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Flying animals of different masses vary widely in body proportions, but the functional implications of this variation are often unclear. We address this ambiguity by developing an integrative allometric approach, which we apply here to hummingbirds to examine how the physical environment, wing morphology and stroke kinematics have contributed to the evolution of their highly specialised flight. Surprisingly, hummingbirds maintain constant wing velocity despite an order of magnitude variation in body weight; increased weight is supported solely through disproportionate increases in wing area. Conversely, wing velocity increases with body weight within species, compensating for lower relative wing area in larger individuals. By comparing inter- and intraspecific allometries, we find that the extreme wing area allometry of hummingbirds is likely an adaptation to maintain constant burst flight capacity and induced power requirements with increasing weight. Selection for relatively large wings simultaneously maximises aerial performance and minimises flight costs, which are essential elements of humming bird life history.

Bird flight is a remarkable adaptation that has allowed the approximately 10 000 extant species to colonize all terrestrial habitats on earth including high elevations, polar regions, distant islands, arid deserts, and many others. Birds exhibit numerous physiological and biomechanical adaptations for flight. Although bird flight is often studied at the level of aerodynamics, morphology, wingbeat kinematics, muscle activity, or sensory guidance independently, in reality these systems are naturally integrated. There has been an abundance of new studies in these mechanistic aspects of avian biology but comparatively less recent work on the physiological ecology of avian flight. Here we review research at the interface of the systems used in flight control and discuss several common themes. Modulation of aerodynamic forces to respond to different challenges is driven by three primary mechanisms: wing velocity about the shoulder, shape within the wing, and angle of attack. For birds that flap, the distinction between velocity and shape modulation synthesizes diverse studies in morphology, wing motion, and motor control. Recently developed tools for studying bird flight are influencing multiple areas of investigation, and in particular the role of sensory systems in flight control. How sensory information is transformed into motor commands in the avian brain remains, however, a largely unexplored frontier. Key words: Aves, comparative biomechanics, neuromuscular control, visual guidance, wing morphing. Le vol des oiseaux est une adaptation remarquable qui a permis aux quelque 10 000 especes actuelles de coloniser tous les habitats terrestres de la planete, dont les regions polaires et de haute altitude, les iles eloignees, les deserts arides et bien d'autres. Les oiseaux presentent de nombreuses adaptations physiologiques et biomecaniques pour le vol. Bien que l'aerodynamique, la morphologie, la cinematique des battements d'ailes, l'activite musculaire et le guidage sensoriel associes au vol d'oiseau soient souvent etudies de maniere independante, en realite, ces systemes sont naturellement integres. S'il y a abondance de nouvelles etudes sur ces aspects mecanistes de la biologie aviaire, moins de travaux recents se sont penches sur l'ecologie physiologique du vol des oiseaux. Nous passons en revue la recherche a l'interface des systemes utilises dans le controle du vol et abordons plusieurs themes communs. La modulation des forces aerodynamiques pour repondre a differents defis est assuree par trois principaux mecanismes, soit la vitesse des ailes autour de l'epaule, la forme a l'interieur de l'aile et l'angle d'attaque. Pour les oiseaux qui battent des ailes, la distinction entre la modulation par la vitesse et par la forme regroupe des etudes variees sur la morphologie, le mouvement des ailes et le controle moteur. Des outils recemment mis au point pour etudier le vol des oiseaux influencent plusieurs champs d'etude, notamment le role des systemes sensoriels dans le controle du vol. La transformation de l'information sensorielle en commandes motrices dans le cerveau des oiseaux demeure toutefois une frontiere largement inexploree. [Traduit par la Redaction] Mots-cles: oiseaux, biomecanique comparative, controle neuromusculaire, guidage visuel, morphing des ailes., Introduction The flying abilities of birds are impressive; casual observation of their soaring, hovering, and manoeuvring can lead one to assume that the graceful and poised motions are almost effortless. [...]

Although ants are lauded for their strength, little is known about the limits of their load-carrying abilities.We determined the maximal loadcarrying capacity of leaf-cutter ants by incrementally adding mass to the leaves they carried. Maximal load-carrying ability scaled isometrically with body size, indicating that larger ants had the capacity to lift the same proportion of their body mass as smaller ants (8.78 times body mass). However, larger ants were captured carrying leaf fragments that represented a lower proportion of their body mass compared with their smaller counterparts. Therefore, when selecting leaves, larger ants retained a higher proportion of their load-carrying capacity in reserve. This suggests that either larger ants require greater power reserves to overcome challenges they encounter along the trail or leaf-cutter ants do not select loads that maximize the overall leaf transport rate of the colony. [ABSTRACT FROM AUTHOR]

Maneuverability is one of the most important and least understood aspects of animal locomotion. The hydrofoil-like flippers of cetaceans are thought to function as control surfaces that effect maneuvers, but quantitative tests of this hypothesis have been lacking. Here, we constructed a simple hydrodynamic model to predict the longitudinal-axis roll performance of fin whales, and we tested its predictions against kinematic data recorded by on-board movement sensors from 27 free-swimming fin whales. We found that for a given swimming speed and roll excursion, the roll velocity of fin whales calculated from our field data agrees well with that predicted by our hydrodynamic model. Although fluke and body torsion may further influence performance, our results indicate that lift generated by the flippers is sufficient to drive most of the longitudinal-axis rolls used by fin whales for feeding and maneuvering. [ABSTRACT FROM AUTHOR]

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The biomechanical and neuromuscular mechanisms used by different animals to generate turns in flight are highly variable. Body size and body plan exert some influence, e.g. birds typically roll their body to orient forces generated by the wings whereas insects are capable of turning via left-right wingbeat asymmetries. Turns are also relatively brief and have low repeatability, with almost every wingbeat serving a different function throughout the change in heading. Here we present an analysis of Anna's hummingbirds (Calypte anna) as they fed continuously from an artificial feeder revolving around the outside of the animal. This setup allowed for examination of sustained changes in yaw without requiring any corresponding changes in pitch, roll or body position. Hummingbirds sustained yaw turns by expanding the wing stroke amplitude of the outer wing during the downstroke and by altering the deviation of the wingtip path during both downstroke and upstroke. The latter led to a shift in the inner-outer stroke plane angle during the upstroke and shifts in the elevation of the stroke plane and in the deviation of the wingtip path during both strokes. These features are generally more similar to how insects, as opposed to birds, turn. However, time series analysis also revealed considerable stroke-to-stroke variation. Changes in the stroke amplitude and the wingtip velocity were highly cross-correlated, as were changes in the stroke deviation and the elevation of the stroke plane. As was the case for wingbeat kinematics, electromyogram recordings from pectoral and wing muscles were highly variable, but no correlations were found between these two features of motor control. The high variability of both kinematic and muscle activation features indicates a high level of wing beat-to-wing beat adjustments during sustained yaw. The activation timing of the muscles was more repeatable than the activation intensity, which suggests that the former may be constrained by harmonic motion and that the latter may play a large role in kinematic adjustments. Comparing the revolution frequency of the feeder with measurements of free flight yaws reveals that feeder tracking, even at one revolution every 2s, is well below the maximum yaw capacity of the hummingbirds. [ABSTRACT FROM AUTHOR]