Biology subjects

Hedrick, T. L.

Publications and source records attributed to Hedrick, T. L..

5 recordsLinked to original sources

bioRxiv2022

Morphological evolution of bird wings follows a mechanical sensitivity gradient determined by the aerodynamics of flapping flight

The physical principles that govern the function of biological structures also mediate their evolution, but the evolutionary drivers of morphological traits within complex structures can be difficult to predict. We used morphological traits measured from 1096 3-dimensional bird wing scans from 178 species to test how two frameworks for relating morphology to evolution interact. We examined whether the modular organization of the wing into handwing and armwing regions, or the relationship between trait morphology and functional output (i.e. mechanical sensitivity, driven here by flapping flight aerodynamics) dominate evolutionary rate ({sigma}2) and mode. Our results support discretization of the armwing and handwing as morphological modules, but morphological disparity and{sigma} 2 varied continuously with the mechanical sensitivity gradient and were not modular. Thus, mechanical sensitivity should be considered an independent driver of evolutionary dynamics, distinct from morphological modularity. TeaserMechanical sensitivity drives wing shape evolution in birds and may be fundamental to the evolution of biomechanical systems.

evolutionary biology↗

bioRxiv2022

How Turkey vultures tune their airspeed to environmental and behavioral factors

Animals must tune their physical performance to changing environmental conditions, and the breadth of environmental tolerance may contribute to delineating the species geographic range. A common environmental challenge that flying animals face is the reduction of air density at high elevation and a reduction in the effectiveness of lift production that accompanies it. Turkey vultures (Cathartes aura) inhabit a >3000 m elevation range, and fly considerably higher, necessitating that they compensate for air density differences through behavior, physiology, or biomechanics. We predicted that birds flying at high elevation would demonstrate higher median flight speeds while maintaining similar glide angles. We used 3-dimensional videography to track Turkey vultures flying at three elevations and found a negative relationship between median airspeed and air density that matched our prediction. Additionally, neither the ratio of horizontal speed to sinking speed nor flapping behavior varied with air density. These results were robust to varying flight behavior (climbing vs. level flight). Finally, we derived a glide polar from the free-flying vultures and showed that they are proficient at tuning their flight speed to minimize their cost of transport during straight-line flight, but transition to a minimum power strategy during gliding turns.

zoology↗

bioRxiv2022

Three-dimensional actuation of hummingbird wings requires diverse effects from the primary flight muscles

Hummingbirds have evolved to hover and maneuver with exceptional flight control. This is directly enabled by their musculoskeletal system that successfully exploits the agile motion of flapping wings. Here, we reveal novel principles of hummingbird wing actuation that provide insights into the evolution and robotic emulation of hummingbird flight. We develop a functional model of hummingbird musculoskeletal system, which predicts instantaneous, three-dimensional torque produced by primary (pectoralis and supracoracoideus) and combined secondary muscles. It also reveals primary muscle contractile behavior, including stress, strain, elasticity, and work. Results show that the primary muscles (i.e., the flight "engine") function as diverse effectors, as they do not simply power the stroke, but also actively deviate and pitch the wing. The secondary muscles produce controlled-tightening effects, by acting against primary muscles in deviation and pitching. The diverse effector capacity of pectoralis is associated with the evolution of a comparatively enormous bicipital crest on humerus.

biophysics↗

bioRxiv2021

ThruTracker: Open-Source Software for 2-D and 3-D Animal Video Tracking

O_LITracking animal movement patterns using videography is an important tool in many biological disciplines ranging from biomechanics to conservation. Reduced costs of technology such as thermal videography and unmanned aerial vehicles has made video-based animal tracking more accessible, however existing software for processing acquired video limits the application of these methods. C_LIO_LIHere, we present a novel software program for high-throughput 2-D and 3-D animal tracking. ThruTracker provides tools to allow video tracking under a variety of conditions with minimal technical expertise or coding background and without the need for paid licenses. Notable capabilities include calibrating the intrinsic properties of thermal cameras; tracking and counting hundreds of animals at a time; and the ability to make 3-D calibrations without dedicated calibration objects. Automated 2-D and 3-D workflows are integrated to allow for analysis of largescale datasets. C_LIO_LIWe tested ThruTracker with two case studies. The 2-D workflow is demonstrated by counting bats emerging from bridges and caves using thermal Videography. Tests show that ThruTracker has a similar accuracy compared to humans under a variety of conditions. The 3-D workflow is shown for making accurate calibrations for tracking bats and birds at wind turbines using only the wind turbine itself as a calibration object. C_LIO_LIThruTracker is a robust software program for tracking moving animals in 2-D and 3-D. Major applications include counting animals such as bats, birds, and fish that form large aggregations, and documenting movement trajectories over medium spatial scales ([~]100,000 m3). When combined with emerging technologies, we expect videographic techniques to continue to see widespread adoption for an increasing range of biological applications. C_LI

animal behavior and cognition↗

bioRxiv2019

Compound-V formations in shorebird flocks

Animal groups have emergent properties that result from simple interactions among individuals. However, we know little about why animals adopt different interaction rules because of sparse sampling among species. Here, we identify an interaction rule that holds across single and mixed-species flocks of four migratory shorebird species spanning a seven-fold range of body masses. The rule, aligning with a 1-wingspan lateral distance to nearest neighbors in the same horizontal plane, scales linearly with wingspan but is independent of nearest neighbor distance and neighbor species. This rule propagates outward to create a global flock structure that we term the compound-V formation. We propose that this formation represents an intermediary between the cluster flocks of starlings and the simple-V formations of geese and other large migratory birds. Analysis of individual wingbeat frequencies and airspeeds indicates that the compound-V formation may be an adaptation for aerodynamic flocking.

evolutionary biology↗