Low Wing Loading Research Articles

Evolution of Traditional Aerodynamic Variables in Bats (Mammalia: Chiroptera) within a Comprehensive Phylogenetic Framework

Chiroptera is the only group of mammals capable of powered flight. The mechanical basis of bat flight is well established, but evolution of its constituent aerodynamic variables remains poorly understood. Here, we determine the macroevolutionary patterns of traditional aerodynamic variables (wing loading, aspect ratio, tip shape index) in a comprehensive phylogeny of Chiroptera using an extensive dataset including key Eocene fossils. We optimized variables as continuous characters and fit models of character evolution to identify shifts in character optima. The reconstructed ancestral chiropteran morphotype presented low wing loading and low-to-intermediate aspect ratio, and remained unaltered for much of the first half of bat evolution (Paleogene). This evolutionary pattern may be explained by stabilizing selection responding to the strong constraints imposed by echolocation and flight on body size, and the physical constraints regarding aerodynamic efficiency acting on wing shape. Posterior specialization in some groups permitted divergence toward novel aerodynamic morphotypes in the second half of chiropteran evolutionary history (Neogene). We linked the most notable aerodynamic changes to ecological release from echolocation constraints (Pteropodidae), dietary-foraging shifts (Phyllostomidae, Noctilionidae), or advantage in face of environmental changes (Molossidae, Taphozoinae). The independently-evolved specialization of fast, enduring flight that allowed Molossidae and Taphozoinae (Emballonuridae) to perform aerial hawking of swarming insects in open spaces was linked to significant shifts in the optima of both wing loading and aspect ratio. These shifts were probably associated with the gradual spread of open-mosaic landscapes at a global scale since the Oligocene.

Wing morphology predicts geographic range size in vespertilionid bats

Why some species are widespread across continents while others are confined geographically remains an open question in ecology and biogeography. Previous research has attempted to explain interspecific variation in geographic range size based on differences in dispersal ability. However, the relationship between dispersal ability and geographic range size remains uncertain, particularly in mammals. The goal of this study is to test whether geographic range size can be predicted by dispersal capacity among vespertilionid bats within a phylogenetic comparative framework. We integrated a large dataset on range area, longitudinal extent, wing morphology (a proxy for dispersal ability), migratory habit, and biogeographic realm across 126 vespertilionid bat species. We used phylogenetic regressions to disentangle the associations between these predictor factors and species range size while controlling for the effects of migration and biogeographic realm. Our analyses revealed that bat species with higher wing loading exhibit larger distribution ranges than those with lower wing loading, and that the size of geographic ranges was associated with wing aspect ratio in bats. These results highlight the relationship between wing morphology and range size in flying mammals, and suggest a role of dispersal capacity in shaping species’ geographic distributions.

Eye and wing structure closely reflects the visual ecology of dung beetles.

An important resource partitioning strategy allowing dung beetles to coexist in the same habitat, while utilising the same food, is species' separation of activity times. After establishing the diel activity period of three closely related, co-occurring dung beetles, we examined their eye and wing morphology. Absolute and relative eye size, and facet size were greater in the nocturnal Escarabaeus satyrus, followed by the crepuscular Scarabaeus zambesianus and then the diurnal Kheper lamarcki. The diurnal K. lamarcki had the highest wing aspect ratio (long, narrow wings), followed by the crepuscular S. zambesianus and the nocturnal E. satyrus (short, broad wings), suggesting that dim-light active species fly slower than diurnal species. In addition, the two species active in dim light had a lower wing loading than the diurnal species, indicating the need for greater manoeuvrability in the dark. Analyses of wing shape revealed that the diurnal K. lamarcki wing had a proportionally larger jugal and anal region than both dim light species. Our results show that different species of dung beetles have a combination of optical and morphological wing adaptations to support their foraging activities in diverse light conditions.

Contrasting effects of habitat discontinuity on three closely related fungivorous beetle species with diverging host-use patterns and dispersal ability.

Understanding how landscape structure influences biodiversity patterns and ecological processes are essential in ecological research and conservation practices. Forest discontinuity is a primary driver affecting the population persistence and genetic structure of forest‐dwelling species. However, the actual impacts on populations are highly species‐specific. In this study, we tested whether dispersal capability and host specialization are associated with susceptibility to forest discontinuity using three closely related, sympatric fungivorous ciid beetle species (two host specialists, Octotemnus assimilis and O. crassus; one host generalist, O. kawanabei). Landscape genetic analyses and the estimation of effective migration surfaces (EEMS) method consistently demonstrated contrasting differences in the relationships between genetic structure and configuration of forest land cover. Octotemnus assimilis, one of the specialists with a presumably higher dispersal capability due to lower wing loading, lacked a definite spatial genetic structure in our study landscape. The remaining two species showed clear spatial genetic structure, but the results of landscape genetic analyses differed between the two species: while landscape resistance appeared to describe the spatial genetic structure of the specialist O. crassus, genetic differentiation of the generalist O. kawanabei was explained by geographic distance alone. This finding is consistent with the prediction that nonforest areas act more strongly as barriers between specialist populations. Our results suggest that differences in host range can influence the species‐specific resistance to habitat discontinuity among closely related species inhabiting the same landscape.

Hymenoptera flight muscle mitochondrial function: Increasing metabolic power increases oxidative stress

Insect flight is a high intensity activity, but biomechanical and metabolic requirements may vary depending on life style and feeding mode. For example, bees generally feed on pollen and nectar, whereas wasps also actively hunt and scavenge heavy prey. These variations in metabolic demands may result in different capacities of metabolic pathways in flight muscle, and utilisation some of these pathways may come at a cost of increased free radical production. To examine how metabolic requirements and oxidative stress vary between species, we explored the variation in flight mechanics and metabolism of the honeybee (Apis mellifera), bumblebee (Bombus terrestris), and German wasp (Vespula germanica). Wing structures and flight muscle properties were compared alongside measures of oxygen flux and reactive oxygen species (ROS) production from permeabilised flight muscle. The wasp wing structure is best adapted for carrying heavy loads, with the highest wing aspect ratio, lowest wing loading, and highest flight muscle ratio. Bumblebees had the lowest wing aspect ratio and flight muscle ratio, and highest wing loading. Although wasps also had the highest rates of oxygen consumption during oxidative phosphorylation, oxygen consumption did not increase in the wasp muscle following chemical uncoupling, while it did for the two bee species. While mitochondrial glycerol 3-phosphate dehydrogenase (mGPDH) mediated oxygen flux was greatest in wasps, muscle fibres released greater amounts of ROS through this pathway. Overall, the wasp has maximised lifting capacities through varying wing and flight muscle mass and by maximising OXPHOS capacities, and this accompanies elevated ROS production.

Design, Optimization and Manufacturing of Metallic Wings of Light Aircraft

Most of the wing structures of modern leisure and sport aircraft, such as LSA, VLA, ultralights, etc., are made of composite materials. These latter allow for high surface quality and lower costs, if compared to metallic solutions with conventional riveted technology, which would be adopted as production volumes are small. Assuming a greater production volume, proper of an industrial production, the metallic solution can become a viable alternative considering an automatic welding technology, instead of riveted junctions. Although welded solutions bring with them issues in terms of fatigue resistance, the low wing loading typical of LSA/VLA allows to mitigate the mass increase and to obtain a proper design. This paper shows how wing structures made of light metallic alloys with welded junctions could be a feasible solution, presenting some results related to the design of an innovative light amphibian object of study within the research project “IDINTOS”. The activities here presented concern the optimization methodology for the design of metallic wing structures, the detail design through Finite Element Methods and the set-up of a technology demonstrator of the manufacturing process.

A new clade of basal Early Cretaceous pygostylian birds and developmental plasticity of the avian shoulder girdle

Early members of the clade Pygostylia (birds with a short tail ending in a compound bone termed "pygostyle") are critical for understanding how the modern avian bauplan evolved from long-tailed basal birds like Archaeopteryx However, the currently limited known diversity of early branching pygostylians obscures our understanding of this major transition in avian evolution. Here, we describe a basal pygostylian, Jinguofortis perplexus gen. et sp. nov., from the Early Cretaceous of China that adds important information about early members of the short-tailed bird group. Phylogenetic analysis recovers a clade (Jinguofortisidae fam. nov.) uniting Jinguofortis and the enigmatic basal avian taxon Chongmingia that represents the second earliest diverging group of the Pygostylia. Jinguofortisids preserve a mosaic combination of plesiomorphic nonavian theropod features such as a fused scapulocoracoid (a major component of the flight apparatus) and more derived flight-related morphologies including the earliest evidence of reduction in manual digits among birds. The presence of a fused scapulocoracoid in adult individuals independently evolved in Jinguofortisidae and Confuciusornithiformes may relate to an accelerated osteogenesis during chondrogenesis and likely formed through the heterochronic process of peramorphosis by which these basal taxa retain the scapulocoracoid of the nonavian theropod ancestors with the addition of flight-related modifications. With wings having a low aspect ratio and wing loading, Jinguofortis may have been adapted particularly to dense forest environments. The discovery of Jinguofortis increases the known ecomorphological diversity of basal pygostylians and highlights the importance of developmental plasticity for understanding mosaic evolution in early birds.

Design and testing of three tailless unmanned aerial vehicle configurations built for surveillance in Antarctic environment

The tailless fixed-wing aircraft have a very compact design and therefore are very attractive as portable unmanned aerial vehicle (UAV) platforms. There is a special need for using such platforms in case of operations in such backlands as Antarctica, because very often the equipment necessary for preparing improvised airfields near Antarctic scientific bases and organizing the UAV flights must be hand-carried. The main aim of this paper is to present the design activity and testing of a number of UAV configurations to be used for aerial monitoring in Antarctic areas and collecting data of local ecosystems. Two UAV flying-wing platforms – MONICA-1 and MONICA-2 – were developed, differing largely with respect to wing-loading and weight-to-power ratios. The light-weight Skywalker X-8 built from the kit and used as a baseline configuration was adapted for special photogrammetric missions. It was found that the main advantage of such light UAV consists in a very simple take-off system (i.e. bungee), however due to low wing loading a usage of this UAV is limited to the so-called ‘weather windows’ of relatively low wind, which do not frequently occur in Antarctica. MONICA-1 is much less sensitive to gust but as a heavy platform it is more difficult to handle in harsh Antarctic environment. To be able to operate in much wider range of the wind, vertical gust and heavy turbulence, typical for Antarctic zones, a special UAV platform – called MONICA-2 – was designed and manufactured. MONICA-2 platform of higher wing loading is smaller than the X-8 and at the same time is able to carry the same photogrammetry equipment. The effort of designers focused on achieving low sensitivity to gust and turbulence by increasing the critical angle of attack and natural static and dynamic stability in the whole range of operational speeds. The paper contains the selected design details and some observations from the flight tests.

Morphometric analysis of wild-caught flies of Drosophila (Diptera: Drosophilidae) species: Altitudinal pattern of body size traits, wing morphology and sexual dimorphism

Literature concerning phenotypic variation among wild-caught drosophilids inhabiting varied ecological habitats is relatively rare. The present study explores pattern of body size traits along altitudinal gradients, and compensation to colder environments and reduced air pressure via adjustment of wing morphology at higher altitudes. Wild adult flies were collected in two extensive surveys during September-October 2014 and April-May 2015. All traits were measured for both the sexes to obtain data on sexual dimorphism. It was found that though these populations differed significantly in their size, as already known, they deviated from the expected reaction norms of size increase along altitudinal gradients as observed in several previous studies. This deviation from normal clinal trend can be attributed to variation in growth rates and development times at different altitudes which has important implications in overall reproductive success. Also, a significant increase in wing area of flies at higher altitude was recorded with dramatically lower wing loadings than flies that developed in comparatively warmer habitats, giving them an aerodynamic advantage at cold temperatures. Thorax width was also analyzed, possibly for the first time in wild-caught flies of Indian populations, revealing sexual dimorphism. The ratio of thorax length to width was greater than one for all species indicating that the thorax is more elongated in females, which may also influence the flight capacity of the sexes.

Species With Greater Aerial Maneuverability Have Higher Frequency of Collisions With Aircraft: A Comparative Study

Antipredator responses may appear unsuccessful when animals are exposed to approaching vehicles, often resulting in mortality. Recent studies have addressed whether certain biological traits are associated with variation in collision risk with cars, but not with higher speed-vehicles like aircraft. Our goal was to establish the association between different species traits (i.e., body mass, eye size, brain size, wing loading, wing aspect ratio) and the frequency of bird collisions with aircraft (hereafter, bird strikes) using a comparative approach controlling for the effects of shared ancestry. We proposed directional predictions as to how each of the species traits would affect the frequency of bird strikes. Considering 39 bird species with all traits represented, the model containing wing loading had the best fit to account for the variance in bird strikes across species. In another model with 54 species exploring the fit to different polynomial models but considering only wing loading, we found that wing loading was negatively and linearly associated with the frequency of bird strikes. Counterintuitively, species with lower wing loading (hence, higher maneuverability) had a higher frequency of bird strikes. We discuss potential non-mutually exclusive explanations (e.g., high wing loading species fly faster, thus gaining some extra time to avoid the aircraft flight path; high wing loading species are hazed more intensively at airports, which could lower collisions, etc.). Ultimately, our findings uncovered that species with low wing loading get struck at a higher rate at airports, which reduces the safety risk for humans because these species tend not to cause damaging strikes, but the consequences of their potentially higher local mortality are unknown.

Experimental Characterization of a Butterfly in Climbing Flight

An optical tracking facility was used to record the free flight of the Monarch butterfly for a large number of sequential flaps. The system automatically tracked reflective markers, which were modified to reduce the effects of additional mass on the flight characteristics. Measurements were analyzed over 75 flights of 9 butterflies in a climbing trajectory covering a large range of climbing rates. The flapping frequency remained fairly constant at 9.8 Hz. The peak-to-peak flapping amplitude varied more significantly with an average of 246.4°. The phase offset between flapping and body undulation averaged 89°. The body oscillation amplitude was 4.9 mm. Simulations using Theodorsen’s equation coupled with a single mass dynamics equation resulted in a body motion that closely agreed with the observed data. The undulation amplitude increased with the flapping amplitude, but decreased with wing loading. Butterflies have the lowest wing loading among insects, consistent with their large body undulation amplitudes. The wing–body phase offset solely depends on the reduced frequency, a consequence of the timing between the noncirculatory and circulatory forces. These results suggest that this novel experimental framework can increase our understanding of biological flight and development of micro flapping robots.

Mixed effects of gating subterranean habitat on bats: A review

ABSTRACTCaves and abandoned mines, roosting environments for many bat species including subterranean obligates, are under human pressure (e.g., recreation) and pose threats to humans. Gating entrances of these subterranean features prevents human entry while protecting habitat for bats. However, bat response to these gates is not well understood and no comprehensive synthesis with species‐specific recommendations on protection measures for bat roosts exists. We reviewed literature on effects of gating subterranean habitat on bats and roost microclimate and found 22 studies and reports from North America, Australia, Europe, and Asia. Ten studies examined effects of gating on bat use, 9 described behavioral responses to gates, and 5 presented effects of gates on roost microclimate. Older gate designs (1950–1970), such as cement walls or iron doors, negatively affected bat use and roost microclimate, but responses to modern (1970s to present), bat‐compatible gate designs varied. Short‐term responses of bats to bat‐compatible gates were negative and included increases in energetically expensive flight behaviors. Although long‐term responses included a mix of population and species trends, we attribute these mixed responses in part to differences in flight agility among species. Bats with moderate to high agility (low wing loading, broad call bandwidths) adjust to gates, but species with low agility (high wing loading and narrow call bandwidths) may abandon sites after gating. Other factors including bat density in roosts and size of the cave or mine entrance also affect acceptance of gates and should be considered in gate design. Current gate designs are adequate for most species. Based on available literature, we recommend use of bat‐compatible gates with horizontal bar spacing of 14.6 cm, bar types that offer high structural rigidity in areas where vandalism is likely, and periodic monitoring of gates to ensure they remain in good condition. © 2017 The Wildlife Society.

Wing size but not wing shape is related to migratory behavior in a soaring bird

Both wing size and wing shape affect the flight abilities of birds. Intra and inter‐specific studies have revealed a pattern where high aspect ratio and low wing loading favour migratory behaviour. This, however, have not been studied in soaring migrants. We assessed the relationship between the wing size and shape and the characteristics of the migratory habits of the turkey vulture Cathartes aura, an obligate soaring migrant. We compared wing size and shape with migration strategy among three fully migratory, one partially migratory and one non‐migratory (resident) population distributed across the American continent. We calculated the aspect ratio and wing loading using wing tracings to characterize the wing morphology. We used satellite‐tracking data from the migratory populations to calculate distance, duration, speed and altitude during migration. Wing loading, but not aspect ratio, differed among the populations, segregating the resident population from the completely migratory ones. Unlike what has been reported in species using flapping flight during migration, the migratory flight parameters of turkey vultures were not related to the aspect ratio. By contrast, wing loading was related to most flight parameters. Birds with lower wing loading flew farther, faster, and higher during their longer journeys. Our results suggest that wing morphology in this soaring species enables lower‐cost flight, through low wing‐loading, and that differences in the relative sizes of wings may increase extra savings during migration. The possibility that wing shape is influenced by foraging as well as migratory flight is discussed. We conclude that flight efficiency may be improved through different morphological adaptations in birds with different flight mechanisms.

Features of owl wings that promote silent flight.

Owls are an order of birds of prey that are known for the development of a silent flight. We review here the morphological adaptations of owls leading to silent flight and discuss also aerodynamic properties of owl wings. We start with early observations (until 2005), and then turn to recent advances. The large wings of these birds, resulting in low wing loading and a low aspect ratio, contribute to noise reduction by allowing slow flight. The serrations on the leading edge of the wing and the velvet-like surface have an effect on noise reduction and also lead to an improvement of aerodynamic performance. The fringes at the inner feather vanes reduce noise by gliding into the grooves at the lower wing surface that are formed by barb shafts. The fringed trailing edge of the wing has been shown to reduce trailing edge noise. These adaptations to silent flight have been an inspiration for biologists and engineers for the development of devices with reduced noise production. Today several biomimetic applications such as a serrated pantograph or a fringed ventilator are available. Finally, we discuss unresolved questions and possible future directions.

Effect of Wind on the Flight of Brown Booby Fledglings

Abstract There is increasing evidence showing that wind velocity affects the flight and foraging behavior of seabirds; however, few studies have examined these effects on seabirds inhabiting tropical oceans where lighter wind conditions usually prevail. The Brown Booby Sula leucogaster is an example of a tropical seabird with relatively low wing loading; strong wind conditions may be expected to impede the stability of their flight. We examined how different wind conditions affected the duration and flying behavior of Brown Booby fledglings during foraging trips by means of direct observation of nest attendance and by attaching video loggers to birds. The duration of foraging trips by fledglings decreased with increasing wind speed, and during flight, the body rotation of fledglings became greater with increasing wind speed. As expected, fledglings were buffeted by strong winds due to their relative inexperience in flight combined with their low wing loading. Fledglings were probably forced to flap agains...

Wake structure and kinematics in two insectivorous bats.

We compare kinematics and wake structure over a range of flight speeds (4.0-8.2 m s(-1)) for two bats that pursue insect prey aerially, Tadarida brasiliensis and Myotis velifer Body mass and wingspan are similar in these species, but M. velifer has broader wings and lower wing loading. By using high-speed videography and particle image velocimetry of steady flight in a wind tunnel, we show that three-dimensional kinematics and wake structure are similar in the two species at the higher speeds studied, but differ at lower speeds. At lower speeds, the two species show significant differences in mean angle of attack, body-wingtip distance and sweep angle. The distinct body vortex seen at low speed in T. brasiliensis and other bats studied to date is considerably weaker or absent in M. velifer We suggest that this could be influenced by morphology: (i) the narrower thorax in this species probably reduces the body-induced discontinuity in circulation between the two wings and (ii) the wing loading is lower, hence the lift coefficient required for weight support is lower. As a result, in M. velifer, there may be a decreased disruption in the lift generation between the body and the wing, and the strength of the characteristic root vortex is greatly diminished, both suggesting increased flight efficiency.This article is part of the themed issue 'Moving in a moving medium: new perspectives on flight'.

Ecomorphological differences in foraging and pattering behavior among storm-petrels in the eastern Pacific Ocean

ABSTRACT For closely related species, differences in morphology can provide insight into the evolutionary history of a taxonomic group, as well as mechanisms for ecological segregation. Storm-petrels are among the smallest seabirds, and their greatest taxonomic diversity occurs in the eastern Pacific Ocean. Some storm-petrels exhibit a unique foraging behavior, known as “pattering” or “sea-anchor soaring,” in which they appear to walk on the surface of the ocean, but this behavior is used to a varying degree among species. We compared morphological traits related to the pattering behavior in 9 species of storm-petrels that breed in the eastern Pacific. Measurements on the wing (wing loading, aspect ratio), beak (size), and leg (length and foot size) were analyzed using a discriminant function analysis (DFA). A thin-plate spline/relative warp analysis was also used to detect subtle differences in wing shape. Species that patter the most have low wing loading, low foot loading, and a long tarsus and were di...

Flight mode affects allometry of migration range in birds.

Billions of birds migrate to exploit seasonally available resources. The ranges of migration vary greatly among species, but the underlying mechanisms are poorly understood. I hypothesise that flight mode (flapping or soaring) and body mass affect migration range through their influence on flight energetics. Here, I compiled the tracks of migratory birds (196 species, weighing 12-10350g) recorded by electronic tags in the last few decades. In flapping birds, migration ranges decreased with body mass, as predicted from rapidly increasing flight cost with increasing body mass. The species with higher aspect ratio and lower wing loading had larger migration ranges. In soaring birds, migration ranges were mass-independent and larger than those of flapping birds, reflecting their low flight costs irrespective of body mass. This study demonstrates that many animal-tracking studies are now available to explore the general patterns and the underlying mechanisms of animal migration.

Intra-specific variation in wing morphology and its impact on take-off performance in blue tits (Cyanistes caeruleus) during escape flights.

ABSTRACTDiurnal and seasonal increases in body mass and seasonal reductions in wing area may compromise a bird's ability to escape, as less of the power available from the flight muscles can be used to accelerate and elevate the animal's centre of mass. Here, we investigated the effects of intra-specific variation in wing morphology on escape take-off performance in blue tits (Cyanistes caeruleus). Flights were recorded using synchronised high-speed video cameras and take-off performance was quantified as the sum of the rates of change of the kinetic and potential energies of the centre of mass. Individuals with a lower wing loading, WL (WL=body weight/wing area) had higher escape take-off performance, consistent with the increase in lift production expected from relatively larger wings. Unexpectedly, it was found that the total power available from the flight muscles (estimated using an aerodynamic analysis) was inversely related to WL. This could simply be because birds with a higher WL have relatively smaller flight muscles. Alternatively or additionally, variation in the aerodynamic load on the wing resulting from differences in wing morphology will affect the mechanical performance of the flight muscles via effects on the muscle's length trajectory. Consistent with this hypothesis is the observation that wing beat frequency and relative downstroke duration increase with decreasing WL; both are factors that are expected to increase muscle power output. Understanding how wing morphology influences take-off performance gives insight into the potential risks associated with feather loss and seasonal and diurnal fluctuations in body mass.

Measuring Intraspecific Variation in Flight-Related Morphology of Monarch Butterflies (Danaus plexippus): Which Sex Has the Best Flying Gear?

Optimal flight in butterflies depends on structural features of the wings and body, including wing size, flight muscle size, and wing loading. Arguably, there is no butterfly for which flight is more important than the monarch (Danaus plexippus), which undergoes long-distance migrations in North America. We examined morphological features of monarchs that would explain the apparent higher migratory success and flight ability of females over males. We examined 47 male and 45 female monarch specimens from a project where monarchs were reared under uniform conditions. We weighed individual body parts, including the thorax (flight muscle) and wings, and computed wing loading and wing thickness for all specimens. When we compared each morphological trait between sexes, we found that females did not differ from males in terms of relative thorax (wing muscle) size. Females were generally smaller than males, but females had relatively thicker wings than males for their size, which suggests greater mechanical strength. Importantly, females had significantly lower wing loading than males (7% lower). This would translate to more efficient flight, which may explain their higher migratory success. Results of this work should be useful for interpreting flight behavior and/or migration success in this and other Lepidopteran species.