Supracoracoideus Muscle Research Articles

3D atlas of tinamou (Neornithes: Tinamidae) pectoral morphology: Implications for reconstructing the ancestral neornithine flight apparatus.

Palaeognathae, the extant avian clade comprising the flightless ratites and flight-capable tinamous (Tinamidae), is the sister group to all other living birds, and recent phylogenetic studies illustrate that tinamous are phylogenetically nested within a paraphyletic assemblage of ratites. As the only extant palaeognaths that have retained the ability to fly, tinamous may provide key information on the nature of the flight apparatus of ancestral crown palaeognaths-and, in turn, crown birds-as well as insight into convergent modifications to the wing apparatus among extant ratite lineages. To reveal new information about the musculoskeletal anatomy of tinamous and facilitate development of computational biomechanical models of tinamou wing function, we generated a three-dimensional musculoskeletal model of the flight apparatus of the extant Andean tinamou (Nothoprocta pentlandii) using diffusible iodine-based contrast-enhanced computed tomography (diceCT). Origins and insertions of the pectoral flight musculature of N. pentlandii are generally consistent with those of other extant volant birds specialized for burst flight, and the entire suite of presumed ancestral neornithine flight muscles are present in N. pentlandii with the exception of the biceps slip. The pectoralis and supracoracoideus muscles are robust, similar to the condition in other extant burst-flying birds such as many extant Galliformes. Contrary to the condition in most extant Neognathae (the sister clade to Palaeognathae), the insertion of the pronator superficialis has a greater distal extent than the pronator profundus, although most other anatomical observations are broadly consistent with the conditions observed in extant neognaths. This work will help form a basis for future comparative studies of the avian musculoskeletal system, with implications for reconstructing the flight apparatus of ancestral crown birds and clarifying musculoskeletal modifications underlying the convergent origins of ratite flightlessness.

Allometry of the pectoral flight muscles in birds: Flight style is related to variability in the mass of the supracoracoideus muscle

AbstractAvian flight is powered by a downstroke force generated by the pectoralis (P) muscle and an upstroke force generated by the supracoracoideus (SC) muscle. Some taxa, notably penguins and hummingbirds, have very low P:SC ratios associated with larger masses of the supracoracoideus. Allometric relationships of these muscles are not reported relative to body mass and presumably the two muscles will exhibit isometry in volant birds. This study collated muscle masses for over 600 species representing 28 orders of birds and used phylogenetically controlled analysis of covariance to test for the effects of taxonomic grouping on the allometry of the flight muscles in birds. The P:SC ratio and the standardized residuals for the allometric relationships, were calculated for different orders. The pectoralis scaled isometrically with body mass but the supracoracoideus muscle exhibited a slight but significant negative allometry. Both muscles showed significant effects of taxonomic group but this effect was magnified for the supracoracoideus. Wing‐propelled divers and hovering hummingbirds had disproportionately high proportions of supracoracoideus muscles but tinamous, gamebirds and pigeons, which exhibit burst flight, also had low P:SC ratios. Many taxonomic groups had a ratio around 10:1 but values of 20:1, recorded for birds of prey and owls, were associated with relatively small masses of the supracoracoideus muscle. The P:SC ratio seems to reflect differing flight styles with the greater variability being more associated with the size of the supracoracoideus, the significance of which has not necessarily been fully appreciated in the morphology and flight action of birds.

Where was WAIR in avian flight evolution?

Abstract The popular hypothesis that the flapping flight of birds evolved through the stage of wing-assisted incline running (WAIR) is tested through calculations of external forces acting on the wings in the downstroke and upstroke during WAIR activity of an adult chukar partridge (Alectoris chukar). Contrary to previous studies of WAIR, it is found that the total vertical impulse provided by the wings is negative (i.e. downward directed). Thus, the wings cancel out about half of the positive (upward-directed) impulse provided by the legs. The function of the wings in WAIR is not to lift the body, but to push it towards the steep slope. It is like a wing, or aerofoil, of a race car, which is tilted at a negative angle of attack to press the car to the ground for greater friction and adhesion of the wheels and to prevent the race car from becoming airborne. The calculated force pattern suggests that the dominant external forces acting on the wings in the sagittal plane during WAIR are not the virtual forces of inertia but the aerodynamic forces. More specifically, it is only the aerodynamic lift that can be responsible for the wing force component acting at right angles to the wingbeat plane in both the downstroke and the upstroke during WAIR. The lift towards the slope during the WAIR upstroke is ensured by separation of the primary flight feathers and their setting at a negative angle of attack. Analysis of the force pattern in the anatomical coordinate space of a bird’s body shows that the main wing muscles in the WAIR downstroke are the humeral retractor muscles and in the WAIR upstroke the humeral elevator muscles. The humeral protractor muscles are not required at all during WAIR. Therefore, the morphologically necessary protractor state of the supracoracoideus muscle in a ‘semi-flying’ ancestor, which is logically explained by the classical hypothesis of a gliding ancestor, does not fit the WAIR hypothesis of flapping flight origin. Wing-assisted incline running should be regarded as a crown locomotor specialization of birds and is not an appropriate model for locomotion in avian ancestors.

The coracoscapular joint of neornithine birds\u2014extensive homoplasy in a widely neglected articular surface of the avian pectoral girdle and its possible functional correlates

A survey is given of the morphological variation of the coracoscapular joint of neornithine birds. In Mesozoic stem group representatives, the coracoid exhibits a deeply concave cotyla scapularis, which articulates with a globose tuberculum coracoideum of the scapula. This morphology is likely to be functionally related to the development of a powerful supracoracoideus muscle and the formation of a triosseal canal as a pulley for the tendon of this muscle. In neornithine birds, the coracoid articulates with the scapula either via a concave cotyla or a flat facies articularis, with the latter largely restricting movements of the coracoid to the paramedian plane. Ancestral state reconstruction suggests that a cotyla scapularis is plesiomorphic for Neornithes and that a flat facies articularis scapularis evolved at least 13 times independently within the clade. For several lineages, the transition to a flat facies articularis scapularis can be traced in the fossil record, and the replacement of a cup-shaped cotyla by a flat articular facet seems to have been due to various functional demands. Often, a flat facies articularis scapularis is associated with reduced shafts of the furcula. A weakly developed furcula enables transverse movements of the coracoid and therefore enables a restriction of the mobility of the coracoscapular joint to the paramedian plane. In taxa with a large crop, a flat facies articularis scapularis is likely to be associated with a reorganization of the pectoral musculature, whereas in procellariiform birds, the transition from a cotyla to a facies articularis appears to have been correlated with the capacity for sustained soaring without wing flapping.

Genetic and physiological variation in two strains of Japanese quail

BackgroundDetecting the genetic and physiological variations in two Japanese quail strains could be used to suggest a new avian model for future breeding studies. Consequently, two estimations were performed on two Japanese quail strains: gray quail strain (GJQS) and white jumbo quail strain (WJQS). The first estimation was conducted on carcass characteristics, breast muscles, breast concentration of collagen type I, and body measurements. In contrast, blood samples were collected for the second estimation for genomic DNA extraction and genetic analysis. ResultsA total of 62 alleles out of 97 specific alleles (63.92%) were detected overall loci (14 microsatellite loci) for the two strains. A total of 27 specific alleles of WJQS were observed, and 35 were obtained for GJQS. The percentage of similarity was 48.09% ranged from 4.35 with UBC001 to 100% with GUJ0051. WJQS had greater body weights and a higher value of pectoral muscle and supracoracoideus muscle than GJQS. The breast muscles of GJQS exhibited a higher concentration of type I collagen than the WJQS. Furthermore, males showed higher concentrations of collagen type I than females. WJQS showed a higher body length, chest girth, chest length, thigh length, thigh girth, drumstick length, and drumstick girth (cm) than GJQS. WJQS showed more significant differences in carcass traits compared with GJQS. ConclusionThe physiological differences between WJQS and GJQS were ascertained with microsatellite markers, which indicated high polymorphism between these strains. These observations provided a scientific basis for evaluating and utilizing the genetic resources of WJQS and GJQS in a future genetic improvement program.

Comparative gross anatomical studies on the shoulder girdle of crested serpent eagle (Spilornis cheela) and brown wood owl (Strix leptogrammica)

The shoulder girdle gives strength and range of motion to the wings of birds and plays a functional role in flight mechanism of birds. The present study was designed to compare the morphological features of shoulder girdle bones in crested serpent eagle and brown wood owl. The shoulder girdle comprised of the scapula, coracoid and fused clavicle i.e. furculum in both species. The proximal extremities of bones of shoulder girdle formed a foramen triosseum in both the species for tendon of supracoracoideus muscle. The proximal end of the scapula of crested serpent eagle presents a pneumatic foramen which was absent in the brown wood owl. The coracoid of crested serpent eagle presents a large pneumatic foramen at the medial surface of the acrocoracoid process. A piercing type of foramen was characteristic in the coracoid of both species. Procoracoid process was triangular in shape with a broad base in both the species with pointed apex in brown wood owl and short apex in crested serpent eagle. The clavicle was thin, slender and highly curved in crested serpent eagle, whereas it was slender and rod-like in brown wood owl. Numerous pneumatic foramina were present in the proximal extremity of the clavicle of the crested serpent eagle, which were few in brown wood owl. The distal extremity of both clavicle fused to form a hypocleideum in crested serpent eagle, which was absent in brown wood owl.

Pectoral girdle morphology of Mesozoic birds and the evolution of the avian supracoracoideus muscle

The evolution of the avian flight musculature is poorly understood and most studies focused on Archaeopteryx. However, important evolutionary changes occurred within Aves, and here the morphology of the pectoral girdle of Mesozoic birds is interpreted in relation to the evolution of the supracoracoideus muscle, which elevates the wing in the upstroke. In the course of avian evolution, the main origin of this muscle shifted from the coracoid onto the sternum. It is hypothesized that resulting space constraints in the cranial portion of the sternum, which also served as the attachment site for the large pectoralis muscle, led to the evolution of a sternal keel. The cranial portion of the sternum of Early Cretaceous Enantiornithes—one of the major clades of Mesozoic birds—lacks a well-developed keel, and the development of the supracoracoideus muscle must have differed from extant birds. This assumption is in concordance with the fact that a triosseal canal, which forms a pulley for the tendon of this muscle in extant birds, appears not to have been developed in Enantiornithes.

EXERCISE-INDUCED DEEP PECTORAL NECROSIS IN WHITE-HEADED PIGEONS (COLUMBA LEUCOMELA)

Abstract: Two white-headed pigeons (Columba leucomela) developed deep pectoral myopathy 2 days after vigorous exercise associated with capture. Clinical signs included lethargy and an inability to raise the wings above the head. Gross pathology consistently revealed marked pallor and edema of the supracoracoideus muscle, and histopathology revealed severe myofiber degeneration. A further two white-headed pigeons presented 7 and 21 days postexercise with similar lesions. Treatment with fluids, physiotherapy, and analgesia was unsuccessful. This is the first report of deep muscle necrosis in Columbiformes.

Individual Variation in Thermogenic Capacity Is Correlated with Flight Muscle Size but Not Cellular Metabolic Capacity in American Goldfinches (Spinus tristis)

Abstract Cold tolerance and overwinter survival are positively correlated with organismal thermogenic capacity (=summit metabolic rate [Msum]) in endotherms. Msum varies seasonally in small-bird populations and may be mechanistically associated with variation in flight muscle size or cellular metabolic capacity, but the relative roles of these traits as drivers of individual variation in thermogenic performance are poorly known. We measured flight muscle size by ultrasonography, pectoralis and supracoracoideus muscle masses, and muscular activities of key aerobic enzymes (citrate synthase, carnitine palmitoyl transferase, and β-hydroxyacyl-CoA dehydrogenase) and correlated these measurements with Msum for individual American goldfinches (Spinus tristis) to test the hypotheses that muscle size and/or cellular metabolic capacity serve as prominent drivers of individual variation in organismal metabolic capacity. Ultrasonographic flight muscle size was weakly positively correlated with Msum ([Formula: see text]). Both log10-transformed Msum and flight muscle mass were significantly correlated with log10 body mass, so we calculated allometric residuals for log Msum and for log flight muscle mass to test their correlation independent of body mass. Flight muscle mass residuals were significantly positively correlated with Msum residuals, and this correlation was primarily driven by variation in pectoralis muscle mass. In contrast, none of the mass-specific activities of any enzyme in any muscle were significantly correlated with Msum. These data suggest that flight muscle size, not cellular metabolic capacity, is the primary driver of individual variation in thermogenic performance in goldfinches. This is consistent with the idea that phenotypic flexibility of flight muscle mass is a general mechanism mediating variation in metabolic performance in response to changing energy demands in birds.

Ecological correlates of variable organ sizes and fat loads in the most northerly wintering shorebirds

Shorebirds at northern latitudes during the nonbreeding season typically carry relatively large lipid stores and exhibit an up-regulation of lean tissues associated with digestion and thermogenesis. Intraspecific variation in these tissues across sites primarily reflects differences in environmental conditions. Rock (Calidris ptilocnemis (Coues, 1873)) and Purple (Calidris maritima (Brünnich, 1764)) sandpipers are closely related species having the most northerly nonbreeding distributions among shorebirds, living at latitudes up to 61°N in Cook Inlet, Alaska, and up to ∼71°N in northern Norway, respectively. Cook Inlet is the coldest known site used by nonbreeding shorebirds, and the region’s mudflats annually experience extensive coverage of foraging sites by sea and shore-fast ice. Accordingly, Rock Sandpipers increase their fat stores to nearly 20% of body mass during winter. In contrast, Purple Sandpipers exploit predictably ice-free rocky intertidal foraging sites and maintain low (<6.5%) fat stores. Rock Sandpipers increase the mass of lean tissues from fall to winter, including contour feathers, stomach, and liver components. They also have greater lean pectoralis and supracoracoideus muscle and liver and kidney tissues compared with Purple Sandpipers in winter. This demonstrates a combined emphasis on digestive processes and thermogenesis, whereas Purple Sandpipers primarily augment organs associated with digestive processes. The high winter fat loads and increased lean tissues of Rock Sandpipers in Cook Inlet reflect the region’s persistent cold and abundant but sporadically unavailable food resources.

Very low force-generating ability and unusually high temperature-dependency in hummingbird flight muscle fibers

Hummingbird flight muscle is estimated to have among the highest mass-specific power output among vertebrates, based on aerodynamic models. However, little is known about the fundamental contractile properties of their remarkable flight muscles. We hypothesized that hummingbird pectoralis fibers generate relatively low force when activated in a tradeoff for high shortening speeds associated with the characteristic high wingbeat frequencies that are required for sustained hovering. Our objective was to measure maximal force-generating ability (maximal force/cross-sectional area, Po/CSA) in single, skinned fibers from the pectoralis and supracoracoideus muscles, which power the wing downstroke and upstroke, respectively, in hummingbirds (Calypte anna) and in another similarly sized species, zebra finch (Taeniopygia guttata), which also has a very high wingbeat frequency during flight but does not perform a sustained hover. Mean Po/CSA in hummingbird pectoralis fibers was very low - 1.6, 6.1 and 12.2 kN m(-2), at 10, 15 and 20°C, respectively. Po/CSA in finch pectoralis fibers was also very low (for both species, ~5% of the reported Po/CSA of chicken pectoralis fast fibers at 15°C). Q10-force (force generated at 20°C/force generated at 10°C) was very high for hummingbird and finch pectoralis fibers (mean=15.3 and 11.5, respectively) compared with rat slow and fast fibers (1.8 and 1.9, respectively). Po/CSA in hummingbird leg fibers was much higher than in pectoralis fibers at each temperature, and the mean Q10-force was much lower. Thus, hummingbird and finch pectoralis fibers have an extremely low force-generating ability compared with other bird and mammalian limb fibers, and an extremely high temperature dependence of force generation. However, the extrapolated maximum force-generating ability of hummingbird pectoralis fibers in vivo (~48 kN m(-2)) is substantially higher than the estimated requirements for hovering flight of C. anna. The unusually low Po/CSA of hummingbird and zebra finch pectoralis fibers may reflect a constraint imposed by a need for extremely high contraction frequencies, especially during hummingbird hovering.

Comparative proteomic characterization of the sarcoplasmic proteins in the pectoralis major and supracoracoideus breast muscles in 2 chicken genotypes

The selection processes that have resulted in broiler (meat) and leghorn (eggs) chickens have had very different effects on the pectoralis major and supracoracoideus muscles. The objective of this study, therefore, was to analyze the one-dimensional proteomic profiles of sarcoplasmic protein fractions isolated from the p. major and supracoracoideus muscles collected from 10 chicks from each genotype to compare developmental differences. The sarcoplasmic protein fraction was analyzed by SDS-PAGE. The mean band percentages were analyzed using a mixed model, with strain and muscle type as main effects. Six bands were found to be significantly different across the 2 strains. Strain differences in glycogen phosphorylase, enolase, elongation factor 1, creatine kinase, fructose-bisphosphate aldolase, and glyceraldehyde 3-phosphate-dehydrogenase suggest a genotype-specific shift in energy metabolism during breast muscle growth and development.

Muscle function in avian flight: achieving power and control

Flapping flight places strenuous requirements on the physiological performance of an animal. Bird flight muscles, particularly at smaller body sizes, generally contract at high frequencies and do substantial work in order to produce the aerodynamic power needed to support the animal's weight in the air and to overcome drag. This is in contrast to terrestrial locomotion, which offers mechanisms for minimizing energy losses associated with body movement combined with elastic energy savings to reduce the skeletal muscles' work requirements. Muscles also produce substantial power during swimming, but this is mainly to overcome body drag rather than to support the animal's weight. Here, I review the function and architecture of key flight muscles related to how these muscles contribute to producing the power required for flapping flight, how the muscles are recruited to control wing motion and how they are used in manoeuvring. An emergent property of the primary flight muscles, consistent with their need to produce considerable work by moving the wings through large excursions during each wing stroke, is that the pectoralis and supracoracoideus muscles shorten over a large fraction of their resting fibre length (33-42%). Both muscles are activated while being lengthened or undergoing nearly isometric force development, enhancing the work they perform during subsequent shortening. Two smaller muscles, the triceps and biceps, operate over a smaller range of contractile strains (12-23%), reflecting their role in controlling wing shape through elbow flexion and extension. Remarkably, pigeons adjust their wing stroke plane mainly via changes in whole-body pitch during take-off and landing, relative to level flight, allowing their wing muscles to operate with little change in activation timing, strain magnitude and pattern.

Effects of flight speed upon muscle activity in hummingbirds

Hummingbirds have the smallest body size and highest wingbeat frequencies of all flying vertebrates, so they represent one endpoint for evaluating the effects of body size on sustained muscle function and flight performance. Other bird species vary neuromuscular recruitment and contractile behavior to accomplish flight over a wide range of speeds, typically exhibiting a U-shaped curve with maxima at the slowest and fastest flight speeds. To test whether the high wingbeat frequencies and aerodynamically active upstroke of hummingbirds lead to different patterns, we flew rufous hummingbirds (Selasphorus rufus, 3 g body mass, 42 Hz wingbeat frequency) in a variable-speed wind tunnel (0-10 m s(-1)). We measured neuromuscular activity in the pectoralis (PECT) and supracoracoideus (SUPRA) muscles using electromyography (EMG, N=4 birds), and we measured changes in PECT length using sonomicrometry (N=1). Differing markedly from the pattern in other birds, PECT deactivation occurred before the start of downstroke and the SUPRA was deactivated before the start of upstroke. The relative amplitude of EMG signal in the PECT and SUPRA varied according to a U-shaped curve with flight speed; additionally, the onset of SUPRA activity became relatively later in the wingbeat at intermediate flight speeds (4 and 6 m s(-1)). Variation in the relative amplitude of EMG was comparable with that observed in other birds but the timing of muscle activity was different. These data indicate the high wingbeat frequency of hummingbirds limits the time available for flight muscle relaxation before the next half stroke of a wingbeat. Unlike in a previous study that reported single-twitch EMG signals in the PECT of hovering hummingbirds, across all flight speeds we observed 2.9+/-0.8 spikes per contraction in the PECT and 3.8+/-0.8 spikes per contraction in the SUPRA. Muscle strain in the PECT was 10.8+/-0.5%, the lowest reported for a flying bird, and average strain rate was 7.4+/-0.2 muscle lengths s(-1). Among species of birds, PECT strain scales proportional to body mass to the 0.2 power (infinityM(b)(0.2)) using species data and infinityM(b)(0.3) using independent contrasts. This positive scaling is probably a physiological response to an adverse scaling of mass-specific power available for flight.

Glycolysis activity in flight muscles of birds according to their physiological function. An experimental model in vitro to study aerobic and anaerobic glycolysis activity separately

An experimental system in vitro is presented to assess the activity of the entire glycolysis in tissue extracts, which allows determining aerobic and anaerobic glycolysis activities separately. Glycolysis activity has been measured in pectoral and supracoracoideus muscles of the homing pigeon and the domestic fowl. These muscles support different aspects of flight in the two birds and are representative models of the two kinds of basic movements, endurance and sprint. The results obtained showed that in type I red fibers (pigeon pectoral), glucose produced a high glycolytic activity, while it was a poor substrate for type IIb white fibers (fowl pectoral and the two supracoracoideus). White fibers, however, attained its maximum glycolytic activity with phosphorylated glucose as substrate. These results demonstrated the validity of the experimental system as a method for assaying the two kinds of glycolytic activity in tissues, and supply new information about the biochemical and physiological features of these types of fibers.

MUSCLE IN LOCOMOTION

Ultimately, muscle powers all flight and swimming in the animal world. Muscular contraction is driven by myosin heads that consume ATP and slide actin filaments along myosin filaments. While much is known about functional specialisation in vertebrate muscle, the approaches that invertebrates have adopted to modulate muscle performance are less well known. William Kier and Frederick Schachat (p. 164) discuss some unusual adaptations found in squid. Squid mantle,fin and arm muscles are obliquely striated (with Z disks linking actin filaments inclined at an angle) and tend to be characterised by long myosin and actin filaments, which are capable of a large contraction range while generating high tensile stresses. However, the tentacle extensor muscle is more similar to cross striated vertebrate skeletal muscle, but with much shorter myofilaments. The result is that the tentacle extensor muscle can contract very rapidly, but generates small tensile stresses. According to Kier and Schachat, the molecular components of both muscle types are virtually indistinguishable, and it is mainly the different architecture that gives rise to the muscles' different properties.Where as squid tentacles have to act fast to grab passing prey, the major muscles involved in flapping bird flight must generate great force while contracting repeatedly as birds take off and remain aloft. Yet, according to Bret Tobalske and Andy Biewener, little is known about the mechanical properties of the second largest flight muscle in birds, the supracoracoideus muscle (p. 170), which was thought to be responsible for flipping the wing upwards at the beginning of an upstroke (supination) during flight. Measuring muscle activity, and bone and muscle strain, in freely flying pigeons, Tobalske and Biewener confirmed that the muscle does indeed flip the wing at the beginning of the upstroke. Also the muscle's elastic tendon stores up to 60% of the muscle's work,presumably releasing the energy later to reduce the metabolic cost of flight. However, two of the team's predictions were not born out; strain in the supracoracoideus muscle was much greater and the power generated by the muscle was less than the team had predicted. Tobalske and Biewener say `it is sobering that our predictions of function from anatomy were only partially correct,' but van Leeuwen describes the team's findings in freely flying birds as `quite an experimental achievement'.Concluding the discussion of muscle function in locomotion, Bertrand Tanner, Michael Regnier and Tom Daniel describe their theoretical work on a three dimensional molecular model of muscle. By modelling the kinetics and molecular structure of half a sarcomere, the team successfully predicts muscle function for Manduca sexta(p. 180). Knowing that the major flight muscle only operates at 40% maximal power and that extra power required for manoeuvres during flight was probably generated by`shifting activation phase [timing] to produce higher mechanical output', the team were also able to model how the timing of activation influences the energetics of contraction. Calculating ATP consumption as well as mechanical work done, power and efficiency, Daniel and colleagues found that the mechanical work generated and ATP consumption vary depending on the timing of myosin activation. Daniel says `to our knowledge, no prior study has shown that myosin cross-bridge ATPase rates vary with phase of activation'.

BIOMECHANICS OF SWIMMING AND FLIGHT

While airborne birds routinely defy gravity and aquatic creatures glide with ease through water, man has largely been restricted to land for all but the last century. How birds and fish manoeuvre with such freedom in their fluid environments has always fascinated humans, and more recently it has

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 ( σ 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 σ 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 σ 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.

The influence of locomotion on air-sac pressures in little penguins.

Air-sac pressures have been reported to oscillate with wing beat in flying magpies and with foot paddling in diving ducks. We sought to determine the impact on air-sac pressure of wing beats during swimming and of the step cycle during walking in little penguins (Eudyptula minor). Fluctuations averaged 0.16+/-0.06 kPa in the interclavicular air sacs, but only 0.06+/-0.04 kPa in the posterior thoracic sac, generating a small differential pressure between sacs of 0.06+/-0.02 kPa (means +/- S.E.M., N=4). These fluctuations occurred at approximately 3 Hz and corresponded to wing beats during swimming, indicated by electromyograms from the pectoralis and supracoracoideus muscles. There was no abdominal muscle activity associated with swimming or exhalation, but the abdominal muscles were active with the step cycle in walking penguins, and oscillations in posterior air-sac pressure (0.08+/-0.038 kPa) occurred with steps. We conclude that high-frequency oscillations in differential air-sac pressure enhance access to and utilization of the O(2) stores in the air sacs during a dive.

Tenectomy of the Supracoracoideus Muscle to Deflight Pigeons (Columba livia) and Cockatiels (Nymphicus hollandicus)

Most of the methods used to deflight birds have one or more disadvantages, including impermanence, poor cosmetic appearance, or impairment of breeding function. We hypothesized that transection of the tendon of the supracoracoideus muscle at its insertion on the proximal humerus would impair a bird's ability to raise the affected wing and thus result in flightlessness. The purpose of this project was to evaluate the effectiveness of unilateral or bilateral surgical tenectomy of the supracoracoideus muscle in deflighting cockatiels and pigeons. Six pigeons (Columba livia) and 9 cockatiels (Nymphicus hollandicus) were included in the study. Three cockatiels were included in a sham group, and 3 birds of each species were included in a unilateral or bilateral tenectomy group. The birds in the sham group did not have flight difficulties at any time after surgery. Three cockatiels and 1 pigeon in the unilateral tenectomy group were flying within 3–6 weeks, respectively, after surgery. A ligament instead of a tendon was inadvertently transected in 2 of the pigeons in the unilateral group. These pigeons were able to fly the day after surgery. We did not euthanize these birds to confirm this suspicion. In the bilateral tenectomy groups, 1 of 2 cockatiels and 2 of 3 pigeons were eventually able to fly short distances within 4 to 6 months after surgery. In the same groups, 1 cockatiel died several hours after surgery and 1 pigeon was euthanized 6 weeks after surgery. The pigeon never regained its ability to right itself when placed on its back. Gross necropsies in both birds confirmed that the tendons of the supracoracoideous muscles had been transected. None of the birds undergoing unilateral or bilateral tenectomy had normal dorsal extension of the affected wing, but each was able to fly well enough to escape if taken outdoors. We concluded that neither unilateral nor bilateral supracoracoideus tenectomy is an effective technique for deflighting cockatiels or pigeons.