Tails Of Birds Research Articles

Wind Tunnel Balance Measurements of Bioinspired Tails for a Fixed Wing MAV

Bird tails play a significant role in aerodynamics and stability during flight. This paper investigates the use of bioinspired horizontal stabilizers for Micro Air Vehicles (MAVs) with Zimmerman wing-body geometry. Five configurations of bioinspired horizontal stabilizers are presented. Then, 3-component external balance force measurements of each horizontal stabilizer are performed in the wind tunnel. The Squared-Fan-Shaped Horizontal Stabilizer (HSF-tail) is selected as the optimal horizontal stabilizer that provides the highest aerodynamic efficiency during cruise flight while maintaining high longitudinal stability on the vehicle. The integration of the HSF-tail increases the aerodynamic efficiency by more than 6% up to a maximum of 17% compared to the other alternatives while maintaining the lowest aerodynamic drag value during the cruise phase. Furthermore, balance measurements to analyze the influence of the HSF-tail deflection on the aerodynamic coefficients are conducted, resulting in increased lift force and reduced aerodynamic drag with negative tail deflections. Lastly, the experimental data is validated with CFD-RANS steady simulations for low angles of attack, obtaining a relative difference on the measurement around 5% for the aerodynamic drag coefficient and around 10% for the lift coefficient during the cruise flight that demonstrates a high degree of accuracy in the aerodynamic coefficients obtained by external balance in the wind tunnel. This work represents a novel approach through the implementation of a horizontal stabilizer inspired by the structure of the tails of birds that is expected to yield significant advancements in both stability and aerodynamic efficiency, with the potential to revolutionize MAV technology.

Design and Kinematic Analysis of Deployable Antenna for Bionic Bird Tail Feather

Design and Kinematic Analysis of Deployable Antenna for Bionic Bird Tail Feather

Numerical Analysis of Bioinspired Tails in a Fixed-Wing Micro Air Vehicle

Bird tails play a key role in aerodynamics and flight stability. They produce extra lift for takeoff and landing maneuvers, enhance wing functions and maintain stability during flight (keeping the bird from yawing, rolling and pitching, or otherwise losing control). This paper investigates the use of bioinspired horizontal stabilizers for Micro Air Vehicles (MAVs) involving a Zimmerman wing-body geometry. A selection of five tail shapes of the main types existing in nature is presented, and a parametric analysis is conducted looking into the influence of the most relevant tail geometric parameters to increase the longitudinal static stability of the vehicle. Based on the parametric study, a smaller subset of candidate tail designs are shortlisted to perform a detailed aerodynamic analysis. Then, steady RANS CFD simulations are conducted for a higher-fidelity study of these candidate tail designs to obtain an optimum of each tail type. The criterion for selection of the optimum tail configuration is the maximum aerodynamic efficiency, CLCD , as well as a high longitudinal static stability. The squared-fan tail provides the highest aerodynamic efficiency while maintaining a high longitudinal stability of the vehicle. In conclusion, this paper provides an innovative study of improving longitudinal stability and aerodynamics through the implementation of bioinspired horizontal stabilizers in vehicles with these characteristics.

Functions of avian elongated tails, with suggestions for future studies

Elongated tails are elaborate plumage traits possessed by a variety of bird species. Sexual selection has long been the dominant hypothesis for explaining why certain species possess such long tails. During the past three decades, however, alternative hypotheses have been proposed and tested. Here, we review evidence, and the lack thereof, for four hypothesised functions of elongated tails in birds: sexual selection, aerodynamic enhancement, anti‐predation signalling and perch balancing. Sexual selection has received the most attention, though with inconsistent support. The other three hypothesised functions, in contrast, have gained less attention, with perch balancing remaining largely speculative. After reviewing and synthesizing information about these functions, we show that our current knowledge of avian elongated tails is not comprehensive. To advance our understanding of this topic, we suggest (1) devising a uniform definition of elongated tails that can be applied to a wide variety of bird species, (2) further investigation of less‐studied functions of such tails, (3) conducting meta‐analyses to discover the origins and trait correlates of elongated tails, (4) considering the possibility that elongated tails serve multiple functions simultaneously, and (5) testing unexplored functions of elongated tails.

Avoiding Vulnerabilities and Attacks with a Proactive Strategy for Web Applications

This paper describes the design principles and manufacturing techniques behind the construction of a life-size 4 degree- offreedom robot bird tail that mimics the pygostyle articulation of a 2.4-meter wingspan eagle bird.

Development of Novel Composite Biomaterials for Use asBiodegradable Adsorbents and or Bio-Carriers DuringWastewater Treatments Using Galerkin’s Finite ElementAnalysis

This paper describes the design principles and manufacturing techniques behind the construction of a life-size 4 degree- offreedom robot bird tail that mimics the pygostyle articulation of a 2.4-meter wingspan eagle bird.

Avian Dinosaur Tail Evolution and Bone Fracture Healing

Bird tails transitioned during the Mesozoic from long to shortened and distally fused. Fusion of the distalmost vertebrae manifests as the bony pygostyle structure, a trait retained in extant avians that contributes to flight aerodynamics. Here, we investigate the mechanism responsible for pygostyle formation. Transcriptomic profiling and histology in extant tail tissue reveal that the immune system is crucial for this important adaptation in avian evolutionary history. Pygostyle formation commences with cell death in the intervertebral discs, within the nucleus pulposus and annulus fibrosus. The nucleus pulposus, previously thought absent in birds, forms differently in fused versus unfused regions of the tail, and its deterioration in the pygostyle is integral to the cascade of events that eventually lead to ankylosis. The complement and coagulation cascades, angiogenesis, neutrophil-like cell function, involvement of both the innate and adaptive immune systems and multiple additional events mirror those observed during bone fracture healing. The key common denominator in both processes that differentiates them from general endochondral ossification is the inflammatory response. These studies indicate that a universal mechanism for bone repair has been co-opted in avian evolution for the formation of a flight-adapted tail structure.

Bio-Inspired Morphing Tail for Flapping-Wings Aerial Robots Using Macro Fiber Composites

The aim of this work is to present the development of a bio-inspired approach for a robotic tail using Macro Fiber Composites (MFC) as actuators. The use of this technology will allow achieving closer to the nature approach of the tail, aiming to mimic a bird tail behavior. The tail will change its shape, performing morphing, providing a new type of actuation methodology in flapping control systems. The work is intended as a first step for demonstrating the potential of these technologies for being applied in other parts of the aerials robotics systems. When compared with traditional actuation approaches, one key advantage that is given by the use of MFC is their ability to adapt to different flight conditions via geometric tailoring, imitating what birds do in nature. Theoretical explanations, design, and experimental validation of the developed concept using different methodologies will be presented in this paper.

Function of the uropygial gland in eiders (Somateria mollissima)

BackgroundThe uropygial gland is an exocrine gland located above the tail of birds that produces a diverse range of biochemicals. It has been hypothesized to be involved in chemical protection, water-proofing and maintenance of plumage brightness. Although these not necessarily mutually exclusive functions have received some empirical support, there has been little empirical research on the function of water-proofing.MethodsHere we analyzed data for 229 individual eiders (Somateria mollissima) collected by Danish hunters during 2016‒2018.ResultsThe Eider is a sea-duck that spends almost its entire life in sea water emphasizing water-proofing of the plumage. The size of the uropygial gland increased with body mass in males, but not in females, and it increased with age. The size of the uropygial gland decreased during winter. Eiders with small uropygial glands grew their feathers at a fast rate. Eiders with large wing areas had large uropygial glands.ConclusionsThese findings are consistent with large uropygial glands playing a role in water-proofing during molt and foraging, but also that uropygial glands may play a role in chemical defense.

From Studying Real Hummingbirds to Designing Hummingbird-Like Robots—A Literature Review

In this paper, the interpretation of hovering flight for hummingbirds is studied from a hummingbird morphology perspective (muscle and skeleton) including weight distribution, followed by a discussion of hovering aerodynamics. Next, by studying the scale laws, geometry similarity, and statistical analysis on wing parameters, the parametric relation between wing performances and weight is studied, followed by flapping wing micro autonomous drones (FWMADs) design. The efficiency of the designed wings based on the scaling law is verified by flying test. Material difference and methods of design are summarized. Last, the morphology of bird's tails is presented, and then the designs of tails are introduced, followed by discussion of tail performances. The results show that the tail could be predicted to apply to the stability of hovering twin-wing FWMADs. The current studies provide a simple but powerful guideline for biologists and engineers who study the morphology of hummingbirds and design FWMADs.

Bird functional traits affect seed dispersal patterns of China\u2019s endangered trees across different disturbed habitats

BackgroundThe most dominant global threat to natural forests and their biodiversity is land-cover change, which has negative impacts on both species persistence and ecosystem functions. Land-cover change could alter animal behaviour and disrupt seed dispersal mutualisms. However, its effects on the role of bird functional traits in seed dispersal are not well studied.MethodsIn the present study, we assessed the contributions of bird functional traits (behavioural traits: food habit, foraging pattern, foraging frequency, and habitat specialisation; morphological traits: weight, body length, wing length, and tail length) to both seed removal patterns and seed dispersal distances of an endangered and native tree species, Chinese yew (Taxus chinensis), in farmland, patchy habitat, and natural habitat, of southeast China.ResultsWe found that the ability of T. chinensis trees to form seed dispersal mutualisms with local birds varied across the different disturbed habitats. As a consequence of these mutualisms, more seeds were removed by birds from the patchy habitat than from the other two habitats. The number of seeds removed increased with bird foraging frequency. Moreover, the dispersal distance from the three habitats differed, and the longest dispersal distances were observed at both the patchy habitat and the farmland site. Seed dispersal distance increased with bird tail and wing length.ConclusionsOur results highlight the importance of bird functional traits in the seed dispersal patterns of endangered trees across disturbed forest habitats, which should be considered for tree conservation and management.

A tale of two tails: developing an avian inspired morphing actuator for yaw control and stability

Motivated by the lack of research in tailless morphing aircraft in addition to the current inability to measure the resultant aerodynamic forces and moments of bird control maneuvers, this work aims to develop and test a multi-functional morphing control surface based on the horizontal tail of birds for a low-radar-signature unmanned aerial vehicle. Customized macro fiber composite actuators were designed to achieve yaw control across a range of sideslip angles by inducing 3D curvature as a result of bending-twisting coupling, a well-known phenomenon in classical fiber composite theory. This allows for yaw control, pitch control, and limited air break control. The structural response of the customized actuators was determined numerically using both a piezoelectric and an equivalent thermal model in order to optimize the fiber direction to allow for maximized deflection in both the vertical and lateral directions. In total, three control configurations were tested experimentally: symmetric deflection for pitch control, single-sided deflection for yaw control, and antisymmetric deflection for air brake control. A Reynolds-averaged-Navier–Stokes fluid simulation was also developed to compare with the experimental results for the unactuated baseline configuration. The actuator was shown to provide better yaw control than traditional split aileron methods, remain effective in larger sideslip angles, and provide directional yaw stability when unactuated. Furthermore, it was shown to provide adequate pitch control in sideslip in addition to limited air brake capabilities. This design is proposed to provide complete aircraft control in concert with spanwise morphing wings.

Receiver discriminability drives the evolution of complex sexual signals by sexual selection.

A hallmark of sexual selection by mate choice is the evolution of exaggerated traits, such as longer tails in birds and more acoustic components in the calls of birds and frogs. Trait elaboration can be opposed by costs such as increased metabolism and greater predation risk, but cognitive processes of the receiver can also put a brake on trait elaboration. For example, according to Weber's Law traits of a fixed absolute difference will be more difficult to discriminate as the absolute magnitude increases. Here, we show that in the Emei music frog (Babina daunchina) increases in the fundamental frequency between successive notes in the male advertisement call, which increases the spectral complexity of the call, facilitates the female's ability to compare the number of notes between calls. These results suggest that female's discriminability provides the impetus to switch from enhancement of signaling magnitude (i.e., adding more notes into calls) to employing a new signal feature (i.e., increasing frequency among notes) to increase complexity. We suggest that increasing the spectral complexity of notes ameliorates some of the effects of Weber's Law, and highlights how perceptual and cognitive biases of choosers can have important influences on the evolution of courtship signals.

Bat flight

Bat flight

Age-related change in carotenoid-based plumage of the American Redstart (Setophaga ruticilla)

Plumage colouration serves a variety of functions for birds, including conspecific signalling, crypsis, and predator–prey interactions. Though much research has been conducted on colour changes in species with delayed plumage maturation, where birds do not exhibit definitive adult plumage until their second breeding season or later, relatively few studies have examined how plumage colour changes once definitive adult plumage has been attained. In this study on male and female American Redstarts (Setophaga ruticilla), which exhibit male delayed plumage maturation, we used reflectance spectrometry to evaluate carotenoid-based tail colour changes over 11 breeding seasons, examining both within-individual and population-level changes. At a population level, males in their first breeding season in definitive adult plumage had a feather hue that was more orange-shifted than birds in their second year in adult plumage, and marginally, but not significantly, more orange-shifted than birds in their third year in adult plumage. Within-individual analysis of males recaptured in subsequent seasons also revealed a shift away from orange towards a more yellow feather hue as individuals aged. Within individuals, red chroma was highest for males in their second year in adult plumage, but it showed no population-level effects. At the population level, female redstarts in their first breeding season displayed plumage with a higher red chroma and a lower brightness than birds in their second breeding season, potentially as a result of differences in the timing and conditions of moult (first-year bird tail feathers were grown in the nest). For adult males and females, there was no difference in plumage colouration between birds that returned to the study site compared to those that failed to return. Together, our results suggest that within-individual change rather than differential survival best explains our findings. We suggest that studies examining age-related colour changes are critical for understanding the evolution of complex signalling systems, such as that of American Redstarts.

A tale of a ‘middle’ tail

Zhongornis refers to a ‘middle’ or ‘intermediate’ bird because its tail was claimed to be transitional between primitive birds with a long bony tail (such as Archaeopteryx and Jeholornis) and those with a short tail ending in a fused tip called the pygostyle (such as Confuciusornis) [1]. This finding is significant, as it appeared to fill a ‘gap’ at a critical stage in the early evolution of birds. However, after a detailed restudy, O’Connor and Sullivan [2] suggest that this juvenile bird from the Early Cretaceous Jehol fauna of China actually possesses 20, rather than 14, tail vertebrae; further, this tail is very similar to those of Epidexipteryx (a scansoriopterygid) and Caudipteryx (an oviraptorosaur) among the theropods. Based on this and other features, the authors reinterpretZhongornis as the sister taxon of scansoriopterygids, and further suggest that this clade (Zhongornis + Scansoriopterygidae) is the sister group of Oviraptorosauria. Surprisingly, despite the discovery of so many beautifully preserved feathered dinosaurs in China, the relationships among them, especially those close to the origin of birds, are still intriguing. This intrigue applies to Oviraptorosauria, the ‘egg thief lizards’, and Scansoriopterygidae, a recently recognized rare arboreal clade. Consider this: you have four tails, one each from an oviraptorosaur dinosaur, a dromaeosaur dinosaur, a primitive bird (Archaeopteryx), and a true bird (Confuciusornis). Like many others, you may have immediately seen (1) a long bony tail similar in dromaeosaurs and primitive birds, (2) a very short tail with a pygostyle unique in true birds, and (3) a reduced tail, an intermediate condition seen in oviraptorosaurs. However, most recent cladistic analyses reveal Oviraptorosauria as the sister group of Paraves, which includes dromaeosaurs and birds [3]. This forces us to interpret the tail similarities between oviraptorosaurs and birds as having evolved convergently. The robust and flexible oviraptorosaur tails, together with their broad tail-feather fans, were uniquely adapted to serve as dynamic intraspecific display structures [4]. However, the origin of oviraptorosaurs remains a mystery, with no Jurassic record. O’Connor and Sullivan’s study indicates that oviraptorosaurs’ cousins (scansoriopterygids) once lived in the Jurassic trees in the north-eastern China, and their differences might result from adaptation to contrasting ecological niches. Will taking Zhongornis’s tail out of the ‘middle’ bird tail allow us to eventually discover the real ‘middle’ creature someday? Perhaps not! A recent genetic and evolutionary development study shows that a single genetic mutation could have occurred in paravian dinosaurs, which both truncated its tail and fused its distal caudal vertebrae into a pygostyle [5]. Moreover, this potential mutation has pleiotropic effects also leading to fusions inmore anterior vertebrae, ribs, and even digits. These fusions have been observed in mice and modern birds, as well as in Confuciusornis and more advanced birds, but not in Jeholornis and Archaeopteryx [5]. The co-occurrence of Confuciusornis and Jeholornis about125millionyears ago also supports this sudden appearance of short-tailed birds. Therefore, the search for the fantastical middle bird may prove to be futile.

From dinosaurs to birds: a tail of evolution.

A particularly critical event in avian evolution was the transition from long- to short-tailed birds. Primitive bird tails underwent significant alteration, most notably reduction of the number of caudal vertebrae and fusion of the distal caudal vertebrae into an ossified pygostyle. These changes, among others, occurred over a very short evolutionary interval, which brings into focus the underlying mechanisms behind those changes. Despite the wealth of studies delving into avian evolution, virtually nothing is understood about the genetic and developmental events responsible for the emergence of short, fused tails. In this review, we summarize the current understanding of the signaling pathways and morphological events that contribute to tail extension and termination and examine how mutations affecting the genes that control these pathways might influence the evolution of the avian tail. To generate a list of candidate genes that may have been modulated in the transition to short-tailed birds, we analyzed a comprehensive set of mouse mutants. Interestingly, a prevalent pleiotropic effect of mutations that cause fused caudal vertebral bodies (as in the pygostyles of birds) is tail truncation. We identified 23 mutations in this class, and these were primarily restricted to genes involved in axial extension. At least half of the mutations that cause short, fused tails lie in the Notch/Wnt pathway of somite boundary formation or differentiation, leading to changes in somite number or size. Several of the mutations also cause additional bone fusions in the trunk skeleton, reminiscent of those observed in primitive and modern birds. All of our findings were correlated to the fossil record. An open question is whether the relatively sudden appearance of short-tailed birds in the fossil record could be accounted for, at least in part, by the pleiotropic effects generated by a relatively small number of mutational events.

Effects of tail length on an escape maneuver of the Red-billed Streamertail

Sexually selected, elongated tails in birds may impair or alter naturally selected functions related to flight. The aim of this study was to test whether experimental manipulation of tail length affected the kinematics of a low-speed escape maneuver. The Red-billed Streamertail (Trochilus polytmus) has the longest tail of any hummingbird and is highly sexually dimorphic in tail length. I hypothesized that streamertails with either a long tail or with the tail removed would perform maneuvers with reduced linear and angular accelerations, relative to maneuvers performed with a short tail. Two high-speed video cameras recorded maneuvers from male and female Red-billed Streamertails under three tail length treatments: short tail, long tail, and no tail. The detailed kinematics of the maneuvers were highly variable. Whereas the birds always performed rolls (rotation about the bird’s X-axis) during the maneuver, there was variation in the relative importance of pitching motions (rotation about the Y-axis) or yawing motions (rotation about the Z-axis), with yawing rotations playing a small role in ‘pitch-roll’ turns, and pitching motions playing a small role in ‘yaw/roll’ turns. Birds missing their entire tail exhibited reduced maximum linear accelerations associated with a curving trajectory. By contrast, birds maneuvering with an elongated tail did not exhibit significantly different kinematics from the controls, suggesting that the greatly elongated tail streamers have relatively small effects on the bird’s ability to maneuver at low speeds. Based on these observations, greatly elongated tails may not pose a large cost to low-speed maneuvering flight.

Crowcam: Camera on bird's tail captures bird ingenuity

Crowcam: Camera on bird's tail captures bird ingenuity

Tail effects on yaw stability in birds

Bird tails, which are an aerodynamic surface in the horizontal plane, are treated with regard to their effects on yaw stability. Reference is made to wings of very small aspect ratio similar to the values of bird tails in order to identify features which are significant for the aerodynamic yawing moment characteristics due to sideslip. It is shown that there are yawing moments of considerable magnitude for this aspect ratio region. Furthermore, the lift coefficient, which also exerts an influence, is included in the treatment of yaw stability. To show more concretely the addressed effects for birds, the yawing moment characteristics of the wing–tail combination of a pigeon, which is considered as a representative example, are treated in detail. For this purpose, a sophisticated aerodynamic method capable to deal with the mutual flow interactions between the tail and the wing is used to compute results of high precision. The yawing moment characteristics of the pigeon wing–tail combination with respect to the sideslip angle and the lift coefficient are determined, with emphasis placed on the contribution of the tail. It is shown that there is a significant contribution of the tail to yaw stability. The findings of this paper on the contribution of the tail to the yawing moment characteristics are supported by an evaluation of existing experimental data. Furthermore, the physical mechanisms are considered which are the reasons for the stabilizing role of the tail. These effects concern the contribution of the drag acting at the tail to the yawing moment. In addition, it is shown that extended legs and feet, when exposed to the airflow, can contribute to yaw stability.