Bat Flight Research Articles

Robotic bat mechanism design

This paper proposes a bat robot mechanism and investigates the kinematics of flying process. After observing the flight of bats for a long period of time and analysing its flying kinematics, a bionic robot was synthesised based on the bat structure to realise the deploying and flapping movements of the double membranous wings. With screw theory, the primary motion of the membranous wings was checked and six actuators were selected for controlling the flapping flight of the bat robot collaboratively. The structure is optimised by a bench test. A method is presented to measure the force output of the bat robot.

Echo interval and not echo intensity drives bat flight behavior in structured corridors

To navigate in the natural environment, animals must adapt their locomotion in response to environmental stimuli. The echolocating bat relies on auditory processing of echo returns to represent its surroundings. Recent studies have shown that echo flow patterns influence bat navigation, but the acoustic basis for flight path selection remains unknown. To investigate this problem, we released bats in a flight corridor with walls constructed of adjacent individual wooden poles, which returned cascades of echoes to the flying bat. We manipulated the spacing and echo strength of the poles comprising each corridor side, and predicted that bats would adapt their flight paths to deviate toward the corridor side returning weaker echo cascades. Our results show that the bat's trajectory through the corridor was not affected by the intensity of echo cascades. Instead, bats deviated toward the corridor wall with more sparsely spaced, highly reflective poles, suggesting that pole spacing, rather than echo intensity, influenced bat flight path selection. This result motivated investigation of the neural processing of echo cascades. We measured local evoked auditory responses in the bat inferior colliculus to echo playback recordings from corridor walls constructed of sparsely and densely spaced poles. We predicted that evoked neural responses would be discretely modulated by temporally distinct echoes recorded from the sparsely spaced pole corridor wall, but not by echoes from the more densely spaced corridor wall. The data confirm this prediction and suggest that the bat's temporal resolution of echo cascades may drive its flight behavior in the corridor.

The relevance of vegetation structures and small water bodies for bats foraging above farmland

Bats are known to forage and commute close to vegetation structures when moving across the agricultural matrix, but the role of isolated landscape elements in arable fields for bat activity is unknown. Therefore, we investigated the influence of small isolated ponds which lie within arable fields close to vegetation structures on the flight and foraging activity of bats. Additionally, we compared species-specific activity measures between forest edges and linear structures such as hedgerows. We repeatedly recorded bat activity using passive acoustic monitoring along 20 transects extending from the vegetation edge up to 200m into the arable field (hereafter: edge-field interface) with a small pond present at five transects per edge type (linear vs. forest). Using generalized linear mixed effect models, we analyzed the effects of edge type, pond presence and the season on species-specific flight and foraging activity within the edge-field interface. We found a higher flight activity of Nyctalus noctula and Pipistrellus pygmaeus above the arable field when a pond was present. Furthermore, Pipistrellus nathusii and Pipistrellus pipistrellus foraged more frequently at forest edges than at linear structures (e.g. hedgerows). Additionally, we found three major patterns of seasonal variation in the activity of bats along the edge-field interface. This study highlights the species-specific and dynamic use of forest and hedgerow or tree line edges by bats and their importance for different bat species in the agricultural landscape. Further, additional landscape elements such as small isolated ponds within arable fields might support the activity of bats above the open agricultural landscape, thereby facilitating agroecosystem functioning. Therefore, additional landscape elements within managed areas should be restored and protected against the conversion into arable land and better linked to surrounding landscape elements in order to efficiently support bats within the agroecosystem.

Phyllostomid bats flying in daylight: a case from the Neotropics

ABSTRACTBats (Chiroptera), one of the most diverse groups in terms of taxonomy, morphology and ecology, are known for their nocturnal behaviour of flight and feeding. Although there is no consensus on the evolution of nocturnality in bats, many authors mention risk of predation, overheating, competition and mobbing by non-competitor species as arguments to justify nocturnal instead of daytime flight in bats. Herein we describe the first records of three genera of phyllostomid bats flying, foraging and drinking water during daytime in the Brazilian Amazon. All taxa were recorded drinking water, and some Phyllostomus sp. individuals were recorded foraging on termites, alongside birds. Risk of dehydration and overheating in roosts, as well as low competition in daytime, may explain the emergence of phyllostomid bats before sunset.

Body lift, drag and power are relatively higher in large-eared than in small-eared bat species.

Bats navigate the dark using echolocation. Echolocation is enhanced by external ears, but external ears increase the projected frontal area and reduce the streamlining of the animal. External ears are thus expected to compromise flight efficiency, but research suggests that very large ears may mitigate the cost by producing aerodynamic lift. Here we compare quantitative aerodynamic measures of flight efficiency of two bat species, one large-eared (Plecotus auritus) and one small-eared (Glossophaga soricina), flying freely in a wind tunnel. We find that the body drag of both species is higher than previously assumed and that the large-eared species has a higher body drag coefficient, but also produces relatively more ear/body lift than the small-eared species, in line with prior studies on model bats. The measured aerodynamic power of P. auritus was higher than predicted from the aerodynamic model, while the small-eared species aligned with predictions. The relatively higher power of the large-eared species results in lower optimal flight speeds and our findings support the notion of a trade-off between the acoustic benefits of large external ears and aerodynamic performance. The result of this trade-off would be the eco-morphological correlation in bat flight, with large-eared bats generally adopting slow-flight feeding strategies.

The soundscape of bat swarms

Brazilian free-tailed bats form large maternal colonies numbering in the millions across the American Southwest. Each night, the bats emerge from their roost to travel to foraging locations. During this emergence, individuals fly together in a dense, linear stream and exhibit collective group behavior. Upon morning return to the roost, the flight behavior of bats change and individuals fly in unpredictable paths, with little to no apparent collective group behavior, creating a swarm. To understand the different sensory challenges each of these flight scenarios pose to bats, we recorded the soundscapes of bats in streams and swarms using four different recording platforms: (1) stationary, ground-based directional and omnidirectional microphones, (2) a zip-line microphone that maneuvered through the bat stream and swarm and was monitored by video, (3) a microphone and thermal camera on a quadcopter that recorded bat flight behavior and signals at high altitudes during swarm re-entry, and (4) a trained hawk that flew through the bat stream while carrying a microphone unit and monitored with unique video. We report on the characteristics and variability of soundscapes for bat swarms, including different noise profiles the bats experience during streaming and swarming and the adaptive time-frequency signatures and flight behavior of individuals during group flight.

Bat flight height monitored from wind masts predicts mortality risk at wind farms

Bat fatalities by collision or barotrauma at wind farms currently raise high conservation concerns. In many countries, pre-installation acoustic surveys are mandatory in order to assess the impacts of wind farm projects. In this purpose, the use of wind masts to estimate bat activity and hence predict collision risk is highly recommended by conservation committees worldwide. Yet, the degree to which collisions may be predicted from acoustic monitoring at wind masts has been strongly debated.To assess this relationship, microphone arrays were installed on 23 wind masts in order to record and locate bat activity on the vertical axis during 3260 nights. For each species, we also calculated a collision susceptibility index, based on fatality data gathered in the literature and corrected for species abundance. We demonstrate that the collision susceptibility index is correlated with the percentage of bat passes at blade height.The acoustic recordings allowed us to establish a reference for the ratios of flight activity above heights of 20–45m high for more than 16 European bat species. The correlation we demonstrate here between the percentage of bat passes at height – recorded from acoustic surveys on wind masts – and bat fatalities strongly supports that activity estimates from wind masts are appropriate for wind turbine impact assessments.

Stereotypy of group flight in Brazilian free-tailed bats

Many bats form colonies and undergo nightly emergence in dense, fast-moving streams. Although the flight mechanics of individual bats have been well studied, the effect of flying in a group has not been studied with large aggregations under natural conditions. We tested the hypothesis that group size affects flight mechanics and behaviour in Brazilian free-tailed bats, Tadarida brasiliensis . We measured the flight path, flight path time and wing beat rate of individual bats by analysing videos of bats in flight and compared values across different flight group sizes. Flight path, flight speed and wing beat rate of individual bats were all unaffected by group size. Additionally, bats maintained a constant wing beat rate regardless of flight speed. These results suggest that Brazilian free-tailed bats experience neither an aerodynamic benefit nor a cost to travelling in groups.

Myotis rufoniger genome sequence and analyses: M. rufoniger's genomic feature and the decreasing effective population size of Myotis bats.

Myotis rufoniger is a vesper bat in the genus Myotis. Here we report the whole genome sequence and analyses of the M. rufoniger. We generated 124 Gb of short-read DNA sequences with an estimated genome size of 1.88 Gb at a sequencing depth of 66× fold. The sequences were aligned to M. brandtii bat reference genome at a mapping rate of 96.50% covering 95.71% coding sequence region at 10× coverage. The divergence time of Myotis bat family is estimated to be 11.5 million years, and the divergence time between M. rufoniger and its closest species M. davidii is estimated to be 10.4 million years. We found 1,239 function-altering M. rufoniger specific amino acid sequences from 929 genes compared to other Myotis bat and mammalian genomes. The functional enrichment test of the 929 genes detected amino acid changes in melanin associated DCT, SLC45A2, TYRP1, and OCA2 genes possibly responsible for the M. rufoniger’s red fur color and a general coloration in Myotis. N6AMT1 gene, associated with arsenic resistance, showed a high degree of function alteration in M. rufoniger. We further confirmed that the M. rufoniger also has bat-specific sequences within FSHB, GHR, IGF1R, TP53, MDM2, SLC45A2, RGS7BP, RHO, OPN1SW, and CNGB3 genes that have already been published to be related to bat’s reproduction, lifespan, flight, low vision, and echolocation. Additionally, our demographic history analysis found that the effective population size of Myotis clade has been consistently decreasing since ~30k years ago. M. rufoniger’s effective population size was the lowest in Myotis bats, confirming its relatively low genetic diversity.

On the possibility (or lack thereof) of agreement between experiment and computation of flows over wings at moderate Reynolds number.

The flight of many birds and bats, and their robotic counterparts, occurs over a range of chord-based Reynolds numbers from 1 × 104 to 1.5 × 105. It is precisely over this range where the aerodynamics of simple, rigid, fixed wings becomes extraordinarily sensitive to small changes in geometry and the environment, with two sets of consequences. The first is that practical lifting devices at this scale will likely not be simple, rigid, fixed wings. The second is that it becomes non-trivial to make baseline comparisons for experiment and computation, when either one can be wrong. Here we examine one ostensibly simple case of the NACA 0012 aerofoil and make careful comparison between the technical literature, and new experiments and computations. The agreement (or lack thereof) will establish one or more baseline results and some sensitivities around them. The idea is that the diagnostic procedures will help to guide comparisons and predictions in subsequent more complex cases.

Calcification of the lower respiratory tract in relation to flight development in Jamaican fruit bats (Phyllostomidae, Artibeus jamaicensis).

The production of echolocation calls in bats along with forces produced by contraction of thoracic musculature used in flight presumably puts relatively high mechanical loads on the lower respiratory tract (LRT). Thus, there are likely adaptations to prevent collapse or distortion of the bronchial tree and trachea during flight in echolocating bats. By clearing and staining (Alcian blue and Alizarin red) LRTs removed from nonvolant neonates, semivolant juveniles, volant subadults, and adult Jamaican fruit bats (Artibeus jamaicensis), I found that calcification of the tracheal, primary bronchial, and secondary bronchial (lobar) cartilage rings occurs over the span of about 3days and coincides with later developmental stages of flight and the increased production of echolocation calls. Tracheal rings that are immediately adjacent to the larynx calcified first, followed by more caudal tracheal rings and then the rings of the primary and secondary bronchi. I suggest that calcification of LRT cartilage rings in echolocating bats provides increased rigidity to counter the thoracic compressions incurred during flight. Calcification of the LRT rings is an adaptation to support the emission of laryngeally produced echolocation calls during flight in bats.

Environmental correlates and energetics of winter flight by bats in southern Alberta, Canada

Winter activity of bats is common, yet poorly understood. Other studies suggest a relationship between winter activity and ambient temperature, particularly temperature at sunset. We recorded echolocation calls to determine correlates of hourly bat activity in Dinosaur Provincial Park, Alberta, Canada. We documented bat activity in temperatures as low as −10.4 °C. We observed big brown bats (Eptesicus fuscus (Palisot de Beauvois, 1796)) flying at colder temperatures than species of Myotis bats (genus Myotis Kaup, 1829). We show that temperature and wind are important predictors of winter activity by E. fuscus and Myotis, and that Myotis may also use changes in barometric pressure to cue activity. In the absence of foraging opportunity, we suggest these environmental factors relate to heat loss and thus the energetic cost of flight. To understand the energetic consequences of bat flight in cold temperatures, we estimated energy expenditure during winter flights of E. fuscus and little brown myotis (Myotis lucifugus (Le Conte, 1831)) using species-specific parameters. We estimated that winter flight uses considerable fat stores and that flight thermogenesis could mitigate energetic costs by 20% or more. We also show that temperature-dependent interspecific differences in winter activity likely stem from differences between species in heat loss and potential for activity–thermoregulatory heat substitution.

Aerodynamic Moment Model Calibration from Distributed Pressure Arrays

In recent years, studies on the role of distributed airflow mechanosensors in bird, bat, and insect flight behaviors have sparked a growing interest in integrating flow sensors, such as pressure or hair sensors, into flight control feedback systems of small unmanned aircraft. It is anticipated that a flight controller based on real-time distributed flow information feedback is more capable of rapidly responding to sudden airflow changes and may exhibit greater stability robustness properties than purely inertial feedback-based flight control laws. However, considering the uncertainty of state-of-the-art microflow sensor technologies, there is an urgent need for model calibration if flow information is to be used to calculate aerodynamic moments and/or forces for controlling aircraft motion. In this paper, a constrained least-squares estimator is developed to calculate the bias of distributed flow information to calibrate an aerodynamic moment model. Simulation and wind-tunnel experiment results demonstrate a significant improvement on the accuracy of the aerodynamic moment calculation after calibration.

An ornithological survey of Gunung Mulu National Park, Sarawak, Malaysian Borneo

ABSTRACT Mount Mulu, an isolated 2,376 m peak in eastern Sarawak, Malaysian Borneo, has not been thoroughly surveyed for bird species since shortly after the creation of Mount Mulu National Park in 1974. The Park is of particular interest for its isolation, spectacular limestone structures, bat flights, and extensive primary forest that ranges from near sea level to the mountain’s peak. We spent 2.5 months surveying, observing, and mist-netting birds in the Park and recorded 244 species across its elevational gradient from 50–1,850 m, including 32 species new to the 1979–82 Mt. Mulu checklists. Here, we report the elevational range of each species we observed, compare our list with these earlier Mt. Mulu checklists compiled 25 years ago, and comment on unique observations.

Perceptual Modalities Guiding Bat Flight in a Native Habitat.

Flying animals accomplish high-speed navigation through fields of obstacles using a suite of sensory modalities that blend spatial memory with input from vision, tactile sensing, and, in the case of most bats and some other animals, echolocation. Although a good deal of previous research has been focused on the role of individual modes of sensing in animal locomotion, our understanding of sensory integration and the interplay among modalities is still meager. To understand how bats integrate sensory input from echolocation, vision, and spatial memory, we conducted an experiment in which bats flying in their natural habitat were challenged over the course of several evening emergences with a novel obstacle placed in their flight path. Our analysis of reconstructed flight data suggests that vision, echolocation, and spatial memory together with the possible exercise of an ability in using predictive navigation are mutually reinforcing aspects of a composite perceptual system that guides flight. Together with the recent development in robotics, our paper points to the possible interpretation that while each stream of sensory information plays an important role in bat navigation, it is the emergent effects of combining modalities that enable bats to fly through complex spaces.

Habitat Preferences of Soprano Pipistrelle Pipistrellus pygmaeus (Leach, 1825) and Common Pipistrelle Pipistrellus pipistrellus (Schreber, 1774) in Two Different Woodlands in North East Scotland.

Alek Rachwald, Tim Bradford, Zbigniew Borowski, and Paul A. Racey (2016) The habitat preferences of the soprano pipistrelle Pipistrellus pygmaeus and the common pipistrelle Pipistrellus pipistrellus living in sympatry, were investigated in north east Scotland, using bat detector transects. Bat flight, foraging and social activity in natural birch woodland was compared with that in managed non-native coniferous woodland. Each area consists of riparian habitat, meadow-forest ecotone and dense forest. The activity of bats was highest in riparian habitat, then meadow, and lowest in dense woodland. P. pygmaeus was more abundant than P. pipistrellus in both areas, although in managed coniferous woodland only narrowly so (43.7% of all recorded bat flights, compared to 40.0% for common pipistrelle). In natural birch woodland, meadow habitat was most preferred by P. pipistrellus, and there was no significant difference between the use of riparian and woodland habitats, whereas in coniferous woodland, riparian habitat was most preferred. P. pygmaeus in both sites preferred riparian habitat, then meadow and forest least of all. The foraging activity of soprano pipistrelles was higher in birch than in coniferous woodland, whereas for the common pipistrelle, it was more evenly distributed. In both sites the lowest number of feeding buzzes was recorded in dense forest. In both study areas social calls were recorded, but many more for P. pygmaeus than for P. pipistrellus, especially in birch woodland. Soprano pipistrelle is a specialist species, focused mostly on riparian habitat, whereas common pipistrelle shows more generalistic behaviour. High number of social calls recorded near the waterbodies could suggest, that such habitat partitioning could be caused also by competitive behaviour.

Metaheuristic profiling to assess performance of hybrid evolutionary optimization algorithms applied to complex wellbore trajectories

Metaheuristic profiling is proposed as an effective technique with which to evaluate the relative contributions of the metaheuristic components of hybrid evolutionary optimization algorithms in progressing searches of feasible solution spaces to locate global optimum values of their objective functions. Although many useful evolutionary algorithms have been successfully proposed and tested to solve a wide range of complex mathematical optimization problems, when applied to real-world optimization tasks their performance can often be improved by hybridization with other metaheuristics. A case is made here that in developing optimization algorithms for specific practical applications it is better to treat the available evolutionary algorithms as part of a “toolbox” of metaheuristic components that can be configured in various hybridized combinations. The technique of metaheuristic profiling is evaluated as means of identifying the relative contributions of individual metaheuristic components in contributing to the discovery of optimum solutions over multiple iterations of hybrid algorithms. The metaheuristic profiling technique of a toolbox of metaheuristic components is evaluated in terms of applying seven hybrid evolutionary algorithms to optimize a previously studied complex well-bore trajectory optimization problem. The seven hybrid evolutionary algorithms developed with multiple metaheuristics are built upon standard: genetic; particle swarm; bee colony; ant colony; harmony search, cuckoo search and bat flight algorithms. Pseudocode for each of the hybrid algorithms studied are provided in an appendix. These codes identify the metaheuristics included and the sequence in which they are applied in the hybrid algorithms. All seven hybrid algorithms are coded in VBA based in Microsoft Excel with the assistance of the metaheuristic profiling technique, to provide reliably reproducible solutions to well-bore trajectory design optimization. Analysis of metaheuristic performance also confirms the benefits of fat-tailed distributions, sampled chaotically, in a novel way, to drive certain metaheuristics.

Dynamic Echo Information Guides Flight in the Big Brown Bat.

Animals rely on sensory feedback from their environment to guide locomotion. For instance, visually guided animals use patterns of optic flow to control their velocity and to estimate their distance to objects (e.g., Srinivasan et al., 1991, 1996). In this study, we investigated how acoustic information guides locomotion of animals that use hearing as a primary sensory modality to orient and navigate in the dark, where visual information is unavailable. We studied flight and echolocation behaviors of big brown bats as they flew under infrared illumination through a corridor with walls constructed from a series of individual vertical wooden poles. The spacing between poles on opposite walls of the corridor was experimentally manipulated to create dense/sparse and balanced/imbalanced spatial structure. The bats’ flight trajectories and echolocation signals were recorded with high-speed infrared motion-capture cameras and ultrasound microphones, respectively. As bats flew through the corridor, successive biosonar emissions returned cascades of echoes from the walls of the corridor. The bats flew through the center of the corridor when the pole spacing on opposite walls was balanced and closer to the side with wider pole spacing when opposite walls had an imbalanced density. Moreover, bats produced shorter duration echolocation calls when they flew through corridors with smaller spacing between poles, suggesting that clutter density influences features of the bat’s sonar signals. Flight speed and echolocation call rate did not, however, vary with dense and sparse spacing between the poles forming the corridor walls. Overall, these data demonstrate that bats adapt their flight and echolocation behavior dynamically when flying through acoustically complex environments.

Hybrid bat flight optimization algorithm applied to complex wellbore trajectories highlights the relative contributions of metaheuristic components

A hybrid bat-flight optimization (BFO) algorithm is described and developed in comparison with the original bat-inspired algorithm (Yang, 2010). The changes made remove the need to evaluate and store velocities from previous iterations to calculate new solutions, thereby reducing the computational requirements without negatively impacting the performance of the algorithm as an efficient optimizer. The hybrid BFO consists of six metaheuristic components that complement each other in their contributions to global and local search of solution spaces. The hybrid BFO algorithm is applied to a well-reported complex wellbore trajectory optimization problem previously used to evaluate the performance of evolutionary optimization algorithms. The hybrid BFO is shown to work effectively and efficiently in finding the optimum solution space, requiring significantly less iterations to do so than a hybrid genetic algorithm applied to the same problem, both developed in VBA code.The performance of the hybrid BFO algorithm is further evaluated by a novel technique of metaheuristic profiling introduced in this work. By recording the origin of each solution generated in each iteration of the algorithm, in terms of which metaheuristic component is responsible for producing it, a profile of the origin of the ten highest-ranking solutions in each iteration is constructed. This profile reveals that the metaheuristic components driven by the frequency, loudness and pulse rate (i.e., the bat-echolocation-inspired metrics used to drive the algorithm) contribute to the solutions derived in complementary, but varying ways as the iterations of the algorithm progress. Metaheuristic profiling is considered to be a promising technique for design, performance comparison, improvement and customization of evolutionary algorithms.

Flapping wing aerodynamics: from insects to vertebrates.

More than a million insects and approximately 11,000 vertebrates utilize flapping wings to fly. However, flapping flight has only been studied in a few of these species, so many challenges remain in understanding this form of locomotion. Five key aerodynamic mechanisms have been identified for insect flight. Among these is the leading edge vortex, which is a convergent solution to avoid stall for insects, bats and birds. The roles of the other mechanisms - added mass, clap and fling, rotational circulation and wing-wake interactions - have not yet been thoroughly studied in the context of vertebrate flight. Further challenges to understanding bat and bird flight are posed by the complex, dynamic wing morphologies of these species and the more turbulent airflow generated by their wings compared with that observed during insect flight. Nevertheless, three dimensionless numbers that combine key flow, morphological and kinematic parameters - the Reynolds number, Rossby number and advance ratio - govern flapping wing aerodynamics for both insects and vertebrates. These numbers can thus be used to organize an integrative framework for studying and comparing animal flapping flight. Here, we provide a roadmap for developing such a framework, highlighting the aerodynamic mechanisms that remain to be quantified and compared across species. Ultimately, incorporating complex flight maneuvers, environmental effects and developmental stages into this framework will also be essential to advancing our understanding of the biomechanics, movement ecology and evolution of animal flight.