bluuebunny/crossref_metadata_2025_split huggingface dataset:
Wake structure and kinematics in two insectivorous bats
Authors: Hubel Tatjana Y. , Hristov Nickolay I. , Swartz Sharon M. , Breuer Kenneth S. 
Published: August 2016

We compare kinematics and wake structure over a range of flight speeds (4.0–8.2 m s−1) for two bats that pursue insect prey aerially,Tadarida brasiliensisandMyotis velifer. Body mass and wingspan are similar in these species, butM. veliferhas broader wings and lower wing loading. By using high-speed videography and particle image velocimetry of steady flight in a wind tunnel, we show that three-dimensional kinematics and wake structure are similar in the two species at the higher speeds studied, but differ at lower speeds. At lower speeds, the two species show significant differences in mean angle of attack, body–wingtip distance and sweep angle. The distinct body vortex seen at low speed inT. brasiliensisand other bats studied to date is considerably weaker or absent inM. velifer. We suggest that this could be influenced by morphology: (i) the narrower thorax in this species probably reduces the body-induced discontinuity in circulation between the two wings and (ii) the wing loading is lower, hence the lift coefficient required for weight support is lower. As a result, inM. velifer,there may be a decreased disruption in the lift generation between the body and the wing, and the strength of the characteristic root vortex is greatly diminished, both suggesting increased flight efficiency.This article is part of the themed issue ‘Moving in a moving medium: new perspectives on flight’.
Does hyperthermia constrain flight duration in a short-distance migrant?
Authors: Guillemette Magella , Woakes Anthony J. , Larochelle Jacques , Polymeropoulos Elias T. , Granbois Jean-Marc , Butler Patrick J. , Pelletier David , Frappell Peter B. , Portugal Steven J. 
Published: August 2016

While some migratory birds perform non-stop flights of over 11 000 km, many species only spend around 15% of the day in flight during migration, posing a question as to why flight times for many species are so short. Here, we test the idea that hyperthermia might constrain flight duration (FD) in a short-distance migrant using remote biologging technology to measure heart rate, hydrostatic pressure and body temperature in 19 migrating eider ducks (Somateria mollissima), a short-distance migrant. Our results reveal a stop-and-go migration strategy where migratory flights were frequent (14 flights day−1) and short (15.7 min), together with the fact that body temperature increases by 1°C, on average, during such flights, which equates to a rate of heat storage index (HSI) of 4°C h−1. Furthermore, we could not find any evidence that short flights were limited by heart rate, together with the fact that the numerous stops could not be explained by the need to feed, as the frequency of dives and the time spent feeding were comparatively small during the migratory period. We thus conclude that hyperthermia appears to be the predominant determinant of the observed migration strategy, and suggest that such a physiological limitation to FD may also occur in other species.This article is part of the themed issue ‘Moving in a moving medium: new perspectives on flight’.
Into rude air: hummingbird flight performance in variable aerial environments
Authors: Ortega-Jimenez V. M. , Badger M. , Wang H. , Dudley R. 
Published: August 2016

Hummingbirds are well known for their ability to sustain hovering flight, but many other remarkable features of manoeuvrability characterize the more than 330 species of trochilid. Most research on hummingbird flight has been focused on either forward flight or hovering in otherwise non-perturbed air. In nature, however, hummingbirds fly through and must compensate for substantial environmental perturbation, including heavy rain, unpredictable updraughts and turbulent eddies. Here, we review recent studies on hummingbirds flying within challenging aerial environments, and discuss both the direct and indirect effects of unsteady environmental flows such as rain and von Kármán vortex streets. Both perturbation intensity and the spatio-temporal scale of disturbance (expressed with respect to characteristic body size) will influence mechanical responses of volant taxa. Most features of hummingbird manoeuvrability remain undescribed, as do evolutionary patterns of flight-related adaptation within the lineage. Trochilid flight performance under natural conditions far exceeds that of microair vehicles at similar scales, and the group as a whole presents many research opportunities for understanding aerial manoeuvrability.This article is part of the themed issue ‘Moving in a moving medium: new perspectives on flight’.
Flight of the dragonflies and damselflies
Authors: Bomphrey Richard J. , Nakata Toshiyuki , Henningsson Per , Lin Huai-Ti 
Published: August 2016

This work is a synthesis of our current understanding of the mechanics, aerodynamics and visually mediated control of dragonfly and damselfly flight, with the addition of new experimental and computational data in several key areas. These are: the diversity of dragonfly wing morphologies, the aerodynamics of gliding flight, force generation in flapping flight, aerodynamic efficiency, comparative flight performance and pursuit strategies during predatory and territorial flights. New data are set in context by brief reviews covering anatomy at several scales, insect aerodynamics, neuromechanics and behaviour. We achieve a new perspective by means of a diverse range of techniques, including laser-line mapping of wing topographies, computational fluid dynamics simulations of finely detailed wing geometries, quantitative imaging using particle image velocimetry of on-wing and wake flow patterns, classical aerodynamic theory, photography in the field, infrared motion capture and multi-camera optical tracking of free flight trajectories in laboratory environments. Our comprehensive approach enables a novel synthesis of datasets and subfields that integrates many aspects of flight from the neurobiology of the compound eye, through the aeromechanical interface with the surrounding fluid, to flight performance under cruising and higher-energy behavioural modes.This article is part of the themed issue ‘Moving in a moving medium: new perspectives on flight’.
Biomechanics and biomimetics in insect-inspired flight systems
Authors: Liu Hao , Ravi Sridhar , Kolomenskiy Dmitry , Tanaka Hiroto 
Published: August 2016

Insect- and bird-size drones—micro air vehicles (MAV) that can perform autonomous flight in natural and man-made environments are now an active and well-integrated research area. MAVs normally operate at a low speed in a Reynolds number regime of 104–105or lower, in which most flying animals of insects, birds and bats fly, and encounter unconventional challenges in generating sufficient aerodynamic forces to stay airborne and in controlling flight autonomy to achieve complex manoeuvres. Flying insects that power and control flight by flapping wings are capable of sophisticated aerodynamic force production and precise, agile manoeuvring, through an integrated system consisting of wings to generate aerodynamic force, muscles to move the wings and a control system to modulate power output from the muscles. In this article, we give a selective review on the state of the art of biomechanics in bioinspired flight systems in terms of flapping and flexible wing aerodynamics, flight dynamics and stability, passive and active mechanisms in stabilization and control, as well as flapping flight in unsteady environments. We further highlight recent advances in biomimetics of flapping-wing MAVs with a specific focus on insect-inspired wing design and fabrication, as well as sensing systems.This article is part of the themed issue ‘Moving in a moving medium: new perspectives on flight’.
Foraging at the edge of the world: low-altitude, high-speed manoeuvering in barn swallows
Authors: Warrick Douglas R. , Hedrick Tyson L. , Biewener Andrew A. , Crandell Kristen E. , Tobalske Bret W. 
Published: August 2016

While prior studies of swallow manoeuvering have focused on slow-speed flight and obstacle avoidance in still air, swallows survive by foraging at high speeds in windy environments. Recent advances in field-portable, high-speed video systems, coupled with precise anemometry, permit measures of high-speed aerial performance of birds in a natural state. We undertook the present study to test: (i) the manner in which barn swallows (Hirundo rustica) may exploit wind dynamics and ground effect while foraging and (ii) the relative importance of flapping versus gliding for accomplishing high-speed manoeuvers. Using multi-camera videography synchronized with wind-velocity measurements, we tracked coursing manoeuvers in pursuit of prey. Wind speed averaged 1.3–2.0 m s−1across the atmospheric boundary layer, exhibiting a shear gradient greater than expected, with instantaneous speeds of 0.02–6.1 m s−1. While barn swallows tended to flap throughout turns, they exhibited reduced wingbeat frequency, relying on glides and partial bounds during maximal manoeuvers. Further, the birds capitalized on the near-earth wind speed gradient to gain kinetic and potential energy during both flapping and gliding turns; providing evidence that such behaviour is not limited to large, fixed-wing soaring seabirds and that exploitation of wind gradients by small aerial insectivores may be a significant aspect of their aeroecology.This article is part of the themed issue ‘Moving in a moving medium: new perspectives on flight'.
Negotiating an ecological barrier: crossing the Sahara in relation to winds by common swifts
Authors: Åkesson Susanne , Bianco Giuseppe , Hedenström Anders 
Published: August 2016

The Sahara Desert is one of the largest land-based barriers on the Earth, crossed twice each year by billions of birds on migration. Here we investigate how common swifts migrating between breeding sites in Sweden and wintering areas in sub-Saharan Africa perform the desert crossing with respect to route choice, winds, timing and speed of migration by analysing 72 geolocator tracks recording migration. The swifts cross western Sahara on a broad front in autumn, while in spring they seem to use three alternative routes across the Sahara, a western, a central and an eastern route across the Arabian Peninsula, with most birds using the western route. The swifts show slower migration and travel speeds, and make longer detours with more stops in autumn compared with spring. In spring, the stopover period in West Africa coincided with mostly favourable winds, but birds remained in the area, suggesting fuelling. The western route provided more tailwind assistance compared with the central route for our tracked swifts in spring, but not in autumn. The ultimate explanation for the evolution of a preferred western route is presumably a combination of matching rich foraging conditions (swarming insects) and favourable winds enabling fast spring migration.This article is part of the themed issue ‘Moving in a moving medium: new perspectives on flight’.
Fine-scale flight strategies of gulls in urban airflows indicate risk and reward in city living
Authors: Shepard Emily L. C. , Williamson Cara , Windsor Shane P. 
Published: August 2016

Birds modulate their flight paths in relation to regional and global airflows in order to reduce their travel costs. Birds should also respond to fine-scale airflows, although the incidence and value of this remains largely unknown. We resolved the three-dimensional trajectories of gulls flying along a built-up coastline, and used computational fluid dynamic models to examine how gulls reacted to airflows around buildings. Birds systematically altered their flight trajectories with wind conditions to exploit updraughts over features as small as a row of low-rise buildings. This provides the first evidence that human activities can change patterns of space-use in flying birds by altering the profitability of the airscape. At finer scales still, gulls varied their position to select a narrow range of updraught values, rather than exploiting the strongest updraughts available, and their precise positions were consistent with a strategy to increase their velocity control in gusty conditions. Ultimately, strategies such as these could help unmanned aerial vehicles negotiate complex airflows. Overall, airflows around fine-scale features have profound implications for flight control and energy use, and consideration of this could lead to a paradigm-shift in the way ecologists view the urban environment.
This article is part of the themed issue ‘Moving in a moving medium: new perspectives on flight’.
Flap or soar? How a flight generalist responds to its aerial environment
Authors: Shamoun-Baranes Judy , Bouten Willem , van Loon E. Emiel , Meijer Christiaan , Camphuysen C. J. 
Published: August 2016

The aerial environment is heterogeneous in space and time and directly influences the costs of animal flight. Volant animals can reduce these costs by using different flight modes, each with their own benefits and constraints. However, the extent to which animals alter their flight modes in response to environmental conditions has rarely been studied in the wild. To provide insight into how a flight generalist can reduce the energetic cost of movement, we studied flight behaviour in relation to the aerial environmental and landscape using hundreds of hours of global positioning system and triaxial acceleration measurements of the lesser black-backed gull (Larus fuscus). Individuals differed largely in the time spent in flight, which increased linearly with the time spent in flight at sea. In general, flapping was used more frequently than more energetically efficient soaring flight. The probability of soaring increased with increasing boundary layer height and time closer to midday, reflecting improved convective conditions supportive of thermal soaring. Other forms of soaring flight were also used, including fine-scale use of orographic lift. We explore the energetic consequences of behavioural adaptations to the aerial environment and underlying landscape and implications for individual energy budgets, foraging ecology and reproductive success.This article is part of the themed issue ‘Moving in a moving medium: new perspectives on flight’.
Ecology of tern flight in relation to wind, topography and aerodynamic theory
Authors: Hedenström Anders , Åkesson Susanne 
Published: August 2016

Flight is an economical mode of locomotion, because it is both fast and relatively cheap per unit of distance, enabling birds to migrate long distances and obtain food over large areas. The power required to fly follows a U-shaped function in relation to airspeed, from which context dependent ‘optimal’ flight speeds can be derived. Crosswinds will displace birds away from their intended track unless they make compensatory adjustments of heading and airspeed. We report on flight track measurements in five geometrically similar tern species ranging one magnitude in body mass, from both migration and the breeding season at the island of Öland in the Baltic Sea. When leaving the southern point of Öland, migrating Arctic and common terns made a 60° shift in track direction, probably guided by a distant landmark. Terns adjusted both airspeed and heading in relation to tail and side wind, where coastlines facilitated compensation. Airspeed also depended on ecological context (searching versus not searching for food), and it increased with flock size. Species-specific maximum range speed agreed with predicted speeds from a new aerodynamic theory. Our study shows that the selection of airspeed is a behavioural trait that depended on a complex blend of internal and external factors.This article is part of the themed issue ‘Moving in a moving medium: new perspectives on flight’.
Soaring energetics and glide performance in a moving atmosphere
Authors: Taylor Graham K. , Reynolds Kate V. , Thomas Adrian L. R. 
Published: August 2016

Here, we analyse the energetics, performance and optimization of flight in a moving atmosphere. We begin by deriving a succinct expression describing all of the mechanical energy flows associated with gliding, dynamic soaring and thermal soaring, which we use to explore the optimization of gliding in an arbitrary wind. We use this optimization to revisit the classical theory of the glide polar, which we expand upon in two significant ways. First, we compare the predictions of the glide polar for different species under the various published models. Second, we derive a glide optimization chart that maps every combination of headwind and updraft speed to the unique combination of airspeed and inertial sink rate at which the aerodynamic cost of transport is expected to be minimized. With these theoretical tools in hand, we test their predictions using empirical data collected from a captive steppe eagle (Aquila nipalensis) carrying an inertial measurement unit, global positioning system, barometer and pitot tube. We show that the bird adjusts airspeed in relation to headwind speed as expected if it were seeking to minimize its aerodynamic cost of transport, but find only weak evidence to suggest that it adjusts airspeed similarly in response to updrafts during straight and interthermal glides.This article is part of the themed issue ‘Moving in a moving medium: new perspectives on flight’.
Memory Replay in Balanced Recurrent Networks
Authors: Chenkov Nikolay , Sprekeler Henning , Kempter Richard 
Published: August 2016

AbstractComplex patterns of neural activity appear during up-states in the neocortex and sharp waves in the hippocampus, including sequences that resemble those during prior behavioral experience. The mechanisms underlying this replay are not well understood. How can small synaptic footprints engraved by experience control large-scale network activity during memory retrieval and consolidation? We hypothesize that sparse and weak synaptic connectivity between Hebbian assemblies are boosted by pre-existing recurrent connectivity within them. To investigate this idea, we connect sequences of assemblies in randomly connected spiking neuronal networks with a balance of excitation and inhibition. Simulations and analytical calculations show that recurrent connections within assemblies allow for a fast amplification of signals that indeed reduces the required number of inter-assembly connections. Replay can be evoked by small sensory-like cues or emerge spontaneously by activity fluctuations. Global—potentially neuromodulatory—alterations of neuronal excitability can switch between network states that favor retrieval and consolidation.Author SummarySynaptic plasticity is the basis for learning and memory, and many experiments indicate that memories are imprinted in synaptic connections. However, basic mechanisms of how such memories are retrieved and consolidated remain unclear. In particular, how can one-shot learning of a sequence of events achieve a sufficiently strong synaptic footprint to retrieve or replay this sequence? Using both numerical simulations of spiking neural networks and an analytic approach, we provide a biologically plausible model for understanding how minute synaptic changes in a recurrent network can nevertheless be retrieved by small cues or even manifest themselves as activity patterns that emerge spontaneously. We show how the retrieval of exceedingly small changes in the connections across assemblies is robustly facilitated by recurrent connectivity within assemblies. This interaction between recurrent amplification within an assembly and the feed-forward propagation of activity across the network establishes a basis for the retrieval of memories.
Climate justice: contested discourse and social transformation
Authors: Scandrett Eurig 
Published: August 2016

Purpose
This paper aims to argue that climate justice constitutes a contested discourse reflecting the material interests of social groups that contribute to its production. For climate justice to have integrity, it must be rooted in the material interests of those social groups negatively affected by, and engaged in struggles against, the hydrocarbon economy. The paper locates contestation of discourse production in an understanding of social movement processes.

Design/methodology/approach
The paper is a theoretical contribution to the debate about climate justice, drawing on data (published and unpublished) from Scotland.

Findings
The paper concludes that scholars engaged in climate justice work should have consideration to the material interest embedded in the discourse. The pedagogical and dialogical work of engagement with the militant particularism of local struggles against the hydrocarbon industry is an important contribution to discourse construction, and ultimately social transformation is required to achieve climate justice.

Research limitations/implications
This is primarily a theoretical paper, although it draws on limited case study data from environmental conflicts in Scotland.

Practical implications
The argument has practical implications for work in climate justice, including research, policy development and social movement mobilisation.

Social implications
This is intended as a contribution to the social transformation required to achieve climate justice.

Originality/value
The paper draws on existing theoretical frameworks, especially Marxian approaches to discourse and social movement studies, to critique and contribute to the newly developing field of climate justice.
Prophetic blogger identification based on buzzword prediction ability
Authors: Zhang Jianwei , Tomonaga Seiya , Nakajima Shinsuke , Inagaki Yoichi , Nakamoto Reyn 
Published: August 2016

Purpose
Identifying important users from social media has recently attracted much attention in the information and knowledge management community. Although researchers have focused on users’ knowledge levels on certain topics or influence degrees on other users in social networks, previous works have not studied users’ prediction ability on future popularity. This paper aims to propose a novel approach to find prophetic bloggers based on their buzzword prediction ability.

Design/methodology/approach
The main approach is to conduct a time-series analysis in the blogosphere considering four factors: post earliness, content similarity, entry frequency and buzzword coverage. Our method has four steps: categorizing a blogger into knowledgeable categories, identifying past buzzwords, analyzing a buzzword’s peak time content and growth period and, finally, evaluating a blogger’s prediction ability on a buzzword and on a category.

Findings
Experimental results on real-world blog data consisting of 150 million entries from 11 million bloggers demonstrate that the proposed approach can find prophetic bloggers and outperforms others that do not take temporal features into account.

Originality/value
To the best of the authors’ knowledge, our approach is the first successful attempt to identify prophetic bloggers. Finding prophetic bloggers can bring great values for two reasons. First, as prophetic bloggers tend to post creative and insightful information, analysis on their blog entries may help find future buzzword candidates. Second, communication with prophetic bloggers can help understand future trends, gain insight into early adopters’ thoughts on new technology or even foresee things that will become popular.