Avian scavengers and the threat from veterinary pharmaceuticals

Veterinary use of the non-steroidal anti-inflammatory drug diclofenac on domesticated ungulates caused populations of resident Gyps vultures in the Indian sub-continent to collapse. The birds died when they fed on carrion from treated animals. Veterinary diclofenac was banned in 2006 and meloxicam was advocated as a ‘vulture-safe’ alternative. We examine the effectiveness of the 2006 ban, whether meloxicam has replaced diclofenac, and the impact of these changes on vultures. Drug residue data from liver samples collected from ungulate carcasses in India since 2004 demonstrate that the prevalence of diclofenac in carcasses in 2009 was half of that before the ban and meloxicam prevalence increased by 44%. The expected vulture death rate from diclofenac per meal in 2009 was one-third of that before the ban. Surveys at veterinary clinics show that diclofenac use in India began in 1994, coinciding with the onset of rapid Gyps declines ascertained from measured rates of declines. Our study shows that one pharmaceutical product has had a devastating impact on Asia''s vultures. Large-scale research and survey were needed to detect, diagnose and quantify the problem and measure the response to remedial actions. Given these difficulties, other effects of pharmaceuticals in the environment may remain undetected.     

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.     

Vulture Genomes Reveal Molecular Adaptations Underlying Obligate Scavenging and Low Levels of Genetic Diversity

Obligate scavenging on the dead and decaying animal matter is a rare dietary specialization that in extant vertebrates is restricted to vultures. These birds perform essential ecological services, yet many vulture species have undergone recent steep population declines and are now endangered. To test for molecular adaptations underlying obligate scavenging in vultures, and to assess whether genomic features might have contributed to their population declines, we generated high-quality genomes of the Himalayan and bearded vultures, representing both independent origins of scavenging within the Accipitridae, alongside a sister taxon, the upland buzzard. By comparing our data to published sequences from other birds, we show that the evolution of obligate scavenging in vultures has been accompanied by widespread positive selection acting on genes underlying gastric acid production, and immunity. Moreover, we find evidence of parallel molecular evolution, with amino acid replacements shared among divergent lineages of these scavengers. Our genome-wide screens also reveal that both the Himalayan and bearded vultures exhibit low levels of genetic diversity, equating to around a half of the mean genetic diversity of other bird genomes examined. However, demographic reconstructions indicate that population declines began at around the Last Glacial Maximum, predating the well-documented dramatic declines of the past three decades. Taken together, our genomic analyses imply that vultures harbor unique adaptations for processing carrion, but that modern populations are genetically depauperate and thus especially vulnerable to further genetic erosion through anthropogenic activities.     

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.     

NSAIDs and scavenging birds: potential impacts beyond Asia's critically endangered vultures

Veterinary treatment of livestock with diclofenac, a non-steroidal anti-inflammatory drug (NSAID), has caused catastrophic declines of Gyps vultures in Asia. This has highlighted a lack of knowledge on the potential impacts of NSAIDs on scavenging birds. Surveys of veterinarians and zoos document the outcomes of the treatment of over 870 scavenging birds from 79 species. As well as diclofenac, carprofen and flunixin were associated with mortality, with deaths observed in 13 and 30% of cases, respectively. Mortality was also found following treatment with ibuprofen and phenylbutazone. NSAID toxicity was reported for raptors, storks, cranes and owls, suggesting that the potential conservation impact of NSAIDs may extend beyond Gyps vultures and could be significant for New World vultures. In contrast, there were no reported mortalities for the NSAID meloxicam, which was administered to over 700 birds from 60 species. The relative safety of meloxicam supports other studies indicating the suitability of this NSAID to replace diclofenac in Asia.     

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.     

An assessment of tree availability as a possible cause of population declines in scavenging raptors

Lack of suitable nesting trees is an increasingly common issue for avian conservation given rampant habitat and tree destruction around the world. In the African savannah, habitat loss and particularly tree damage caused by elephants have been suggested as possible factors in the decline of large bird species. Given the recent declines of vultures and other scavenging raptors, it is critical to understand if nest availability is a limiting factor for these threatened populations. Loss of woodland, partially due to elephant populations, has been reported for the Mara‐Serengeti ecosystem. Data on characteristics of trees used for nesting were collected for white‐backed, lappet‐faced, white‐headed vulture, and tawny eagle nests in Masai Mara National Reserve, Kenya. Nest tree characteristics were compared with the distribution of a random subsample of trees to assess nest preferences and determine suitability of available trees. Nearest neighbor distances were estimated as well as availability of preferred nesting trees to determine if tree availability is a limiting factor for tree‐nesting vultures. Tree availability was found to greatly exceed nesting needs for African vultures and tawny eagles. We thus conclude that on a landscape scale, tree availability is not a limiting factor for any of the species considered here (white‐backed, lappet‐faced, white‐headed vultures and tawny eagles).     

Nesting habitat preference of the African White-backed Vulture Gyps africanus and the effects of anthropogenic disturbance

The African White-backed Vulture Gyps africanus is widely distributed across sub-Saharan Africa but populations are in decline. Loss of suitable habitat for foraging and breeding are among the most important causes, and future conservation will require identification of suitable remaining habitat and the threats to it and to the vultures in it. Like many large raptors, African White-backed Vultures have a long breeding cycle and thus spend much of each year near their nest site, but ecological correlates of nest sites have not been quantified for any African vulture species. We use nest-site data for African White-backed Vultures collected during aerial and ground surveys and habitat data derived from a GIS to develop statistical models that estimate the probability of nest presence in relation to habitat characteristics, and test these models against an independent dataset. The models predicted that both direct and indirect disturbance by humans limit the potential distribution. Suitable habitat needs to be identified and receive adequate protection from poaching. Poaching of vultures is thought to be mainly for use in traditional medicine and does not target any particular species, so all vulture species can be considered equally at risk. We predict the likelihood of individuals nesting in currently unprotected areas should they become protected. These predictions show that readily available GIS data combined with relatively simple statistical modelling can provide meaningful large-scale predictions of habitat availability.     

Large Bird Declines with Increasing Human Pressure in Savanna Woodlands (Burkina Faso)

The impacts of human pressure, habitat changes, and efficiency of conservation measures on the non-passerine bird community were assessed in the Sudanian belt of Burkina Faso. Three regions with increasingly large protected areas and higher conservation status were compared. In each region, natural savanna woodlands were also compared to traditionally cultivated areas. Six groups of diurnal raptors and six groups of other large bird species were counted along 167 5-km transect counts during the dry season. Within savanna woodlands, the only significant and consistent declines from the little disturbed Eastern National Parks to the more populated and exploited Western forest reserves were those of the largest terrestrial game birds (Guinea fowl, Bustard, Ground Hornbill), eagles and vultures, which became virtually extinct in the least protected areas. Although some species groups maintained substantial, if not higher populations in cultivated areas (rollers, non-game terrestrial birds, several raptors), the overall abundance of both raptor and non-raptor species declined markedly (50–65%) from natural savanna woodlands to tree-dotted cultivated and fallow fields. Again large game birds, eagles and vultures were absent from every agricultural areas censused. Yet, all of them were still commonly recorded in the same natural and cultivated areas during surveys I conducted in the same regions from 1968 to 1973. The main factors correlated with large bird extinctions or declines from national parks to mere forest reserves and from natural woodlands to fields were first related to hunting, then to habitat degradation and fragmentation through intensive cattle grazing and wood cutting and extension of cultivated areas.     

Do Power Lines and Protected Areas Present a Catch-22 Situation for Cape Vultures (Gyps coprotheres)?

Cape vulture Gyps coprotheres populations have declined across their range due to multiple anthropogenic threats. Their susceptibility to fatal collisions with the expanding power line network and the prevalence of carcasses contaminated with illegal poisons and other threats outside protected areas are thought to be the primary drivers of declines in southern Africa. We used GPS-GSM units to track the movements and delineate the home ranges of five adult (mean ±SD minimum convex polygon area  =  121,655±90,845 km²) and four immature (mean ±SD minimum convex polygon area  =  492,300±259,427 km²) Cape vultures to investigate the influence of power lines and their use of protected areas. The vultures travelled more than 1,000 km from the capture site and collectively entered five different countries in southern Africa. Their movement patterns and core foraging ranges were closely associated with the spatial distribution of transmission power lines and we present evidence that the construction of power lines has allowed the species to extend its range to areas previously devoid of suitable perches. The distribution of locations of known Cape vulture mortalities caused by interactions with power lines corresponded to the core ranges of the tracked vultures. Although some of the vultures regularly roosted at breeding colonies located inside protected areas the majority of foraging activity took place on unprotected farmland. Their ability to travel vast distances very quickly and the high proportion of time they spend in the vicinity of power lines and outside protected areas make Cape vultures especially vulnerable to negative interactions with the expanding power line network and the full range of threats across the region. Co-ordinated cross-border conservation strategies beyond the protected area network will therefore be necessary to ensure the future survival of threatened vultures in Africa.     

How do roads affect the habitat use of an assemblage of scavenging raptors?

Scavengers may benefit from the availability of dead animals along roads that result from collisions with vehicles. However, roads are also considered risky places for many species. Animal habitat selection patterns usually balance energy intake with mortality risk. In this work we analyzed the foraging space use of an assemblage of diurnal scavenging raptors in relation to distance from roads in northwest Patagonia. We selected patches at different distances from roads, and placed a sheep carcass in each patch during the night (n = 18 carcasses in total). In general, carcasses near roads were detected by diurnal scavenging raptors much faster than those far from roads. Smaller raptors such as southern caracaras (Caracara plancus), chimango caracaras (Milvago chimango), and black vultures (Coragyps atratus), were commonly associated with roads both in terms of overall detections and scavenging activities. Southern and chimango caracaras proved to be very good at detecting carcasses, were faster to land in order to feed from them, and were found in greater numbers near roads than far from them. Even though Andean condors (Vultur gryphus) and black-chested buzzard-eagles (Geranoaetus melanoleucus) flew all over the area, they chose to feed far from roads. Our work emphasizes that some scavengers have taken advantage of the novel food resources provided by roads whereas others are reluctant to feed near them. Within a scenario of an increasing number of roads, some species can extend their distributions favoring competition and biotic homogenization processes within original communities. We highlight the importance of taking into account large flying scavengers in land-use planning. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

When hunting benefits raptors: a case study of game species and vultures

Management of hunting activity to serve as a tool for sustainable development has become a key issue in conservation biology. However, little evidence is available showing positive impacts of hunting on ecosystem conservation, limiting its capability to be used as a conservation tool. We analysed hunting and its positive influence on the ecology and conservation of the griffon vulture (Gyps fulvus), a scavenger with a relevant function in the ecosystem, in the Cantabrian Mountains, NW Spain. Use of the area by vultures was addressed by looking for cliffs used as roosts or colonies, and consumption of game species by vultures was evaluated through field surveys and questionnaires to hunters. Results revealed a strong spatiotemporal adjustment in the use of the area by vultures and hunting events, especially of red deer and wild boar. Vultures occupied roosting sites very close to the main hunting sectors of these game species and often were seen consuming their carcasses. The spatiotemporal pattern of roost use by vultures strongly overlapped with hunting of red deer. The numbers of both red deer and wild boar hunting episodes within 3.5 km around the roosts were the best predictors of vulture occurrence and number. Our estimates show that hunting could feed around 1,800 vultures/6 months. Hunting can thus influence species at the top of the ecosystem (scavengers) and could aid sustainable management of griffon vulture populations, reconciling hunting and conservation. However, negative and positive impacts should be taken into account simultaneously for an overall evaluation of hunting on ecosystem conservation.     

African Vultures Don’t Follow Migratory Herds: Scavenger Habitat Use Is Not Mediated by Prey Abundance

The ongoing global decline in vulture populations raises major conservation concerns, but little is known about the factors that mediate scavenger habitat use, in particular the importance of abundance of live prey versus prey mortality. We test this using data from the Serengeti-Mara ecosystem in East Africa. The two hypotheses that prey abundance or prey mortality are the main drivers of vulture habitat use provide alternative predictions. If vultures select areas based only on prey abundance, we expect tracked vultures to remain close to herds of migratory wildebeest regardless of season. However, if vultures select areas where mortality rates are greatest then we expect vultures to select the driest regions, where animals are more likely to die of starvation, and to be attracted to migratory wildebeest only during the dry season when wildebeest mortality is greatest. We used data from GSM-GPS transmitters to assess the relationship between three vulture species and migratory wildebeest in the Mara-Serengeti ecosystem. Results indicate that vultures preferentially cluster around migratory herds only during the dry season, when herds experience their highest mortality. Additionally during the wet season, Ruppell’s and Lappet-faced vultures select relatively dry areas, based on Normalized Difference Vegetation Index, whereas White-backed vultures preferred wetter areas during the wet season. Differences in habitat use among species may mediate coexistence in this scavenger guild. In general, our results suggest that prey abundance is not the primary driver of avian scavenger habitat use. The apparent reliance of vultures on non-migratory ungulates during the wet season has important conservation implications for vultures in light of on-going declines in non-migratory ungulate species and use of poisons in unprotected areas.     

The role of griffon vultures Gyps africanus and Gyps ruppellii as scavengers

In the Serengeti, predator kills formed from 8 to 45 % of the carcasses that griffon vultures fed upon, the remaining carcasses coming from animals that had died from other causes. But since vultures obtained only very small amounts of food from predator kills, they had to rely for their food supply chiefly on the carcasses that were derived from other causes. In the Serengeti the large proportion of migratory ungulates prevent the mammalian predators from building up to a population size that can be responsible for a large proportion of ungulate mortality. It is estimated that the mammalian predators only take about one quarter of the potential food supply available for carnivores. The remaining ungulates die from various other causes, and so provide food for scavengers which varies in abundance and location with the seasons. This is a food supply which mammalian scavengers cannot easily use but griffon vultures, with their adaptations for gliding flight, are able to exploit it. These vultures therefore exploit a basically different food supply from predators and probably evolved as scavengers of migratory ungulate populations.     

The effect of social facilitation on foraging success in vultures: a modelling study

The status of many Gyps vulture populations are of acute conservation concern as several show marked and rapid decline. Vultures rely heavily on cues from conspecifics to locate carcasses via local enhancement. A simulation model is developed to explore the roles vulture and carcass densities play in this system, where information transfer plays a key role in locating food. We find a sigmoid relationship describing the probability of vultures finding food as a function of vulture density in the habitat. This relationship suggests a threshold density below which the foraging efficiency of the vulture population will drop rapidly towards zero. Management strategies should closely study this foraging system in order to maintain effective foraging densities.     

Wing and hindlimb myology of vultures and raptors (Accipitriformes) in relation to locomotion and foraging

Herein, we compare functional muscle properties among convergent forms of large, obligate avian scavengers. We performed quantitative analyses of all the muscle masses and cross‐sectional areas (CSA) of the wings and hindlimbs of five species from two families, Cathartidae (New World vultures; Cathartes aura and Vultur gryphus) and Accipitridae (Old World vultures and raptors; Gyps africanus, Aquila rapax, and Buteo lineatus). These species comprise two paraphyletic functional groups, raptors (Aquila and Buteo) and vultures (Gyps, Cathartes, and Vultur). Our ordination analyses based on all of the muscles of the wings, hindlimbs, and wing and hindlimb muscles combined produced patterns that appeared to be more related to phylogeny, with a hint of a functional signal in wing muscle CSA. However, when wing muscles were grouped according to their functional roles (upstroke, downstroke, and wing stabilization), the percentages of mass and CSA allocated to the upstroke and stabilizing muscles were 1.4–5% greater in the vultures than in the raptors. Conversely, when hindlimb muscles were grouped according to their roles in grasping and terrestrial locomotion, the percentages of mass and CSA allocated to grasping muscles were 5.9–14% greater in the raptors. Our results provide a baseline for future lines of inquiry aimed at understanding how muscle mass and CSA are affected differentially across locomotor modules, possibly in response to differential demands on wing and hindlimb function experienced by these disparate accipitriform clades.     

When David Beats Goliath: The Advantage of Large Size in Interspecific Aggressive Contests Declines over Evolutionary Time

Body size has long been recognized to play a key role in shaping species interactions. For example, while small species thrive in a diversity of environments, they typically lose aggressive contests for resources with larger species. However, numerous examples exist of smaller species dominating larger species during aggressive interactions, suggesting that the evolution of traits can allow species to overcome the competitive disadvantage of small size. If these traits accumulate as lineages diverge, then the advantage of large size in interspecific aggressive interactions should decline with increased evolutionary distance. We tested this hypothesis using data on the outcomes of 23,362 aggressive interactions among 246 bird species pairs involving vultures at carcasses, hummingbirds at nectar sources, and antbirds and woodcreepers at army ant swarms. We found the advantage of large size declined as species became more evolutionarily divergent, and smaller species were more likely to dominate aggressive contests when interacting with more distantly-related species. These results appear to be caused by both the evolution of traits in smaller species that enhanced their abilities in aggressive contests, and the evolution of traits in larger species that were adaptive for other functions, but compromised their abilities to compete aggressively. Specific traits that may provide advantages to small species in aggressive interactions included well-developed leg musculature and talons, enhanced flight acceleration and maneuverability, novel fighting behaviors, and traits associated with aggression, such as testosterone and muscle development. Traits that may have hindered larger species in aggressive interactions included the evolution of morphologies for tree trunk foraging that compromised performance in aggressive contests away from trunks, and the evolution of migration. Overall, our results suggest that fundamental trade-offs, such as those associated with body size, are more likely to break down over evolutionary time, changing the rules that govern species interactions and structure ecological communities.     

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.     

Producing and scrounging can have stabilizing effects at multiple levels of organization

This study shows, for the first time, that the evolution of a simple behavior, scrounging, at the individual level can have effects on populations, food chains, and community structure. In particular, the addition of scrounging in consumer populations can allow multiple consumers to coexist while exploiting a single prey. Also, scrounging in the top predator of a tritrophic food chain can stabilize interactions between the top predator, its prey, and its prey's prey. This occurs because the payoffs to scrounging for food in a population are negative frequency dependent, allowing scroungers to invade a population and to coexist with producers at a frequency which is density‐dependent. The presence of scroungers, who do not search for resources but simply use those found by others (producers) reduces the total amount of resource acquired by the group. As scrounging increases with group size, this leads to less resource acquired per individual as the group grows. Ultimately, this limits the size of the group, its impact on its prey, and its ability to outcompete other species. These effects can promote stability and thus increase species diversity. I will further suggest that prey may alter their spatial distribution such that scrounging will be profitable among their predators thus reducing predation rate on the prey.