Aerodynamics of hovering flight in the long-eared bat Plecotus auritus.
Steady-state aerodynamic and momentum theories were used for calculations of the lift and drag coefficients of Plecotus auritus in hovering flight. The lift coefficient obtained varies between 3-1 and 6-4, and the drag coefficient between --5-0 and 10-5, for the possible assumptions regarding the effective angles of attack during the upstroke. This demonstrates that hovering flight in Plecotus auritus can not be explained by quasi-steady-state aerodynamics. Thus, non-steady-state aerodynamics must prevail. (+info)
Temperature regulation and heat dissipation during flight in birds.
Core and skin temperature were measured by radiotelemetry in starlings (Sturnus vulgaris) during 30 min flights in a wind tunnel. Core temperature was independent of ambient temperature from 0 to 28 degrees C. The temporal mean of the monitored core temperature during flight was 42-7 degrees C in one bird and 44-0 degrees C in another. These temperatures are 2-4 degrees C higher than the resting temperature in starlings, and are among the highest steady-state temperatures observed in any animal. Skin temperature on the breast was within a few degrees of core temperature. In some locations skin temperature was higher at low ambient temperatures than at intermediate ambient temperatures. An analysis of the data shows that a high core temperature does not function as an aid to head dissipation. On the contrary, insulation is adjusted to maintain a high temperature, presumably because it is necessary for flight. The increase in skin temperature at low ambient temperatures is believed to be a result of a decrease in heat flow through the breast feathers brought about by feather adjustments, to compensate for an unavoidable increase in heat flow in unfeathered or poorly feathered parts of the body. (+info)
Phase-dependent presynaptic modulation of mechanosensory signals in the locust flight system.
In the locust flight system, afferents of a wing hinge mechanoreceptor, the hindwing tegula, make monosynaptic excitatory connections with motoneurons of the elevator muscles. During flight motor activity, the excitatory postsynaptic potentials (EPSPs) produced by these connections changed in amplitude with the phase of the wingbeat cycle. The largest changes occurred around the phase where elevator motoneurons passed through their minimum membrane potential. This phase-dependent modulation was neither due to flight-related oscillations in motoneuron membrane potential nor to changes in motoneuron input resistance. This indicates that modulation of EPSP amplitude is mediated by presynaptic mechanisms that affect the efficacy of afferent synaptic input. Primary afferent depolarizations (PADs) were recorded in the terminal arborizations of tegula afferents, presynaptic to elevator motoneurons in the same hemiganglion. PADs were attributed to presynaptic inhibitory input because they reduced the input resistance of the afferents and were sensitive to the gamma-aminobutyric acid antagonist picrotoxin. PADs occurred either spontaneously or were elicited by spike activity in the tegula afferents. In summary, afferent signaling in the locust flight system appears to be under presynaptic control, a candidate mechanism of which is presynaptic inhibition. (+info)
Assembly of thick filaments and myofibrils occurs in the absence of the myosin head.
We investigated the importance of the myosin head in thick filament formation and myofibrillogenesis by generating transgenic Drosophila lines expressing either an embryonic or an adult isoform of the myosin rod in their indirect flight muscles. The headless myosin molecules retain the regulatory light-chain binding site, the alpha-helical rod and the C-terminal tailpiece. Both isoforms of headless myosin co-assemble with endogenous full-length myosin in wild-type muscle cells. However, rod polypeptides interfere with muscle function and cause a flightless phenotype. Electron microscopy demonstrates that this results from an antimorphic effect upon myofibril assembly. Thick filaments assemble when the myosin rod is expressed in mutant indirect flight muscles where no full-length myosin heavy chain is produced. These filaments show the characteristic hollow cross-section observed in wild type. The headless thick filaments can assemble with thin filaments into hexagonally packed arrays resembling normal myofibrils. However, thick filament length as well as sarcomere length and myofibril shape are abnormal. Therefore, thick filament assembly and many aspects of myofibrillogenesis are independent of the myosin head and these processes are regulated by the myosin rod and tailpiece. However, interaction of the myosin head with other myofibrillar components is necessary for defining filament length and myofibril dimensions. (+info)
The role of orientation flights on homing performance in honeybees.
Honeybees have long served as a model organism for investigating insect navigation. Bees, like many other nesting animals, primarily use learned visual features of the environment to guide their movement between the nest and foraging sites. Although much is known about the spatial information encoded in memory by experienced bees, the development of large-scale spatial memory in naive bees is not clearly understood. Past studies suggest that learning occurs during orientation flights taken before the start of foraging. We investigated what honeybees learn during their initial experience in a new landscape by examining the homing of bees displaced after a single orientation flight lasting only 5-10 min. Homing ability was assessed using vanishing bearings and homing speed. At release sites with a view of the landmarks immediately surrounding the hive, 'first-flight' bees, tested after their very first orientation flight, had faster homing rates than 'reorienting foragers', which had previous experience in a different site prior to their orientation flight in the test landscape. First-flight bees also had faster homing rates from these sites than did 'resident' bees with full experience of the terrain. At distant sites, resident bees returned to the hive more rapidly than reorienting or first-flight bees; however, in some cases, the reorienting bees were as successful as the resident bees. Vanishing bearings indicated that all three types of bees were oriented homewards when in the vicinity of landmarks near the hive. When bees were released out of sight of these landmarks, hence forcing them to rely on a route memory, the 'first-flight' bees were confused, the 'reorienting' bees chose the homeward direction except at the most distant site and the 'resident' bees were consistently oriented homewards. (+info)
Mechanical versus physiological determinants of swimming speeds in diving Brunnich's guillemots.
For fast flapping flight of birds in air, the maximum power and efficiency of the muscles occur over a limited range of contraction speeds and loads. Thus, contraction frequency and work per stroke tend to stay constant for a given species. In birds such as auks (Alcidae) that fly both in air and under water, wingbeat frequencies in water are far lower than in air, and it is unclear to what extent contraction frequency and work per stroke are conserved. During descent, compression of air spaces dramatically lowers buoyant resistance, so that maintaining a constant contraction frequency and work per stroke should result in an increased swimming speed. However, increasing speed causes exponential increases in drag, thereby reducing mechanical versus muscle efficiency. To investigate these competing factors, we have developed a biomechanical model of diving by guillemots (Uria spp.). The model predicted swimming speeds if stroke rate and work per stroke stay constant despite changing buoyancy. We compared predicted speeds with those of a free-ranging Brunnich's guillemot (U. lomvia) fitted with a time/depth recorder. For descent, the model predicted that speed should gradually increase to an asymptote of 1.5-1.6 m s-1 at approximately 40 m depth. In contrast, the instrumented guillemot typically reached 1.5 m s-1 within 10 m of the water surface and maintained that speed throughout descent to 80 m. During ascent, the model predicted that guillemots should stroke steadily at 1.8 m s-1 below their depth of neutral buoyancy (62 m), should alternate stroking and gliding at low buoyancies from 62 to 15 m, and should ascend passively by buoyancy alone above 15 m depth. However, the instrumented guillemot typically ascended at 1.25 m s-1 when negatively buoyant, at approximately 1.5 m s-1 from 62 m to 25 m, and supplemented buoyancy with stroking above 25 m. Throughout direct descent, and during ascent at negative and low positive buoyancies (82-25 m), the guillemot maintained its speed within a narrow range that minimized the drag coefficient. In films, guillemots descending against high buoyancy at shallow depths increased their stroke frequency over that of horizontal swimming, which had a substantial glide phase. Model simulations also indicated that stroke duration, relative thrust on the downstroke versus the upstroke, and the duration of gliding can be varied to regulate swimming speed with little change in contraction speed or work per stroke. These results, and the potential use of heat from inefficient muscles for thermoregulation, suggest that diving guillemots can optimize their mechanical efficiency (drag) with little change in net physiological efficiency. (+info)
Wing rotation and the aerodynamic basis of insect flight.
The enhanced aerodynamic performance of insects results from an interaction of three distinct yet interactive mechanisms: delayed stall, rotational circulation, and wake capture. Delayed stall functions during the translational portions of the stroke, when the wings sweep through the air with a large angle of attack. In contrast, rotational circulation and wake capture generate aerodynamic forces during stroke reversals, when the wings rapidly rotate and change direction. In addition to contributing to the lift required to keep an insect aloft, these two rotational mechanisms provide a potent means by which the animal can modulate the direction and magnitude of flight forces during steering maneuvers. A comprehensive theory incorporating both translational and rotational mechanisms may explain the diverse patterns of wing motion displayed by different species of insects. (+info)
Flight speed and body mass of nectar-feeding bats (Glossophaginae) during foraging.
Aerodynamic theory predicts that minimum power (Vmp) and maximum range (Vmr) flight speeds increase when the body mass of an individual animal increases. To evaluate whether foraging bats regulate their flight speed within a fixed speed category relative to Vmp or Vmr, I investigated how the natural daily changes in body mass caused by feeding affected the flight speed of neotropical nectar-feeding bats (Phyllostomidae: Glossophaginae) within a strictly defined, stereotyped behavioural context. Individual bats were maintained in a flight tunnel (lengths of five different types 14-50 m) with a fully automated feeding, weighing (using an electronic balance at the roost) and flight speed measuring system. Flight speeds were measured during normal nocturnal foraging activity by an undisturbed bat while it flew between the two ends of the flight tunnel to obtain food from two computer-controlled nectar-feeders. For a comparison of flight enclosure measurements with field data, flight speeds were also obtained from unrestrained bats foraging in their natural environment (Costa Rica). Foraging flight speeds spanned a range of at least a factor 3 within a single species, which demonstrates the wide range of speeds possible to these animals. Significant, positive correlations between flight speed and the natural individual variability in body mass were found in nearly all cases, with body mass exponents ranging between 0.44 and 2.1. Bats flying at normal speeds were therefore not near their upper limit of muscle power. The most reliable measurements of speed increase with mass (with individual mass changes of up to 30%) were close to the increase theoretically predicted for Vmp and Vmr for an individual bat (with constant wing span and area), which should vary as M0.42, where M is mass. This provides evidence that the glossophagine bats attemped to maintain their flight speed within a fixed speed category relative to Vmp or Vmr during foraging. Among differently sized species of glossophagine bat (N=4), flight speeds V varied with V=20M0.23, in agreement with the mass exponent of 0.21 expected from aerodynamic models for interspecific variation. In addition to the mass effect, at least five other variables significantly influenced flight speed. (1) Both mean and maximum flight speeds increased with the length and the cross-sectional area of the flight tunnel. Mean (maximum) flight speeds of 11-12 g Glossophaga soricina bats (in m s-1) were 4.6 (5.3) over a 7 m and 7. 3 (10.5) over a 50 m flight path. (2) The flight speed range adopted by a bat during one night could vary significantly between nights, independently of body mass and the effect of the size of the flight enclosure. (3) Bats flew significantly faster under illumination than in darkness. This effect was shown (i) by bats kept under natural ambient illumination that initiated foraging during the twilight phase of the evening, (ii) when bats continued to feed into the light phase directly after the dark-light transition in the laboratory and (iii) during foraging under constant, artificial illumination. (4) After a period of rest, the initial flight speed during a foraging bout was significantly increased by 25%, but declined to the mean level within 20 s of activity. (5) Flight speed could differ significantly between foraging (flight from feeder to feeder) versus non-foraging (flight from end to end of the enclosure without visiting the feeders) flights. The results of this study demonstrate a clear ability of bats to regulate their flight speed in response to small natural changes in body mass as predicted by aerodynamic theory for Vmp and Vmr. The set point in flight speed regulation, however, was influenced by multiple additional variables. (+info)