Wing and leg bone microstructure reflects migratory demands in resident and migrant populations of the Dark-eyed Junco (Junco hyemalis)

Migration is the primary strategy that temperate birds use to avoid overwintering under harsh conditions. As a consequence, migratory birds have evolved specific morphological features in their wings and skeleton. However, in addition to varying in overall shape and size, bone can also change at the microstructural level by, for example, increasing its thickness. Such changes are critical to preventing fracture and damage under repeated loading (fatigue), yet it is not known whether migratory behaviour influences bone microstructure. To address this gap in the literature, we performed micro-computed tomography on skeletons of resident and migrant subspecies of the Dark-eyed Junco Junco hyemalis. We investigated the differences in the major wing bone, the humerus, and the major leg bone, the femur. In each bone, we studied the microarchitecture of the two types of bone tissue: cortical bone, the thick outer layer of bone; and trabecular bone, which is the porous network of bone tissue at the ends of long bones. We used linear models to quantify morphological features with respect to body mass and migratory behaviour. Humeri from migratory birds were thinner, wider and had higher overall geometric stiffness, i.e. a higher polar moment of inertia, relative to humeri from resident birds. These features may help keep their bones stiff to maintain their increased body mass during migration. In contrast, migrant femora were shorter, thinner and had lower geometric stiffness than femora of residents, potentially to reduce total body mass. Tissue mineral density was lower in both the humerus and the femur of migratory birds. In addition, migratory subspecies had less trabecular bone (lower bone volume fraction) due primarily to a loss of trabecular thickness. Migratory behaviour may thus select for improved stiffness and fatigue resistance in the wing bones and reduced mass of leg bones. Our work demonstrates how important insights into morphological adaptation can be obtained by investigating bone microstructure.     

The evolution of vertebrate flight

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.     

Metabolism during flight in two species of bats, Phyllostomus hastatus and Pteropus gouldii.

The energetic cost of flight in a wind-tunnel was measured at various combinations of speed and flight angle from two species of bats whose body masses differ by almost an order of magnitude. The highest mean metabolic rate per unit body mass measured from P. hastatus (mean body mass, 0.093 kg) was 130.4 Wkg-1, and that for P. gouldii (mean body mass, 0.78 kg) was 69.6 Wkg-1. These highest metabolic rates, recorded from flying bats, are essentially the same as those predicted for flying birds of the same body masses, but are from 2.5 to 3.0 times greater than the highest metabolic rates of which similar-size exercising terrestrial mammals appear capable. The lowest mean rate of energy utilization per unit body mass P. hastatus required to sustain level flight was 94.2 Wkg-1 and that for P. gouldii was 53.4 Wkg-1. These data from flying bats together with comparable data for flying birds all fall along a straight line when plotted on double logarithmic coordinates as a function of body mass. Such data show that even the lowest metabolic requirements of bats and birds during level flight are about twice the highest metabolic capabilities of similar-size terrestrial mammals. Flying bats share with flying birds the ability to move substantially greater distance per unit energy consumed than walking or running mammals. Calculations show that P. hastatus requires only one-sixth the energy to cover a given distance as does the same-size terrestrial mammal, while P. gouldii requires one-fourth the energy of the same-size terrestrial mammal. An empirically derived equation is presented which enables one to make estimates of the metabolic rates of bats and birds during level flight in nature from body mass data alone. Metabolic data obtained in this study are compared with predictions calculated from an avian flight theory.     

The Evolution of Bat Vestibular Systems in the Face of Potential Antagonistic Selection Pressures for Flight and Echolocation

The vestibular system maintains the body’s sense of balance and, therefore, was probably subject to strong selection during evolutionary transitions in locomotion. Among mammals, bats possess unique traits that place unusual demands on their vestibular systems. First, bats are capable of powered flight, which in birds is associated with enlarged semicircular canals. Second, many bats have enlarged cochleae associated with echolocation, and both cochleae and semicircular canals share a space within the petrosal bone. To determine how bat vestibular systems have evolved in the face of these pressures, we used micro-CT scans to compare canal morphology across species with contrasting flight and echolocation capabilities. We found no increase in canal radius in bats associated with the acquisition of powered flight, but canal radius did correlate with body mass in bat species from the suborder Yangochiroptera, and also in non-echolocating Old World fruit bats from the suborder Yinpterochiroptera. No such trend was seen in members of the Yinpterochiroptera that use laryngeal echolocation, although canal radius was associated with wing-tip roundedness in this group. We also found that the vestibular system scaled with cochlea size, although the relationship differed in species that use constant frequency echolocation. Across all bats, the shape of the anterior and lateral canals was associated with large cochlea size and small body size respectively, suggesting differential spatial constraints on each canal depending on its orientation within the skull. Thus in many echolocating bats, it seems that the combination of small body size and enlarged cochlea together act as a principal force on the vestibular system. The two main groups of echolocating bats displayed different canal morphologies, in terms of size and shape in relation to body mass and cochlear size, thus suggesting independent evolutionary pathways and offering tentative support for multiple acquisitions of echolocation.     

Massive, solidified bone in the wing of a volant courting bird

One pervasive morphological feature of tetrapods is the pipe-like, often marrow-filled, structure of the limb or long bones. This 'hollow' form maximizes flexural strength and stiffness with the minimum amount of bony material, and is exemplified by truly hollow (air-filled), or pneumatic, humeri in many modern birds. High-resolution microCT scans of the wings of two male club-winged manakins (Machaeropterus deliciosus) uncovered a notable exception to the hollow-tube rule in terrestrial vertebrates; males exhibited solidified ulnae more than three times the volume of birds of comparable body size, with significantly higher tissue mineral densities. The humeri exhibited similar (but less extreme) modifications. Each of the observed osteological modifications increases the overall mass of the bone, running counter to pervasive weight-reducing optimizations for flight in birds. The club-winged manakin is named for a pair of unique wing feathers found in adult males; these enlarged feathers attach directly to the ulna and resonate to produce a distinctive sound used in courtship displays. Given that the observed modifications probably assist in sound production, the club-winged manakin represents a case in which sexual selection by female choice has generated an ecologically 'costly' forelimb morphology, unique in being specialized for sound production at a presumed cost in flight efficiency.     

Size scaling and stiffness of avian primary feathers: implications for the flight of Mesozoic birds

The primary feathers of birds are subject to cyclical forces in flight causing their shafts (rachises) to bend. The amount the feathers deflect during flight is dependent upon the flexural stiffness of the rachises. By quantifying scaling relationships between body mass and feather linear dimensions in a large data set of living birds, we show that both feather length and feather diameter scale much closer to predictions for geometric similarity than they do to elastic similarity. Scaling allometry also indicates that the primary feathers of larger birds are relatively shorter and their rachises relatively narrower, compared to those of smaller birds. Two-point bending tests indicated that larger birds have more flexible feathers than smaller species. Discriminant functional analyses (DFA) showed that body mass, primary feather length and rachis diameter can be used to differentiate between different magnitudes of feather bending stiffness, with primary feather length explaining 63% of variance in rachis stiffness. Adding fossil measurement data to our DFA showed that Archaeopteryx and Confuciusornis do not overlap with extant birds. This strongly suggests that the bending stiffness of their primary feathers was different to extant birds and provides further evidence for distinctive flight styles and likely limited flight ability in Archaeopteryx and Confuciusornis.     

Structure, form, and function of flight in engineering and the living world

By combining appearance and behavior in animals with physical laws, we can get an understanding of the adaptation and evolution of various structures and forms. Comparisons can be made between animal bodies and various technical constructions. Technical science and theory during the latest decades have resulted in considerable insight into biological adaptations, but studies on structures, forms, organs, systems, and processes in the living world, used in the right way, have also aided the engineer in finding wider and better solutions to various problems, among them in the design of micro-air vehicles (MAVs). In this review, I discuss the basis for flight and give some examples of where flight engineering and nature have evolved similar solutions. In most cases technology has produced more advanced structures, but sometimes animals are superior. I include how different animals have solved the problem of producing lift, how animal wings meet the requirements of strength and rigidity, how wing forms are adapted to various flight modes, and how flight kinematics are related to flight behavior and speed. The dynamics of vorticity is summarized. There are a variety of methods for the determination of flight power; it has been estimated adequately by lifting-line theory, by physiological measurements, and from mass loss and food intake. In recent years alternative methods have been used, in which the mechanical power for flight is estimated from flight muscle force used during the downstroke. Refinements of these methods may create new ways of estimating flight power more accurately. MAVs operate at the same Reynolds numbers as large insects and small birds and bats. Therefore, studies on animal flight are valuable for MAV design, which is discussed here.     

中国中生代鸟类后肢骨骼的长度比例特征及栖息习性的分析

通过对18目59科137例现生不同栖息习性鸟类的后肢3块骨骼(股骨、胫跗骨和跗跖骨)长度比例的观察和特征分析,推断出鸟类的栖息习性与后肢3块骨骼中各骨骼长度所占总长度的比例存在密切的关系。即在所有鸟类的后肢骨骼中,胫跗骨的长度占3块骨骼的比例为最大;地栖鸟类后肢骨骼中股骨的长度要短于跗跖骨;树栖鸟类后肢骨骼中股骨的长度要长于跗跖骨。鸟类后肢3块骨骼的长度比例特征是鸟类长期对栖息等行为适应的结果。在此基础上,对中国中生代14例鸟类的栖息习性进行了分析,利用三元投影的统计方法,并以国内外新生代(古近纪和新近纪)21例鸟类标本作为对比参考,得出辽西中生代不同类型鸟类的栖息行为特征:基干鸟类以树栖为主要习性,其中个别鸟类还具有攀援的习性,而反鸟类则是典型的树栖鸟类,今鸟类兼有树、地栖的习性。研究表明,在现行的鸟类系统发育框架下,树栖适应(及攀援)代表了鸟类演化历史中最原始的生活方式。这一结论也支持鸟类飞行的树栖起源假说。中生代鸟类栖息习性分异的多样性反映了早期鸟类演化过程中自身以及与其他同期生物在生态空间和食物资源的竞争的加剧和对环境的不断适应。     

Bone histological correlates of high-frequency flapping flight and body mass in the furculae of birds: a phylogenetic approach

A parsimony optimization of the presence of high-frequency flapping flight onto a phylogeny of 29 species of birds shows that this is a derived character state that has been acquired at least four independent times: by the last common ancestor of Alcidae, that of Podicipedidae, that of Anatidae, and that of Rallidae. Cineradiographic analysis has shown that the furculae of birds underwent extraordinary deformations during the wingbeat cycle. Cyclical deformations are known to produce microfractures in the bone tissue, which may be a stimulus for Haversian remodelling, a mechanism of resorption and reconstruction of bone tissue that may repair bone microdamage. In the present study, we performed a comparative analysis in a phylogenetic context to test the effect of the frequency of cyclical deformations and body mass on the rate of Haversian remodelling in the furculae of birds. A variation partitioning analysis showed that the type of flight (high-frequency flapping flight vs. other kinds of flight of lower wing beat frequency) and body mass explained a significant portion of Haversian bone density (the outcome of Haversian remodelling) and that the phylogeny also explained a significant part of this variation. This phylogenetic signal on Haversian bone density variation may be the outcome of phylogenetic signal on the proximate causes producing Haversian remodelling.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 729–738.     

Regional,ontogenetic, and sex‐related variations in elastic properties of cortical bone in baboon mandibles

Understanding the mechanical features of cortical bone and their changes with growth and adaptation to function plays an important role in our ability to interpret the morphology and evolution of craniofacial skeletons. We assessed the elastic properties of cortical bone of juvenile and adult baboon mandibles using ultrasonic techniques. Results showed that, overall, cortical bone from baboon mandibles could be modeled as an orthotropic elastic solid. There were significant differences in the directions of maximum stiffness, thickness, density, and elastic stiffness among different functional areas, indicating regional adaptations. After maturity, the cortical bone becomes thicker, denser, and stiffer, but less anisotropic. There were differences in elastic properties of the corpus and ramus between male and female mandibles which are not observed in human mandibles. There were correlations between cortical thicknesses and densities, between bone elastic properties and microstructural configuration, and between the directions of maximum stiffness and bone anatomical axes in some areas. The relationships between bone extrinsic and intrinsic properties bring us insights into the integration of form and function in craniofacial skeletons and suggest that we need to consider both macroscopic form, microstructural variation, and the material properties of bone matrix when studying the functional properties and adaptive nature of the craniofacial skeleton in primates. The differences between baboon and human mandibles is at variance to the pattern of differences in crania, suggesting differences in bone adaption to varying skeletal geometries and loading regimes at both phylogenetic and ontogenetic levels. Am J Phys Anthropol, 2010. © 2009 Wiley‐Liss, Inc.     

Trabecular architecture in the humeral metaphyses of non-avian reptiles (Crocodylia,Squamata and Testudines): Lifestyle,allometry and phylogeny

The lifestyle of extinct tetrapods is often difficult to assess when clear morphological adaptations such as swimming paddles are absent. According to the hypothesis of bone functional adaptation, the architecture of trabecular bone adapts sensitively to physiological loadings. Previous studies have already shown a clear relation between trabecular architecture and locomotor behavior, mainly in mammals and birds. However, a link between trabecular architecture and lifestyle has rarely been examined. Here, we analyzed trabecular architecture of different clades of reptiles characterized by a wide range of lifestyles (aquatic, amphibious, generalist terrestrial, fossorial, and climbing). Humeri of squamates, turtles, and crocodylians have been scanned with microcomputed tomography. We selected spherical volumes of interest centered in the proximal metaphyses and measured trabecular spacing, thickness and number, degree of anisotropy, average branch length, bone volume fraction, bone surface density, and connectivity density. Only bone volume fraction showed a significant phylogenetic signal and its significant difference between squamates and other reptiles could be linked to their physiologies. We found negative allometric relationships for trabecular thickness and spacing, positive allometries for connectivity density and trabecular number and no dependence with size for degree of anisotropy and bone volume fraction. The different lifestyles are well separated in the morphological space using linear discriminant analyses, but a cross-validation procedure indicated a limited predictive ability of the model. The trabecular bone anisotropy has shown a gradient in turtles and in squamates: higher values in amphibious than terrestrial taxa. These allometric scalings, previously emphasized in mammals and birds, seem to be valid for all amniotes. Discriminant analysis has offered, to some extent, a distinction of lifestyles, which however remains difficult to strictly discriminate. Trabecular architecture seems to be a promising tool to infer lifestyle of extinct tetrapods, especially those involved in the terrestrialization.     

Finite element calculated uniaxial apparent stiffness is a consistent predictor of uniaxial apparent strength in human vertebral cancellous bone tested with different boundary conditions

Strong correspondence between the uniaxial apparent strength and stiffness of cancellous bone allows the use of stiffness as a predictor of bone strength. Measured values of mechanical properties in cancellous bone can be different between experiments due to different experimental conditions. In the current study, bone volume fraction, experimentally determined and finite element (FE) predicted stiffness were examined as predictors of cancellous bone ultimate strength in two different groups each of which was tested using a different end constraint. It is demonstrated that, although always significant, the relationships of strength with bone volume fraction and experimentally determined stiffness are different between test groups. Apparent stiffness, estimated by FE modeling, predicts the ultimate strength of human cancellous bone consistently for all examined experimental protocols.     

Palaeogenomics of pterosaurs and the evolution of small genome size in flying vertebrates

The two living groups of flying vertebrates, birds and bats, both have constricted genome sizes compared with their close relatives. But nothing is known about the genomic characteristics of pterosaurs, which took to the air over 70 Myr before birds and were the first group of vertebrates to evolve powered flight. Here, we estimate genome size for four species of pterosaurs and seven species of basal archosauromorphs using a Bayesian comparative approach. Our results suggest that small genomes commonly associated with flight in bats and birds also evolved in pterosaurs, and that the rate of genome-size evolution is proportional to genome size within amniotes, with the fastest rates occurring in lineages with the largest genomes. We examine the role that drift may have played in the evolution of genome size within tetrapods by testing for correlated evolution between genome size and body size, but find no support for this hypothesis. By contrast, we find evidence suggesting that a combination of adaptation and phylogenetic inertia best explains the correlated evolution of flight and genome-size contraction. These results suggest that small genome/cell size evolved prior to or concurrently with flight in pterosaurs. We predict that, similar to the pattern seen in theropod dinosaurs, genome-size contraction preceded flight in pterosaurs and bats.     

Comparing aerodynamic efficiency in birds and bats suggests better flight performance in birds

Flight is one of the energetically most costly activities in the animal kingdom, suggesting that natural selection should work to optimize flight performance. The similar size and flight speed of birds and bats may therefore suggest convergent aerodynamic performance; alternatively, flight performance could be restricted by phylogenetic constraints. We test which of these scenarios fit to two measures of aerodynamic flight efficiency in two passerine bird species and two New World leaf-nosed bat species. Using time-resolved particle image velocimetry measurements of the wake of the animals flying in a wind tunnel, we derived the span efficiency, a metric for the efficiency of generating lift, and the lift-to-drag ratio, a metric for mechanical energetic flight efficiency. We show that the birds significantly outperform the bats in both metrics, which we ascribe to variation in aerodynamic function of body and wing upstroke: Bird bodies generated relatively more lift than bat bodies, resulting in a more uniform spanwise lift distribution and higher span efficiency. A likely explanation would be that the bat ears and nose leaf, associated with echolocation, disturb the flow over the body. During the upstroke, the birds retract their wings to make them aerodynamically inactive, while the membranous bat wings generate thrust and negative lift. Despite the differences in performance, the wake morphology of both birds and bats resemble the optimal wake for their respective lift-to-drag ratio regimes. This suggests that evolution has optimized performance relative to the respective conditions of birds and bats, but that maximum performance is possibly limited by phylogenetic constraints. Although ecological differences between birds and bats are subjected to many conspiring variables, the different aerodynamic flight efficiency for the bird and bat species studied here may help explain why birds typically fly faster, migrate more frequently and migrate longer distances than bats.     

Avian wing proportions and flight styles: first step towards predicting the flight modes of mesozoic birds

We investigated the relationship between wing element proportions and flight mode in a dataset of living avian species to provide a framework for making basic estimates of the range of flight styles evolved by Mesozoic birds. Our results show that feather length (f(prim)) and total arm length (ta) (sum of the humerus, ulna and manus length) ratios differ significantly between four flight style groups defined and widely used for living birds and as a result are predictive for fossils. This was confirmed using multivariate ordination analyses, with four wing elements (humerus, ulna/radius, manus, primary feathers), that discriminate the four broad flight styles within living birds. Among the variables tested, manus length is closely correlated with wing size, yet is the poorest predictor for flight style, suggesting that the shape of the bones in the hand wing is most important in determining flight style. Wing bone thickness (shape) must vary with wing beat strength, with weaker forces requiring less bone. Finally, we show that by incorporating data from Mesozoic birds, multivariate ordination analyses can be used to predict the flight styles of fossils.     

Post-hatching growth and development of the pectoral and pelvic limbs in the black noddy, Anous minutus

The black tern (Anous minutus) uses a semi-precocial growth strategy. Terrestrial locomotor capacity occurs soon after hatching, but pectoral limb development is delayed and flight is not possible until about post-hatching day 50. A growth series (hatchlings to fledglings) was used to explore how limb musculoskeletal development varied with body mass. In the pelvic limb, bone lengths scaled isometrically or with negative allometry. Gastrocnemius muscle mass and the failure load and stiffness of the tibiotarsus scaled isometrically. In the pectoral limb, pectoralis and supracoracoideus muscle masses increased with strong positive allometry that was mirrored by increases in wing bone strength and stiffness. Bending strength (sigma(ult)) and modulus (E) remained fairly constant throughout development to fledging for all limb bones. The moment of inertia (I) scaled with negative allometry for the tibiotarsus and with strong positive allometry in the wing bones. Differences in sigma(ult) and E of the tibiotarsus between pre-fledged chicks and adults was due, primarily, to increases in bone density rather than increases in the moment of inertia of the skeletal elements, whereas sigma(ult) of wing bones was a function of increases in both bone density and I. Early development of functional pelvic limbs in tree-nesting birds is relatively unusual, and presumably reflects a familial trait that does not appear to compromise breeding success in this species.     

L’origine et l’évolution des oiseaux : 35 années de progrès

The origin and evolution of birds: 35 years of progress. Birds are dinosaurs – specifically, small feathered and flighted theropod dinosaurs that probably originated in Laurasia during the Late Jurassic over 140 million years ago. They are most closely related to other small theropods such as dromaeosaurs and troodontids, terrestrial predators that were fleet-footed hunters. The origin of birds is a classic example of two kinds of macroevolution: the phylogenetic origin of the group, and the sequential assembly of adaptations such as flight that are indelibly associated with birds. These adaptations were not assembled all at once. Rather, a great many characteristics associated with birds and flight first appeared in non-avian dinosaurs, where they were used for many purposes other than flight. These included insulation, brooding, and probably display and species recognition. Birds diversified steadily but gradually after their origin, which is identified with the origin of flight (Archaeopteryx); forelimb and other flight-associated features evolved more rapidly than features associated with the posterior skeleton. The first birds grew more slowly than extant birds do, and more like other small Mesozoic dinosaurs; like them, they probably matured sexually well before they completed their active skeletal growth. The origin of flight is not a problem of “trees down” or “ground up,” but rather an examination of the order in which diagnostic flight characters evolved, and what each stage can reveal about the functions and habits of bird outgroups at those evolutionary junctures.     

Feeding mechanisms in bats: variation within the constraints of flight

By any standard, bats are a successful group of mammals andthe evolution of flight and echolocation were certainly keyinnovations behind their success. That is only part of the story,however. Bats have diversified into trophic niches that rangefrom insectivory to feeding on blood, fruit, or nectar. Whileflight places fundamental constraints on the shape of the postcranialskeleton, skull shape in bats is remarkably diverse. Morphologicalstudies of individual families and sympatric assemblages demonstratethat variation in skull shape is clearly associated with trophicspecialization. Field experiments demonstrate that species-specificbiting behaviors during feeding are common and analyses indicatethat the evolution of cranial morphology and feeding behaviorare correlated. Modeling experiments further suggest that feeding(loading) behaviors and skull shape are functionally linked.If the skulls of bats are under selective pressure for minimalmass because of the energetic demands of flight, then they maybe more "optimized" to meet mechanical demands than are theskulls of other mammals. This would make bats a unique modelsystem for studying the evolution of diversity in skull shapeand its functional implications for the evolution of feedingstrategies in mammals.     

Post-hatching growth and development of the pectoral and pelvic limbs in the black noddy, Anous minutus.

The black tern (Anous minutus) uses a semi-precocial growth strategy. Terrestrial locomotor capacity occurs soon after hatching, but pectoral limb development is delayed and flight is not possible until about post-hatching day 50. A growth series (hatchlings to fledglings) was used to explore how limb musculoskeletal development varied with body mass. In the pelvic limb, bone lengths scaled isometrically or with negative allometry. Gastrocnemius muscle mass and the failure load and stiffness of the tibiotarsus scaled isometrically. In the pectoral limb, pectoralis and supracoracoideus muscle masses increased with strong positive allometry that was mirrored by increases in wing bone strength and stiffness. Bending strength (sigma(ult)) and modulus (E) remained fairly constant throughout development to fledging for all limb bones. The moment of inertia (I) scaled with negative allometry for the tibiotarsus and with strong positive allometry in the wing bones. Differences in sigma(ult) and E of the tibiotarsus between pre-fledged chicks and adults was due, primarily, to increases in bone density rather than increases in the moment of inertia of the skeletal elements, whereas sigma(ult) of wing bones was a function of increases in both bone density and I. Early development of functional pelvic limbs in tree-nesting birds is relatively unusual, and presumably reflects a familial trait that does not appear to compromise breeding success in this species.     

A morphometric study of the lungs of different sized bats: correlations between structure and function of the chiropteran lung.

1. The lungs of four species of bats, Phyllostomus hastatus (PH, mean body mass, 98 g), Pteropus lylei (PL, 456 g), Pteropus alecto (PA, 667 g), and Pteropus poliocephalus (PP, 928 g) were analysed by morphometric methods. These data increase fivefold the range of body masses for which bat lung data are available, and allow more representative allometric equations to be formulated for bats. 2. Lung volume ranged from 4.9 cm3 for PH to 39 cm3 for PP. The volume density of the lung parenchyma (i.e. the volume proportion of the parenchyma in the lung) ranged from 94% in PP to 89% in PH. Of the components of the parenchyma, the alveoli composed 89% and the blood capillaries about 5%. 3. The surface area of the alveoli exceeded that of the blood-gas (tissue) barrier and that of the capillary endothelium whereas the surface area of the red blood cells as well as that of the capillary endothelium was greater than that of the tissue barrier. PH had the thinnest tissue barrier (0.1204 microns) and PP had the thickest (0.3033 microns). 4. The body mass specific volume of the lung, that of the volume of pulmonary capillary blood, the surface area of the blood-gas (tissue) barrier, the diffusing capacity of the tissue barrier, and the total morphometric pulmonary diffusing capacity in PH all substantially exceeded the corresponding values of the pteropid species (i.e. PL, PA and PP). This conforms with the smaller body mass and hence higher unit mass oxygen consumption of PH, a feature reflected in the functionally superior gas exchange performance of its lungs. 5. Morphometrically, the lungs of different species of bats exhibit remarkable differences which cannot always be correlated with body mass, mode of flight and phylogeny. Conclusive explanations of these pulmonary structural disparities in different species of bats must await additional physiological and flight biomechanical studies. 6. While the slope, the scaling factor (b), of the allometric equation fitted to bat lung volume data (b = 0.82) exceeds the value for flight VO2max (b = 0.70), those for the surface area of the blood-gas (tissue) barrier (b = 0.74), the pulmonary capillary blood volume (b = 0.74), and the total morphometric lung diffusing capacity for oxygen (b = 0.69) all correspond closely to the VO2max value. 7. Allometric comparisons of the morphometric pulmonary parameters of bats, birds and non-flying mammals reveal that superiority of the bat lung over that of the non-flying mammal.(ABSTRACT TRUNCATED AT 400 WORDS)