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Illustration of a Turkey Vulture engaged in contorted soaring near tree height. The flight path, ~10 s in duration, deviates horizontally and vertically from a linear flight path while maintaining both altitude and general direction.
Source publication
Birds use atmospheric updrafts to subsidize soaring flight. We observed highly variable soaring flight by Black Vultures (Coragyps atratus) and Turkey Vultures (Cathartes aura) in Virginia, USA, that was inconsistent with published descriptions of terrestrial avian flight. Birds engaging in this behavior regularly deviated vertically and horizontal...
Context in source publication
Context 1
... flight pattern we describe here occurred when a focal bird flew with numerous vertical and horizontal deviations from a straight-line path (Figure 1). In spite of these small- scale deviations characteristic of the behavior, focal subjects generally maintained a mostly linear flight path with little net change in altitude or direction. ...
Citations
... Three of the studied birds performed a unique pattern of soaring over the sea, where they moved in an s-shape, similar to the control flight observed in large soaring raptors [39]. We did not observe this soaring pattern over the land. ...
... Larger species of soaring raptors, such as Turkey Vultures Cathartes aura, follow a characteristically tortuous flight path when gliding at low altitudes, changing their vertical and horizontal direction while maintaining the same altitude. This behavior was explained by the use of shear-induced turbulence generated in areas where weather conditions are not optimal for the formation of thermals [39]. Although turbulences can explain this S-shaped soaring behavior, we observed an increase in altitude. ...
Background
For soaring birds, the ability to benefit from variable airflow dynamics is crucial, especially while crossing natural barriers such as vast water bodies during migration. Soaring birds also take advantage of warm rising air, so-called thermals, that allow birds to ascend passively to higher altitudes with reduced energy costs. Although it is well known that soaring migrants generally benefit from supportive winds and thermals, the potential of uplifts and other weather factors enabling soaring behavior remains unsolved.
Methods
In this study, we GPS-tracked 19 Red Kites, Milvus milvus , from the Central European population that crossed the Adriatic Sea on their autumn migration. Migratory tracks were annotated with weather data (wind support, side wind, temperature difference between air and surface—proxy for thermal uplift, cloud cover, and precipitation) to assess their effect on Red Kites' decisions and soaring performance along their migration across the Adriatic Sea and land.
Results
Wind support affected the timing of crossing over the Adriatic Sea. We found that temperature differences and horizontal winds positively affected soaring sea movement by providing lift support in otherwise weak thermals. Furthermore, we found that the soaring patterns of tracked raptors were affected by the strength and direction of prevailing winds.
Conclusion
Thanks to modern GPS–GSM telemetry devices and available data from online databases, we explored the effect of different weather variables on the occurrence of soaring behavior and soaring patterns of migratory raptors. We revealed how wind affected the soaring pattern and that tracked birds could soar in weak thermals by utilizing horizontal winds, thus reducing energy costs of active flapping flight over vast water bodies.
... Vultures may roost in urban areas where they forage on trash and roadkill and use thermal currents from impervious surface cover for flight (Novaes and Cintra 2013;Campbell 2014). The contrasting surface temperatures of fragmented landscapes produce strong thermal currents that can serve as an attractant for roosting (Mallon et al. 2016;Novoselova et al. 2020). Roosts at greater elevations may be selected because they create greater uplift, which aids in flight (Thompson et al. 1990). ...
Roost locations can be an important contributor to vulture conflicts with humans, but factors influencing roost-site selection at a landscape level remain largely unexplored. Further, there has been little research comparing how these factors vary between nocturnal and diurnal roosting sites. We used remote cameras to document daily variation in vulture use of 21 roosts (20 communication/water towers and 1 natural roost) near Beaufort, South Carolina, USA from October 2019–August 2020. Numbers of vultures on roosts increased with decreasing urban cover and with greater distance to water, but were not influenced by habitat fragmentation or elevation. Roosts surrounded by greater proportions of urban cover were used more often during the day, whereas roosts adjacent to less urban cover were more commonly used at night. We suggest that this relationship results from a greater daytime association with human development, areas that likely provide food and favorable soaring conditions for vultures. Vultures tended to depart nocturnal roosts before sunrise and return within two hours of sunset, indicating that aircraft collision risk resulting from movement around nocturnal roosts would be elevated during these times. Several communication towers routinely had > 100 vultures roosting on them at once, likely contributing to conflict with humans. Our findings reiterate the generalism of these species and their capacity to exploit novel structures for roosting, which has likely contributed to range expansions and resultant increases in human-vulture conflicts over the past several decades.
... Our results on vultures resource selection are consistent with previous studies that found that black vultures avoid forest areas, whereas turkey vultures use forest areas more often [24,25]. Black vultures have higher wing loading than turkey vultures [63], which makes it difficult to exploit updrafts close to the ground and forest canopy [64]. This may explain why black vultures avoided forest areas before, during, and after extreme weather events; they would need larger energy investment to take-off. ...
... Conversely, turkey vultures selected for forest areas during the winter storm and the occurrence of tornadoes. Their ability to fly close to the forest canopy facilitates the use of forest areas providing protection against wind gusts and low temperatures [26,64]. ...
Extreme weather events such as hurricanes and tornadoes have been found to change the spatial and temporal abundance of raptors by decreasing survival and forcing the emigration of individuals, or by increasing habitat heterogeneity and facilitating recolonization of disturbed areas. Nonetheless, little is known about how extreme weather events could affect raptors’ movements and their space use in areas disturbed by large-scale weather events. We studied how extreme weather affected the movements of black and turkey vultures (Coragyps atratus and Cathartes aura, respectively) in Mississippi, USA, facing Hurricane Zeta in November 2020, winter storm Viola in February 2021, and tornados MS-43 and MS-44 in May 2021. We GPS-tracked 28 vultures in the paths of these events. We compared movement rates, net-squared displacements, and use of forest cover, before, during, and after the events. Since storm avoidance behavior has been observed in other birds, we expected that vultures would shift their movements out of the path of these events before storms hit. Further, we forecasted that vultures would make greater use of forested areas as protection against harsh conditions such as strong winds and heavy rain. Vultures responded differently to each weather event; they shifted their movements out of the predicted path of the hurricane and tornadoes but not the snowstorm. These findings reveal that both species use avoidance behavior and adjust their navigation and hazard detection accordingly. Avoidance behavior was more pronounced in turkey vultures than in black vultures. In general, vultures did not make greater use of forest areas as we expected, but turkey vultures did select forest areas during the snowstorm. We propose that olfaction and audition may be key in vultures’ response to extreme weather events.
... So adept are they at exploiting local updrafts that gulls are even able to soar small-scale landscape features such as roads and tree lines [24]. The accompanying turbulence makes this a challenge, but may be actively exploited by some specialist soarers such as turkey vultures that also fly along tree lines [74]; see below. Gulls flying ahead of seafront buildings have been found to favour parts of the wind field in which the effects of gusts are reduced [22]. ...
... Turkey vultures (figure 1d), for example, have a 30% lower wing-loading than black vultures (figure 1c) of similar body mass, which allows them to ascend in weaker thermal conditions and hence earlier in the day [79]. Conversely, it makes them less well suited to covering long distances after leaving a thermal, which may at least partly explain why they remain closer to the ground than species with higher wing-loadings [74,79]. Specific foodsearching strategies may influence this preference, as flying closer to the ground may help in sensing odour cues versus relying on visual cues at higher altitudes. ...
... Both phenomena are used by pelagic birds to glide great distances without flapping, and the largest albatrosses have been tracked flying using this technique for over 13 days at 950 km per day [111]. Spatial gradients are also ubiquitous in well-developed turbulence and may therefore be used by birds for gradient soaring [74], but as these gradients are usually unpredictable, they effectively blend with gust soaring. Equation (2.1) shows that the specific energy flow associated with gradient soaring is ...
The use of flying robots (drones) is increasing rapidly, but their utility is limited by high power demand, low specific energy storage and poor gust tolerance. By contrast, birds demonstrate long endurance, harvesting atmospheric energy in environments ranging from cluttered cityscapes to open landscapes, coasts and oceans. Here, we identify new opportunities for flying robots, drawing upon the soaring flight of birds. We evaluate mechanical energy transfer in soaring from first principles and review soaring strategies encompassing the use of updrafts (thermal or orographic) and wind gradients (spatial or temporal). We examine the extent to which state-of-the-art flying robots currently use each strategy and identify several untapped opportunities including slope soaring over built environments, thermal soaring over oceans and opportunistic gust soaring. In principle, the energetic benefits of soaring are accessible to flying robots of all kinds, given atmospherically aware sensor systems, guidance strategies and gust tolerance. Hence, while there is clear scope for specialist robots that soar like albatrosses, or which use persistent thermals like vultures, the greatest untapped potential may lie in non-specialist vehicles that make flexible use of atmospheric energy through path planning and flight control, as demonstrated by generalist flyers such as gulls, kites and crows.
... Flying animals will experience gusts when velocity fluctuations are of a magnitude at least as large as the wing chord or span. Experiments, mostly done in laboratory conditions, have shown that gusts can impact flight control [10,11] and flight costs [12][13][14]. As such, gustiness is relevant for birds irrespective of their flight style and body mass. ...
All animals that operate within the atmospheric boundary layer need to respond to aerial turbulence. Yet little is known about how flying animals do this because evaluating turbulence at fine scales (tens to approx. 300 m) is exceedingly difficult. Recently, data from animal-borne sensors have been used to assess wind and updraft strength, providing a new possibility for sensing the physical environment. We tested whether highly resolved changes in altitude and body acceleration measured onboard solo-flying pigeons (as model flapping fliers) can be used as qualitative proxies for turbulence. A range of pressure and acceleration proxies performed well when tested against independent turbulence measurements from a tri-axial anemometer mounted onboard an ultralight flying the same route, with stronger turbulence causing increasing vertical displacement. The best proxy for turbulence also varied with estimates of both convective velocity and wind shear. The approximately linear relationship between most proxies and turbulence levels suggests this approach should be widely applicable, providing insight into how turbulence changes in space and time. Furthermore, pigeons were able to fly in levels of turbulence that were unsafe for the ultralight, paving the way for the study of how freestream turbulence affects the costs and kinematics of animal flight.
... These act as outboard and external sources of energy during different soaring flight mode types. The topography of any particular region and the hindrances that it causes can also be included whilst discussing turbulent atmospheric conditions [3] [4]. Weather conditions of different terrains and regions aid in the lift generating techniques used by different bird species [5]. ...
This review tends to shed light on the eagle's aerodynamic attributes along with its inbuilt structural control surfaces that facilitate its high maneuverability. Apart from this, few aspects of the eagle's wing morphing techniques, its aerofoil, and its aerodynamic stability are also being highlighted. The aim is to highlight the bio-mimicable traits of an eagle which can be incorporated into bionic UAVs. This work acts as a base for current and future works involving slotted wingtips and bionic control surfaces. The traits discussed are being used to design mechanical control surfaces and wingtips that resemble the eagle's slotted wings and control surfaces. These works when combined with compliant mechanisms can help improve roll and yaw control of a UAV along with drag reduction. This review also highlights the aerodynamics of flapping; specifically of the hummingbird. From the hummingbird's aerodynamics to its hovering techniques; all of its main features are being highlighted. These birds have demonstrated a wide range of aerodynamic traits which if mimicked to near perfection could pave the way for new-age drones. Maneuverability and enhanced aerodynamic optimality could be the outset of extreme sustainability measures with these birds paving the way with their evolutionary flight measures. Apart from their aerodynamic traits, a few aspects of their wing morphing techniques and their evolutionary hereditary traits are also being highlighted.
... The different soaring behaviour of these two species also underline their contrasting foraging strategies. While black vultures tend to soar high using thermal uplift, from where they have a wide range of sight, turkey vultures are particularly prone to use contorted soaring, a low altitude soaring mode that relies on shear-induced turbulence (Mallon et al. 2015). ...
New World vultures have been considerably studied regarding their sense of smell. Cathartes species present a remarkable development of their olfactory apparatus, and experiments conducted with the turkey vulture (Cathartes aura) demonstrated that they can locate carrion exclusively by smell at considerable distances. Black vultures (Coragyps atratus), because of their less developed olfactory apparatus, have been compared with the turkey vulture as a phylogenetically related species lacking the sense of smell. However, little evidence from behavioural studies supports the lack of olfaction of black vultures. We conducted a field experiment where we presented urban black vultures a binary choice of decaying fish and sand (serving as control) inside plastic bags. Birds chose the fish bait in 81% of the times they approached the plastic bags. The probability of reaction decreased significantly with the distance between the birds and the fish bait, being virtually null at 40–50 m away. Furthermore, birds clearly reacted more when the fish presented higher decaying time (7 compared to 2 days). These results show that olfaction is not only used by black vultures but is probably the most relevant sense when they search for food hidden in plastic bags and in piles of unsorted waste, which is the most common foraging environment for this species in urban areas where they are very abundant.
... Additionally, fragmented landscapes could be beneficial by combining these attributes from developed land with open areas that facilitate detection of carrion 21 . The interfaces of open areas and forests occurring as a result of habitat fragmentation may facilitate flight through obstruction currents, produced when wind strikes the tree line 18,26,27 . Furthermore, landscape fragmentation results in contrasting surface temperatures, which produces strong thermal currents that vultures heavily use for flight 23 . ...
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.
... Soaring birds are especially sensitive to changing weather conditions because they rely on the availability of environmental updrafts to subsidize flight. Although terrestrial birds can soar using orographic updrafts [9] or turbulence [10] to subsidize flight, thermals [8] are the most important type of updraft for most soaring migrants because thermals are widely distributed across the landscape [11], allow birds to reach altitudes necessary for fast cross-country soaring, and allow for straight, efficient flight paths [12]. Thermals (i.e., vortices of ascending hot air surrounded by descending cooler air) [11,13] are generated by differential heating of the earth's surface. ...
... Next, we evaluated when Turkey Vultures began their stopovers, relative to changing local weather conditions. As obligate scavengers, Turkey Vultures have several behavioral and physiological adaptations to minimize energetic costs [10,26,27]. We hypothesized that, to further minimize energetic costs, Turkey Vultures should fly as long as weather conditions allow for energy-efficient soaring flight and would stop as soon as weather conditions deteriorate, rather than switch to flapping flight [28,29]. ...
Background:
Migrating birds experience weather conditions that change with time, which affect their decision to stop or resume migration. Soaring migrants are especially sensitive to changing weather conditions because they rely on the availability of environmental updrafts to subsidize flight. The timescale that local weather conditions change over is on the order of hours, while stopovers are studied at the daily scale, creating a temporal mismatch.
Methods:
We used GPS satellite tracking data from four migratory Turkey Vulture (Cathartes aura) populations, paired with local weather data, to determine if the decision to stopover by migrating Turkey Vultures was in response to changing local weather conditions. We analyzed 174 migrations of 34 individuals from 2006 to 2019 and identified 589 stopovers based on variance of first passage times. We also investigated if the extent of movement activity correlated with average weather conditions experienced during a stopover, and report general patterns of stopover use by Turkey Vultures between seasons and across populations.
Results:
Stopover duration ranged from 2 h to more than 11 days, with 51 % of stopovers lasting < 24 h. Turkey Vultures began stopovers immediately in response to changes in weather variables that did not favor thermal soaring (e.g., increasing precipitation fraction and decreasing thermal updraft velocity) and their departure from stopovers was associated with improvements in weather that favored thermal development. During stopovers, proportion of activity was negatively associated with precipitation but was positively associated with temperature and thermal updraft velocity.
Conclusions:
The rapid response of migrating Turkey Vultures to changing weather conditions indicates weather-avoidance is one of the major functions of their stopover use. During stopovers, however, the positive relationship between proportion of movement activity and conditions that promote thermal development suggests not all stopovers are used for weather-avoidance. Our results show that birds are capable of responding rapidly to their environment; therefore, for studies interested in external drivers of weather-related stopovers, it is essential that stopovers be identified at fine temporal scales.
... Cloud cover was the main weather variable which could directly impact both birds' visibility and thermal uplift velocity (Mallon et al., 2016;Shamoun-Baranes et al., 2017). Thus, we used cloud cover as a proxy of visibility and potential driver of flight altitude, as it could influence white storks to fly at lower altitudes, closer to a collision risk altitude. ...
... Cloud cover can influence flight altitudes not only through limiting visibility during twilight hours and in foggy days, but also through lower uplift velocities. This behaviour is described for other soaring birds such as turkey vultures (Cathartes aura) and black vultures (Coragyps atratus), that tend to engage less in thermal soaring when cloud cover is high (Mallon et al., 2016), and consequently, fly at lower altitudes. ...
Anthropogenic structures are increasingly encroaching wildlife habitats, creating conflicts between humans and animals. Scaling up renewable energy requires new infrastructures such as power lines, that cause high mortality among birds since they act as obstacles to flight and are used for perching and nesting, which can result in collisions or electrocutions. These interactions often endanger wildlife populations and may also result in high financial costs for companies. Flight behaviour plays a crucial role in collision risk, and the study of flight altitudes enables us to understand what drives birds to fly at collision risk altitudes. This allows the identification of high-risk areas, conditions and bird behaviours, and the implementation of mitigation measures by power line companies. In this study, we use boosted random tree modelling to identify drivers of white stork (Ciconia ciconia) flight altitudes and to investigate the factors that lead them to fly at collision risk altitudes. We found that the main drivers of flight altitude for this soaring bird species were time of day, distance to the nearest landfill site and cloud cover density. Bird age, habitat type and season were comparatively less important. Collision risk increases during crepuscular hours near landfill sites, also in days with high cloud cover density and during the breeding season. In recent years, hundreds to thousands of storks congregate daily at landfill sites to take advantage of the predictability and superabundance of anthropogenic food waste. Some of these sites have high density of power lines, becoming collision risk hotspots for storks and other landfill users. Despite being susceptible to collision, our results suggest that white storks can avoid power lines to a certain extent, by changing their flight altitude at ca. 80 m from these structures. This study shows that the implementation of mitigation measures for existing power lines should be prioritized in areas in the vicinity of landfill sites within white stork distribution ranges, and the projection of new lines should avoid those areas. These measures would benefit species vulnerable to mortality due to power line collision, and it would also reduce associated power outages and economic costs.
