The visual fields of Common Guillemots Uria aalge and Atlantic Puffins Fratercula arctica: foraging,vigilance and collision vulnerability

Significant differences in avian visual fields are found between closely related species that differ in their foraging technique. We report marked differences in the visual fields of two auk species. In air, Common Guillemots Uria aalge have relatively narrow binocular fields typical of those found in non‐passerine predatory birds. Atlantic Puffins Fratercula arctica have much broader binocular fields similar to those that have hitherto been recorded in passerines and in a penguin. In water, visual fields narrow considerably and binocularity in the direction of the bill is probably abolished in both auk species. Although perceptual challenges associated with foraging are similar in both species during the breeding season, when they are piscivorous, Puffins (but not Guillemots) face more exacting perceptual challenges when foraging at other times, when they take a high proportion of small invertebrate prey. Capturing this prey probably requires more accurate, visually guided bill placement and we argue that this is met by the Puffin's broader binocular field, which is retained upon immersion; its upward orientation may enable prey to be seen in silhouette. These visual field configurations have potentially important consequences that render these birds vulnerable to collision with human artefacts underwater, but not in air. They also have consequences for vigilance behaviour.     

Differences in foraging ecology determine variation in visual fields in ibises and spoonbills (Threskiornithidae)

Variations in visual field topography among birds have been interpreted as adaptations to the specific perceptual challenges posed by the species’ foraging ecology. To test this hypothesis we determined visual field topography in four bird species which have different foraging ecologies but are from the same family: Puna Ibis Plegadis ridgwayi (probes for prey in the soft substrates of marsh habitats), Northern Bald Ibis Geronticus eremita (surface pecks for prey in dry terrestrial habitats), African Spoonbill Platalea alba and Eurasian Spoonbill Platalea leucorodia (bill‐sweeps for prey in shallow turbid waters). All four species employ tactile cues provided by bill‐tip organs for prey detection. We predicted that the visual fields of these species would show general features similar to those found in other birds whose foraging is guided by tactile cues from the bill (i.e. bill falling outside the frontal binocular field and comprehensive visual coverage of the celestial hemisphere). However, the visual fields of all four species showed general features characteristic of birds that take food directly in the bill under visual guidance (i.e. a narrow and vertically long binocular field in which the projection of the bill tip is approximately central and with a blind area above and behind the head). Visual fields of the two spoonbills were very similar but differed from those of the ibises, which also differed between themselves. In the spoonbills, there was a blind area below the bill produced by the enlarged spatulate bill tip. We discuss how these differences in visual fields are related to the perceptual challenges of these birds’ different foraging ecologies, including the detection, identification and ingestion of prey. In particular we suggest that all species need to see binocularly around the bill and between the opened mandibles for the identification of caught prey items and its transport to the back of the mouth. Our findings support the hypothesis that sensory challenges associated with differences in foraging ecology, rather than shared ancestry or the control of locomotion, are the main determinants of variation in visual field topography in birds.     

SOARING BEHAVIOUR AND PERFORMANCE OF SOME EAST AFRICAN BIRDS, OBSERVED FROM A MOTOR-GLIDER

Various species of soaring birds were studied by following them in a motor-glider, mainly over the Serengeti National Park, Tanzania. The characteristics of thermal convection in the study area are described in general terms. The two vulture species of the genus Gyps live by scavenging among the herds of migratory ungulates, especially Wildebeest. They are not territorial, and gather in large numbers on kills. When raising young they may be obliged by game movements to forage at long distances from their nests. Their cross-country performance is adequate for a foraging radius of over 100 km in dry-season conditions. Their ability to compete with Spotted Hyaenas is thought to depend partly on this factor and partly on an advantage in arriving early at kills. These two species appear to find food more by watching other vultures than by searching for it directly. The Lappet-faced and White-headed Vultures are thought to be sedentary, and to depend on thorough searching of a fixed foraging territory, rather than on following migratory game. They have lower wing loadings than the Gyps vultures, and were not seen cross-country flying. They never gather in large numbers. The Hooded Vulture is a solitary nester, but it does fly across country, and does gather at kills. Vultures soar individually, and seem to be good at exploiting such phenomena as thermal streets. They do not travel in flocks. Tawny and Martial Eagles react positively to the glider, and are suspected of regarding it as potential prey. White Storks migrate between Europe and Africa, and also travel about within East Africa, by thermal soaring. They soar in flocks, and unlike vultures rely on co-ordinated social behaviour to locate thermals. In choosing their route, they often fail to react to obvious weather signs. They enter cumulus clouds from the bottom when thermalling, but probably do not climb far above cloudbase. Marabou Storks soar individually, but also sometimes travel in flocks. When doing so, they show less lateral spreading than White Storks, which reduces the effectiveness of the flock as a thermal-finding unit; on the other hand, they do seem to react to visible weather signs, like vultures or glider pilots. White Pelicans, which travel by thermal soaring between different lakes in the Rift Valley, show the most highly co-ordinated social soaring behaviour. Unlike White Storks, they fly in formation even when circling. Storks and pelicans showed more signs of alarm when approached by the glider than did the vultures or birds of prey. This could be due to their being preyed upon in flight, for instance by Martial Eagles. The basis of conventional thermal cross-country flying is outlined, and it is explained why the high wing loadings of the Gyps vultures are appropriate to their peripatetic habits. A method of thermal soaring without circling is discussed, and shown to be more readily feasible for small than for large birds. Some differences in soaring techniques between birds and glider pilots are interpreted in the light of this calculation. A case in which Black Kites apparently used this technique to soar in random turbulence is described. The cross-country speed attainable by thermal soaring should be similar to the cruising speed under power in both large and small birds. Rough calculations of the energy costs suggest that a large bird (White Stork) should reduce its fuel consumption by a factor of 23 by soaring rather than flying under power, whereas this factor would be only 2–4 for a small bird (Bonelli's Warbler). Other reasons why thermal soaring is an advantageous means of travel for large but not for small birds are also indicated.     

Visual fields and foraging ecology of Blacksmith Lapwings Vanellus armatus

The visual fields of Blacksmith Lapwings Vanellus armatus show the characteristics of visual guided foragers that use precision pecking for prey capture – a binocular field of narrow width and limited vertical extent, with the projection of the bill close to its centre and a large blind area above and behind the head. The topography of the total field, particularly the binocular field, is similar to that of European Golden Plovers Pluvialis apricaria. We suggest that the ‘foot‐trembling’ behaviour associated with foraging in Plovers is not under visual guidance but forces the escape of hidden prey, which is detected when the prey item moves into the binocular field to enable its capture in the bill. Foot‐trembling thus functions to extend the effective foraging area of a bird beyond the limits of its visual field.     

Visual fields,foraging and collision vulnerability in Gyps vultures

The visual fields of vultures contain a small binocular region and large blind areas above, below and behind the head. Head positions typically adopted by foraging vultures suggest that these visual fields provide comprehensive visual coverage of the ground below, prohibit the eyes from imaging the sun and provide extensive visual coverage laterally. However, vultures will often be blind in the direction of travel. We conclude that by erecting structures such as wind turbines, which extend into open airspace, humans have provided a perceptual challenge that the vision of foraging vultures cannot overcome.     

Visual configuration of two species of Falconidae with different foraging ecologies

Significant interspecific differences in avian vision occur, even in congeneric species, and these have been correlated with differences in the perceptual challenges associated with foraging. Although diurnal raptors are assumed to be mainly visually guided in their foraging, they differ markedly in their foraging tactics and this may result in different visual demands. Among the Falconidae (Falconiformes), most falcons forage mainly on the wing for highly mobile prey, whereas caracaras forage on the ground for carrion and insects. We assessed whether Saker Falcon Falco cherrug and Southern Caracara Caracara plancus differ in their visual abilities by determining the visual fields and foveal characteristics of both species. Using an ophthalmoscopic reflex technique, we found a higher degree of binocular overlap in the caracaras than in the falcons. The high binocular overlap (47°) of the Southern Caracara may facilitate object manipulation (e.g. moving rocks) when foraging. We used an ultra‐high resolution spectral‐domain optical coherence tomography to determine foveal characteristics. We found two foveas (depressions in the retina where high visual resolution is expected) in the falcons (one central and one temporal) but only a central fovea in the caracaras. The presence of a shallower temporal fovea in Saker Falcons may help to fixate visually upon a highly mobile prey item during pursuit. We conclude that these differences in visual field configurations and foveal characteristics reflect different foraging demands, suggesting that the extraction of visual information is finely tuned to the demands of their foraging tactics.     

Vision and the foraging technique of Great Cormorants Phalacrocorax carbo: pursuit or close‐quarter foraging?

Predatory diving birds, such as cormorants (Phalacrocoracidae), have been generally regarded as visually guided pursuit foragers. However, due to their poor visual resolution underwater, it has recently been hypothesized that Great Cormorants do not in fact employ a pursuit-dive foraging technique. They appear capable of detecting typical prey only at short distances, and primarily use a foraging technique in which prey may be detected only at close quarters or flushed from a substratum or hiding place. In birds, visual field parameters, such as the position and extent of the region of binocular vision, and how these are altered by eye movements, appear to be determined primarily by feeding ecology. Therefore, to understand further the feeding technique of Great Cormorants we have determined retinal visual fields and eye movement amplitudes using an ophthalmoscopic reflex technique. We show that visual fields and eye movements in cormorants exhibit close similarity with those of other birds, such as herons (Ardeidae) and hornbills (Bucerotidae), which forage terrestrially typically using a close-quarter prey detection or flushing technique and/or which need to examine items held in the bill before ingestion. We argue that this visual field topography and associated eye movements is a general characteristic of birds whose foraging requires the detection of nearby mobile prey items from within a wide arc around the head, accurate capture of that prey using the bill, and visual examination of the caught prey held in the bill. This supports the idea that cormorants, although visually guided predators, are not primarily pursuit predators, and that their visual fields exhibit convergence towards a set of characteristics that meet the perceptual challenges of close-quarter prey detection or flush foraging in both aquatic and terrestrial environments.     

Evidence that vulture restaurants increase the local abundance of mammalian carnivores in South Africa

Vulture restaurants are used worldwide as a conservation tool to provide threatened vultures with a source of supplementary carrion free from anthropogenic contaminants such as poisons and veterinary drugs. While the impacts of supplementary feeding sites on ecosystem and scavenging community dynamics have been investigated in Europe, no information is currently available for southern Africa. This study presents evidence that providing supplementary carrion for vultures stimulated an increase in local abundance of two species of mammalian carnivores, the brown hyaena (Hyaena brunnea) and the black‐backed jackal (Canis mesomelas). These findings require that the wider impacts of providing supplementary carrion for conserving threatened species are fully investigated.     

The visual fields of two ground‐foraging birds,House Finches and House Sparrows,allow for simultaneous foraging and anti‐predator vigilance

In birds, differences in the extent and position of the binocular visual field reflect adaptations to varying foraging strategies, and the extent of the lateral portion of the field may reflect anti‐predator strategies. The goal of this study was to describe and compare the visual fields of two ground‐foraging passerines, House Finch Carpodacus mexicanus and House Sparrow Passer domesticus. We found that both species have a binocular field type that is associated with the accurate control of bill position when pecking. Both species have eye movements of relatively large amplitude, which can produce substantial variations in the configuration of the binocular fields. We propose that in these ground foragers, their relatively wide binocular fields could function to increase foraging efficiency by locating multiple rather than single food items prior to pecking events. The lateral fields of both species are wide enough to facilitate the detection of predators or conspecifics while head‐down foraging. This suggests that foraging and scanning are not mutually exclusive activities in these species, as previously assumed. Furthermore, we found some slight, but significant, differences between species: House Sparrow binocular fields are both wider and vertically taller, and the blind area is wider than in House Finches. These differences may be related to variations in the degree of eye movements and position of the orbits in the skull.     

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.     

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.     

We are what we eat,plus some per mill: Using stable isotopes to estimate diet composition in Gyps vultures over space and time

1. Dietary studies in birds of prey involve direct observation and examination of food remains at resting and nesting sites. Although these methods accurately identify diet in raptors, they are time‐consuming, resource‐intensive, and associated with biases from the feeding ecology of raptors like Gyps vultures. Our study set out to estimate diet composition in Gyps vultures informed by stable isotopes that provide a good representation of assimilated diet from local systems.
2. We hypothesized that differences in Gyps vulture diet composition is a function of sampling location and that these vultures move between Serengeti National Park and Selous Game Reserve to forage. We also theorized that grazing ungulates are the principal items in Gyps vulture diet.
3. Through combined linear and Bayesian modeling, diet derived from δ¹³C in Gyps vultures consisted of grazing herbivores across sites, with those in Serengeti National Park consuming higher proportions of grazing herbivores (>87%). δ¹³C differences in vulture feather subsets did not indicate shifts in vulture diet and combined with blood δ¹³C, vultures fed largely on grazers for ~159 days before they were sampled. Similarly, δ¹⁵N values indicated Gyps vultures fed largely on herbivores. δ³⁴S ratios separated where vultures fed when the two sites were compared. δ³⁴S variation in vultures across sites resulted from baseline differences in plant δ³⁴S values, though it is not possible to match δ³⁴S to specific locations.
4. Our findings highlight the relevance of repeated sampling that considers tissues with varying isotopic turnover and emerging Bayesian techniques for dietary studies using stable isotopes. Findings also suggested limited vulture movement between the two local systems. However, more sampling coupled with environmental data is required to fully comprehend this observation and its implications to Gyps vulture ecology and conservation.

     

Vision and the foraging technique of skimmers (Rynchopidae)

In birds, the position and extent of the region of binocular vision appears to be determined primarily by feeding ecology. Of prime importance is the degree to which vision is used for the precise control of bill position when foraging. Skimmers (Rynchops, Rynchopidae, Charadriiformes) exhibit a unique foraging behaviour and associated structural adaptations. When foraging they fly low and straight over water with the mouth open and the mandible partially submerged. Items that are hit by the lower mandible are grasped by a rapid reflex bill closure. It is believed that this unique ‘skimming’ foraging technique is guided by tactile rather than visual cues. It is predicted therefore that the visual fields of skimmers will have similar topography to those of other tactile feeding birds. We determined retinal visual fields in Black Skimmers Rynchops niger using an ophthalmoscopic reflex technique. Contrary to expectation the visual fields of Black Skimmers are not like those of other tactile feeders. They show high similarity with those of birds that feed by precision‐pecking. The projection of the bill tip when the mouth is closed and when open (as in skimming) falls within the frontal binocular field and there is an extensive blind area above and behind the head. We argue that this visual field topography functions to achieve accurate bill positioning with respect to the water surface when skimming and, because foraging skimmers cannot determine the identity of what they are seizing as they skim, to permit the visual identification of prey items held between the mandibles after they have been taken from the water surface. When skimming, only a small portion of the binocular field, approximately 5° wide and extending 5° above the horizontal, looks in the direction of travel. The small size of this forward‐facing region of binocularity in skimmers suggests that control of locomotion in birds does not necessarily require extensive binocularity in the direction of travel.     

Systematics within Gyps vultures: a clade at risk

Background  

Populations of the Oriental White-backed Vulture (Gyps bengalensis) have declined by over 95% within the past decade. This decline is largely due to incidental consumption of the non-steroidal anti-inflammatory veterinary pharmaceutical diclofenac, commonly used to treat domestic livestock. The conservation status of other Gyps vultures in southern Asia is also of immediate concern, given the lack of knowledge regarding status of their populations and the continuing existence of taxonomic uncertainties. In this study, we assess phylogenetic relationships for all recognized species and the majority of subspecies within the genus Gyps. The continuing veterinary use of diclofenac is an unknown but potential risk to related species with similar feeding habits to Gyps bengalensis. Therefore, an accurate assessment of the phylogenetic relationships among Gyps vultures should aid in their conservation by clarifying taxonomic uncertainties, and enabling inference of their respective relatedness to susceptible G. bengalensis.     

Sexing Cape Vulture Gyps coprotheres based on head morphometrics

The Cape Vulture Gyps coprotheres is considered sexually monomorphic in the literature, but visual differences in head shape between the sexes have been observed. Furthermore, head morphometrics of other Gyps species show statistically significant variation between the sexes. We show that head morphometrics can be used to determine the sex of Cape Vultures. Males generally have wider and shorter heads, and larger bill depths than females. Discriminant function analysis with data from 63 individuals identified the three most predictive variables in sex determination to be head width, head length and bill depth. We also provide an equation that can be used in conjunction with head measurements as a method to determine the sex of Cape Vultures in the field with an overall accuracy of 84% (92% accuracy for females and 72% for males).     

Factors influencing perch selection by communally roosting Turkey Vultures

ABSTRACT Many birds roost communally during at least part of their annual cycle, suggesting that for them the advantages of living in a group outweigh the disadvantages. However, perch sites within a roost may vary in quality because of differences in degree of exposure to the elements, predators, and fecal droppings. Individuals should select perches in the roost that minimize costs while enabling them to experience the benefits of communal roosting. We studied communally roosting Turkey Vultures (Cathartes aura) in northeastern Iowa (USA) from late August to mid‐October, when hatching‐year (HY) birds had joined the roost and were distinguishable from after‐hatching‐year (AHY) birds. On 82 d during our 4‐yr study (2004–2007), we noted the age class and perch position of vultures on two communication towers used as a preroost site. Perches used by vultures were classified as top‐level (with no perches above them) or lower‐level (with other perches above them). Top‐level perches were preferred by Turkey Vultures. Of 1713 birds recorded, 71% were on top‐level perches, even though only 39% of available perches were top‐level. Vultures did not use lower perches if top perches on that tower were unoccupied. The percentage of birds using lower perches increased as the number of vultures present increased, suggesting that top‐level perches were occupied first. AHY birds used top‐level perches more often than expected and HY birds used top‐level perches less often than expected, implying that age‐related dominance affected perch selection. On 61 of 82 d (74%), top‐level perches of both towers were occupied and, on 8 d (10%), only top perches on one tower were occupied. However, on 13 d (16%), both top‐level and lower‐level perches were occupied on one tower while no vultures perched on the other tower, suggesting that social attraction to other vultures can override a general preference for top‐level perches. Thus, our results provide evidence that social attraction, age‐related dominance, and preference for higher perches are proximate factors influencing perch selection in communally roosting Turkey Vultures. Ultimate factors that may be responsible for Turkey Vultures preferring higher roosting perches are reduced risk of predation, less exposure to fecal droppings that might reduce their plumage quality, and better visual information for locating food sources.     

Foraging Ranges of Immature African White-Backed Vultures (Gyps africanus) and Their Use of Protected Areas in Southern Africa

Vultures in the Gyps genus are declining globally. Multiple threats related to human activity have caused widespread declines of vulture populations in Africa, especially outside protected areas. Addressing such threats requires the estimation of foraging ranges yet such estimates are lacking, even for widespread (but declining) species such as the African white-backed vulture (Gyps africanus). We tracked six immature African white-backed vultures in South Africa using GPS-GSM units to study their movement patterns, their use of protected areas and the time they spent in the vicinity of supplementary feeding sites. All individuals foraged widely; their combined foraging ranges extended into six countries in southern Africa (mean (± SE) minimum convex polygon area  = 269,103±197,187 km²) and three of the vultures travelled more than 900 km from the capture site. All six vultures spent the majority of their tracking periods outside protected areas. South African protected areas were very rarely visited whereas protected areas in northern Botswana and Zimbabwe were used more frequently. Two of the vultures visited supplementary feeding sites regularly, with consequent reduced ranging behaviour, suggesting that individuals could alter their foraging behaviour in response to such sites. We show that immature African white-backed vultures are capable of travelling throughout southern Africa, yet use protected areas to only a limited extent, making them susceptible to the full range of threats in the region. The standard approach of designating protected areas to conserve species is unlikely to ensure the protection of such wide-ranging species against threats in the wider landscape.     

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.     

Removing the threat of diclofenac to critically endangered Asian vultures

Veterinary use of the nonsteroidal anti-inflammatory (NSAID) drug diclofenac in South Asia has resulted in the collapse of populations of three vulture species of the genusGyps to the most severe category of global extinction risk. Vultures are exposed to diclofenac when scavenging on livestock treated with the drug shortly before death. Diclofenac causes kidney damage, increased serum uric acid concentrations, visceral gout, and death. Concern about this issue led the Indian Government to announce its intention to ban the veterinary use of diclofenac by September 2005. Implementation of a ban is still in progress late in 2005, and to facilitate this we sought potential alternative NSAIDs by obtaining information from captive bird collections worldwide. We found that the NSAID meloxicam had been administered to 35 captiveGyps vultures with no apparent ill effects. We then undertook a phased programme of safety testing of meloxicam on the African white-backed vultureGyps africanus, which we had previously established to be as susceptible to diclofenac poisoning as the endangered AsianGyps vultures. We estimated the likely maximum level of exposure (MLE) of wild vultures and dosed birds by gavage (oral administration) with increasing quantities of the drug until the likely MLE was exceeded in a sample of 40G. africanus. Subsequently, sixG. africanus were fed tissues from cattle which had been treated with a higher than standard veterinary course of meloxicam prior to death. In the final phase, ten Asian vultures of two of the endangered species(Gyps bengalensis,Gyps indicus) were dosed with meloxicam by gavage; five of them at more than the likely MLE dosage. All meloxicam-treated birds survived all treatments, and none suffered any obvious clinical effects. Serum uric acid concentrations remained within the normal limits throughout, and were significantly lower than those from birds treated with diclofenac in other studies. We conclude that meloxicam is of low toxicity toGyps vultures and that its use in place of diclofenac would reduce vulture mortality substantially in the Indian subcontinent. Meloxicam is already available for veterinary use in India.     

The subtlety of simple eyes: the tuning of visual fields to perceptual challenges in birds

Birds show interspecific variation both in the size of the fields of individual eyes and in the ways that these fields are brought together to produce the total visual field. Variation is found in the dimensions of all main parameters: binocular region, cyclopean field and blind areas. There is a phylogenetic signal with respect to maximum width of the binocular field in that passerine species have significantly broader field widths than non-passerines; broadest fields are found among crows (Corvidae). Among non-passerines, visual fields show considerable variation within families and even within some genera. It is argued that (i) the main drivers of differences in visual fields are associated with perceptual challenges that arise through different modes of foraging, and (ii) the primary function of binocularity in birds lies in the control of bill position rather than in the control of locomotion. The informational function of binocular vision does not lie in binocularity per se (two eyes receiving slightly different information simultaneously about the same objects from which higher-order depth information is extracted), but in the contralateral projection of the visual field of each eye. Contralateral projection ensures that each eye receives information from a symmetrically expanding optic flow-field from which direction of travel and time to contact targets can be extracted, particularly with respect to the control of bill position.