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Chapter 8. Flying, Gliding, and Soaring
For decades, studies have highlighted links between wind patterns and the behavior, ecology, distribution, energetics and life history of seabirds. However, only relatively recently have advancements in tracking technologies and improvements in the resolution of globally-available wind data allowed wind impacts on seabirds to be quantified across multiple spatiotemporal scales. Here, we review and synthesize current knowledge of the effects of wind on seabirds. We first describe global patterns of wind circulation and relevant atmospheric processes and discuss the relationship between seabird morphology, flight performance and behavior relative to wind. We then develop a conceptual model linking seabird movement strategies to wind, morphology, flight capabilities and central-place constraint. Finally, we examine how wind influences seabird populations via effects on flight efficiency and energetics, and wind impacts associated with climate variability and severe weather. We conclude by highlighting research priorities for advancing our understanding of the effects of wind on seabird ecology and behavior; these include assessing how and to what extent seabirds use ocean waves for efficient flight, understanding how seabirds sense and anticipate wind patterns, and examining how wind has shaped seabird evolution. Future research should also focus on assessing how wind modulates habitat accessibility, and how this knowledge could be incorporated into theory of seabird habitat use. Moreover, approaches that focus on mechanistic links between climate, wind and demography are needed to assess population-level effects, and will be imperative to understanding how seabirds may be impacted by climate-driven changes to wind patterns.
Flying is the main means of locomotion for most avian species, and it requires a series of adaptations of the skeleton and of feather distribution on the wing. Flight type is directly associated with the mechanical constraints during flight, which condition both the morphology and microscopic structure of the bones. Three primary flight styles are adopted by avian species: flapping, gliding, and soaring, with different loads among the main wing bones. The purpose of this study was to evaluate the cross‐sectional microstructure of the most important skeletal wing bones, humerus, radius, ulna, and carpometacarpus, in griffon vultures (Gyps fulvus) and greater flamingos (Phoenicopterus roseus). These two species show a flapping and soaring flight style, respectively. Densitometry, morphology, and laminarity index were assessed from the main bones of the wing of 10 griffon vultures and 10 flamingos. Regarding bone mineral content, griffon vultures generally displayed a higher mineral density than flamingos. Regarding the morphology of the crucial wing bones involved in flight, while a very slightly longer humerus was observed in the radius and ulna of flamingos, the ulna in griffons was clearly longer than other bones. The laminarity index was significantly higher in griffons. The results of the present study highlight how the mechanics of different types of flight may affect the biomechanical properties of the wing bones most engaged during flight. “This study is based on comparative analysis about the possible effects of flying style on morphometric aspects of the wing bones of greater flamingo (Phoenicopterus roseus) (a) and griffon vulture (Gyps fulvus) (b). Our experiments underline that the griffon’s wing bones display both higher laminarity index and bone mineral content than flamingo. The study may support evidence that the mechanics of different types of flight may act on both biomechanical and morphometric properties of the bones most engaged in flight.”
During a dive, peregrine falcons (Falco peregrinus) can reach a velocity of up to 320 km h- 1. Our computational fluid dynamics simulations show that the forces that pull on the wings of a diving peregrine can reach up to three times the falcon's body mass at a stoop velocity of 80 m s- 1 (288 km h- 1). Since the bones of the wings and the shoulder girdle of a diving peregrine falcon experience large mechanical forces, we investigated these bones. For comparison, we also investigated the corresponding bones in European kestrels (Falco tinnunculus), sparrow hawks (Accipiter nisus) and pigeons (Columba livia domestica). The normalized bone mass of the entire arm skeleton and the shoulder girdle (coracoid, scapula, furcula) was significantly higher in F. peregrinus than in the other three species investigated. The midshaft cross section of the humerus of F. peregrinus had the highest second moment of area. The mineral densities of the humerus, radius, ulna, and sternum were highest in F. peregrinus, indicating again a larger overall stability of these bones. Furthermore, the bones of the arm and shoulder girdle were strongest in peregrine falcons.
"Flying" frogs have evolved independently several times among anurans. In all cases flyers are distinguished from their nonflying arboreal relatives by a unique set of morphological features and behavioral postures. Using both live animal field tests and wind tunnel models, this study examines the importance of this characteristic morphology and limb position on five aerial performance variables: horizontal traveling distance, minimum glide speed, maximum time aloft, maneuverability, and stability. Comparison of relative performance between a model frog with a generalized nonflying morphology and limb position and a model frog with flying morphology and limb position reveals that the morphological and positional features associated with "flying" actually decrease horizontal traveling distance but improve maneuverability. This finding suggests that maneuverability rather than horizontal travel may be the key performance parameter in the evolution of "flying" frogs. More generally, this study illustrates that (1) derived morphological and postural features do not necessarily change a suite of performance variables in the same way, and (2) the performance consequences of postural shifts are a function of morphology. These findings indicate that the potential complexity of morphological and behavioral interactions in the evolution of new adaptive types is much greater than previously considered.
Wenn ein Tier in der Lage ist, sich in der Luft zu halten, sagen wir, dass es fliegen kann und flugfähig ist. Die Prinzipien des Fluges der Vertebraten sind im Grunde verstanden, aber die Analyse ist kompliziert und Vereinfachungen sind auf beinahe jeder Ebene nötig. Viel von dem, was wir über die Aerodynamik des Fluges wissen, stammt aus unserem Verständnis von Flugzeugen mit starren Flügeln, und wenn diese Prinzipien auf There mit schlagenden Flügeln angewandt werden, schleichen sich unweigerlich Fehler ein. Sogar, wenn Wirbeltiere unter relativ einheitlichen Bedingungen fliegen (im Freien oder in einem Windkanal), mussen she häufig leichte Korrekturen durchführen, um Veränderungen der äußeren Bedingungen zu kompensieren. Wenn eine Möwe in wechselhaftem Wind manövriert, müssen ununterbrochen und sehr schnell größere Korrekturen vorgenommen werden, von denen viele von einem Flugzeug, das vom Menschen gebaut ist, nicht ausgeführt werden könnten. Es ist eine Herausforderung, die morphologische und verhaltensphysiologische Basis einer solchen Leistung zu untersuchen. Dank genialer Methoden haben wir in den letzten Jahrzehnten große Fortschritte gemacht. Es ist zu erwarten, dass genaue Beobachtung und die einfallsreiche Anwendung ausgefeilter Technologien uns weiterhin mit Entdeckungen über diese komplizierten Aktivitäten belohnen werden.
Muskeln arbeiten grundsätzlich unter zwei Bedingungen:
einer optimalen Überlappung der Sarkomerfilamente, was Sarkomerlängen von 2,6–1,8 μm entspricht (Strukturbedingung),
einem optimalen Verhältnis der Verkürzungsgeschwindigkeit von 0,15–0,4 der maximal möglichen (V/Vmax; Dynamikbedingung).
Unter diesen beiden Voraussetzungen kann eine Muskelfaser ihre maximale mechanische Leistung erbringen.
Flight is the characteristic adaptation of birds. The energetic cost of moving a unit of weight a unit distance in air (the dimensionless cost of transport) is rather low. For a given body mass, flying is a far more inexpensive way to move than is running, although it is more expensive than swimming (Schmidt-Nielsen 1984). But, despite the low cost of transport, flying requires a high rate of energy expenditure per unit time, and, therefore, flight is one of the most demanding adaptations found in nature. Four animal groups have evolved flapping flight—insects, pterosaurs, birds, and bats—all of which show advanced morphological and physiological specializations associated with aerial locomotion.
As central-place foragers, seabirds from colonies located close to multiple and/or productive marine habitats might experience increased foraging opportunities and enhanced resilience to food shortages. We tested whether this hypothesis might explain divergent trends in 3 populations of black-legged kittiwakes Rissa tridactyla, a surface-feeding piscivore, in the eastern Bering Sea. We simultaneously studied the foraging behavior, diet, nutritional stress, and breeding performance of chick-rearing kittiwakes from 2 continental shelf colonies (St. Paul and St. George) and an oceanic colony (Bogoslof). Although shelf-based forage fishes were rare or absent in bird diets during the cold study year, not all kittiwakes from the 3 colonies concentrated foraging along the productive shelf break habitats. Compared to the oceanic colony, birds from both shelf-located colonies had lower chick provisioning rates, higher levels of nutritional stress, and lower breeding performance. Although birds from both shelf-based colonies foraged in nearby neritic habitats during daytime, birds from St. George, a stable population located closest to the continental shelf break, also conducted long overnight trips to the ocean basin to feed on lipid-rich myctophids. In contrast, birds from St. Paul, a declining population located farthest from shelf break/oceanic habitats, fed exclusively over the shelf and obtained less high-energy food. Birds from Bogoslof, an increasing population, foraged mainly on myctophids close to the colony in the oceanic basin and Aleutian coast habitats. Our study suggests that proximity to multiple foraging habitats may explain divergent population trends among colonies of kittiwakes in the southeastern Bering Sea.
The most commonly cited apomorphy of Archosauriformes is an opening in the snout known as the antorbital cavity. Despite the ubiquity and prominence of the antorbital cavity, its function and importance in craniofacial evolution have been problematic. Discovering the significance of the antorbital cavity is a two step process: first, establishing the function of the bony cavity (that is, its soft-tissue relations), and second, determining the biological role of the enclosed structure. The first step is the most fundamental, and hence is examined at length. Three hypotheses for the function of the antorbital cavity have been advanced, suggesting that it housed (1) a gland, (2) a muscle, or (3) a paranasal air sinus. Thus, resolution is correctly viewed as a “soft-tissue problem,” and is addressed within the context of the extant phylogenetic bracket (EPB) approach for reconstructing the unpreserved features of fossil organisms. The soft-anatomical relations of the antorbital cavity (or any bony structure) are important because (1) soft tissues generally have morphogenetic primacy over bony tissues and (2) inferences about soft tissues are the foundation for a cascading suite of paleobiological inferences. The EPB approach uses the shared causal associations between soft tissues and their osteological correlates (i.e., the signatures imparted to the bones by the soft tissues) that are observed in the extant outgroups of the fossil taxon of interest to infer the soft-anatomical attributes of the fossil; based on the assessment at the outgroup node, a hierarchy characterizing the strength of the inference can be constructed. This general approach is applied to the problem of the function of the antorbital cavity, taking each hypothesized soft-tissue candidate—gland, muscle, and air sac—in turn, (1) establishing the osteological correlates of each soft-tissue system in the EPB of any fossil archosaur (i.e., extant birds and crocodilians), (2) formulating a hypothesis of homology based on similarities in these causal associations between birds and crocodilians, (3) testing this hypothesis by surveying fossil archosaurs for the specified osteological correlates, and (4) accepting or rejecting the hypothesis based on its phylogenetic congruence. Using this approach, fossil archosaurs can be reliably reconstructed with a Glandula nasalis, M. pterygoideus, pars dorsalis, and Sinus antorbitalis that are homologous with those of extant archosaurs; however, the osteological correlates of only the antorbital paranasal air sinus involve the several structures associated with the antorbital cavity. Additional evidence for the pneumatic nature of the antorbital cavity comes from the presence of numerous accessory cavities (especially in theropod dinosaurs) surrounding the main antorbital cavity. To address the origin of the antorbital cavity, the EPB approach was applied to basal archosauriforms; the data are not as robust, but nevertheless suggest that the cavity appeared as a housing for a paranasal air sinus. The second step in discovering the evolutionary significance of the antorbital cavity is to assess the function of the enclosed paranasal air sac. In fact, the function of all pneumaticity is investigated here. Rather than the enclosed volume of air (i.e., the empty space) being functionally important, better explanations result by focusing on the pneumatic epithelial diverticulum itself. It is proposed here that the function of the epithelial air sac is simply to pneumatize bone in an opportunistic manner within the constraints of a particular biomechanical loading regime. Trends in facial evolution in three clades of archosaurs (crocodylomorphs, ornithopod dinosaurs, and theropod dinosaurs) were examined in light of this new perspective. Crocodylomorphs and ornithopods both show trends for reduction and enclosure of the antorbital cavity (but for different reasons), whereas theropods show a trend for relatively poorly constrained expansion. These findings are consistent with the view of air sacs as opportunistic pneumatizing machines, with weight reduction and design optimality as secondary effects.
Flapping flight is a highly effective form of locomotion which has permitted the radiation of birds into a wide range of niches. In this chapter I explore how the mechanics of flapping flight have molded the flight adaptations of birds. The paper has three main threads. First, I describe recent theoretical and experimental studies on flapping flight aerodynamics and demonstrate how the mechanical requirements of locomotion are reflected in wingbeat kinematics, in vortex wake structure, and in the action of the pectoral musculature. Next, I consider how flight performance varies with size; scaling has become a central tool in the analysis of flight in birds and has proved a useful means of predicting how different mechanical, physiological, and ecological parameters change in importance with size, morphology, and behavior. However, scaling is frequently misinterpreted: it is size-dependence of the constraints on adaptation which lead to allometric consistency in avian flight morphology, and many of these constraints can be related directly to flight mechanics. Finally, I use a multivariate analysis of wing morphology to demonstrate how these constraints interact to different degrees in different birds and underlie correlations among flight morphology, ecology, and behavior. These threads are then brought together in a discussion of the conjectural relationships between fitness and the evolution of specializations in flight morphology.
Abiomechanicallyparsimonioushypothesisfortheevolutionofflap- ping flight in terrestrial vertebrates suggests progression within an arboreal context from jumping to directed aerial descent, gliding with control via appendicular motions, and ultimately to powered flight. The more than 30 phylogenetically independent lineages of arboreal vertebrate gliders lend strong indirect support to the eco- logical feasibility of such a trajectory. Insect flight evolution likely followed a similar sequence, but is unresolved paleontologically. Re- centlydescribedfallingbehaviorsinarborealantsprovidethefirstev- idence demonstrating the biomechanical capacity for directed aerial descent in the complete absence of wings. Intentional control of body trajectories as animals fall from heights (and usually from veg- etation) likely characterizes many more taxa than is currently recog- nized. Understanding the sensory and biomechanical mechanisms used by extant gliding animals to control and orient their descent is central to deciphering pathways involved in flight evolution.
Flight initiation distance (FID) is the distance at which an individual animal takes flight when approached by a human. This behavioural measure of risk-taking reflects the risk of being captured by real predators, and it correlates with a range of life history traits, as expected if flight distance optimizes risk of predation. Given that FID provides information on risk of predation, we should expect that physiological and morphological mechanisms that facilitate flight and escape predict interspecific variation in flight distance. Haematocrit is a measure of packed red blood cell volume and as such indicates the oxygen transport ability and hence the flight muscle contracting reaction of an individual. Therefore, we predicted that species with short flight distances, that allow close proximity between a potential prey individual and a predator, would have high haematocrit. Furthermore, we predicted that species with large wing areas and hence relatively low costs of flight and species with large aspect ratios and hence high manoeuvrability would have evolved long flight speed. Consistent with these predictions, we found in a sample of 63 species of birds that species with long flight distances for their body size had low levels of haematocrit and large wing areas and aspect ratios. These findings provide evidence consistent with the evolution of risk-taking behaviour being underpinned by physiological and morphological mechanisms that facilitate escape from predators and add to our understanding of predator-prey coevolution.
This paper addresses how the wing membrane and skeletal system in bats are developmentally and functionally integrated during morphogenesis in the little brown bat (Myotis
lucifugus). A truss network is used to quantify changes in the size and shape of the wing membrane during morphogenesis. Growth of the forearm and of third and fifth digits of the manus are also quantified. Principal component analysis indicates that changes in size of the wing (PC-1) contribute 78% of growth variation, whereas shape changes (PC-2, PC-3) contribute only about 18% of growth variation. ANOVA run on component scores shows significant differences in size (PC-1) of the wing between juveniles and sub-adults, whereas no significant difference in shape (PC-2 and 3) of the wing occurs during morphogenesis. In addition, growth compensation is shown to occur among sequentially developing skeletal elements comprising the hand wing. Coefficients of variation were significantly higher for phalangeal lengths than for total wing length and width. Compensation scores generated by summing residual scores produced by bivariate plots of wing bone elements show variable levels of compensation among individuals. However, a plot of scores against wing length shows compensation to occur throughout morphogenesis as scores are not correlated with wing size (r = 0.089). Apparently, selection has favoured a developmental system within which wing shape is conserved while simultaneous plasticity in the hand skeleton helps maintain functional integrity during rapid morphogenesis.
We studied the wing morphology, echolocation calls, foraging behaviour and flight speed of Tylonycteris pachypus and Tylonycteris robustula in Longzhou County, South China during the summer (June–August) of 2005. The wingspan, wing loading and aspect ratio of the two species were relatively low, and those of T. pachypus were lower compared with T. robustula. The echolocation calls of T. pachypus and T. robustula consist of a broadband frequency modulated (FM) sweep followed by a short narrowband FM sweep. The dominant frequency of calls of T. pachypus was 65.1 kHz, whereas that of T. robustula was 57.7 kHz. The call frequencies (including highest frequency of the call, lowest frequency of the call and frequency of the call that contained most energy) of T. pachypus were higher than those of T. robustula, and the pulse duration of the former was longer than that of the latter. The inter-pulse interval and bandwidth of the calls were not significantly different between the two species. Tylonycteris pachypus foraged in more complex environments than T. robustula, although the two species were both netted in edge habitats (around trees or houses), along pathways and in the tops of trees. Tylonycteris pachypus flew slower (straight level flight speed, 4.3 m s−1) than T. robustula (straight level flight speed, 4.8 m s−1). We discuss the relationship between wing morphology, echolocation calls, foraging behaviour and flight speed, and demonstrate resource partitioning between these two species in terms of morphological and behavioural factors.
The gliding angle of the Mahogany Glider Petaurus gracilis and the Sugar Glider Petaurus breviceps was determined from field studies by measuring the height of launch and landing of glides and the distance travelled. This showed no significant difference between these two species in glide ratio, which averaged 1.91 and 1.82 m distance per 1 m loss in altitude, respectively, nor in glide angle which averaged 28.26° and 29.69° for the Mahogany Glider and Sugar Glider, respectively. Significant differences were found between them for height of launch (19.75 and 11.96 m, respectively), height of landing (4.48 and 1.95 m, respectively), diameter at breast height of landing tree (44.12 and 23.22 cm, respectively), and glide distance (29.71 and 20.42 m, respectively). An examination of the ratio of interorbital width to maximum skull width of gliding and nongliding possums was measured from museum skulls to examine whether gliders have eyes wider apart, to allow triangulation of distance in preparation for gliding. Gliding possums showed a trend toward having a larger interorbital width than nongliding possums, although there appear to be several factors acting on the interorbital width. Museum study skins of all gliding marsupials were measured to determine the relationship between patagium surface area and body mass which showed a clear relationship (r2 = 0.9688). A comparison of gliding behaviour, patagium, development of limbs, tail morphology and mass was also made between gliding marsupials and other gliding mammals.
The pectoralis muscle (M. pectoralis) of many premier soaring birds contains a smaller, accessory, deep belly in addition to the much larger superficial belly found in all flying birds. Here we describe the muscle fiber types in both the superficial and deep bellies of the pectoralis of one such adept soaring species, the white pelican (Pelecanus erythrorhynchos).Histochemical techniques are used to demonstrate both nicotinamide adenine dinucleotide (reduced) and myofibrillar adenosine triphosphatase activities within the muscle fibers. Immunocytochemical methods employing several monoclonal antibodies, each directed against a different myosin heavy chain epitope of the chicken, are also used to characterize the fibers. While the superficial belly of the muscle consists entirely of fast-twitch oxidative-glycolytic fibers, the deep belly is composed exclusively of slow fibers. These slow fibers are labelled by two different antibodies specific for chicken slow myosin. We suggest that the fibers of the superficial belly are best suited to flapping flight, and that the fibers of the deep belly would be recruited only during soaring flight. Furthermore, we hypothesize that the deep belly found in the pectoralis of soaring species probably evolved from a deep neuromuscular compartment of the superficial belly.
Song flight, which is an aerial song display especially used by many open country bird species, is expected to be energetically very costly. Any morphological adaptation reducing the magnitude of this cost thus would be favored by selection. Male skylarks Alauda arvensis perform frequent song flights during a period of nearly half the year. Skylarks are sexually size dimorphic in most body traits, but particularly in wing area and wing span, which is absolutely and relatively larger in males than in females. Wing loadings, aspect ratios, and flight costs therefore are smaller in males than in females. I investigated the effect of wing area and aspect ratio on the duration of the song flights of individual birds by timing their duration before and after an experimental manipulation of wing area. Male skylarks were caught, ringed, and released (control I), had the tips of their wing feathers cut (control II), or had the tips of their wing feathers reduced by approximately 10 mm. There were no statistically significant differences in morphology or duration of songs between treatment groups before experimental treatments. However, males having the tips of their wing feathers reduced by ca. 10 mm performed only greatly abbreviated song flights. Original wing loading and aspect ratio also affected the duration of song flights, since male skylarks with low wing loadings and high aspect ratios performed longer song flights than did males with high wing loadings and low aspect ratios. This was the case both before and after experimental treatment. Wing area is suggested to reflect the ability of individual skylarks to invest in morphological structures allowing an increased song output.
Predator pressure is normally very difficult to assess, and most reports tend to be anecdotal. However, it has been estimated
that an annual predation rate of 25% may apply to Microcebus populations (Goodman et al., 1993). Such a rate, albeit for a particularly small prosimian, implies strong selective pressure in favor of adaptations that
reduce predation, and it seems reasonable to assess adaptations with predation in mind. Predator avoidance by vigilance is
usually seen as an attribute of social foragers (see, e.g., Terborgh & Janson, 1986), to which category many of the Lemuridae, and arguably some Indriidae and Lepilemuridae, belong. However, the small body
size and nocturnality of those prosimians described as “solitary foragers” are often regarded as facilitating alternative
predator avoidance strategy, crypsis (e.g., Clutton-Brock & Harvey, 1977; Stanford, 2002).
Wing bone histology in three species of birds was characterized in order to test hypotheses related to the relationship between skeletal microstructure and inferred wing loading during flight. Data on the degree of laminarity (the proportion of circular vascular canals) and the occurrence of secondary osteons were obtained from three species that utilize different primary flight modes: the Double-crested cormorant, a continuous flapper; the Brown pelican, a static soarer; and the Laysan albatross, a dynamic soarer. Laminarity indices were calculated for four quadrants for each of the three main wing elements. Ulnae and carpometacarpi were predicted to exhibit quadrant specific patterns of laminarity due to hypothesized differences in locally applied loads related to the attachment of flight feathers. However, few differences among the quadrants were identified. No significant differences were identified among the three elements, which is notable as different bones are likely experiencing different loading conditions. These results do not support the concept of bone functional adaptation in the primary structure of the wing elements. Significant differences in laminarity were found among the three primary flight modes. The dynamic soaring birds exhibited significantly lower laminarity than the flapping and static soaring birds. These results support the proposed hypothesis that laminarity is an adaptation for resisting torsional loading. This may be explained by overall wing shape: whereas dynamic soaring birds have long slender wings, flappers and static soaring birds have broader wings with a larger wing chord that would necessarily impart a higher torsional moment on the feather-bearing bones.
A comparison of the isometric forces and levers of the pectoralis muscle in red-tailed hawks (Buteo jamaicensis) and barred owls (Strix varia) was done to identify differences that may correlate with their different flight styles. The pectoralis consists of two heads, the anterior m. sternobrachialis (SB) and the posterior m. thoracobrachialis (TB). These are joined at an intramuscular tendon and are supplied by separate primary nerve branches. As in other birds, the two heads have distinct fiber orientations in red-tailed hawks and barred owls. SB's fiber orientation (posterolateral and mediolateral from origin to insertion) provides pronation and protraction of the humerus during adduction. Electromyographic studies in pigeons show that it is active in early downstroke and during level flight. TB is more active during take-off and landing in pigeons. The anterolateral orientation (from origin to insertion) of its fibers provides a retractive component to humeral adduction used to control the wing during landing. In our study, the maximum isometric force produced by the combined pectoralis heads did not differ significantly between the hawk and owl, however, the forces were distributed differently between the two muscle heads. In the owl, SB and TB were capable of producing equal amounts of force, but in the hawk, SB produced significantly less force than did TB. This may reflect the need for a large TB to control landing in both birds during prey-strike, with the owl maintaining both protractive (using SB) and retractive (using TB) abilities. Pronation and protraction may be less important in the flight behavior of the hawk, but its prey-strike behavior may require the maintenance of a substantial TB for braking and controlled stalling, as it initiates strike behavior.
As a postural behavior, gliding and soaring flight in birds requires less energy than flapping flight. Slow tonic and slow twitch muscle fibers are specialized for sustained contraction with high fatigue resistance and are typically found in muscles associated with posture. Albatrosses are the elite of avian gliders; as such, we wanted to learn how their musculoskeletal system enables them to maintain spread-wing posture for prolonged gliding bouts. We used dissection and immunohistochemistry to evaluate muscle function for gliding flight in Laysan and Black-footed albatrosses. Albatrosses possess a locking mechanism at the shoulder composed of a tendinous sheet that extends from origin to insertion throughout the length of the deep layer of the pectoralis muscle. This fascial "strut" passively maintains horizontal wing orientation during gliding and soaring flight. A number of muscles, which likely facilitate gliding posture, are composed exclusively of slow fibers. These include Mm. coracobrachialis cranialis, extensor metacarpi radialis dorsalis, and deep pectoralis. In addition, a number of other muscles, including triceps scapularis, triceps humeralis, supracoracoideus, and extensor metacarpi radialis ventralis, were found to have populations of slow fibers. We believe that this extensive suite of uniformly slow muscles is associated with sustained gliding and is unique to birds that glide and soar for extended periods. These findings suggest that albatrosses utilize a combination of slow muscle fibers and a rigid limiting tendon for maintaining a prolonged, gliding posture.
Avian wing elements have been shown to experience both dorsoventral bending and torsional loads during flapping flight. However, not all birds use continuous flapping as a primary flight strategy. The pelecaniforms exhibit extraordinary diversity in flight mode, utilizing flapping, flap-gliding, and soaring. Here we (1) characterize the cross-sectional geometry of the three main wing bone (humerus, ulna, carpometacarpus), (2) use elements of beam theory to estimate resistance to loading, and (3) examine patterns of variation in hypothesized loading resistance relative to flight and diving mode in 16 species of pelecaniform birds. Patterns emerge that are common to all species, as well as some characteristics that are flight- and diving-mode specific. In all birds examined, the distal most wing segment (carpometacarpus) is the most elliptical (relatively high I(max) /I(min) ) at mid-shaft, suggesting a shape optimized to resist bending loads in a dorsoventral direction. As primary flight feathers attach at an oblique angle relative to the long axis of the carpometacarpus, they are likely responsible for inducing bending of this element during flight. Moreover, among flight modes examined the flapping group (cormorants) exhibits more elliptical humeri and carpometacarpi than other flight modes, perhaps pertaining to the higher frequency of bending loads in these elements. The soaring birds (pelicans and gannets) exhibit wing elements with near-circular cross-sections and higher polar moments of area than in the flap and flap-gliding birds, suggesting shapes optimized to offer increased resistance to torsional loads. This analysis of cross-sectional geometry has enhanced our interpretation of how the wing elements are being loaded and ultimately how they are being used during normal activities.
Flight–defined as the ability to produce useful aerodynamic forces by flapping the wings–is one of the most striking adaptations in vertebrates. Its origin has been surrounded by considerable controversy, due in part to terminological inconsistencies, in part to phylogenetic uncertainty over the sister groups and relationships of birds, bats and pterosaurs, and in part to disagreement over the interpretation of the available fossil evidence and over the relative importance of morphological, mechanical and ecological specializations. Study of the correlation between functional morphology and mechanics in contemporary birds and bats, and in particular of the aerodynamics of flapping wings, clarifies the mechanical changes needed in the course of the evolution of flight. This strongly favours a gliding origin of tetrapod flight, and on mechanical and ecological grounds the alternative cursorial and fluttering hypotheses (neither of which is at present well‐defined) may be discounted. The argument is particularly strong in bats, but weaker in birds owing to apparent inconsistencies with the fossil evidence. However, study of the fossils of the Jurassic theropod dinosaur Archaeopteryx, the sister‐group of the stem‐group proto‐birds, supports this view. Its morphology indicates adaptation for flapping flight at the moderately high speeds which would be associated with gliding, but not for the slow speeds which would be required for incipient flight in a running cursor, where the wingbeat is aerodynamically and kinematically considerably more complex. Slow flight in birds and bats is a more derived condition, and vertebrate flapping flight apparently evolved through a gliding stage.
Living rodents show great diversity in their locomotor habits, including semiaquatic, arboreal, fossorial, ricochetal, and gliding species from multiple families. To assess the association between limb morphology and locomotor habits, the appendicular skeletons of 65 rodent genera from 16 families were measured. Ecomorphological analyses of various locomotor types revealed consistent differences in postcranial skeletal morphology that relate to functionally important traits. Behaviorally similar taxa showed convergent morphological characters, despite distinct evolutionary histories. Semiaquatic rodents displayed relatively robust bones, enlarged muscular attachments, short femora, and elongate hind feet. Arboreal rodents had relatively elongate humeri and digits, short olecranon processes of the ulnae, and equally proportioned fore and hind limbs. Fossorial rodents showed relatively robust bones, enlarged muscular attachments, short antebrachii and digits, elongate manual claws, and reduced hind limb elements. Ricochetal rodents displayed relatively proximal insertion of muscles, disproportionate limbs, elongate tibiae, and elongate hind feet. Gliding rodents had relatively elongate and gracile bones, short olecranon processes of the ulnae, and equally proportioned fore and hind limbs. The morphological differences observed here can readily be used to discriminate extant rodents with different locomotor strategies. This suggests that the method could be applied to extinct rodents, regardless of ancestry, to accurately infer their locomotor ecologies. When applied to an extinct group of rodents, we found two distinct ecomorphs represented in the beaver family (Castoridae), semiaquatic and semifossorial. There was also a progressive trend toward increased body size and increased aquatic specialization in the giant beaver lineage (Castoroidinae).
The gliding abilities of paromomyid plesiadapiforms are evaluated through a functional analysis of long bone morphology in a comparative sample of modern gliders and related nongliders. Relationships between body mass, long bone lengths, and long bone midshaft cross-sectional areas are explored. Theory suggests that gliders should have long humeri and femora to improve aspect ratio, and that larger gliders should have relatively longer limb bones than smaller gliders to minimize drag and patagial loading at greater body masses. Comparisons between extant taxa support these predictions: gliders have relatively longer humeri and femora than those of nongliders, and glider long bone lengths scale with positive allometry, while the scaling of nonglider long bones does not differ from isometry. Preliminary analysis of distal to proximal limb segment proportions further suggests that bone lengthening is, to some extent, related to patagial attachment site, although humeri and femora are relatively long in all of the gliders, regardless of attachment site. The proportions of paromomyids relative to those of extant mammals do not support a gliding interpretation for these fossils.
Mean lift coefficients have been calculated for hawkmoth flight at a range of speeds in order to investigate the aerodynamic significance of the kinematic variation which accompanies changes in forward velocity. The coefficients exceed the maximum steady-state value of 0.71 at all except the very fastest speeds, peaking at 2.0 or greater between 1 and 2 m s−1. Unsteady high-lift mechanisms are therefore most important during hovering and slow forward flight. In combination with the wingtip paths relative to the surrounding air, the calculated mean lift coefficients illustrate how the relative contributions of the two halfstrokes to the force balance change with increasing forward speed. Angle of incidence data for fast forward flight suggest that the sense of the circulation is not reversed between the down- and upstrokes, indicating a flight mode qualitatively different from that proposed for lower-speed flight in the hawkmoth and other insects. The mid-downstroke angle of incidence is constant at 30–40 ° across the speed range. The relationship between power requirements and flight speed is explored; above 5 m s−1, further increases in forward velocity are likely to be constrained by available mechanical power, although problems with thrust generation and flight stability may also be involved.
Hawkmoth wing and body morphology, and the differences between males and females, are evaluated in aerodynamic terms. Steady-state force measurements show that the hawkmoth body is amongst the most streamlined for any insect.
Flight is the overriding characteristic of birds that has influenced most of their morphological, physiological, and behavioral features. Flight adaptations are essential for survival in the wide variety of environments that birds occupy. Therefore, locomotor structure, including skeletal and muscular characteristics, is adapted to reflect the flight style necessitated by different ecological niches. Red-tailed hawks (Buteo jamaicensis) soar to locate their prey, Cooper's hawks (Accipiter cooperii) actively chase down avian prey, and ospreys (Pandion haliaetus) soar and hover to locate fish. In this study, wing ratios, proportions of skeletal elements, and relative sizes of selected flight muscles were compared among these species. Oxidative and glycolytic enzyme activities of several muscles were also analyzed via assays for citrate synthase (CS) and for lactate dehydrogenase (LDH). It was found that structural characteristics of these three raptors differ in ways consistent with prevailing aerodynamic models. The similarity of enzymatic activities among different muscles of the three species shows low physiological differentiation and suggests that wing architecture may play a greater role in determining flight styles for these birds.
Gliding flight has independently evolved many times in vertebrates. Direct evidence of gliding is rare in fossil records and is unknown in mammals from the Mesozoic era. Here we report a new Mesozoic mammal from Inner Mongolia, China, that represents a previously unknown group characterized by a highly specialized insectivorous dentition and a sizable patagium (flying membrane) for gliding flight. The patagium is covered with dense hair and supported by an elongated tail and limbs; the latter also bear many features adapted for arboreal life. This discovery extends the earliest record of gliding flight for mammals to at least 70 million years earlier in geological history, and demonstrates that early mammals were diverse in their locomotor strategies and lifestyles; they had experimented with an aerial habit at about the same time as, if not earlier than, when birds endeavoured to exploit the sky.
Gliding is an energetically efficient mode of locomotion that has evolved independently, and in different ways, in several tetrapod groups. Here, we report on an acrodontan lizard from the Early Cretaceous Jehol Group of China showing an array of morphological traits associated with gliding. It represents the only known occurrence of this specialization in a fossil lizard and provides evidence of an Early Cretaceous ecological diversification into an aerial niche by crown-group squamates. The lizard has a dorsal-rib-supported patagium, a structure independently evolved in the Late Triassic basal lepidosauromorph kuehneosaurs and the extant agamid lizard Draco, revealing a surprising case of convergent evolution among lepidosauromorphans. A patagial character combination of much longer bilaterally than anteroposteriorly, significantly thicker along the leading edge than along the trailing edge, tapered laterally to form a wing tip, and secondarily supported by an array of linear collagen fibers is not common in gliders and enriches our knowledge of gliding adaptations among tetrapods.
• Squamata
• Acrodonta
• gliding adaptation
• Liaoning
• patagium
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