Software techniques for two- and three-dimensional kinematic measurements of biological and biomimetic systems

Uncalibrated Single-Camera View Video Tracking of Head Impact Speeds Using Model-Based Image Matching

PURPOSE

This study evaluates the accuracy of a model-based image matching (MBIM) approach with model calibration for tracking head impact speeds in uncalibrated spaces from single-camera views.

METHODS

Two validation datasets were used. The first included 36 videos of guided NOCSAE headform drops at varying camera positions (heights, distances, camera angles) where a speed gate measured vertical impact speed. The second dataset had eight videos of participants performing ladder falls with marked helmets, captured using a 12-camera motion capture system to track head impact speeds. Each video was tracked frame-by-frame, matching a 3D NOCSAE headform model to the head using MBIM software. Accuracy was assessed by comparing captured to MBIM-tracked speeds by the mean difference and Root Mean Square Error (RMSE). A linear model assessed the influence of camera position.

RESULTS

For ideal camera views (90 degrees, height 1 or 1.4 m), MBIM-tracked vertical speeds were 0.04 ± 0.15 m/s faster than the true speed (RMSE 0.15 m/s; 2.3 ± 6.2% error). Across all 36 NOCSAE videos, MBIM-tracked vertical speeds were 0.03 ± 0.19 m/s faster (RMSE 0.19 m/s; 1.8 ± 6.9 % error). In participant videos, MBIM-tracked resultant speeds were 0.01 ± 0.33 m/s slower (RMES 0.31; 0.7 ± 9.5% error) compared to motion capture.

CONCLUSION

MBIM with model calibration can analyze head impact kinematics from single-camera footage without environment calibration, achieving reasonable accuracy compared to other systems. Analyzing head impact kinematics from uncalibrated single-camera footage presents significant opportunities for assessing previously untraceable videos.

Closing the air gap: the use of drones for studying wildlife ecophysiology

Techniques for non-invasive sampling of ecophysiological data in wild animals have been developed in response to challenges associated with studying captive animals or using invasive methods. Of these, drones, also known as Unoccupied Aerial Vehicles (UAVs), and their associated sensors, have emerged as a promising tool in the ecophysiology toolkit. In this review, we synthesise research in a scoping review on the use of drones for studying wildlife ecophysiology using the PRISMA-SCr checklist and identify where efforts have been focused and where knowledge gaps remain. We use these results to explore current best practices and challenges and provide recommendations for future use. In 136 studies published since 2010, drones aided studies on wild animal body condition and morphometrics, kinematics and biomechanics, bioenergetics, and wildlife health (e.g. microbiomes, endocrinology, and disease) in both aquatic and terrestrial environments. Focal taxa are biased towards marine mammals, particularly cetaceans. While conducted globally, research is primarily led by institutions based in North America, Oceania, and Europe. The use of drones to obtain body condition and morphometric data through standard colour sensors and single camera photogrammetry predominates. Techniques such as video tracking and thermal imaging have also allowed insights into other aspects of wildlife ecophysiology, particularly when combined with external sampling techniques such as biologgers. While most studies have used commercially available multirotor platforms and standard colour sensors, the modification of drones to collect samples, and integration with external sampling techniques, have allowed multidisciplinary studies to integrate a suite of remote sensing methods more fully. We outline how technological advances for drones will play a key role in the delivery of both novel and improved wildlife ecophysiological data. We recommend that researchers prepare for the influx of drone-assisted advancements in wildlife ecophysiology through multidisciplinary and cross-institutional collaborations. We describe best practices to diversify across species and environments and use current data sources and technologies for more comprehensive results.

Anatomical distribution and flight control function of wing sensory hairs in Seba's short-tailed bat

Bats use sensory systems such as echolocation and vision to track prey, avoid obstacles, and inform their trajectories. In addition, though less studied, bats also have extensive networks of sensory hairs across their wings. Preliminary evidence has shown that these hairs are involved in flow sensing and relay sensory information during flight. However, little is known about the functional role of sensory hairs in flight control or potential intraspecific variation in hair distribution. Through a morphological study of specimens of Seba's short-tailed bat (Carollia perspicillata), we find relatively low intraspecific variability in sensory hair distribution and consistent regional density patterns. We compare flight kinematics from the same species in wind tunnel experiments before and after removal of sensory hairs from the ventral wings. Depilation of sensory hairs resulted in changes to kinematic variables at the whole- and within-wingbeat levels, such as wingbeat frequency, chordwise wing folding, and wing extension. Taken together, these findings indicate that sensory hairs relay sensory information and function to alter fine-scale wing shape and positioning, thereby impacting flight kinematics and dynamics.

Functional Divergence of Scorpion Pedipalps: Musculoskeletal Specialization Toward Opposing Performance Optima

When selective pressures for different functions act simultaneously on a structure, morphological diversification can be shaped by adaptation toward distinct functional optima. Systems may evolve along a performance gradient, optimizing different aspects of function in response to ecological demands. We investigated two scorpion species representing the morphological extremes of chela (pincer) shape. Scorpion chelae exhibit remarkable morphological diversity associated with ecological roles, and their performance varies along a force-velocity continuum. To explore how structural and muscular adaptations shape performance, we developed a biomechanical model integrating synchrotron microtomography, muscle architecture, and performance data. Our findings reveal that these species exhibit distinct structural and muscular arrangements, each optimized for a different performance outcome. The short-fingered species maximize closing force through increased mechanical advantage and longer sarcomeres, enhancing muscle contraction efficiency. In contrast, the slender-chela species optimizes closing velocity through muscle orientations that favor rapid acceleration. While additional functional demands likely influence these designs, one morphology appears specialized for quickly capturing prey, while the other seems to be adapted for prey crushing. These divergent performance optima may have played a key role in shaping the trophic ecology of scorpions and influencing the evolution of their venom.

Shorter-duration escapes driven by Drosophila giant interneurons promote survival during predation

Large axon-diameter descending neurons are metabolically costly but transmit information rapidly from sensory neurons in the brain to motor neurons in the nerve cord. They have thus endured as a common feature of escape circuits in many animal species where speed is paramount. Though often considered isolated command neurons triggering fast-reaction-time, all-or-none escape responses, giant neurons are one of multiple parallel pathways enabling selection between behavioural alternatives. Such degeneracy among escape circuits makes it unclear if and how giant neurons benefit prey fitness. Here we competed Drosophila melanogaster flies with genetically silenced giant fibres (GFs) against flies with functional GFs in an arena with wild-caught damselfly predators and found that GF silencing decreases prey survival. Kinematic analysis of damselfly attack trajectories shows that decreased prey survival results from predator capture of GF-silenced flies during some attack speeds and approach distances that would normally elicit successful escapes. In previous studies with a virtual looming stimulus, we proposed a model in which GFs enforce the selection of a short-duration take-off sequence as opposed to reducing reaction time. Our findings here demonstrate that, during real predation scenarios, the GFs indeed promote prey survival by influencing action selection as a means to increase escape probability.

Underwater paddling kinematics and hydrodynamics in a surface swimming duck versus a diving duck

Some duck species mostly swim on the water surface while others frequently dive underwater. We compared the paddling kinematics of mandarin ducks (Axis galericulata) that feed on the surface and diving ferruginous pochards (Aythya nyroca) that feed underwater. Both species were trained to perform the same horizontal, submerged swimming at 1 m depth in a controlled set-up. Mandarins used alternate foot paddling exclusively, while pochards varied their gait between alternate foot paddling and simultaneous paddling with both feet. Unlike mandarins, pochards swam with their body tilted at an angle that was negatively correlated with the swimming speed and limited their foot motion to a smaller arc. Hydrodynamic modeling revealed that lift generated by the webbed foot provided thrust to propel both duck species forward. However, mandarins' feet generated lift-based upthrust that interfered with the need to counter their buoyancy, while pochards directed the foot lift to provide vertical downthrust against their buoyancy. The relatively subtle differences in foot motion between the two species result in a substantial hydrodynamic effect that may hint at the kinematic changes required when transitioning from surface to submerged swimming in the evolution of foot-propelled diving waterfowl.

Call production and wingbeat coupling is flexible and species-specific in echolocating bats

Echolocation and flight are two key behavioral innovations that contribute to the evolutionary success and diversification of bats, which are classified phylogenetically into two suborders: Yinpterochiroptera and Yangochiroptera. Considerable research has identified a coupling between call production and wingbeat in flying bats, although only a few have quantified the relationship and all were restricted to bats from the suborder Yangochiroptera. Here, we quantitatively compared the coupling between call production and wingbeat in two representative species of bats, Hipposideros pratti of the suborder Yinpterochiroptera and Myotis pilosus of the suborder Yangochiroptera, under identical experimental settings. We found that (1) both species exhibited the temporal coupling of call production and wingbeat; (2) the degree of coupling is species-specific, with M. pilosus showing a tighter coupling between call timing and wingbeat cycle than H. pratti; (3) the coupling is a plastic trait, as evidenced by the effect of environmental clutter in H. pratti; and (4) there is no evidence that the coupling of call production and wingbeat limits the source level control in either species. We suggest that the coupling between call production and wingbeat is flexible and species-specific, which may not compromise precise echolocation control in bats.

Reversible kink instability drives ultrafast jumping in nematodes and soft robots

Entomopathogenic nematodes (EPNs) exhibit a bending-elastic instability, or kink, before becoming airborne, a feature previously hypothesized but not substantiated to enhance jumping performance. Here, we provide the evidence that this kink is crucial for improving launch performance. We demonstrate that EPNs actively modulate their aspect ratio, forming a liquid-latched α-shaped loop over a slow timescale [Formula: see text] (1 second), and then rapidly open it [Formula: see text] (10 microseconds), achieving heights of 20 body lengths and generating power of ∼104 watts per kilogram. Using a bioinspired physical model [termed the soft jumping model (SoftJM)], we explored the mechanisms and implications of this kink. EPNs control their takeoff direction by adjusting their head position and center of mass, a mechanism verified through phase maps of jump directions in numerical simulations and SoftJM experiments. Our findings reveal that the reversible kink instability at the point of highest curvature on the ventral side enhances energy storage using the nematode's limited muscular force. We investigated the effect of the aspect ratio on kink instability and jumping performance using SoftJM and quantified EPN cuticle stiffness with atomic force microscopy measurements, comparing these findings with those of Caenorhabditis elegans. This investigation led to a stiffness-modified SoftJM design with a carbon fiber backbone, achieving jumps of ∼25 body lengths. Our study reveals how harnessing kink instabilities, a typical failure mode, enables bidirectional jumping in soft robots on complex substrates like sand, offering an approach for designing limbless robots for controlled jumping, locomotion, and even planetary exploration.

An inverse problems approach to micro-PIV for measuring flow around freely flying tiny insects

Brightfield micro-particle image velocimetry (micro-PIV) has traditionally been limited to aqueous media and by a poor signal to noise ratio. Here, we introduce a brightfield micro-PIV system suitable for measuring the 2D flows generated by freely flying sub-millimeter insects while simultaneously measuring the 3D wing and body kinematics. Our methodology couples a novel aerosolization system and an inverse problems approach to image preprocessing to alleviate these limitations. Using optimization, the inverse problems approach obtains each particle's position relative to the focal plane and generates a synthetic image comprising the in-focus and nearly in-focus particles and excluding noise from out-of-focus particles. We find that a 0.85 mm tobacco whitefly (Bemisia tabaci) utilizes a deep U-shaped wingtip trajectory to generate a 0.5 m s-1 downward jet as the wings clap together. Our technique can validate numerical simulations of tiny insect flight and measure the aerodynamics of various insect species exhibiting high morphological diversity.

Landing on a swinging perch: peach-faced lovebirds prefer extremes

Birds frequently must land (safely) on moving branches, and seemingly accomplish this with acrobatic precision. To examine how birds target and land on moving supports, we investigated how lovebirds approach and land on a swinging perch, driven at three sinusoidal frequencies. Flight kinematics were recorded, together with landing forces and pitch torque via a perch-mounted sensor. In support of our hypothesis for stable landings, lovebirds timed half their landings (51.3%) when the perch was approaching either extreme of motion near zero velocity, exhibiting a robust bimodal strategy for landing-phase timing. Horizontal landing forces exceeded vertical forces across all landing conditions, reflecting the shallow flight trajectory (-13.2 deg relative to horizontal) lovebirds adopted to decelerate and land. A uniform body pitch angle (81.9±0.46 deg mean±s.e.m.) characterized landing across all conditions, with lovebirds using the horizontal perch reaction force to assist in braking when landing. Body pitch after landing was not well correlated and was generally opposite to the initial direction and magnitude of landing pitch torque. Flexion of the bird's hindlimb joints at landing reduced landing torque by aligning the bird's center of mass trajectory more closely to the perch. Landing pitch torque and body pitch rotation increased uniformly in response to increased perch swing frequency. In contrast to landing forces, pitch torque varied irregularly across landing conditions. Our results indicate that lovebirds regulate their approach trajectory and velocity to time the phase of landing to a moving perch, providing insight for designing biologically inspired unmanned aerial vehicles capable of landing on moving targets.

Compensatory sensory mechanisms in naïve blind cavefish navigating novel environments after lateral line ablation

Fishes navigating complex aquatic environments rely on various sensory systems, primarily the lateral line system and vision, to guide their movements. One interesting example is the Mexican blind cavefish (Astyanax mexicanus). This fish relies on the lateral line system as it navigates through the environment without the aid of sight. It is unclear, however, how they might navigate through a novel environment when the lateral line is not functional. In this study, we used high-speed videography to quantify whether naïve blind cavefish alter locomotor behavior, navigation patterns, and the use of body and fins to explore a novel environment with obstacles when the lateral line is ablated. Blind cavefish with an intact lateral line demonstrated deliberate slower exploratory movements and navigated around obstacles with fewer touching events. Conversely, fish with ablated lateral line exhibited increased speed to potentially improve flow sensing. Fish with an ablated lateral line also touched obstacles more often, suggesting a reliance on fin and snout mechanoreception for navigation. These results show the blind cavefish have compensatory sensory mechanisms to navigate novel environments when their major sensory system is not functioning.

Adhesion and injury cues enhance blackworm capture by freshwater planaria

In aquatic ecosystems, freshwater planarians ( Dugesia spp .) function as predators, employing specialized adaptations for capturing live prey. This exploratory study examines the predatory interactions between the freshwater planarian Dugesia spp . and the California blackworm ( Lumbriculus variegatus ). Observations demonstrate that Dugesia is capable of capturing prey more than twice its own length. The predation process involves a dual adhesion mechanism whereby the planarian adheres simultaneously to the blackworm and the substrate, effectively immobilizing its prey. Despite the rapid escape response of blackworms, characterized by a reversing spiral swimming gait, planarian adhesion frequently prevents successful escape, although notably larger blackworms exhibit increased escape success. Subsequently, Dugesia employs an eversible pharynx to initiate ingestion, consuming the internal tissues of the blackworm through suction. Injury in blackworms emerged as a significant predictor of predation events, suggesting the potential involvement of chemical cues in prey detection, although this warrants further investigation. This study provides insights into the biomechanics and behaviors of predation involving two interacting muscular hydrostats, highlighting the critical adaptations that enable planarians to subdue and consume relatively large, mobile prey.

Kinematics and aerodynamics of in-flight drinking in bats

Bats, the only mammals with powered flight, provide inspiration to engineer highly manoeuvrable flapping wing aerial vehicles due to their ability in performing several complex manoeuvres. While straight flight manoeuvres have been extensively studied, drinking flight manoeuvres have not. We have studied two insectivorous bat species in terms of wing kinematics and aerodynamics during drinking flight: Hipposideros pratti and Rhinolophus ferrumequinum. During drinking, both bat species decrease their flapping amplitude and simultaneously increase their flapping frequency. The flapping angle during drinking flight manoeuvre is higher throughout the wingbeat compared with straight flight manoeuvre, while the sweep angle variation is reduced. Furthermore, the wing attains the most folded state earlier in the wingbeat during in-flight drinking. In addition, the angle of attack on the handwing at the end of downstroke is higher by almost 30[Formula: see text]-40[Formula: see text] in drinking flight indicating an active control to manipulate the aerodynamic forces as per the requirements of the manoeuvre. Finally, our force analysis reveals that the lift coefficient for drinking flight is more than twice that for straight flight. We discuss the potential role of ground effect in this lift enhancement.

Interleg coordination in free-walking bug Erthesina fullo (Hemiptera: Pentatomidae)

Insects can adapt their walking patterns to complex and varied environments and retain the ability to walk even after significant changes in their physical attributes, such as amputation. Although the interleg coordination of intact insects has been widely described in previous studies, the adaptive walking patterns in free-walking insects with amputation of 1 or more legs are still unclear. The pentatomid bug Erthesina fullo exhibits a tripod gait, when walking freely on horizontal substrates, like many other insects. In this study, amputations were performed on this species to investigate changes in interleg coordination. The walking parameters were analyzed, such as the locations of touchdown and liftoff, cycle period, walking speed, and head displacement of intact and amputated insects. The results show that E. fullo displays adaptive interleg coordination in response to amputations. With 1 amputated leg, bugs changed to a 3-unit gait, whereas with 2 amputated legs they employed a wave gait. These data are helpful in exploring the motion mode control in walking insects and provide the theoretical basis for the gait control strategy of robots, when leg failure occurs.

Insect wing flexibility improves the aerodynamic performance of small revolving wings

Insect wings are flexible, elastically deforming under loads experienced during flapping. The adaptive value of this flexibility was tested using a revolving wing set-up. We show that the wing flexibility of the beetle Batocera rufomaculata suppresses the reduction in lift coefficient that is expected to occur with a reduction of wing size compared to rigid propeller blades. Moreover, the scaling of wing flexibility with size is intra-specifically tuned through changes in wing-vein cross-section, resulting in smaller wings achieving proportionally larger chordwise deformations compared to larger wings, when loaded with aerodynamic forces. These elastic deformations control the separation of flow from the wing as a function of angle-of-attack, as evidenced by the turbulence activity in the flow field directly beneath the revolving wings. The study underlines the contribution of flexibility to control the flow over insect wings through passive wing deformations without the need for input or feedback from the nervous system.

Daily activity rhythms, sleep, and pregnancy are fundamentally related in the Pacific beetle mimic cockroach, Diploptera punctata

Sleep and pregnancy are contentious bedfellows; sleep disorders and disturbances are associated with adverse pregnancy outcomes, although much is still unknown about this relationship. Sleep and pregnancy have been studied in many models, but most focus heavily on mammals. However, pregnancy is ubiquitous across the animal kingdom - a hallmark of convergent evolution; similarly sleep is a shared feature across diverse species. Here, we present an ideal model in which to study the dynamics between sleep and pregnancy in invertebrates. The Pacific beetle mimic cockroach, Diploptera punctata, is a viviparous cockroach species that uses milk proteins to nourish its young with a broodsac over a three month pregnancy. However, little is known about the relationship between this unique reproductive biology and daily rhythms of activity and sleep. We established that D. punctata displayed a peak in activity shortly following sunset, with males significantly more active than females. When scavenging behavior was examined, males and non-pregnant females emerged more often and traveled further from a shelter compared to pregnant females, suggesting reduced risk-taking behavior in late pregnancy. Chronic disturbance of sleep during pregnancy negatively impacted embryo development by increasing gestational duration and decreasing the transcription of milk proteins. These findings indicate that sleep is key to embryo development and that pregnancy has a significant impact on the daily rhythms of activity in Diploptera punctata. More broadly, we present a tractable invertebrate model for understanding the relationship between sleep and pregnancy, which will aid in the exploration of the poorly understood interface between these two ubiquitous and highly conserved traits.

Plant-pollinator trait matching affects pollen transfer but not feeding efficiency of Australian honeyeaters (Aves, Meliphagidae)

Animal pollination is common among flowering plants. Increased morphological matching between floral and pollinator traits is thought to increase pollen transfer and feeding efficiency, but we lack studies that empirically demonstrate this. Working with Australian honeyeaters, we find that there is positive correlation between bill-corolla matching and pollen deposition at flowers, but no correlation with how efficiently birds can extract floral nectar. The species with the lowest bill-corolla matching deposited the fewest pollen grains but had the highest feeding efficiency, showing that bill-corolla matching expectations were met on the plant side of this interaction but not on the pollinator side. Finally, we find different interspecific patterns of pollen deposition at the scales of a single flower visit versus the landscape, due to differences in patterns of plant visitation. This work illustrates the need for more studies that directly correlate trait matching to fitness proxies of plants and avian pollinators.

Kinetics of Symmetrical Versus Asymmetrical In-Phase Gaits During Arboreal Locomotion

Quadrupedal animals traveling on arboreal supports change aspects of locomotion to avoid slipping and falls. This study compares locomotor biomechanics in two small mammals: first, the gray short-tailed opossum (Monodelphis domestica) predominantly trots, which is a symmetrical gait. The second species, the Siberian chipmunk (Tamias sibiricus), primarily bounds or half-bounds. Trotting and bounding differ fundamentally in three aspects: location and timing of hand and foot placement; in the way that the trunk bends (trotting, mediolateral bending; bounding, flexion, and extension); and in the dynamics of the center of mass. Both species ran on a flat track and a 2 cm diameter cylindrical track, instrumented with a force plate or pole. For bounding chipmunks, the force pole was modified to measure force only on the right side. We measured speed, duty factor, and force, and calculated vertical, braking, propulsive, and net mediolateral impulses. Vertical and fore-aft impulses were different between trotting opossums and bounding chipmunks, but between trackway types, these impulses were similar within each species. The modifications used by each species to travel on arboreal supports were similar, except in one important respect. Net mediolateral impulse in opossums changed from laterally directed on the flat trackway to medial on the arboreal. But in chipmunks, these impulses on the flat track were medially-directed, and on the arboreal track, the amount of variability was substantially greater. We conclude that chipmunks-and perhaps any bounding animal-are less consistent from stride to stride in their locomotion. This inconsistency requires constant medial and lateral impulses to correct their trajectory when traveling on arboreal surfaces.

Maple samaras recover autorotation following raindrop collisions

Samaras are known for their elegant and robust autorotation, a resilience that persists in the adverse conditions imposed by high-speed raindrops. Like flying insects, samaras descending from tall trees are likely to be struck by raindrops in an intense storm. In this study, we detail the collision dynamics for impact regions across the samara body and the drop-shedding mechanisms that samaras exhibit to return to autorotation. Impacts across the samara body can pitch the samara up to 60 degrees and, in some cases, induce spanwise roll. Raindrops may shatter or remain intact upon impact, pushing the undamaged samara downward before autorotation is recovered. Drops that strike near the wingtip elicit the greatest recovery distance, while impacts onto the nutlet mass are the least disruptive to the samara and most likely to cause the drop to induce fragmentation. Faster drops allow for quicker drop shedding and a subsequent rapid return to autorotation in less than 50 ms. Our results indicate that samaras are robust to raindrop impacts and consistently recover autorotation, resulting in a minor reduction in dispersal distance. To recover, the entire drop is shed from the spinning samara over a time closely tied to the shedding mode and ensuing drop rejection forces.

Upstroke wing clapping in bats and bat-inspired robots offers efficient lift generation

Wing articulation is critical for the efficient flight of bird- and bat-sized animals. Inspired by the flight of Cynopterus brachyotis, the lesser short-nosed fruit bat, we built a two-degree-of-freedom flapping wing platform with variable wing folding capability. In the late upstroke, the wings 'clap' and produce an air jet that significantly increases lift production, with a positive peak matched to that produced in the downstroke. Though ventral clapping has been observed in avian flight, the potential aerodynamic benefit of this behaviour is yet to be rigorously assessed. We used multiple approaches-quasi-steady modelling, direct force/power measurement and particle image velocimetry (PIV) experiments in a wind tunnel-to understand critical aspects of lift and power variation in relation to wing folding magnitude over Strouhal numbers at St = 0.2-0.4. While lift increases monotonically with folding amplitude in that range, power economy (ratio of lift/power) is more nuanced. At St = 0.2-0.3, it increases with wing folding amplitude monotonically. At St = 0.3-0.4, it features two maxima-one at medium folding amplitude (approx. 30°) and the other at maximum folding. These findings illuminate two strategies available to flapping wing animals and robots-symmetry-breaking lift augmentation and appendage-based jet propulsion.

Sexual dimorphism in jump kinematics and choreography in peacock spiders

Jumping requires a rapid release of energy to propel an animal. Terrestrial animals achieve this by relying on the power generated by muscles, or by storing and rapidly releasing elastic energy. Jumping spiders are distinctive in using a combination of hydraulic pressure and muscular action to propel their jumps. Though males and females of jumping spiders vary in body mass, sex-specific differences in jumping have never been studied. Here, we investigated the sexual dimorphism in the jump choreography and kinematics of spiders. We used high-speed videography (5000 frames s-1) to record locomotory jumps of males and females of the Australian splendid peacock spider, Maratus splendens. Using micro-computed tomography (µCT) imaging, we identified the animals' centre of mass and tracked its displacement throughout the jump. Our study revealed that peacock spiders exhibited the fastest acceleration among all known jumping spiders. Males demonstrated significantly shorter take-off times and steeper jump take-off angles compared with females. Our findings suggest that the third pair of legs acts as the propulsive leg in both male and female spiders. As males of M. splendens use leg III as part of the courtship display, we discuss the extreme selection pressure on this leg that drives two significant functions.

Collective swimming pattern and synchronization of fish pairs (Gobiocypris rarus) in response to flow with different velocities

Collective behaviors in moving fish originate from social interactions, which are thought to be driven by beneficial factors, such as predator avoidance and reduced energy expenditure. Despite numerical simulations and physical experiments aiming at the hydrodynamic mechanisms and interaction rules, how shoaling is influenced by flow velocity and group size is still only partially understood. In this study, spatial distributions, kinematics, and synchronization states between pairs (smallest subsystem of a shoal) of Gobiocypris rarus were investigated in a recirculating swim tunnel with increasing flow velocities from 0.1 to 0.5 m/s (Ucrit = 0.6 m/s). Tests of single fish were also conducted as the control group. The results of spatial distributions showed that fish pairs preferred to swim in the side-by-side configuration under high flows, while under low flows the neighboring fish's positions were more uniformly distributed around the focal fish in the transverse direction. Kinematic analysis revealed that fish pairs adopted similar tail beats (i.e., frequency and Strouhal number) as single fish in low flows, while in high flows both the frequency and Strouhal number of fish pairs were slightly lower. Moreover, the synchronization rates of fish pairs were found to increase with flow velocities, suggesting that synchronized swimming may be beneficial, especially in high flows.

Distinct morphological drivers of jumping and maneuvering performance in gerbils

Theoretically, animals with longer hindlimbs are better jumpers, while those with shorter hindlimbs are better maneuverers. Yet, experimental evidence of this relationship in mammals is lacking. We compared jump force and maneuverability in a lab population of Mongolian gerbils (Meriones unguiculatus). We hypothesized that gerbils with long legs (ankle to knee) and thighs (knee to hip) would produce the greatest jump forces, while gerbils with short legs and thighs would be able to run most rapidly around turns. Consistent with these hypotheses, gerbils with longer legs produced greater jump forces after accounting for sex and body mass: a 1 mm greater leg length provided 1 body weight unit greater jump force on average. Furthermore, gerbils with shorter thighs were more maneuverable: a 1 mm greater thigh length reduced turn speed by 5%. Rather than a trade-off, however, there was no significant correlation between jump force and turn speed. There was also no correlation between jump force and total hindlimb length, and a weak positive correlation between corner-turning speed and total hindlimb length. These experiments revealed how distinct hindlimb segments contributed in different ways to each performance measure: legs to jumping and thighs to maneuvering. Understanding how variations in limb morphology contribute to overall gerbil locomotor performance may have important impacts on fitness in natural habitats.

Experimental Biomechanics of Neonatal Brachial Plexus Avulsion Injuries Using a Piglet Model

BACKGROUND

A brachial plexus avulsion occurs when the nerve root separates from the spinal cord during birthing trauma, such as shoulder dystocia or a difficult vaginal delivery. A complete paralysis of the affected levels occurs post-brachial plexus avulsion. Despite being reported in 10-20% of brachial plexus birthing injuries, it remains poorly diagnosed during the acute stages of injury, leading to poor intervention approaches. The poor diagnosis of brachial plexus avulsion injury can be attributed to the currently unavailable biomechanics of brachial plexus avulsion. While the biomechanical properties of neonatal brachial plexus are available, the forces required to avulse a neonatal brachial plexus remain unknown.

METHODS

This study aims to provide detailed biomechanics of the required forces and corresponding strains for neonatal brachial plexus avulsion. Biomechanical tensile testing was performed on an isolated, clinically relevant piglet spinal cord and brachial plexus complex, and the required avulsion forces and strains were measured.

RESULTS

The reported failure forces and corresponding strains were 3.9 ± 1.6 N at a 27.9 ± 6.5% strain, respectively.

CONCLUSION

The obtained data are required to understand the avulsion injury biomechanics and provide the necessary experimental data for computational model development that serves as an ideal surrogate for understanding complicated birthing injuries in newborns.

Tail Tales: How Ecological Context Mediates Signal Effectiveness in a Lizard

Animal signals are complex, comprising multiple components influenced by ecological factors and viewing perspectives that together impact their overall effectiveness. Our study explores how these factors affect the efficacy of multi-component signals in the Qinghai toad-headed agama, Phrynocephalus vlangalii. Using 3D animations, we simulated natural environments to evaluate how tail coiling and tail lashing-two primary tail displays-vary in effectiveness from both conspecific and predator perspectives under different ecological conditions. Baseline comparisons showed no significant difference in effectiveness between tail coiling and tail lashing without environmental constraints, though side-on tail coiling was consistently more effective than front-on displays. When noise proximity was introduced, tail lashing was more effective when the noise source was nearby, but this advantage diminished with distance. Conversely, tail coiling maintained consistent effectiveness across varying noise proximities, especially from a side-on view. In complex habitats with diverse plant species and varying wind conditions, tail lashing proved more effective, particularly from a front-on perspective, while tail coiling excelled from a side-on view. From a predator's perspective, tail lashing was slightly more effective under low wind conditions at close distances, though its visibility decreased with higher wind speeds. These findings highlight the adaptive significance of multi-component signals and the critical role of signal orientation in enhancing communication. This research offers insights into the evolutionary pressures shaping animal communication strategies.

Tree Frogs Alter Their Behavioral Strategies While Landing On Vertical Perches

As an arboreal animal, tree frogs face diverse challenges when landing on perches, including variations in substrate shape, diameter, flexibility, and angular distribution, with potentially significant consequences for failed landings. Research on tree frog landing behavior on perches, especially concerning landing on vertical substrates, remains limited. This study investigated the landing strategies (forelimb, abdomen, and hindlimb) of tree frogs on vertical perches, considering perch diameter. Although all three strategies were observed across perches of different diameters, their frequencies differed. Forelimb landing was most common across all perch diameters, with its frequency increasing with perch diameter, while abdomen and hindlimb landing strategies were more prevalent on smaller diameter perches. During the process from take-off to landing, the body axis underwent some deviation owing to the asymmetric movement of the left and right limbs; however, these deviations did not significantly differ among landing strategies. Additionally, different landing strategies led to variations in the landing forces, with abdominal landings generating significantly higher impact forces than the other two strategies. These findings provide insights into the biomechanics and biological adaptations of tree frogs when landing on challenging substrates, such as leaves or branches.

Hummingbirds use compensatory eye movements to stabilize both rotational and translational visual motion

To maintain stable vision, behaving animals make compensatory eye movements in response to image slip, a reflex known as the optokinetic response (OKR). Although OKR has been studied in several avian species, eye movements during flight are expected to be minimal. This is because vertebrates with laterally placed eyes typically show weak OKR to nasal-to-temporal motion (NT), which simulates typical forward locomotion, compared with temporal-to-nasal motion (TN), which simulates atypical backward locomotion. This OKR asymmetry is also reflected in the pretectum, wherein neurons sensitive to global visual motion also exhibit a TN bias. Hummingbirds, however, stabilize visual motion in all directions through whole-body movements and are unique among vertebrates in that they lack a pretectal bias. We therefore predicted that OKR in hummingbirds would be symmetrical. We measured OKR in restrained hummingbirds by presenting gratings drifting across a range of speeds. OKR in hummingbirds was asymmetrical, although the direction of asymmetry varied with stimulus speed. Hummingbirds moved their eyes largely independently of one another. Consistent with weak eye-to-eye coupling, hummingbirds also exhibited disjunctive OKR to visual motion simulating forward and backward translation. This unexpected oculomotor behaviour, previously unexplored in birds, suggests a potential role for compensatory eye movements during flight.

Frictional adhesion of geckos predicts maximum running performance in nature

Despite the myriad studies examining the diversity and mechanisms of gecko adhesion in the lab, we have a poor understanding of how this translates to locomotion in nature. It has long been assumed that greater adhesive strength should translate to superior performance in nature. Using 13 individuals of Bradfield's Namib day gecko (Rhoptropus bradfieldi) in Namibia, I tested the hypothesis that maximum running performance in nature (speed and acceleration) is driven by maximum frictional adhesive strength. Specifically, those individuals with greater frictional adhesion should escape with faster speed and acceleration because of increased contact with the surface from which to apply propulsive forces. I tested this prediction by quantifying laboratory adhesive performance and then releasing the geckos into the field while simultaneously recording the escape using high-speed videography. Additional measurements included how this species modulates maximum running speed (stride length and/or stride frequency) and how temperature influences field performance. I found that maximum acceleration was significantly correlated with maximum frictional adhesive strength, whereas maximum sprinting speed was only correlated with increases in stride frequency (not stride length) and temperature. Thus, different measures of performance (acceleration and speed) are limited by very different variables. Acceleration is key for rapidly escaping predation and, given their correlation, maximum frictional adhesion likely plays a key role in fitness.

Behavior and biomechanics: flapping frequency during tandem and solo flights of cliff swallows

Aerodynamic models of bird flight, assuming power minimization, predict a quadratic relationship (i.e. U-shaped curve) between flapping frequency and airspeed. This relationship is supported by experimental bird flight data from wind tunnels, but the degree to which it characterizes natural flight, and the extent to which birds might modify it to accommodate other behaviors, is less known. We hypothesized that the U-shaped relationship would vary or vanish when minimizing power is not a primary consideration. We analyzed videos of wild cliff swallows (Petrochelidon pyrrhonota) engaged in solo and tandem (i.e. following or being followed by a conspecific) flights to collect bird flapping frequencies and airspeeds. Solo birds had a U-shaped flapping frequency to speed relationship. Birds engaged in tandem flights had the opposite pattern; their flapping frequencies varied with speed as an inverse U-shaped curve and were up to 2.1 times higher than solo birds at the same speed.

Kinematics and Flow Field Analysis of Allomyrina dichotoma Flight

In recent years, bioinspired insect flight has become a prominent research area, with a particular focus on beetle-inspired aerial vehicles. Studying the unique flight mechanisms and structural characteristics of beetles has significant implications for the optimization of biomimetic flying devices. Among beetles, Allomyrina dichotoma (rhinoceros beetle) exhibits a distinct wing deployment-flight-retraction sequence, whereby the interaction between the hindwings and protective elytra contributes to lift generation and maintenance. This study investigates A. dichotoma's wing deployment, flight, and retraction behaviors through motion analysis, uncovering the critical role of the elytra in wing folding. We capture the kinematic parameters throughout the entire flight process and develop an accurate kinematic model of A. dichotoma flight. Using smoke visualization, we analyze the flow field generated during flight, revealing the formation of enhanced leading-edge vortices and attached vortices during both upstroke and downstroke phases. These findings uncover the high-lift mechanism underlying A. dichotoma's flight dynamics, offering valuable insights for optimizing beetle-inspired micro aerial vehicles.

Variations in humeral and femoral strains across body sizes and limb posture in American alligators

Bone loading is a crucial factor that constrains locomotor capacities of terrestrial tetrapods. To date, limb bone strains and stresses have been studied across various animals, with a primary emphasis on consistent bone loading in mammals of different sizes and variations in loading regimes across different clades and limb postures. However, the relationships between body size, limb posture and limb bone loading remain unclear in animals with non-parasagittally moving limbs, limiting our understanding of the evolution of limb functions in tetrapods. To address this, we investigated in vivo strains of the humerus and femur in juvenile to subadult American alligators as they walked with various limb postures. We found that principal strains on the ventromedial cortex of the femoral midshaft increased with larger sizes among the three individuals displaying similar limb postures. This indicates that larger individuals experience greater limb bone strains when maintaining similar limb postures to smaller individuals. Axial and shear strains in the humerus were generally reduced with a more erect limb posture, while trends in the femur varied among individuals. Given that larger alligators have been shown to adopt a more erect limb posture, the transition from sprawling to erect limb posture, particularly in the forelimb, might be linked to the evolution of larger body sizes in archosaurs, potentially as a means to mitigate limb bone loading. Moreover, both the humerus and femur experienced decreased shear loads compared with axial loads with a more erect limb posture, suggesting proportional changes in bone loading regimes throughout the evolution of limb posture.

Training all-mechanical neural networks for task learning through in situ backpropagation

Recent advances unveiled physical neural networks as promising machine learning platforms, offering faster and more energy-efficient information processing. Compared with extensively-studied optical neural networks, the development of mechanical neural networks remains nascent and faces significant challenges, including heavy computational demands and learning with approximate gradients. Here, we introduce the mechanical analogue of in situ backpropagation to enable highly efficient training of mechanical neural networks. We theoretically prove that the exact gradient can be obtained locally, enabling learning through the immediate vicinity, and we experimentally demonstrate this backpropagation to obtain gradient with high precision. With the gradient information, we showcase the successful training of networks in simulations for behavior learning and machine learning tasks, achieving high accuracy in experiments of regression and classification. Furthermore, we present the retrainability of networks involving task-switching and damage, demonstrating the resilience. Our findings, which integrate the theory for training mechanical neural networks and experimental and numerical validations, pave the way for mechanical machine learning hardware and autonomous self-learning material systems.

Rapid sensorimotor adaptation to auditory midbrain silencing in free-flying bats

Echolocating bats rely on rapid processing of auditory information to guide moment-to-moment decisions related to echolocation call design and flight path selection. The fidelity of sonar echoes, however, can be disrupted in natural settings due to occlusions, noise, and conspecific jamming signals. Behavioral sensorimotor adaptation to external blocks of relevant cues has been studied extensively, but little is known about adaptations that mitigate internal sensory flow interruption. How do bats modify their sensory-guided behaviors in natural tasks when central auditory processing is interrupted? Here, we induced internal sensory interruptions by reversibly inactivating excitatory neurons in the inferior colliculus (IC) using ligand-activated inhibitory designer receptors exclusively activated by designer drugs (DREADDs). Bats were trained to navigate through one of three open windows in a curtain to obtain a food reward, while their echolocation and flight behaviors were quantified with synchronized ultrasound microphone and stereo video recordings. Under control conditions, bats reliably steered through the open window, only occasionally contacting the curtain edge. Suppressing IC excitatory activity elevated hearing thresholds, disrupted overall performance in the task, increased the frequency of curtain contact, and led to striking compensatory sensorimotor adjustments. DREADDs-treated bats modified flight trajectories to maximize returning echo information and adjusted sonar call design to boost detection of obstacles. Sensorimotor adaptations appeared immediately and did not change over successive trials, suggesting that these behavioral adaptations are mediated through existing neural circuitry. Our findings highlight the remarkable rapid adaptive strategies bats employ to compensate for internal sensory interruptions to effectively navigate their environments.

Collective movement increases initial accuracy and path efficiency in talitrid amphipod orientation

Talitrid amphipods are an extensively studied system for navigation due to their robust ability to navigate back to the optimal burrowing zone after foraging and could be a model system in which to study the impacts of collective behaviour on short-distance navigation and orientation. We investigated whether talitrid amphipods (Megalorchestia pugettensis) differ in their orientation abilities when released individually versus in a group. When released individually, the amphipods took longer to start moving (p < 0.001), travelled longer paths (p = 0.003), moved faster (p = 0.016), had a different initial bearing (p = 0.003) and exhibited more spread in their initial bearing (p = 0.009) than when released in groups. There was no difference between individuals and groups in terms of their trial time nor in the direction or spread of their final orientation. This study introduces a tractable, invertebrate species in which to study the impacts of collective movement and reveals previously unexamined differences in orientation abilities for talitrid amphipods released independently versus in a group that have implications for experimental design in this system.

How do fish miss? Attack strategies of threespine stickleback capturing non-evasive prey

Most predators rely on capturing prey for survival, yet failure is common. Failure is often attributed to prey evasion, but predator miscalculation and/or inaccuracy may also drive an unsuccessful event. We addressed the latter using threespine stickleback as predators and bloodworms (non-evasive) as prey. High-speed videography of the entire attack allowed us to determine the strike tactics leading to successful or missed strikes. We analyzed movements and morphological traits from 57 individuals. Our results reveal that kinematics drive the strike outcome and that failed strikes primarily arise from incorrect timing of mouth opening, often beginning too far from the prey for suction to be effective. This likely stems from the lack of integration between locomotion and feeding systems. Our study begins to unravel the important link between behavior and success in fish feeding.

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.

Hummingbirds rapidly respond to the removal of visible light and control a sequence of rate-commanded escape manoeuvres in milliseconds

Hummingbirds routinely execute a variety of stunning aerobatic feats, which continue to challenge current notions of aerial agility and controlled stability in biological systems. Indeed, the control of these amazing manoeuvres is not well understood. Here, we examined how hummingbirds control a sequence of manoeuvres within milliseconds, and tested whether and when they use vision during this rapid process. We repeatedly elicited escape flights in calliope hummingbirds, removed visible light during each manoeuvre at various instants and quantified their flight kinematics and responses. We show that the escape manoeuvres were composed of rapidly controlled sequential modules including evasion, reorientation, nose-down dive, forward flight and nose-up to hover. The hummingbirds did not respond to the light removal during evasion and reorientation until a critical light-removal time; afterwards, they showed two categories of luminance-based responses that rapidly altered manoeuvring modules to terminate the escape. We also show that hummingbird manoeuvres were rate-commanded and required no active braking (i.e. their body angular velocities were proportional to the change of wing motion patterns, a trait that probably alleviates the computational demand on flight control). This work uncovers key traits of hummingbird agility, which can also inform and inspire designs for next-generation agile aerial systems.

Protocol to record and analyze primate leaping in three dimensions in the wild

Several studies comparing primate locomotion under lab versus field conditions have shown the importance of implementing both types of studies, as each has their advantages and disadvantages. However, three-dimensional (3D) motion capture of primates has been challenging under natural conditions. In this study, we provide a detailed protocol on how to collect 3D biomechanical data on primate leaping in their natural habitat that can be widely implemented. To record primate locomotion in the dense forest we use modified GoPro Hero Black cameras with zoom lenses that can easily be carried around and set up on tripods. We outline details on how to obtain camera calibrations at greater heights and how to process the collected data using the MATLAB camera calibration app and the motion tracking software DLTdv8a. We further developed a new MATLAB application "WildLeap3D" to generate biomechanical performance metrics from the derived x, y, z coordinates of the leaps. We provide details on how to collect data on support diameter, compliance, and orientation, and combine these with the jumps to study locomotor performance in an ecological context. We successfully reconstructed leaps of wild primates in the 3D space under natural conditions and provided data on four representative leaps. We provide exemplar data on primate velocity and acceleration during a leap and show how our protocol can be used to analyze segmental kinematics. This study will help to make motion capture of freely moving animals more accessible and help further our knowledge about animal locomotion and movement.

Desert Ant (Melophorus bagoti) Dumpers Learn from Experience to Improve Waste Disposal and Show Spatial Fidelity

The Central Australian red honey-pot ant Melophorus bagoti maintains non-cryptic ground-nesting colonies in the semi-desert habitat, performing all the activities outside the nest during the hottest periods of summer days. These ants rely on path integration and view-based cues for navigation. They manage waste by taking out unwanted food, dead nestmates, and some other wastes, typically depositing such items at distances > 5 m from the nest entrance, a process called dumping. We found that over multiple runs, dumpers headed in the same general direction, showing sector fidelity. Experienced ants dumped waste more efficiently than naive ants. Naive individuals, lacking prior exposure to the outdoor environment around the nest, exhibited much scanning and meandering during waste disposal. In contrast, experienced ants dumped waste with straighter paths and a notable absence of scanning behaviour. Furthermore, experienced dumpers deposited waste at a greater distance from the nest compared to their naive counterparts. We also investigated the navigational knowledge of naive and experienced dumpers by displacing them 2 m away from the nest. Naive dumpers were not oriented towards the nest in their initial trajectory at any of the 2 m test locations, whereas experienced dumpers were oriented towards the nest at all test locations. Naive dumpers were nest-oriented as a group, however, at the test location nearest to where they dumped their waste. These differences suggest that in red honey ants, learning supports waste disposal, with dumping being refined through experience. Dumpers gain greater spatial knowledge through repeated runs outside the nest, contributing to successful homing behaviour.

Evaluation of fabric-based pneumatic actuator enclosure and anchoring configurations in a pediatric soft robotic exosuit

Introduction

Soft robotics play an increasing role in the development of exosuits that assist, and in some cases enhance human motion. While most existing efforts have focused on the adult population, devices targeting infants are on the rise. This work investigated how different configurations pertaining to fabric-based pneumatic shoulder and elbow actuator embedding on the passive substrate of an exosuit for pediatric upper extremity motion assistance can affect key performance metrics.

Methods

The configurations varied based on actuator anchoring points onto the substrate and the type of fabric used to fabricate the enclosures housing the actuators. Shoulder adduction/abduction and elbow flexion/extension were treated separately. Two different variants (for each case) of similar but distinct actuators were considered. The employed metrics were grouped into two categories; reachable workspace, which includes joint range of motion and end-effector path length; and motion smoothness, which includes end-effector path straightness index and jerk. The former category aimed to capture first-order terms (i.e., rotations and displacements) that capture overall gross motion, while the latter category aimed to shed light on differential terms that correlate with the quality of the attained motion. Extensive experimentation was conducted for each individual considered configuration, and statistical analyses were used to establish distinctive strengths, weaknesses, and trade-offs among those configurations.

Results

The main findings from experiments confirm that the performance of the actuators can be significantly impacted by variations in the anchoring and fabric properties of the enclosures while establishing interesting trade-offs. Specifically, the most appropriate anchoring point was not necessarily the same for all actuator variants. In addition, highly stretchable fabrics not only maintained but even enhanced actuator capabilities, in comparison to the less stretchable materials which turned out to hinder actuator performance.

Conclusion

The established trade-offs can serve as guiding principles for other researchers and practitioners developing upper extremity exosuits.

Intermittent swimming and muscle power output in brook trout, Salvelinus fontinalis

Slow and sustainable intermittent swimming has recently been described in several Centrarchid fishes, such as bluegill and largemouth bass. This swimming behavior involves short periods of body-caudal fin undulation alternating with variable periods of coasting. This aerobic muscle powered swimming appears to reduce energetic costs for slow, sustainable swimming, with fish employing a "fixed-gear" or constant tailbeat frequency and modulating swimming speed by altering the length of the coasting period. We asked if this swimming behavior was found in other fish species by examining volitional swimming by brook trout in a static swimming tank. Further, we employed muscle mechanics experiments to explore how intermittent swimming affects muscle power output in comparison to steady swimming behavior. Brook trout regularly employ an intermittent swimming form when allowed to swim volitionally, and consistently showed a tailbeat frequency of ~2 Hz. Coasting duration had a significant, inverse relationship to swimming speed. Across a range of slow, sustainable swimming speeds, tailbeat frequency increased modestly with speed. The duration of periods of coasting decreased significantly with increasing speed. Workloop experiments suggest that intermittent swimming reduces fatigue, allowing fish to maintain high power output for longer compared to continuous activity. This study expands the list of species that employ intermittent swimming, suggesting this behavior is a general feature of fishes.

Inertial coupling of the hummingbird body in the flight mechanics of an escape manoeuvre

When a hovering hummingbird performs a rapid escape manoeuvre in response to a perceived threat from the front side, its body may go through simultaneous pitch, yaw and roll rotations. In this study, we examined the inertial coupling of the three-axis body rotations and its effect on the flight mechanics of the manoeuvre using analyses of high-speed videos as well as high-fidelity computational modelling of the aerodynamics and inertial forces. We found that while a bird's pitch-up was occurring, inertial coupling between yaw and roll helped slow down and terminate the pitch, thus serving as a passive control mechanism for the manoeuvre. Furthermore, an inertial coupling between pitch-up and roll can help accelerate yaw before the roll-yaw coupling. Different from the aerodynamic mechanisms that aircraft and animal flyers typically rely on for flight control, we hypothesize that inertial coupling is a built-in mechanism in the flight mechanics of hummingbirds that helps them achieve superb aerial agility.

Using Pose Estimation and 3D Rendered Models to Study Leg-Mediated Self-righting by Lanternflies

The ability to upright quickly and efficiently when overturned on the ground (terrestrial self-righting) is crucial for living organisms and robots. Previous studies have mapped the diverse behaviors used by various animals to self-right on different substrates, and proposed physical models to explain how body morphology can favor specific self-righting methods. However, to our knowledge, no studies have quantified and modeled all of an animal's limb motions during these complicated behaviors. Here, we studied terrestrial self-righting by immature invasive spotted lanternflies (Lycorma delicatula), an insect species that must frequently recover from being overturned after jumping and falling in its native habitat. These nymphs self-righted successfully in 92-100% of trials on three substrates with different friction and roughness, with no significant difference in the time or number of attempts required. They accomplished this using three stereotypic sequences of movements. To understand these motions, we combined 3D poses tracked on multi-view high-speed video with articulated 3D models created using photogrammetry and Blender rendering software. The results were used to calculate the mechanical properties (e.g., potential and kinetic energy, angular speed, stability margin, torque, force, etc.) of these insects during righting trials. We used an inverted physical pendulum model (a "template") to estimate the kinetic energy available in comparison to the increase in potential energy required to flip over. While these insects began righting using primarily quasistatic motions, they also used dynamic leg motions to achieve final tip-over. However, this template did not describe important features of the insect's center of mass trajectory and rotational dynamics, necessitating the use of an "anchor" model comprising the 3D rendered body model and six articulated two-segment legs to model the body's internal degrees of freedom and capture the role of the legs' contribution to inertial reorientation. This anchor elucidated the sequence of highly coordinated leg movements these insects used for propulsion, adhesion, and inertial reorientation during righting, and how they frequently pivot about a body contact point on the ground to flip upright. In the most frequently used method, diagonal rotation, these motions allowed nymphs to spin their bodies to upright with lower force with a greater stability margin compared to the other less frequently used methods. We provide a concise overview of necessary background on 3D orientation and rotational dynamics, and the resources required to apply these low-cost modeling methods to other problems in biomechanics.

Combining Computational Fluid Dynamics and Experimental Data to Understand Fish Schooling Behavior

Understanding the flow physics behind fish schooling poses significant challenges due to the difficulties in directly measuring hydrodynamic performance and the three-dimensional, chaotic, and complex flow structures generated by collective moving organisms. Numerous previous simulations and experiments have utilized computational, mechanical, or robotic models to represent live fish. And existing studies of live fish schools have contributed significantly to dissecting the complexities of fish schooling. But the scarcity of combined approaches that include both computational and experimental studies, ideally of the same fish schools, has limited our ability to understand the physical factors that are involved in fish collective behavior. This underscores the necessity of developing new approaches to working directly with live fish schools. An integrated method that combines experiments on live fish schools with computational fluid dynamics (CFD) simulations represents an innovative method of studying the hydrodynamics of fish schooling. CFD techniques can deliver accurate performance measurements and high-fidelity flow characteristics for comprehensive analysis. Concurrently, experimental approaches can capture the precise locomotor kinematics of fish and offer additional flow information through particle image velocimetry (PIV) measurements, potentially enhancing the accuracy and efficiency of CFD studies via advanced data assimilation techniques. The flow patterns observed in PIV experiments with fish schools and the complex hydrodynamic interactions revealed by integrated analyses highlight the complexity of fish schooling, prompting a reevaluation of the classic Weihs model of school dynamics. The synergy between CFD models and experimental data grants us comprehensive insights into the flow dynamics of fish schools, facilitating the evaluation of their functional significance and enabling comparative studies of schooling behavior. In addition, we consider the challenges in developing integrated analytical methods and suggest promising directions for future research.

Encoding spatiotemporal asymmetry in artificial cilia with a ctenophore-inspired soft-robotic platform

A remarkable variety of organisms use metachronal coordination (i.e. numerous neighboring appendages beating sequentially with a fixed phase lag) to swim or pump fluid. This coordination strategy is used by microorganisms to break symmetry at small scales where viscous effects dominate and flow is time-reversible. Some larger organisms use this swimming strategy at intermediate scales, where viscosity and inertia both play important roles. However, the role of individual propulsor kinematics-especially across hydrodynamic scales-is not well-understood, though the details of propulsor motion can be crucial for the efficient generation of flow. To investigate this behavior, we developed a new soft robotic platform using magnetoactive silicone elastomers to mimic the metachronally coordinated propulsors found in swimming organisms. Furthermore, we present a method to passively encode spatially asymmetric beating patterns in our artificial propulsors. We investigated the kinematics and hydrodynamics of three propulsor types, with varying degrees of asymmetry, using Particle Image Velocimetry and high-speed videography. We find that asymmetric beating patterns can move considerably more fluid relative to symmetric beating at the same frequency and phase lag, and that asymmetry can be passively encoded into propulsors via the interplay between elastic and magnetic torques. Our results demonstrate that nuanced differences in propulsor kinematics can substantially impact fluid pumping performance. Our soft robotic platform also provides an avenue to explore metachronal coordination at the meso-scale, which in turn can inform the design of future bioinspired pumping devices and swimming robots.

The Silverjaw Minnow, Ericymba buccata: An Extraordinary Lateral Line System and its Contribution to Prey Detection

Fishes use their mechanosensory lateral line (LL) system to detect local water flows in different behavioral contexts, including the detection of prey. The LL system is comprised of neuromast receptor organs on the skin (superficial neuromasts) and within bony canals (canal neuromasts). Most fishes have one cranial LL canal phenotype, but the silverjaw minnow (Ericymba buccata) has two: narrow canals dorsal and caudal to the eye and widened canals ventral to the eye and along the mandible. The ventrally directed widened LL canals have been hypothesized to be an adaptation for detection of their benthic prey. Multiple morphological methods were used to describe the narrow and widened canals and canal neuromasts in detail. The primary distribution of hundreds of superficial neuromasts and taste buds ventral to the eye and on the mandible (described here for the first time) suggests additional sensory investment for detecting flow and chemical stimuli emanating from benthic prey. The hypothesis that the LL system mediates prey localization was tested by measuring five parameters in behavioral trials in which the combination of sensory modalities available to fish was manipulated (four experimental treatments). Fish detected and localized prey regardless of available sensory modalities and they were able to detect prey in the dark in the absence of LL input (LL ablation with neomycin sulfate) revealing that chemoreception was sufficient to mediate benthic prey detection, localization, and consumption. However, elimination of LL input resulted in a change in the angle of approach to live (mobile) prey even when visual input was available, suggesting that mechanosensory input contributes to the successful detection and localization of prey. The results of this study demonstrate that the extraordinary LL canal system of the silverjaw minnow, in addition to the large number of superficial neuromasts, and the presence of numerous extraoral taste buds, likely represent adaptations for multimodal integration of sensory inputs contributing to foraging behavior in this species. The morphological and behavioral results of this study both suggest that this species would be an excellent model for future comparative structural and functional studies of sensory systems in fishes.

Biomechanics of Insect Flight Stability and Perturbation Response

Insects must fly in highly variable natural environments filled with gusts, vortices, and other transient aerodynamic phenomena that challenge flight stability. Furthermore, the aerodynamic forces that support insect flight are produced from rapidly oscillating wings of time-varying orientation and configuration. The instantaneous flight forces produced by these wings are large relative to the average forces supporting body weight. The magnitude of these forces and their time-varying direction add another challenge to flight stability, because even proportionally small asymmetries in timing or magnitude between the left and right wings may be sufficient to produce large changes in body orientation. However, these same large-magnitude oscillating forces also offer an opportunity for unexpected flight stability through nonlinear interactions between body orientation, body oscillation in response to time-varying inertial and aerodynamic forces, and the oscillating wings themselves. Understanding the emergent stability properties of flying insects is a crucial step toward understanding the requirements for evolution of flapping flight and decoding the role of sensory feedback in flight control. Here, we provide a brief review of insect flight stability, with some emphasis on stability effects brought about by oscillating wings, and present some preliminary experimental data probing some aspects of flight stability in free-flying insects.

Wax "Tails" Enable Planthopper Nymphs to Self-Right Midair and Land on Their Feet

The striking appearance of wax 'tails'-posterior wax projections on planthopper nymphs-has captivated entomologists and naturalists alike. Despite their intriguing presence, the functional roles of these formations remain largely unexplored. This study leverages high-speed imaging to uncover the biomechanical implications of wax structures in the aerial dynamics of planthopper nymphs (Ricania sp.). We quantitatively demonstrate that removing wax tails significantly increases body rotations during jumps. Specifically, nymphs without wax undergo continuous rotations, averaging 4.2 ± 1.8 per jump, in contrast to wax-intact nymphs, who do not complete a full rotation, averaging only 0.7 ± 0.2 per jump. This along with significant reductions in angular and translational velocity from takeoff to landing suggest that aerodynamic drag forces on wax structures effectively counteract rotation. These stark differences in body rotation correlate with landing success: Nymphs with wax intact achieve a near perfect landing rate of 98.5%, while those without wax manage only a 35.5% success rate. Jump trajectory analysis reveals that wax-intact jumps transition from parabolic to asymmetric shapes at higher takeoff velocities and show a significantly greater reduction in velocity from takeoff to landing compared to wax-removed jumps, demonstrating how wax structures help nymphs achieve more stable and controlled descents. Our findings confirm the aerodynamic self-righting functionality of wax tails in stabilizing planthopper nymph landings, advancing our understanding of the complex relationship between wax morphology and aerial maneuverability, with broader implications for wingless insect aerial adaptations and bioinspired robotics.

Biomechanical and morphological determinants of maximal jumping performance in callitrichine monkeys

Jumping is a crucial behavior in fitness-critical activities including locomotion, resource acquisition, courtship displays and predator avoidance. In primates, paleontological evidence suggests selection for enhanced jumping ability during their early evolution. However, our interpretation of the fossil record remains limited, as no studies have explicitly linked levels of jumping performance with interspecific skeletal variation. We used force platform analyses to generate biomechanical data on maximal jumping performance in three genera of callitrichine monkeys falling along a continuum of jumping propensity: Callimico (relatively high propensity jumper), Saguinus (intermediate jumping propensity) and Callithrix (relatively low propensity jumper). Individuals performed vertical jumps to perches of increasing height within a custom-built tower. We coupled performance data with high-resolution micro-CT data quantifying bony features thought to reflect jumping ability. Levels of maximal performance between species - e.g. maximal take-off velocity of the center of mass (CoM) - parallel established gradients of jumping propensity. Both biomechanical analysis of jumping performance determinants (e.g. CoM displacement, maximal force production and peak mechanical power during push-off) and multivariate analyses of bony hindlimb morphology highlight different mechanical strategies among taxa. For instance, Callimico, which has relatively long hindlimbs, followed a strategy of fully extending of the limbs to maximize CoM displacement - rather than force production - during push-off. In contrast, relatively shorter-limbed Callithrix depended mostly on relatively high push-off forces. Overall, these results suggest that leaping performance is at least partially associated with correlated anatomical and behavioral adaptations, suggesting the possibility of improving inferences about performance in the fossil record.

Springing into action: Comparing escape responses between bipedal and quadrupedal rodents

Predation is a fundamental selective pressure on animal morphology, as morphology is directly linked with physical performance and evasion. Bipedal heteromyid rodents, which are characterized by unique morphological traits such as enlarged hindlimbs, appear to be more successful than sympatric quadrupedal rodents at escaping predators such as snakes and owls, but no studies have directly compared the escape performance of bipedal and quadrupedal rodents. We used simulated predator attacks to compare the evasive jumping ability of bipedal kangaroo rats (Dipodomys) to that of three quadrupedal rodent groups-pocket mice (Chaetodipus), woodrats (Neotoma), and ground squirrels (Otospermophilus). Jumping performance of pocket mice was remarkably similar to that of kangaroo rats, which may be driven by their shared anatomical features (such as enlarged hindlimb muscles) and facilitated by their relatively small body size. Woodrats and ground squirrels, in contrast, almost never jumped as a startle response, and they took longer to perform evasive escape maneuvers than the heteromyid species (kangaroo rats and pocket mice). Among the heteromyids, take-off velocity was the only jump performance metric that differed significantly between species. These results support the idea that bipedal body plans facilitate vertical leaping in larger-bodied rodents as a means of predator escape and that vertical leaping likely translates to better evasion success.