently, we strongly recommend that ketoprofen is not used for veterinary treatment of livestock in Asia and in other regions of the world where vultures access livestock carcasses. The only alternative to diclofenac that should be promoted as safe for vultures is the NSAID meloxicam.     

A change in the breeding season of Rüppell's Griffon Vultures Gyps rueppellii in the Serengeti in response to changes in ungulate populations

Breeding by Rüppell's Griffon Vultures Gyps rueppellii is synchronized but the time of breeding of colonies in the Serengeti region of Tanzania has changed by 5 months over the period between 1969–1970 and 1985. During this interval there have been considerable changes in the ungulate populations within the feeding range of the vultures, resulting in an increase to the food supply available to the birds. It is suggested that this species may have two alternative breeding seasons, the selective value of each depending on the magnitude of the food supply.     

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.     

A dead giveaway: Foraging vultures and other avian scavengers respond to auditory cues

Carrion represents an unpredictable and widely distributed primary food source for vultures and other avian scavengers. Avian scavengers in African savanna ecosystems are reported to rely exclusively on visual stimuli to locate carcasses. However, carnivores’ predation of large mammalian herbivores and subsequent competition for access to the carcass can result in considerable noise, often audible over long distances and for prolonged periods. Vultures and other avian scavengers may therefore detect and respond to these auditory cues, as do the mammalian carnivores alongside which vultures have coevolved, but this has not been investigated to date. Working in the Serengeti ecosystem, Tanzania, we used diurnal auditory broadcasts to simulate predation and competitive carnivore feeding interactions. Based on the current understanding of avian scavenger ecology, we hypothesized that avian responses to call‐in stations would be evoked exclusively by visual, rather than auditory, cues. We therefore predicted that (a) the arrival of avian scavengers at call‐in stations should be preceded and facilitated by mammalian carnivores and that (b) the arrival of avian scavengers would be positively correlated with the number of mammalian scavengers present, which would increase detectability. We recorded 482 birds during 122 separate playback events. In 22% of these instances, avian scavengers arrived first, ruling out responses based exclusively on visual observations of mammalian carnivores, thereby contradicting our first prediction. Furthermore, the first avian arrivals at survey sessions were inversely related to the number of hyenas and jackals present, contradicting our second prediction. Since no bait or carcasses were used during the experiments, these responses are indicative of the birds’ ability to detect and respond to audio stimuli. Our findings challenge the current consensus of sensory perception and foraging in these species and provide evidence that avian scavengers have the ability to use sound to locate food resources.     

Foraging movements of Eurasian griffon vultures (Gyps fulvus): implications for supplementary feeding management

The outbreak of bovine spongiform encephalopathy provoked restrictive European sanitary legislation that forced farmers to remove livestock carcasses from the wild. This had serious repercussions for the scavenger raptor guild. Against this background, we developed a study to analyse the foraging movements of Eurasian griffon vultures (Gyps fulvus) in northern Spain. We ringed 241 griffon vultures with alphanumeric plastic rings in Biscay between 2000 and 2011 and set experimental feeding stations in 24 sites over an area of 10,614 km²; recording re-sightings of the ringed vultures between 2005 and 2012. Using these re-sighting records, we tested whether birds randomly moved long distances whilst searching for food, or if vulture re-sightings were restricted to a few feeding sites within a limited area. We summarised 329 field-work days, with an average of 2.06 ringed vultures re-sighted per day, accounting for 1,017 re-sightings. Adult vultures were detected in three separate foraging nuclei within the study area. Movements out of the main foraging nuclei were statistically less frequent than would be expected if adult vultures accessed all resources at a similar rate. Once established at breeding areas, subadult vultures behaved in the same way as adults. Our results suggest that vultures’ home ranges are largely restricted to zones close to breeding areas. This has important consequences from a conservation point of view, suggesting that management decisions should take into consideration spatial scale effects.     

Bone crushing carnivores and their significance to osteodystrophy in griffon vulture chicks

The natural removal of 89 ungulate carcasses by predators and scavengers was monitored in various wildlife reserves and ranching areas of South Africa. Carnivores responsible for the bone remains were determined. Spotted hyaenas and, to a lesser extent, Brown hyaenas, were the only carnivores that regularly chewed bones. When hyaenas were absent, months of weathering were required before the smaller bones became disarticulated and able to be removed by vultures. The bone-collecting behaviour and related aspects of breeding of two species of griffon vulture were studied at five different nesting colonies in southern Africa—one Cape vulture colony and one White-backed vulture colony in or near wildlife reserves, as well as two Cape vulture colonies and one White-backed vulture colony in ranching land. A total of 2825 bones was found in or below the vulture nests. These bones were categorized and measured. Hyaena-produced bone fragments were found only in the colonies in the wild areas—none of the 387 chicks examined here had osteodystrophy (metabolic bone disease). By contrast, in the ranching areas, vultures collected larger and less fragmented bones. Many Cape vulture chicks had osteodystrophy (130 of 1917 examined), as did two White-backed vulture chicks (of 196 examined). In 1977, artificial feeding stations, 'restaurants' where carcass skeletons were crushed, were established for Cape vultures. Since then, the incidence of osteodystrophy has declined from 17% to 2–5% in 1983. It is clear that bone fragments are an essential dietary requirement, providing calcium for correct skeletal growth of griffon vulture chicks.     

Changing vulnerability to predation related to season and sex in an African ungulate assemblage

The consequences of predation for prey population dynamics depend on the extent to which this mortality is predisposed by malnutrition or senescence, or additive in the sense that animals that would otherwise not have died at that time were killed. In places lacking effective predators, few adult ungulates die during the summer or wet season months when food is plentifully available. Hence the seasonal distribution of predator kills as well as the age and sex classes of the prey indicates the extent to which malnutrition contributes to mortality as well as other influences on vulnerability. Using records of animal deaths assembled over 35 years in South Africa's Kruger National Park, these patterns were investigated for 12 ungulate species forming the prey of lions, and for three other large predators with respect to one prey species. Buffalo, kudu and giraffe were more strongly represented in kills made during the late dry season, while wildebeest and zebra made relatively greater contributions during the wet season. Impala, waterbuck, warthog and rarer antelope species became more prominent in kills during transitional periods between seasons. Five prey species showed an elevation in representation of males in lion kills during the mating season, as well as impala for all predator species. Females were more prominently represented in kills during the time of late gestation and parturition for three prey species. Hence reproductive activities as well as changing vegetation cover and food resources affected vulnerability to predation. Shifts in susceptibility to predation over the seasonal cycle corresponded with rainfall‐related variation in the annual representation of these ungulate species in lion kills. The availability of vulnerable prey species, age and sex classes at different stages of the seasonal cycle helps maintain a high abundance of lions. These factors contribute to the strong additive impact that predation has had on the abundance of some of these ungulate populations.     

Dietary shifts in two vultures after the demise of supplementary feeding stations: consequences of the EU sanitary legislation

Among vertebrates, specialization in scavenging has appeared only in “true” Gyps vultures, which usually base their diet almost exclusively on carcasses of medium and large-sized mammals, whereas all other scavengers rely on broader ranges of prey. The availability of food for scavengers in Western Europe has not been limited during recent decades permitting the existence and growth of huge vulture populations. From 2000 onwards, however, EU sanitary legislation has progressively limited the abandonment of dead animals in the field resulting in a sudden reduction of food availability with unknown ecological and conservation consequences. Here, we examine the dietary response of a tandem of carrion eaters, the griffon vulture (Gyps fulvus) and the Egyptian vulture (Neophron percnopterus), showing different degrees of dietary specialization. Our results showed that after the reduction in numbers of supplementary feeding stations (vulture restaurants) the niche breadth of the griffon vulture has broadened and now includes significant amounts of wild rabbits (Oryctolagus cuniculus) and garbage. The diet of the Egyptian vulture, on the contrary, did not vary substantially. The diet overlap showed patterns probably conditioned by interspecific competition and the progressive exploitation of unpredictable carcasses. On a short-term scale, consequences for smaller scavengers could be negative due to the monopolization of resources by the dominant and much more abundant griffon vulture, however in the long-term all guild species would benefit from the exploitation of unpredictable carcasses, which could enhance the possibilities of coexistence.     

A seasonal feast: long-term analysis of feeding behaviour in the spotted hyaena (Crocuta crocuta)

The feeding behaviour of the Talek clan of spotted hyaenas in the Masai Mara National Reserve, Kenya, was monitored continuously for 7 years. Talek hyaenas adapted to large temporal variations in prey abundance by being opportunistic predators. During the first half of the year, the hyaenas fed on resident ungulates, and their diet consisted mainly of topi and Thomson's gazelles. Upon arrival of the migratory herds of wildebeest and zebra from the Serengeti, Talek hyaenas switched to feeding on the wildebeest which provided them with a superabundance of food for about 3 months. After the migratory animals returned to the Serengeti, Talek hyaenas experienced a period of reduced prey abundance due to the temporary dispersion of resident ungulates. At this time hyaenas hunted the few remaining wildebeest, and also increased their use of the remaining resident animals. Although Talek hyaenas were generally opportunistic in their feeding behaviour, they did exhibit clear dietary preference for larger prey species, particularly wildebeest. Finally, carrion comprised only 5% of the biomass consumed by Talek hyaenas, the lowest proportion of carrion in the diet of any Crocuta population studied to date.     

Temporal resource partitioning mediates vertebrate coexistence at carcasses: The role of competitive and facilitative interactions

Unravelling how biodiversity is maintained despite species competition for shared resources has been a central question in community ecology, and is gaining relevance amidst the current biodiversity crisis. Yet, we have still a poor understanding of the mechanisms that regulate species coexistence and shape the structure of assemblages in highly competitive environments such as carrion pulsed resources. Here, we study how large vertebrates coexist in scavenger assemblages by adapting their diel activity at large ungulate carcasses in NW Spain. We used camera traps to record vertebrate scavengers consuming 34 carcasses of livestock and hunted wild ungulates, which allowed us to assess also differences regarding carcass origin. To evaluate temporal resource partition among species, we estimated the overlap of diel activity patterns and the mean times of each scavenger at carcasses. We recorded 16 species of scavengers, 7 mammals and 9 birds, and found similar richness at both types of carcasses. Birds and mammals showed contrasting diel activity patterns, with birds using carcasses during daytime (mean= 11:38 h) and mammals mostly at night (23:09 h). The unimodal activity patterns of scavengers showed asynchronous peaks among species. Subordinate species modified their activity patterns at carcasses used by apex species to reduce temporal overlap. Also, diel activity patterns of vultures closely followed those of corvids, suggesting facilitation processes in which corvids would enhance carcass detection by vultures. Two mammal species (12.5%) increased nocturnality at carcasses of hunted ungulates, which could be a response to human disturbance. Our results suggest that both temporal segregation and coupling mediate the coexistence of large vertebrates at carcasses. These mechanisms might lead to richer scavenger assemblages and thereby more efficient ones in driving critical ecosystem functions related to carrion consumption, such as energy and nutrient recycling and biodiversity maintenance.     

The cost of migratory prey: seasonal changes in semi‐domestic reindeer distribution influences breeding success of Eurasian lynx in northern Norway

Migratory prey is a widespread phenomenon that has implications for predator–prey interactions. By creating large temporal variation in resource availability between seasons it becomes challenging for carnivores to secure a regular year‐round supply of food. Some predators may respond by following their migratory prey, however, most predators are sedentary and experience strong seasonal variation in resource availability. Increased predation on alternative prey may dampen such seasonal resource fluctuations, but reduced reproduction rates in predators is a predicted consequence of migratory primary prey behavior that has received little empirical attention. We used data from 23 GPS collared Eurasian lynx Lynx lynx monitored during 2007–2013 in northern Norway, to examine how spatio‐temporal variation in the migratory behavior of semi‐domestic reindeer Rangifer tarandus influences lynx spatial organization and reproductive success using estimates of seasonal home range overlap and breeding success. We found that lynx of both sexes maintained seasonally stable home ranges and exhibited site fidelity across years, independent of whether they had access to reindeer throughout the year or experienced a scarcity of reindeer in winter due to migration. However, lynx without access to reindeer in winter showed a decreased probability of reproducing and a tendency for lowered kitten survival into their first winter, when compared to female lynx with reindeer available year around. This supports the hypothesis that sedentary predators experience demographic costs in systems with migratory primary prey. Changes in the migratory behavior of ungulates, including disrupted migrations, is therefore likely to have bottom–up effects on the population dynamics of sedentary predators as well as the previously documented consequences for ungulate population dynamics.     

Effectiveness of action in India to reduce exposure of Gyps vultures to the toxic veterinary drug diclofenac

Contamination of their carrion food supply with the non-steroidal anti-inflammatory drug diclofenac has caused rapid population declines across the Indian subcontinent of three species of Gyps vultures endemic to South Asia. The governments of India, Pakistan and Nepal took action in 2006 to prevent the veterinary use of diclofenac on domesticated livestock, the route by which contamination occurs. We analyse data from three surveys of the prevalence and concentration of diclofenac residues in carcasses of domesticated ungulates in India, carried out before and after the implementation of a ban on veterinary use. There was little change in the prevalence and concentration of diclofenac between a survey before the ban and one conducted soon after its implementation, with the percentage of carcasses containing diclofenac in these surveys estimated at 10.8 and 10.7%, respectively. However, both the prevalence and concentration of diclofenac had fallen markedly 7-31 months after the implementation of the ban, with the true prevalence in this third survey estimated at 6.5%. Modelling of the impact of this reduction in diclofenac on the expected rate of decline of the oriental white-backed vulture (Gyps bengalensis) in India indicates that the decline rate has decreased to 40% of the rate before the ban, but is still likely to be rapid (about 18% year(-1)). Hence, further efforts to remove diclofenac from vulture food are still needed if the future recovery or successful reintroduction of vultures is to be feasible.     

Can Wild Ungulate Carcasses Provide Enough Biomass to Maintain Avian Scavenger Populations? An Empirical Assessment Using a Bio-Inspired Computational Model

Background

The reduction in the amount of food available for European avian scavengers as a consequence of restrictive public health policies is a concern for managers and conservationists. Since 2002, the application of several sanitary regulations has limited the availability of feeding resources provided by domestic carcasses, but theoretical studies assessing whether the availability of food resources provided by wild ungulates are enough to cover energetic requirements are lacking.

Methodology/Findings

We assessed food provided by a wild ungulate population in two areas of NE Spain inhabited by three vulture species and developed a P System computational model to assess the effects of the carrion resources provided on their population dynamics. We compared the real population trend with to a hypothetical scenario in which only food provided by wild ungulates was available. Simulation testing of the model suggests that wild ungulates constitute an important food resource in the Pyrenees and the vulture population inhabiting this area could grow if only the food provided by wild ungulates would be available. On the contrary, in the Pre-Pyrenees there is insufficient food to cover the energy requirements of avian scavenger guilds, declining sharply if biomass from domestic animals would not be available.

Conclusions/Significance

Our results suggest that public health legislation can modify scavenger population trends if a large number of domestic ungulate carcasses disappear from the mountains. In this case, food provided by wild ungulates could be not enough and supplementary feeding could be necessary if other alternative food resources are not available (i.e. the reintroduction of wild ungulates), preferably in European Mediterranean scenarios sharing similar and socio-economic conditions where there are low densities of wild ungulates. Managers should anticipate the conservation actions required by assessing food availability and the possible scenarios in order to make the most suitable decisions.     

The need for integrative approaches to understand and conserve migratory ungulates

Over the last two centuries overhunting, anthropogenic barriers and habitat loss have disrupted many ungulate migrations. We review the literature on ungulate migration disruptions and find that for many species the disruption of migratory routes causes a rapid population collapse. Previous research has focused on the proximal ecological factors that might favour migration, particularly spatiotemporal variation in resources and predation. However, this does not provide an adequate basis for understanding and mitigating anthropogenic effects on migratory populations. Migration is a complex behaviour and we advocate an integrative approach that incorporates population dynamics, evolution, genetics, behaviour and physiology, and that borrows insights and approaches from research on other taxa. We draw upon research on avian migration to illustrate research approaches that might also be fruitful in ungulates. In particular, we suggest that the migratory cycle should be evaluated in the context of seasonal population limitation, an approach we highlight with a preliminary demographic perturbation analysis of the Serengeti wildebeest ( Connochaetes taurinus ) population. We provide suggestions for avenues of future research and highlight areas where we believe rapid progress can be made by applying recent advances in theory, technology and analytical approaches.     

Vertebrate predators have minimal cascading effects on plant production or seed predation in an intact grassland ecosystem

The strength of trophic cascades in terrestrial habitats has been the subject of considerable interest and debate. We conducted an 8-year experiment to determine how exclusion of vertebrate predators, ungulates alone (to control for ungulate exclusion from predator exclusion plots) or none of these animals influenced how strongly a three-species assemblage of rodent consumers affected plant productivity. We also examined whether predator exclusion influenced the magnitude of post-dispersal seed predation by mice. Both ungulates and rodents had strong direct effects on graminoid biomass. However, rodent impacts on plant biomass did not differ across plots with or without predators and/or ungulates. Deer mice removed more seeds from seed depots on predator exclusion plots, suggesting trait-mediated indirect effects of predators, but this short-term behavioural response did not translate into longer-term impacts on seed survival. These results suggest that vertebrate predators do not fundamentally influence primary production or seed survival in our system.     

Carcass size shapes the structure and functioning of an African scavenging assemblage

The particle size of the food resource strongly determines the structure and dynamics of food webs. However, the ecological implications of carcass size variation for scavenging networks structure and functioning have been largely overlooked. Here we investigate differences in scavenging patterns due to carcass size in a complex vertebrate scavenger community, Hluhluwe‐iMfolozi Park, South Africa, while taking into account seasonality. We monitored the consumption of three types of experimental carcasses: ‘small’ (< 10 kg), ‘medium’ (10–100 kg) and ‘large’ (> 100 kg). We employed general lineal models to explore the influence of carcass size on 1) scavenging network structure (scavenger species richness per carcass) and 2) functioning (carcass detection time, consumption time, consumption rate and percentage of carrion consumed). We also tested whether the structure of the scavenging network of each carcass size was nested, i.e. whether the scavenging assemblage in species‐poor carcasses was a subset of the assemblage consuming species‐rich carcasses. We found strong evidence indicating that carcass size is a major factor governing the associated scavenger assemblage. Scavenger species richness per carcass and carcass consumption time and rate increased with carcass size, while carcass detection time and percentage of carrion biomass consumed were negatively related to carcass size. Strikingly, most of the carrion biomass was consumed by facultative scavengers, represented by large mammalian carnivores, rather than by obligate scavengers (i.e. vultures). Scavenging network nestedness tended to be higher at larger carcasses, and nestedness was sensitive to the removal of the most connected species in the network (spotted hyena) rather than vultures. When comparing scavenging and predation assemblages, crucial size‐dependent differences emerge. Also, we identified a traditionally ignored mechanism by which hunting large prey could be relatively less profitable for predators, namely the costs associated with competition from scavengers and decomposers.     

Effects of vulture exclusion on carrion consumption by facultative scavengers

Vultures provide an essential ecosystem service through removal of carrion, but globally, many populations are collapsing and several species are threatened with extinction. Widespread declines in vulture populations could increase the availability of carrion to other organisms, but the ways facultative scavengers might respond to this increase have not been thoroughly explored. We aimed to determine whether facultative scavengers increase carrion consumption in the absence of vulture competition and whether they are capable of functionally replacing vultures in the removal of carrion biomass from the landscape. We experimentally excluded 65 rabbit carcasses from vultures during daylight hours and placed an additional 65 carcasses that were accessible to vultures in forested habitat in South Carolina, USA during summer (June–August). We used motion‐activated cameras to compare carrion use by facultative scavenging species between the experimental and control carcasses. Scavenging by facultative scavengers did not increase in the absence of competition with vultures. We found no difference in scavenger presence between control carcasses and those from which vultures were excluded. Eighty percent of carcasses from which vultures were excluded were not scavenged by vertebrates, compared to 5% of carcasses that were accessible to vultures. At the end of the 7‐day trials, there was a 10.1‐fold increase in the number of experimental carcasses that were not fully scavenged compared to controls. Facultative scavengers did not functionally replace vultures during summer in our study. This finding may have been influenced by the time of the year in which the study took place, the duration of the trials, and the spacing of carcass sites. Our results suggest that under the warm and humid conditions of our study, facultative scavengers would not compensate for loss of vultures. Carcasses would persist longer in the environment and consumption of carrion would likely shift from vertebrates to decomposers. Such changes could have substantial implications for disease transmission, nutrient cycling, and ecosystem functioning.