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Thomas Alerstam - One of the best experts on this subject based on the ideXlab platform.
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Seasonal modulation of flight speed among nocturnal passerine migrants: differences between short- and long-distance migrants
Behavioral Ecology and Sociobiology, 2014Co-Authors: Cecilia Nilsson, Johan Bäckman, Thomas AlerstamAbstract:Migrating birds are expected to fly at higher Airspeeds when minimizing time rather than energy costs of their migratory journeys. Spring migration has often been suggested to be more time selected than autumn migration, because of the advantage of early arrival at breeding sites. We have earlier demonstrated that nocturnal passerine migrants fly at higher Airspeeds during spring compared to autumn, supporting time-selected spring migration. In this study, we test the hypothesis that seasonal Airspeeds are modulated differently between short- and long-distance migrants, because of a stronger element of time selection for autumn migration over long distances. In support of this hypothesis, we demonstrate that the seasonal difference in Airspeed is significantly larger (spring Airspeed exceeding autumn Airspeed by a factor of 1.16 after correcting for the influence of altitude, wind and climb/descent on Airspeed) among short-distance compared to long-distance (factor 1.12) migrants. This result is based on a large sample of tracking radar data from 3 years at Falsterbo, South Sweden. Short-distance migrants also tend to fly with more favourable winds during autumn, indicating relaxed time constraints (being able to afford to wait for favourable winds) compared to long-distance migrants. These results indicate surprisingly fine-tuned seasonal modulation of Airspeed and responses to wind, associated with behavioural strategies adapted to different levels of time selection pressures during spring and autumn migration.
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nocturnal passerine migrants fly faster in spring than in autumn a test of the time minimization hypothesis
Animal Behaviour, 2012Co-Authors: Hakan Karlsson, Cecilia Nilsson, Johan Bäckman, Thomas AlerstamAbstract:It has been suggested that time selection and precedence in arrival order are more important during spring than autumn migration. Migrating birds are expected to fly at faster Airspeeds if they minimize duration rather than energy costs of migration, and they are furthermore expected to complete their journeys by final sprint flights if it is particularly important to arrive at the destination before competitors. We tested these hypotheses by tracking-radar studies of nocturnal passerine migrants during several spring and autumn seasons at Lund (56°N) and Abisko (68°N) at the southern and northern ends of the Scandinavian Peninsula, respectively. The samples from these two sites represent migrants that are mostly rather far from (Lund) or close to (Abisko) their breeding destinations. We found that the birds were flying at clearly faster Airspeeds in spring than in autumn at both study sites, with spring speeds exceeding autumn speeds by, on average, 16%, after taking effects of wind conditions and vertical flight speeds into account. This difference in speeds could not be explained by seasonal differences in body mass or wing morphology and thus supports the hypothesis of time-selected spring migration. There was also a significantly larger seasonal difference in Airspeed at Abisko than at Lund, suggesting that the birds may have shown an inclination to sprint on their final spring flights to the breeding destinations, although this possible extra sprint effort was modest.
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confronting the winds orientation and flight behaviour of roosting swifts apus apus
Proceedings of The Royal Society B: Biological Sciences, 2001Co-Authors: Johan Bäckman, Thomas AlerstamAbstract:Swifts, Apus apus, spend the night aloft and this offers an opportunity to test the degree of adaptability of bird orientation and flight to different ecological situations. We predicted the swifts' behaviour by assuming that they are adapted to minimize energy expenditure during the nocturnal flight and during a compensatory homing flight if they become displaced by wind. We tested the predictions by recording the swifts' altitudes, speeds and directions under different wind conditions with tracking radar; we found an agreement between predictions and observations for orientation behaviour, but not for altitude and speed regulation. The swifts orientated consistently into the head wind, with angular concentration increasing with increasing wind speed. However, contrary to our predictions, they did not select altitudes with slow or moderate winds, nor did they increase their Airspeed distinctly when flying into strong head winds. A possible explanation is that their head-wind orientation is sufficient to keep nocturnal displacement from their home area within tolerable limits, leaving flight altitude to be determined by other factors (correlated with temperature), and Airspeed to show only a marginal increase in strong winds. The swifts were often moving "backwards", heading straight into the wind but being overpowered by wind speeds exceeding their Airspeed. The regular occurrence of such flights is probably uniquely associated with the swifts' remarkable habit of roosting on the wing.
Robert B Srygley - One of the best experts on this subject based on the ideXlab platform.
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Airspeed adjustment and lipid reserves in migratory neotropical butterflies
Functional Ecology, 2008Co-Authors: Robert B Srygley, Robert DudleyAbstract:Summary 1Aerodynamic theory predicts that migrant fliers should reduce their speed of flight as endogenous energy reserves are gradually consumed. This prediction was tested for butterfly species (Pieridae and Nymphalidae) that engage in annual rainy season migrations through central Panama. 2Direct Airspeed measurements were made on butterflies in natural free flight, followed by chloroform : methanol extractions of abdominal lipids from the same insects. 3Among individuals within particular species/gender subsets, Airspeeds during flight were higher with greater lipid content following adjustment for body mass. Although it was not possible to measure lipid content repeatedly on a single insect, these comparisons among individuals for five migratory species suggest that butterflies reduce their flight speed as lipid reserves are progressively depleted. 4Because choice of Airspeed can strongly influence the rate of energetic expenditure, these results together with previously described strategies of wind drift compensation in the same taxa demonstrate sophisticated long-distance orientation and optimization strategies by migratory Neotropical butterflies flying within the boundary layer.
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wind drift compensation in migrating dragonflies pantala odonata libellulidae
Journal of Insect Behavior, 2003Co-Authors: Robert B SrygleyAbstract:Tailwind drift compensation serves to maximize a migrant's flight distance on a given amount of energy, and crosswind drift compensation serves to hold a course true and minimize the distance flown. With full or part compensation, Airspeeds are predicted to increase with greater crosswind drift. To test whether migrating dragonflies compensated for wind drift, I measured the velocity and heading of Pantala hymenaea and P. flavescens in natural flight over a lake and the ambient wind speed and direction. P. hymenaea flew north-easterly (58°), whereas P. flavescens flew significantly more east–north easterly (74°) throughout the day. Pantala spp. demonstrated part compensation for changes in crosswind drift within individuals (mean compensation = 54%, P = 0.0000), evidence for use of a ground reference to correct for drift when flying over water. Among individuals, P. flavescens compensated for crosswind drift. P. hymenaea overcompensated and then drifted downwind on one morning and compensated for crosswind drift on the next. As predicted from optimal migration theory, Airspeed (5.0 m/s for both species with no tailwind) decreased with tailwind velocity both among individuals (data for both species pooled [n = 19], P < 0.0001) and within each individual as it crossed the lake (P = 0.0016).
Ryozo Ooka - One of the best experts on this subject based on the ideXlab platform.
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formulation of human body heat transfer coefficient under various ambient temperature air speed and direction based on experiments and cfd
Building and Environment, 2019Co-Authors: Shan Gao, Ryozo OokaAbstract:Abstract The purpose of this study is to confirm the effects of ambient temperature, Airspeed, and wind direction on the heat transfer between human body and surrounding environment. First, a thermal manikin (TM) with fixed surface temperature (33 °C) was placed in a climate chamber with ambient temperatures of 20 °C, 24 °C, and 28 °C, at Airspeed of under 0.1 m/s to confirm the effect of ambient temperature on heat transfer coefficient. In order to confirm effects of Airspeed and wind direction, the same TM was then put in a wind tunnel with Airspeeds ranging from 0.25 m/s to 1.4 m/s. The TM was set to face upwind, downwind, and perpendicular to the wind. Computational fluid dynamics (CFD) analysis was performed with conditions matching those of the experiment by using a computational TM with the same shape as that used in the experiment. In addition, numerical simulation of upward airflow condition and downward airflow condition in the standing posture with Airspeed levels of 0.05–1.4 m/s was carried out. Higher ambient temperatures led to a decrease in the convective heat transfer coefficient and an increase in the radiative heat transfer coefficient. For airflows in the horizontal direction, whole-body convective heat transfer coefficient was the largest when the TM was facing downwind. For airflows in the vertical direction, the whole-body convective heat transfer coefficient for downward airflow was larger at Airspeeds of 0.05–0.3 m/s. In contrast, when Airspeed exceeded 0.3 m/s, the results were opposite.
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effects of ambient temperature Airspeed and wind direction on heat transfer coefficient for the human body by means of manikin experiments and cfd analysis
E3S Web of Conferences, 2019Co-Authors: Ryozo Ooka, Wonseok OhAbstract:The purpose of this study is to confirm the effect of ambient temperature, Airspeed, and wind direction on the heat transfer around the human body. A fixed surface temperature (33 °C) thermal manikin (TM) with 16 segments was employed. First, the manikin was placed in a climate chamber with ambient temperatures of 20 °C, 24 °C, and 28 °C, at Airspeeds of less than 0.1 m/s to represent calm condition. Higher ambient temperatures led to a decrease in the convective heat transfer coefficient. The convective heat transfer coefficients for the sitting posture were higher than those of the standing posture. The same TM was then put in a wind tunnel with Airspeeds ranging from 0.25 m/s to 1.4 m/s to represent forced convection. The TM was set to face upwind, downwind, and perpendicular to the wind (i.e., its right side facing the wind). Regression models for the convective heat transfer coefficient and Airspeed for different wind directions and postures were derived. In contrast to the calm condition, the convective heat transfer coefficients for the sitting posture were lower than those for the standing posture. The convective heat transfer coefficients for the standing posture were largest when the TM was facing downwind, and smallest when the right side of the TM was facing the wind. To verify the results of the experiment, computational fluid dynamics (CFD) analysis was performed with conditions matching those of the experiment by using a computational TM with the same shape as that used in the experiment. The boundary conditions of the CFD analysis were set from the experiment. The CFD analysis results were consistent with the experimental data.
Robert Dudley - One of the best experts on this subject based on the ideXlab platform.
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backward flight in hummingbirds employs unique kinematic adjustments and entails low metabolic cost
The Journal of Experimental Biology, 2012Co-Authors: Nir Sapir, Robert DudleyAbstract:SUMMARY Backward flight is a frequently used transient flight behavior among members of the species-rich hummingbird family (Trochilidae) when retreating from flowers, and is known from a variety of other avian and hexapod taxa, but the biomechanics of this intriguing locomotor mode have not been described. We measured rates of oxygen uptake () and flight kinematics of Anna9s hummingbirds, Calypte anna (Lesson), within a wind tunnel using mask respirometry and high-speed videography, respectively, during backward, forward and hovering flight. We unexpectedly found that in sustained backward flight is similar to that in forward flight at equivalent Airspeed, and is about 20% lower than hovering . For a bird that was measured throughout a range of backward Airspeeds up to a speed of 4.5 m s −1 , the power curve resembled that of forward flight at equivalent Airspeeds. Backward flight was facilitated by steep body angles coupled with substantial head flexion, and was also characterized by a higher wingbeat frequency, a flat stroke plane angle relative to horizontal, a high stroke plane angle relative to the longitudinal body axis, a high ratio of maximum:minimum wing positional angle, and a high upstroke:downstroke duration ratio. Because of the convergent evolution of hummingbird and some hexapod flight styles, flying insects may employ similar kinematics while engaged in backward flight, for example during station keeping or load lifting. We propose that backward flight behavior in retreat from flowers, together with other anatomical, physiological, morphological and behavioral adaptations, enables hummingbirds to maintain strictly aerial nectarivory.
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hovering and forward flight energetics in anna s and allen s hummingbirds
Physiological and Biochemical Zoology, 2010Co-Authors: Christopher J Clark, Robert DudleyAbstract:Abstract Aerodynamic theory predicts that the mechanical costs of flight are lowest at intermediate flight speeds; metabolic costs of flight should trend similarly if muscle efficiency is constant. We measured metabolic rates for nine Anna’s hummingbirds (Calypte anna) and two male Allen’s hummingbirds (Selasphorus sasin) feeding during flight from a free‐standing mask over a range of Airspeeds. Ten of 11 birds exhibited higher metabolic costs during hovering than during flight at intermediate Airspeeds, whereas one individual exhibited comparable costs at hovering and during forward flight up to speeds of ∼7 m s−1. Flight costs of all hummingbirds increased at higher Airspeeds. Relative to Anna’s hummingbirds, Allen’s hummingbirds exhibited deeper minima in the power curve, possibly due to higher wing loadings and greater associated costs of induced drag. Although feeding at a mask in an airstream may reduce body drag and, thus, the contributions of parasite power to overall metabolic expenditure, these ...
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flight costs of long sexually selected tails in hummingbirds
Proceedings of The Royal Society B: Biological Sciences, 2009Co-Authors: Christopher J Clark, Robert DudleyAbstract:The elongated tails adorning many male birds have traditionally been thought to degrade flight performance by increasing body drag. However, aerodynamic interactions between the body and tail can be substantial in some contexts, and a short tail may actually reduce rather than increase overall drag. To test how tail length affects flight performance, we manipulated the tails of Anna’s hummingbirds (Calypte anna) by increasing their length with the greatly elongated tail streamers of the red-billed streamertail (Trochilus polytmus) and reducing their length by removing first the rectrices and then the entire tail (i.e. all rectrices and tail covert feathers). Flight performance was measured in a wind tunnel by measuring (i) the maximum forward speed at which the birds could fly and (ii) the metabolic cost of flight while flying at Airspeeds from 0 to 14 m s K1 . We found a significant interaction effect between tail treatment and Airspeed: an elongated tail increased the metabolic cost of flight by up to 11 per cent, and this effect was strongest at higher flight speeds. Maximum flight speed was concomitantly reduced by 3.4 per cent. Also, removing the entire tail decreased maximum flight speed by 2 per cent, suggesting beneficial aerodynamic effects for tails of normal length. The effects of elongation are thus subtle and Airspeedspecific, suggesting that diversity in avian tail morphology is associated with only modest flight costs.
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Airspeed adjustment and lipid reserves in migratory neotropical butterflies
Functional Ecology, 2008Co-Authors: Robert B Srygley, Robert DudleyAbstract:Summary 1Aerodynamic theory predicts that migrant fliers should reduce their speed of flight as endogenous energy reserves are gradually consumed. This prediction was tested for butterfly species (Pieridae and Nymphalidae) that engage in annual rainy season migrations through central Panama. 2Direct Airspeed measurements were made on butterflies in natural free flight, followed by chloroform : methanol extractions of abdominal lipids from the same insects. 3Among individuals within particular species/gender subsets, Airspeeds during flight were higher with greater lipid content following adjustment for body mass. Although it was not possible to measure lipid content repeatedly on a single insect, these comparisons among individuals for five migratory species suggest that butterflies reduce their flight speed as lipid reserves are progressively depleted. 4Because choice of Airspeed can strongly influence the rate of energetic expenditure, these results together with previously described strategies of wind drift compensation in the same taxa demonstrate sophisticated long-distance orientation and optimization strategies by migratory Neotropical butterflies flying within the boundary layer.
Qinghao Meng - One of the best experts on this subject based on the ideXlab platform.
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a wind estimation method with an unmanned rotorcraft for environmental monitoring tasks
Sensors, 2018Co-Authors: Jiaying Wang, Bing Luo, Ming Zeng, Qinghao MengAbstract:Wind velocity (strength and direction) is an important parameter for unmanned aerial vehicle (UAV)-based environmental monitoring tasks. A novel wind velocity estimation method is proposed for rotorcrafts. Based on an extended state observer, this method derives the wind disturbance from rotors' speeds and rotorcraft's acceleration and position. Then the wind disturbance is scaled to calculate the Airspeed vector, which is substituted into a wind triangle to obtain the wind velocity. Easy-to-implement methods for calculating the rotorcraft's thrust and drag coefficient are also proposed, which are important parameters to obtain the wind drag and the Airspeed, respectively. Simulations and experiments using a quadrotor in both hovering and flight conditions have validated the proposed method.