Bird Flight Research Articles

3D printed feathers with embedded aerodynamic sensing

Bird flight is often characterized by outstanding aerodynamic efficiency, agility and adaptivity in dynamic conditions. Feathers play an integral role in facilitating these aspects of performance, and the benefits feathers provide largely derive from their intricate and hierarchical structures. Although research has been attempted on developing membrane-type artificial feathers for bio-inspired aircraft and micro air vehicles (MAVs), fabricating anatomically accurate artificial feathers to fully exploit the advantages of feathers has not been achieved. Here, we present our 3D printed artificial feathers consisting of hierarchical vane structures with feature dimensions spanning from 10-2to 102mm, which have remarkable structural, mechanical and aerodynamic resemblance to natural feathers. The multi-step, multi-scale 3D printing process used in this work can provide scalability for the fabrication of artificial feathers tailored to the specific size requirements of aircraft wings. Moreover, we provide the printed feathers with embedded aerodynamic sensing ability through the integration of customized piezoresistive and piezoelectric transducers for strain and vibration measurements, respectively. Hence, the 3D printed feather transducers combine the aerodynamic advantages from the hierarchical feather structure design with additional aerodynamic sensing capabilities, which can be utilized in future biomechanical studies on birds and can contribute to advancements in high-performance adaptive MAVs.

Distributed feather-inspired flow control mitigates stall and expands flight envelope

Multiple rows of feathers, known as the covert feathers, contour the upper and lower surfaces of bird wings. These feathers have been observed to deploy passively during high angle of attack maneuvers and are suggested to play an aerodynamic role. However, there have been limited attempts to capture their underlying flow physics or assess the function of multiple covert rows. Here, we first identify two flow control mechanisms associated with a single covert-inspired flap and their location sensitivity: a pressure dam mechanism and a previously unidentified shear layer interaction mechanism. We then investigate the additivity of these mechanisms by deploying multiple rows of flaps. We find that aerodynamic benefits conferred by the shear layer interaction are additive, whereas benefits conferred by the pressure dam effect are not. Nevertheless, both mechanisms can be exploited simultaneously to maximize aerodynamic benefits and mitigate stall. In addition to wind tunnel experiments, we implement multiple rows of covert-inspired flaps on a bird-scale remote-controlled aircraft. Flight tests reveal passive deployment trends similar to those observed in bird flight and comparable aerodynamic benefits to wind tunnel experiments. These results indicate that we can enhance aircraft controllability using covert-inspired flaps and form insights into the aerodynamic role of covert feathers in avian flight.

Design of stiffness-variable dielectric elastomer wing based on seagull characteristics and its application in avian flight bionics

ABSTRACT Dielectric elastomers (DE), renowned for their lightweight, rapid response, high energy density, and efficient conversion, have garnered significant attention in the realm of avian flight bionics. However, a lack of understanding of the mechanical principles underlying flapping wing biomimetics has hindered accurate simulations of actual bird flight postures. To address this, a stiffness-variable DE-based wing (DEW) has been designed, inspired by the characteristics of seagulls, to mimic the wing deformations across different bird flight phases. The evolution of the DEW’s deformation is modeled based on the differential equation describing the bending curve of a DE cantilever beam. By applying different voltage cycles, three continuous avian flight postures have been replicated: takeoff, cruising, and hovering. The simulation results demonstrate that the stiffness-variable DEW effectively mimics the wing deformations observed in birds during different flight postures, closely resembling real-world flight conditions. This study has the potential to serve as an important reference for exploring changes in bird flight behavior, thereby advancing the application of DE materials in the field of soft robotics.

Complexity in Chick‐a‐Dee Calls of Mountain Chickadees (Poecile gambeli): Call Variation Associated With Flock Size and Flight

ABSTRACTThe chick‐a‐dee call of chickadees, tits, and titmice is a vocal system used in a wide range of social contexts by both sexes throughout the year and is one of the more structurally complicated vocal systems outside of human language. Relatively little is known about the chick‐a‐dee calls of mountain chickadees, Poecile gambeli, however. This is an important species for increasing our comparative understanding of variation in chick‐a‐dee calls as they are one of the chickadee species with the largest naturally occurring flock sizes. Flock size relates to the social complexity of flocks, and the social complexity hypothesis for communication predicts that individuals in more complex social groups should communicate with greater complexity than individuals in simpler social groups. Correlational and experimental evidence in support of the hypothesis has been found in the calls of a wide range of species, including Carolina chickadees, P. carolinensis. Here, we provide the first description of the variation in note composition and note‐ordering rules in calls from mountain chickadee flocks in California and Colorado. California flocks were found to be significantly larger than Colorado flocks. Analysis of note‐type usage and transition probabilities between note types found that calls of California birds were more complex than calls of Colorado birds, supporting a key prediction of the social complexity hypothesis for communication. We also found relatively high rates of reversals of note‐ordering rules in mountain chickadee calls, which might help explain the complexity of the chick‐a‐dee calls of this species. Additionally, birds in flight produced calls with different note compositions when compared to perched birds. Generally, the note‐type ordering and transition probabilities of calls of mountain chickadees seem comparable to other better‐studied chickadee species, although their frequent note‐type order rule reversals suggest potential syntax‐like properties in this call system.

Avian-inspired embodied perception in biohybrid flapping-wing robotics

Avian feather intricate adaptable architecture to wing deformations has catalyzed interest in feathered flapping-wing aircraft with high maneuverability, agility, and stealth. Yet, to mimic avian integrated somatic sensation within stringent weight constraints, remains challenging. Here, we propose an avian-inspired embodied perception approach for biohybrid flapping-wing robots. Our feather-piezoelectric mechanoreceptor leverages feather-based vibration structures and flexible piezoelectric materials to refine and augment mechanoreception via coupled oscillator interactions and robust microstructure adhesion. Utilizing convolutional neural networks with the grey wolf optimizer, we develop tactile perception of airflow velocity and wing flapping frequency proprioception. This method also senses pitch angle via airflow direction and detects wing morphology through feather collisions. Our low-weight, accurate perception of flapping-wing robot flight states is validated by motion capture. This investigation constructs a biomechanically integrated embodied perception system in flapping-wing robots, which holds significant promise in reflex-based control of complex flight maneuvers and natural bird flight surveillance.

Noise reduction of an airfoil model covered by bio-inspired herringbone riblets

It is curious that whether the typical herringbone pattern of bird flight feathers plays a role in attenuating aeroacoustic noise. Being motivated by this, experiments are conducted to investigate noise reduction of the NACA0012 (National Advisory Committee for Aeronautics) airfoil-based model with one side surface covered by bio-inspired herringbone patterns of riblets. The herringbone-ribbed surface is defined by the divergent angle β (= 60°) of the riblets pattern, the spanwise wavelength λ (= 0.2c and 0.4c) of the pattern, and the riblet height h (= 0.6%c and 1.2%c), where c is the chord length of the airfoil. While far-field sound pressure fluctuations are measured via microphones in an anechoic wind tunnel, flow fields around the model are captured using particle image velocimetry (PIV) in a water tunnel. The effective angle of attack of the test models ranges from αeff = −11.1° to 11.1° and Reynolds number considered is from Re = 2.3 × 105 to 7.8 × 105. Compared with the baseline smooth models, the models with the riblet pattern on the pressure side are able to substantially suppress the tonal noise, associated with considerable reduction in the overall noise. The reduction in the overall sound pressure levels of the tonal noise and the overall noise are up to 21.3 dB and 20.5 dB, respectively, at αeff = −2.2° and Re = 3.6 × 105. The noise reduction is attributed to the transition of laminar to turbulent boundary layers over the herringbone-ribbed surface, particularly in the saddle location where the spanwise-repeated herringbone pattern converges. Behavior of shear layers separating from the trailing edge of the model is examined, corroborating the proposition that the acoustic feedback loop is impaired by the herringbone-ribbed surface.

BirdWingData: Wingspan and wing area data of birds compiled from multiple literature sources and original measurements

AbstractWing morphology plays a pivotal role in avian flight capabilities and ecological adaptations across diverse environments. Consequently, wing measurement data are used frequently in comparative analyses and hypothesis exploration to understand avian evolution. Among the parameters representing wing morphology, wingspan and wing area are relatively challenging to obtain compared to simpler measures such as wing length and hand‐wing index. This study aimed to enhance accessibility to existing wingspan and wing area data by compiling measurements from 25 literature sources, in addition to unpublished data. The dataset covers 856 species across 95 families and 28 orders. Although the inclusion proportion varies widely among orders, ranging from 0% to 100%, this initial dataset forms a foundation for a more comprehensive database on avian wing morphology. The complete dataset for this abstract published in the Data Paper section of the journal is available in electronic format in MetaCat in JaLTER at http://db.cger.nies.go.jp/JaLTER/metacat/metacat/ERDP-2024-04.1/jalter-en. The dataset will be updated continuously, with the latest version available on figshare in CSV and Microsoft Excel formats (https://doi.org/10.6084/m9.figshare.23537892.v2).

Considering What Animals “Need to Do” in Enclosure Design: Questions on Bird Flight and Aviaries

Considering What Animals “Need to Do” in Enclosure Design: Questions on Bird Flight and Aviaries

Investigation of models to estimate flight performance of gliding birds from wakes.

Mathematical models based on inviscid flow theory are effective at predicting the aerodynamic forces on large-scale aircraft. Avian flight, however, is characterized by smaller sizes, slower speeds, and increased influence of viscous effects associated with lower Reynolds numbers. Therefore, inviscid mathematical models of avian flight should be used with caution. The assumptions used in such models, such as thin wings and streamlined bodies, may be violated by birds, potentially introducing additional error. To investigate the applicability of the existing models to calculate the aerodynamic performance of bird flight, we compared predictions using simulated wakes with those calculated directly from forces on the bird surface, both derived from computational fluid dynamics of a high-fidelity barn owl geometry in free gliding flight. Two lift models and two drag models are assessed. We show that the generalized Kutta-Joukowski model, corrected by the streamwise velocity, can predict not only the lift but also span loading well. Drag was predicted best by a drag model based on the conservation of fluid momentum in a control volume. Finally, we estimated force production for three raptor species across nine gliding flights by applying the best lift model to wake flow fields measured with particle tracking velocimetry.

Numerical simulation of manta ray swimming using a smoothed-particle hydrodynamics method and investigation of the vortical structures in the wake

A three-dimensional smoothed-particle hydrodynamics (SPH) method is used to study the moving boundary problem of a swimming manta ray, focusing on Eulerian and Lagrangian coherent structures. The manta ray's boundary motion is predefined by a specific equation. The calculated hydrodynamic results and Eulerian coherent structures are compared with data from the literature. To improve computational stability and efficiency, the δ+-SPH model used in this study incorporates tensile instability control and an improved adaptive particle-refinement technique. By comparing and analyzing the Eulerian and Lagrangian coherent structures, the relationship between these vortex structures and hydrodynamic force generation is examined, revealing the jet mechanism in the manta ray's wake. The SPH method presented herein is robust and efficient for calculating biomimetic propulsion problems involving moving boundaries with large deformations, and it can accurately identify vortex structures. The approach of this study provides an effective simulation tool for investigating biomimetic propulsion problems such as bird flight and fish swimming.

CGull: A Non-Flapping Bioinspired Composite Morphing Drone.

Despite the tremendous advances in aircraft design that led to successful powered flights of aircraft as heavy as the Antonov An-225 Mriya, which weighs 640 tons, or as fast as the NASA-X-43A, which reached a record of Mach 9.6, many characteristics of bird flight have yet to be utilized in aircraft designs. These characteristics enable various species of birds to fly efficiently in gusty environments and rapidly change their momentum in flight without having modern thrust vector control (TVC) systems. Vultures and seagulls, as examples of expert gliding birds, can fly for hours, covering more than 100 miles, without a single flap of their wings. Inspired by the Great Black-Backed Gull (GBBG), this paper presents "CGull", a non-flapping unmanned aerial vehicle (UAV) with wing and tail morphing capabilities. A coupled two degree-of-freedom (DOF) morphing mechanism is used in CGull's wings to sweep the middle wing forward and the outer feathered wing backward, replicating the GBBG's wing deformation. A modular two DOF mechanism enables CGull to pitch and tilt its tail. A computational model was first developed in MachUpX to study the effects of wing and tail morphing on the generated forces and moments. Following the biological construction of birds' feathers and bones, CGull's structure is mainly constructed from carbon-fiber composite shells. The successful flight test of the proof-of-concept physical model proved the effectiveness of the proposed morphing mechanisms in controlling the UAV's path.

Risk Assessment of Bird Collisions with a Wind Turbine Based on Flight Parameters

The study addresses the challenge of bird collisions with wind turbines by developing an autonomous risk assessment method. The research uses data from the stereoscopic Bird Protection System (BPS) to anticipate potential collision threats by analysing flight parameters and distance from turbines. The danger factor depends on the flight characteristics of the identified bird species and the parameters of the wind turbine control system. The paper proposes an online quantitative risk assessment model that operates in real time, with the aim of minimising unnecessary turbine shutdowns while improving bird conservation. The model is validated through field data from bird flights. The findings suggest that adaptive management of turbine operations based on real-time bird flight data can significantly reduce collision risks without compromising energy production efficiency. The research underscores the balance between ecological considerations and the economic viability of wind energy, proposing an adaptive strategy that reduces unnecessary turbine stoppages while ensuring the safety of avian species.

A Deep Learning Framework for Real-Time Bird Detection and Its Implications for Reducing Bird Strike Incidents.

Bird strikes are a substantial aviation safety issue that can result in serious harm to aircraft components and even passenger deaths. In response to this increased tendency, the implementation of new and more efficient detection and prevention technologies becomes urgent. The paper presents a novel deep learning model which is developed to detect and alleviate bird strike issues in airport conditions boosting aircraft safety. Based on an extensive database of bird images having different species and flight patterns, the research adopts sophisticated image augmentation techniques which generate multiple scenarios of aircraft operation ensuring that the model is robust under different conditions. The methodology evolved around the building of a spatiotemporal convolutional neural network which employs spatial attention structures together with dynamic temporal processing to precisely recognize flying birds. One of the most important features of this research is the architecture of its dual-focus model which consists of two components, the attention-based temporal analysis network and the convolutional neural network with spatial awareness. The model's architecture can identify specific features nested in a crowded and shifting backdrop, thereby lowering false positives and improving detection accuracy. The mechanisms of attention of this model itself enhance the model's focus by identifying vital features of bird flight patterns that are crucial. The results are that the proposed model achieves better performance in terms of accuracy and real time responses than the existing bird detection systems. The ablation study demonstrates the indispensable roles of each component, confirming their synergistic effect on improving detection performance. The research substantiates the model's applicability as a part of airport bird strike surveillance system, providing an alternative to the prevention strategy. This work benefits from the unique deep learning feature application, which leads to a large-scale and reliable tool for dealing with the bird strike problem.

Studies on V-Formation and Echelon Flight Utilizing Flapping-Wing Drones

V-Formation and echelon formation flights can be seen used by migratory birds throughout the year and have left many scientists wondering why they choose very specific formations. Experiments and analytical studies have been completed on the topic of the formation flight of birds and have shown that migratory birds benefit aerodynamically by using these formations. However, many of these studies were completed using fixed-wing models, while migratory birds both flap and glide while in formation. This paper reports the design of and experiments with a flapping-wing model rather than only a fixed-wing model. In order to complete this study, two different approaches were used to generate a flapping-wing model. The first was a computational study using an unsteady vortex–lattice (UVLM) solver to simulate flapping bodies. The second was an experimental design using both custom-built flapping mechanisms and commercially bought flapping drones. The computations and various experimental trials confirmed that there is an aerodynamic benefit from flying in either V-formation or echelon flight while flapping. It is shown that each row of birds experiences an increase in aerodynamic performance based on positioning within the formation.

Comparative genomics reveals convergent signals associated with the high metabolism and longevity in birds and bats.

Birds and bats have long lifespans relative to their body size compared with non-flying animals. However, the genomic basis associated with longer lifespan of flying species despite their higher metabolism was unclear. In this study, we hypothesized that genes involved in the regulation of metabolism and lifespan changed with the acquisition of flight and searched for genes that show specific evolutionary patterns in flying species. As a result, we identified several genes that show different evolutionary rates in bird and bat lineages. Genes in pathways involved in lifespan regulation were conserved in birds, while they evolved at an accelerated rate in bats. We also searched for genes in which convergent amino acid substitutions occurred in birds and bats and found such substitutions in genes involved in cancer, reactive oxygen species control and immunity. Our study revealed genomic changes associated with the acquisition of flight in birds and bats and suggested that multiple genes involved in the regulation of lifespan and metabolism support both high metabolism and longevity in flying species.

ECR Spotlight – Mario Martinez Groves-Raines

ECR Spotlight is a series of interviews with early-career authors from a selection of papers published in Journal of Experimental Biology and aims to promote not only the diversity of early-career researchers (ECRs) working in experimental biology but also the huge variety of animals and physiological systems that are essential for the ‘comparative’ approach. Mario Martinez Groves-Raines is an author on ‘ Steady as they hover: kinematics of kestrel wing and tail morphing during hovering flights’, published in JEB. Mario is a PhD Student in the lab of Dr Shane Windsor (University of Bristol, UK), Dr Abdulghani Mohamed (RMIT, Australia) and Professor Simon Watkins (RMIT, Australia), investigating the flight of birds from an aerodynamics and flight control perspective, learning and inspiring new flight techniques for human-made aircraft.

The Aerodynamic Mechanisms of the Formation Flight of Migratory Birds: A Narrative Review

The Aerodynamic Mechanisms of the Formation Flight of Migratory Birds: A Narrative Review

A UDF-Based Approach for the Dynamic Stall Evaluation of Airfoils for Micro-Air Vehicles.

A numerical method for generating dynamic stall using ANSYS Fluent and a user-defined function (UDF), with the complete script shared for reference, is introduced and tested. The study draws inspiration from bird flight, exploring dynamic stall as a method for achieving enhanced aerodynamic performance. The numerical method was tested on NACA 0012 airfoils with corresponding chord lengths of c1=40 mm, c2=150 mm, and c3=300 mm at Reynolds numbers ranging from Re1=2.8×104 up to Re5=1.04×106. Airfoil oscillations were settled for all cases at ω=0.55 Hz. Detached eddy simulation (DES) is employed as the turbulence model for the simulations presented, ensuring the accurate representation of the flow characteristics and dynamic stall phenomena. The study provides a detailed methodology, encouraging further exploration by researchers, especially young academics and students.

On the physiology of high-altitude flight and altitudinal migration in birds.

Many bird species fly at high altitudes for short periods and/or shift seasonally in altitude during migration, but little is known about the physiology of these behaviors. Transient high-altitude flight, or short-term flight at extreme altitudes, is a strategy used by lowland-native birds, often in the absence of topographic barriers. Altitudinal migration, or seasonal roundtrip movement in altitude between the breeding and non-breeding seasons, is a form of migration that occurs as a regular part of the annual cycle and results in periods of seasonal residency at high altitudes. Despite their nuanced differences, these two behaviors share a common challenge: Exposure to reduced oxygen environments during at least part of the migratory journey. In this perspective piece, we compare what is known about the physiology of oxygen transport during transient high-altitude flight and altitudinal migration by highlighting case studies and recent conceptual advances from work on captive and wild birds. We aim to open avenues for integrative research on the ecology, evolution, and physiology of high-flying and mountain-climbing birds.

Energy supply during nocturnal endurance flight of migrant birds: effect of energy stores and flight behaviour

BackgroundMigrating birds fly non-stop for hours or even for days. They rely mainly on fat as fuel complemented by a certain amount of protein. Studies on homing pigeons and birds flying in a wind-tunnel suggest that the shares of fat and protein on total energy expenditure vary with flight duration and body fat stores. Also, flight behaviour, such as descending flight, is expected to affect metabolism. However, studies on free flying migrant birds under natural conditions are lacking.MethodsOn a Swiss Alpine pass, we caught three species of nocturnal migrant passerines out of their natural migratory flight. Since most night migrants start soon after dusk, we used time since dusk as a measure of flight duration. We used plasma concentrations of metabolites of the fat, protein, and carbohydrate metabolism as indicators of relative fuel use. We used flight altitudes of birds tracked with radar and with atmospheric pressure loggers to characterize flight behaviour.ResultsThe indicators of fat catabolism (triglycerides, very low-density lipoproteins, glycerol) were positively correlated with body energy stores, supporting earlier findings that birds with high fat stores have a higher fat catabolism. As expected, plasma levels of triglycerides, very low-density lipoproteins, glycerol and ß-hydroxy-butyrate increased at the beginning of the night, indicating that nocturnal migrants increased their fat metabolism directly after take-off. Surprisingly, fat catabolism as well as glucose levels decreased in the second half of the night. Data from radar observations showed that the number of birds aloft, their mean height above ground and vertical flight speed decreased after midnight. Together with the findings from atmospheric pressure-loggers put on three species, this shows that nocturnal migrants migrating over continental Europe descend slowly during about 1.5 h before final landfall at night, which results in 11–30% energy savings according to current flight models.ConclusionsWe suggest that this slow descent reduces energy demands to an extent which is noticeable in the plasma concentration of lipid, protein, and carbohydrate metabolites. The slow descent may facilitate the search for a suitable resting habitat and serve to refill glycogen stores needed for foraging and predator escape when landed.