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

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

Impacts of biomass production at civil airports on grassland bird conservation and aviation strike risk.

Growing concerns about climate change, foreign oil dependency, and environmental quality have fostered interest in perennial native grasses (e.g., switchgrass [Panicum virgatum]) for bioenergy production while also maintaining biodiversity and ecosystem function. However, biomass cultivation in marginal landscapes such as airport grasslands may have detrimental effects on aviation safety as well as conservation efforts for grassland birds. In 2011-2013, we investigated effects of vegetation composition and harvest frequency on seasonal species richness and habitat use of grassland birds and modeled relative abundance, aviation risk, and conservation value of birds associated with biomass crops. Avian relative abundance was greater in switchgrass monoculture plots during the winter months, whereas Native Warm-Season Grass (NWSG) mixed species plantings were favored by species during the breeding season. Conversely, treatment differences in aviation risk and conservation value were not biologically significant. Only 2.6% of observations included avian species of high hazard to aircraft, providing support for semi-natural grasslands as a feasible landcover option at civil airports. Additionally, varied harvest frequencies across a mosaic of switchgrass monocultures and NWSG plots allows for biomass production with multiple vegetation structure options for grassland birds to increase seasonal avian biodiversity and habitat use.

Brown tree snake (Boiga irregularis) population density and carcass locations following exposure to acetaminophen.

Mass aerial delivery of dead mouse baits treated with acetaminophen has been evaluated as a means to reduce brown tree snake (Boiga irregularis) populations over large areas, increasing the likelihood of wide-scale eradication on Guam. Given the high density of snakes in some areas of their invasive range, eradication efforts could result in a resource pulse that may influence food web dynamics and the indirect transport of acetaminophen among trophic levels. We evaluated abundance, habitat type, and snake size (i.e., age) within two study sites on Guam, a secondary limestone forest (upland) and an abandoned coconut plantation (coastal), to determine how experimentally dosing snakes with acetaminophen is likely to influence carrion availability. We found snakes trapped in 3.24 ha plots occurred in greater abundance (population size = 72.5 snakes; SE = 8.8) and were significantly larger (978.6 mm, SE = 14.9) in the coastal than in the upland site (population size = 26.9, SE = 21.5; length = 903.0 mm, SE = 15.9). Despite these differences, carcasses of snakes that died after consuming acetaminophen-laced mice (80 mg) were recovered in consistent locations between sites, with 92 % located on the ground, 4 % in trees, and 4 % found in rock cavities at both sites. Given that most snakes were found on the ground rather than in the tree canopy, our results suggest that many poisoned snake carcasses will be accessible to a wide range of potential scavengers, possibly influencing food web dynamics and potentially contributing to indirect toxicant transfer within affected ecosystems.

Speed kills: ineffective avian escape responses to oncoming vehicles.

Animal-vehicle collisions cause high levels of vertebrate mortality worldwide, and what goes wrong when animals fail to escape and ultimately collide with vehicles is not well understood. We investigated alert and escape behaviours of captive brown-headed cowbirds (Molothrus ater) in response to virtual vehicle approaches of different sizes and at speeds ranging from 60 to 360 km h(-1). Alert and flight initiation distances remained similar across vehicle speeds, and accordingly, alert and flight initiation times decreased at higher vehicle speeds. Thus, avoidance behaviours in cowbirds appeared to be based on distance rather than time available for escape, particularly at 60-150 km h(-1); however, at higher speeds (more than or equal to 180 km h(-1)) no trend in response behaviour was discernible. As vehicle speed increased, cowbirds did not have enough time to assess the approaching vehicle, and cowbirds generally did not initiate flight with enough time to avoid collision when vehicle speed exceeded 120 km h(-1). Although potentially effective for evading predators, the decision-making process used by cowbirds in our study appears maladaptive in the context of avoiding fast-moving vehicles. Our methodological approach and findings provide a framework to assess how novel management strategies could affect escape rules, and the sensory and cognitive abilities animals use to avoid vehicle collisions.

Behavioral traits and airport type affect mammal incidents with U.S. civil aircraft.

Wildlife incidents with aircraft cost the United States (U.S.) civil aviation industry >US$1.4 billion in estimated damages and loss of revenue from 1990 to 2009. Although terrestrial mammals represented only 2.3 % of wildlife incidents, damage to aircraft occurred in 59 % of mammal incidents. We examined mammal incidents (excluding bats) at all airports in the Federal Aviation Administration (FAA) National Wildlife Strike Database from 1990 to 2010 to characterize these incidents by airport type: Part-139 certified (certificated) and general aviation (GA). We also calculated relative hazard scores for species most frequently involved in incidents. We found certificated airports had more than twice as many incidents as GA airports. Incidents were most frequent in October (n = 215 of 1,764 total) at certificated airports and November (n = 111 of 741 total) at GA airports. Most (63.2 %) incidents at all airports (n = 1,523) occurred at night but the greatest incident rate occurred at dusk (177.3 incidents/hr). More incidents with damage (n = 1,594) occurred at GA airports (38.6 %) than certificated airports (19.0 %). Artiodactyla (even-toed ungulates) incidents incurred greatest (92.4 %) damage costs (n = 326; US$51.8 million) overall and mule deer (Odocoileus hemionus) was the most hazardous species. Overall, relative hazard score increased with increasing log body mass. Frequency of incidents was influenced by species relative seasonal abundance and behavior. We recommend airport wildlife officials evaluate the risks mammal species pose to aircraft based on the hazard information we provide and consider prioritizing management strategies that emphasize reducing their occurrence on airport property.

Inefficacy of mallard flight responses to approaching vehicles.

Vehicle collisions with birds are financially costly and dangerous to humans and animals. To reduce collisions, it is necessary to understand how birds respond to approaching vehicles. We used simulated (i.e., animals exposed to video playback) and real vehicle approaches with mallards (Anas platyrynchos) to quantify flight behavior and probability of collision under different vehicle speeds and times of day (day vs. night). Birds exposed to simulated nighttime approaches exhibited reduced probability of attempting escape, but when escape was attempted, fled with more time before collision compared to birds exposed to simulated daytime approaches. The lower probability of flight may indicate that the visual stimulus of vehicle approaches at night (i.e., looming headlights) is perceived as less threatening than when the full vehicle is more visible during the day; alternatively, the mallard visual system might be incompatible with vehicle lighting in dark settings. Mallards approached by a real vehicle exhibited a delayed margin of safety (both flight initiation distance and time before collision decreased with speed); they are the first bird species found to exhibit this response to vehicle approach. Our findings suggest mallards are poorly equipped to adequately respond to fast-moving vehicles and demonstrate the need for continued research into methods promoting effective avian avoidance behaviors.

Trace metal transfer to passerines inhabiting wastewater treatment wetlands.

Wastewater treatment wetlands are cost-effective strategies for remediating trace metals in industrial effluent. However, biogeochemical exchange between wastewater treatment wetlands and adjacent environments provides opportunities for trace metals to cycle in surrounding ecosystems. The transfer of trace metals to wildlife inhabiting treatment wetlands must be considered when evaluating wetland success. Using passerine birds as bioindicators, we conducted a multi-tissue analysis to investigate the mobilization of zinc, copper, and lead derived from wastewater to terrestrial wildlife in treatment wetlands and surrounding habitat. In addition, we evaluate the strength of relationships between metal concentrations in non-lethal (blood and feathers) and lethal (muscle and liver) sample types for estimation of toxicity risk. From July 2020 to August 2021, 177 passerines of seven species were captured at two wetlands constructed to treat industrial wastewater and two reference wetlands in the coastal plain of South Carolina. Feather, blood, liver, and muscle samples from each bird were analyzed for fourteen metals using inductively coupled plasma mass spectrometry and direct mercury analysis. Passerines inhabiting wastewater treatment wetlands accumulated higher concentrations of zinc in liver, copper in blood, and lead in feathers than passerines in reference wetlands, but neither blood nor feather concentrations were correlated with internal tissue concentrations. Of all the detected metals, only mercury in the blood showed a strong predictive relationship with mercury in internal tissues. This study indicates that trace metals derived from wastewater are bioavailable and exported to terrestrial wildlife and that passerine biomonitoring is a valuable tool for assessing metal transfer from treatment wetlands. Regular blood sampling can reveal proximate trace metal exposure but cannot predict internal body burdens for most metals.

Oblique color vision in an open-habitat bird: spectral sensitivity, photoreceptor distribution and behavioral implications.

Color vision is not uniform across the retina because of differences in photoreceptor density and distribution. Retinal areas with a high density of cone photoreceptors may overlap with those with a high density of ganglion cells, increasing hue discrimination. However, there are some exceptions to this cell distribution pattern, particularly in species with horizontal visual streaks (bands of high ganglion cell density across the retina) that live in open habitats. We studied the spectral sensitivity and distribution of cone photoreceptors involved in chromatic and achromatic vision in the Canada goose (Branta canadiensis), which possesses an oblique rather than horizontal visual streak at the ganglion cell layer. Using microspectrophotometry, we found that the Canada goose has a violet-sensitive visual system with four visual pigments with absorbance peaks at 409, 458, 509 and 580 nm. The density of most cones involved in chromatic and achromatic vision peaked along a band across the retina that matched the oblique orientation of the visual streak. With the information on visual sensitivity, we calculated chromatic and achromatic contrasts of different goose plumage regions. The regions with the highest visual saliency (cheek, crown, neck and upper tail coverts) were the ones involved in visual displays to maintain flock cohesion. The Canada goose oblique visual streak is the retinal center for chromatic and achromatic vision, allowing individuals to sample the sky and the ground simultaneously or the horizon depending on head position. Overall, our results show that the Canada goose visual system has features that make it rather different from that of other vertebrates living in open habitats.

Airports offer unrealized potential for alternative energy production.

Scaling up for alternative energy such as solar, wind, and biofuel raises a number of environmental issues, notably changes in land use and adverse effects on wildlife. Airports offer one of the few land uses where reductions in wildlife abundance and habitat quality are necessary and socially acceptable, due to risk of wildlife collisions with aircraft. There are several uncertainties and limitations to establishing alternative energy production at airports, such as ensuring these facilities do not create wildlife attractants or other hazards. However, with careful planning, locating alternative energy projects at airports could help mitigate many of the challenges currently facing policy makers, developers, and conservationists.

Integrating terrestrial scavenging ecology into contemporary wildlife conservation and management.

Scavenging plays a vital role in maintaining ecosystem health and contributing to ecological functions; however, research in this sub-discipline of ecology is underutilized in developing and implementing wildlife conservation and management strategies. We provide an examination of the literature and recommend priorities for research where improved understanding of scavenging dynamics can facilitate the development and refinement of applied wildlife conservation and management strategies. Due to the application of scavenging research broadly within ecology, scavenging studies should be implemented for informing management decisions. In particular, a more direct link should be established between scavenging dynamics and applied management programs related to informing pharmaceutical delivery and population control through bait uptake for scavenging species, prevention of unintentional poisoning of nontarget scavenging species, the epidemiological role that scavenging species play in disease dynamics, estimating wildlife mortalities, nutrient transfer facilitated by scavenging activity, and conservation of imperiled facultative scavenging species. This commentary is intended to provide information on the paucity of data in scavenging research and present recommendations for further studies that can inform decisions in wildlife conservation and management. Additionally, we provide a framework for decision-making when determining how to apply scavenging ecology research for management practices and policies. Due to the implications that scavenging species have on ecosystem health, and their overall global decline as a result of anthropic activities, it is imperative to advance studies in the field of scavenging ecology that can inform applied conservation and management programs.

Can we use antipredator behavior theory to predict wildlife responses to high-speed vehicles?

Animals seem to rely on antipredator behavior to avoid vehicle collisions. There is an extensive body of antipredator behavior theory that have been used to predict the distance/time animals should escape from predators. These models have also been used to guide empirical research on escape behavior from vehicles. However, little is known as to whether antipredator behavior models are appropriate to apply to an approaching high-speed vehicle scenario. We addressed this gap by (a) providing an overview of the main hypotheses and predictions of different antipredator behavior models via a literature review, (b) exploring whether these models can generate quantitative predictions on escape distance when parameterized with empirical data from the literature, and (c) evaluating their sensitivity to vehicle approach speed using a simulation approach wherein we assessed model performance based on changes in effect size with variations in the slope of the flight initiation distance (FID) vs. approach speed relationship. The slope of the FID vs. approach speed relationship was then related back to three different behavioral rules animals may rely on to avoid approaching threats: the spatial, temporal, or delayed margin of safety. We used literature on birds for goals (b) and (c). Our review considered the following eight models: the economic escape model, Blumstein's economic escape model, the optimal escape model, the perceptual limit hypothesis, the visual cue model, the flush early and avoid the rush (FEAR) hypothesis, the looming stimulus hypothesis, and the Bayesian model of escape behavior. We were able to generate quantitative predictions about escape distance with the last five models. However, we were only able to assess sensitivity to vehicle approach speed for the last three models. The FEAR hypothesis is most sensitive to high-speed vehicles when the species follows the spatial (FID remains constant as speed increases) and the temporal margin of safety (FID increases with an increase in speed) rules of escape. The looming stimulus effect hypothesis reached small to intermediate levels of sensitivity to high-speed vehicles when a species follows the delayed margin of safety (FID decreases with an increase in speed). The Bayesian optimal escape model reached intermediate levels of sensitivity to approach speed across all escape rules (spatial, temporal, delayed margins of safety) but only for larger (> 1 kg) species, but was not sensitive to speed for smaller species. Overall, no single antipredator behavior model could characterize all different types of escape responses relative to vehicle approach speed but some models showed some levels of sensitivity for certain rules of escape behavior. We derive some applied applications of our findings by suggesting the estimation of critical vehicle approach speeds for managing populations that are especially susceptible to road mortality. Overall, we recommend that new escape behavior models specifically tailored to high-speeds vehicles should be developed to better predict quantitatively the responses of animals to an increase in the frequency of cars, airplanes, drones, etc. they will face in the next decade.

Carcass appearance does not influence scavenger avoidance of carnivore carrion.

The selection or avoidance of certain carrion resources by vertebrate scavengers can alter the flow of nutrients in ecosystems. Evidence suggests higher trophic level carrion is scavenged by fewer vertebrate species and persists longer when compared to lower trophic level carrion, although it is unclear how scavengers distinguish between carcasses of varying species. To investigate carnivore carrion avoidance and explore sensory recognition mechanisms in scavenging species, we investigated scavenger use of intact and altered (i.e., skin, head, and feet removed) coyote-Canis latrans (carnivore) and wild pig-Sus scrofa (omnivore) carcasses experimentally placed at the Savannah River Site, SC, USA. We predicted carnivore carcasses would persist longer due to conspecific and intraguild scavenger avoidance. Further, we hypothesized visually modifying carcasses would not reduce avoidance of carnivore carrion, given scavengers likely depend largely on chemical cues when assessing carrion resources. As expected, mammalian carnivores largely avoided scavenging on coyote carcasses, resulting in carnivore carcasses having longer depletion times than wild pig carcasses at intact and altered trials. Therefore, nutrients derived from carnivore carcasses are not as readily incorporated into higher trophic levels and scavengers largely depend on olfactory cues when assessing benefits and risks associated with varying carrion resources.

Testing the terrain hypothesis: Canada geese see their world laterally and obliquely.

The distribution of ganglion cells in the retina determines the specific regions of the visual field with high visual acuity, and thus reflects the perception of a species' visual environment. The terrain hypothesis proposes that animals living in open areas should have a horizontal visual streak across the retina with high ganglion cell density to increase visual acuity along the horizon. We tested this hypothesis in Canada geese (Branta canadensis) by assessing retinal topography, visual field configuration, and scanning behavior. We found that geese have an oblique rather than a horizontal visual streak across the retina: from a dorsal-nasal to a ventral-temporal position. Geese showed narrow blind areas, which increased the range of their lateral vision, and a relatively large degree of eye movement. Canada geese have relatively wide binocular fields and can see their bill tips. Goose head movement rates were low compared to species with a single fovea, and head movement rates increased in visually obstructed habitats. Canada geese have high acuity across their retina, which would allow them to simultaneously scan the ground and the sky when the head is up and parallel to the ground, as well as align the visual streak with the horizon when the head is tilted downwards. Their visual streak, along with their large eye size, may reduce the need for large amplitude head movements during vigilance bouts in visually unobstructed habitats. Overall, the visual system of geese combines features related to the detection of predators/conspecifics in open areas (visual streak, large lateral field, reduced head movements) as well as visual specializations that would allow for monitoring both the ground and sky (oblique streak) and for extracting and handling of food items (wide binocular fields, visualization of the bill tip).

Responses of turkey vultures to unmanned aircraft systems vary by platform.

A challenge that conservation practitioners face is manipulating behavior of nuisance species. The turkey vulture (Cathartes aura) can cause substantial damage to aircraft if struck. The goal of this study was to assess vulture responses to unmanned aircraft systems (UAS) for use as a possible dispersal tool. Our treatments included three platforms (fixed-wing, multirotor, and a predator-like ornithopter [powered by flapping flight]) and two approach types (30 m overhead or targeted towards a vulture) in an operational context. We evaluated perceived risk as probability of reaction, reaction time, flight-initiation distance (FID), vulture remaining index, and latency to return. Vultures escaped sooner in response to the fixed-wing; however, fewer remained after multirotor treatments. Targeted approaches were perceived as riskier than overhead. Vulture perceived risk was enhanced by flying the multirotor in a targeted approach. We found no effect of our treatments on FID or latency to return. Latency was negatively correlated with UAS speed, perhaps because slower UAS spent more time over the area. Greatest visual saliency followed as: ornithopter, fixed-wing, and multirotor. Despite its appearance, the ornithopter was not effective at dispersing vultures. Because effectiveness varied, multirotor/fixed-wing UAS use should be informed by management goals (immediate dispersal versus latency).

Landscape transformations produce favorable roosting conditions for turkey vultures and black vultures.

Recent increases in turkey vulture (Cathartes aura) and black vulture (Coragyps atratus) populations in North America have been attributed in part to their success adapting to human-modified landscapes. However, the capacity for such landscapes to generate favorable roosting conditions for these species has not been thoroughly investigated. We assessed the role of anthropogenic and natural landscape elements on roosting habitat selection of 11 black and 7 turkey vultures in coastal South Carolina, USA using a GPS satellite transmitter dataset derived from previous research. Our dataset spanned 2006-2012 and contained data from 7916 nights of roosting. Landscape fragmentation, as measured by land cover richness, influenced roosting probability for both species in all seasons, showing either a positive relationship or peaking at intermediate values. Roosting probability of turkey vultures was maximized at intermediate road densities in three of four seasons, and black vultures showed a positive relationship with roads in fall, but no relationship throughout the rest of the year. Roosting probability of both species declined with increasing high density urban cover throughout most of the year. We suggest that landscape transformations lead to favorable roosting conditions for turkey vultures and black vultures, which has likely contributed to their recent proliferations across much of the Western Hemisphere.

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

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

CauseSpec: a database of global terrestrial vertebrate cause-specific mortality.

As wildlife populations continue to decline worldwide, human-caused mortality of terrestrial vertebrates is of increasing importance. However, there is a limited understanding of how direct anthropogenic mortality compares in magnitude to natural mortality. Here, we present CauseSpec, a database of global terrestrial vertebrate cause-specific mortality. We compiled studies that used telemetry to monitor terrestrial vertebrates and determine cause of death. We distinguished between anthropogenic and natural mortality and also documented the specific mortality source where possible (e.g., harvest, vehicle collision, predation, and starvation). This database consists of 1,134 studies that collectively monitored the fates of 123,747 individual animals. From this, there are 43,998 deaths of known cause among 307 species. It is an updated version of the data set used in Hill et al. (2019) and will continue to be updated in the future. These data can be combined with data on species morphology and behavior to examine how species attributes influence susceptibility to various mortality sources. Our database also includes the geographic coordinates of the study site so that site attributes can be included in analyses. We also distinguish between adults and juveniles where possible, allowing for age-specific mortality analyses. Study start and end dates are available as well so that analyses of temporal changes in mortality are possible. Last, users can select all cause-specific mortality studies from a single species to perform a species-level analysis. The data set will allow users to circumvent a literature search, facilitating more rapid publication of large-scale vertebrate mortality studies and elucidating mortality patterns of terrestrial vertebrates around the world. There are no copyright or proprietary restrictions. We would like researchers to cite this paper if the associated database is used to find studies of interest for analysis.

Social information affects Canada goose alert and escape responses to vehicle approach: implications for animal-vehicle collisions.

BACKGROUND: Animal-vehicle collisions represent substantial sources of mortality for a variety of taxa and can pose hazards to property and human health. But there is comparatively little information available on escape responses by free-ranging animals to vehicle approach versus predators/humans. METHODS: We examined responses (alert distance and flight-initiation distance) of focal Canada geese (Branta canadensis maxima) to vehicle approach (15.6 m·s-1) in a semi-natural setting and given full opportunity to escape. We manipulated the direction of the vehicle approach (direct versus tangential) and availability of social information about the vehicle approach (companion group visually exposed or not to the vehicle). RESULTS: We found that both categorical factors interacted to affect alert and escape behaviors. Focal geese used mostly personal information to become alert to the vehicle under high risk scenarios (direct approach), but they combined personal and social information to become alert in low risk scenarios (tangential approach). Additionally, when social information was not available from the companion group, focal birds escaped at greater distances under direct compared to tangential approaches. However, when the companion group could see the vehicle approaching, focal birds escaped at similar distances irrespective of vehicle direction. Finally, geese showed a greater tendency to take flight when the vehicle approached directly, as opposed to a side step or walking away from the vehicle. CONCLUSIONS: We suggest that the perception of risk to vehicle approach (likely versus unlikely collision) is weighted by the availability of social information in the group; a phenomenon not described before in the context of animal-vehicle interactions. Notably, when social information is available, the effects of heightened risk associated with a direct approach might be reduced, leading to the animal delaying the escape, which could ultimately increase the chances of a collision. Also, information on a priori escape distances required for surviving a vehicle approach (based on species behavior and vehicle approach speeds) can inform planning, such as location of designated cover or safe areas. Future studies should assess how information from vehicle approach flows within a flock, including aspects of vehicle speed and size, metrics that affect escape decision-making.

Evidence of niche differentiation for two sympatric vulture species in the Southeastern United States.

BACKGROUND: As obligate scavengers utilizing similar habitats, interspecific competition undoubtedly occurs between resident black (Coragyps atratus) and turkey (Cathartes aura) vultures. In the interest of exploring how sympatric species coexist through habitat segregation, we examined resource selection of resident black and turkey vultures in the southeastern United States (US) for evidence of niche differentiation. METHODS: Using fine-scale movement data, we assessed interspecific seasonal differences in monthly roost reuse frequency and roost site fidelity, as well as monthly flight, roost, and diurnal rest site resource selection based on > 2.8 million locations of 9 black vultures and 9 turkey vultures tracked from September 2013 to August 2015 using Groupe Spécial Mobile/Global Positioning System (GSM/GPS) transmitters. RESULTS: Black vultures generally exhibited greater roost fidelity as well as a greater maximum number of nights spent at a single roost than turkey vultures. Patterns of flight, roost, and resting habitat selection within the home range varied monthly as well as between species, providing evidence for habitat segregation and niche differentiation by sympatric vultures. In particular, our results indicate the importance of wooded wetlands for resting and roosting locations for both species, and revealed clear differences in the use of forested habitats between species during flight, resting, and roosting behavioral states. CONCLUSIONS: By examining differences in resource selection and spatial ecology of black and turkey vultures across a range of behaviors, this study demonstrates mechanisms of niche differentiation in these ecologically similar species, and enhances potential for conservation and informed management of this important group of birds.

Quantification of avian hazards to military aircraft and implications for wildlife management.

Collisions between birds and military aircraft are common and can have catastrophic effects. Knowledge of relative wildlife hazards to aircraft (the likelihood of aircraft damage when a species is struck) is needed before estimating wildlife strike risk (combined frequency and severity component) at military airfields. Despite annual reviews of wildlife strike trends with civil aviation since the 1990s, little is known about wildlife strike trends for military aircraft. We hypothesized that species relative hazard scores would correlate positively with aircraft type and avian body mass. Only strike records identified to species that occurred within the U.S. (n = 36,979) and involved United States Navy or United States Air Force aircraft were used to calculate relative hazard scores. The most hazardous species to military aircraft was the snow goose (Anser caerulescens), followed by the common loon (Gavia immer), and a tie between Canada goose (Branta canadensis) and black vulture (Coragyps atratus). We found an association between avian body mass and relative hazard score (r2 = 0.76) for all military airframes. In general, relative hazard scores per species were higher for military than civil airframes. An important consideration is that hazard scores can vary depending on aircraft type. We found that avian body mass affected the probability of damage differentially per airframe. In the development of an airfield wildlife management plan, and absent estimates of species strike risk, airport wildlife biologists should prioritize management of species with high relative hazard scores.