Dennis Evangelista
US Naval Academy, Systems Engineering, Faculty Member
- Education, Computer Science, Biomechanics, Evolutionary Biomechanics, Flight Dynamics and Control, Flapping Flight, and 19 moreInsect flight, Marine Biology, Biology, Biomechanics of Plant, Zoology, Evolution, Integrative Biology, Physiology, Heat Transfer, Seed Dispersal, Parameter estimation, Antarctica, Elasticity (Solid Mechanics), Kinematics, Energetics, Flight, Antarctica Ecology, Hovering, and Ecomechanicsedit
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Research Interests: Geology, Physics, Biomechanics, Biology, Aerodynamics, and 4 moreEvolution, Medicine, Avialae, and Animal Flight
Research Interests: Computer Science, Artificial Intelligence, Computer Vision, Photogrammetry, Chiroptera, and 15 moreStereoscopy, Biological Sciences, Software, Bundle Adjustment, Tracking, Kinematics, Calibration, Animals, Videography, Three Dimensional, Stereography, Experimental Biology, Biomechanical Phenomena, Swallows, and Medical and Health Sciences
Nondimensional aerodynamic parameters versus disk loading (eq. 3) for all autorotative descents of Manifera talaris models and Agathis australis models and seeds. A, Reynolds number (Re, eq. 1). B, Advance ratio (J, eq. 2). C, Effective... more
Nondimensional aerodynamic parameters versus disk loading (eq. 3) for all autorotative descents of Manifera talaris models and Agathis australis models and seeds. A, Reynolds number (Re, eq. 1). B, Advance ratio (J, eq. 2). C, Effective lift coefficient (CL,eff, eq. 7). D, Effective drag coefficient (CD,eff, eq. 6)
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Synopsis Aerodynamic studies using physical models of fossil organisms can provide quantitative information about how performance of defined activities, such as gliding, depends on specific morphological features. Such analyses allow us... more
Synopsis Aerodynamic studies using physical models of fossil organisms can provide quantitative information about how performance of defined activities, such as gliding, depends on specific morphological features. Such analyses allow us to rule out hypotheses about the function of extinct organisms that are not physically plausible and to determine if and how specific morphological features and postures affect performance. The purpose of this article is to provide a practical guide for the design of dynamically scaled physical models to study the gliding of extinct animals using examples from our research on the theropod dinosaur, †Microraptor gui, which had flight feathers on its hind limbs as well as on its forelimbs. Analysis of the aerodynamics of †M. gui can shed light on the design of gliders with large surfaces posterior to the center of mass and provide functional information to evolutionary biologists trying to unravel the origins of flight in the dinosaurian ancestors and ...
Chimney swifts (<i>Chaetura pelagica</i>) are highly manoeuvrable birds notable for roosting overnight in chimneys, in groups of hundreds or thousands of birds, before and during their autumn migration. At dusk, birds gather... more
Chimney swifts (<i>Chaetura pelagica</i>) are highly manoeuvrable birds notable for roosting overnight in chimneys, in groups of hundreds or thousands of birds, before and during their autumn migration. At dusk, birds gather in large numbers from surrounding areas near a roost site. Thewhole flock then employs an orderly, but dynamic, circling approach pattern before rapidly entering a small aperture <i>en masse</i>. We recorded the three-dimensional trajectories of ≈1 800 individual birds during a 30 min period encompassing flock formation, circling, and landing, and used these trajectories to test several hypotheses relating to flock or group behaviour. Specifically, we investigated whether the swifts use local interaction rules based on topological distance (e.g. the <i>n</i> nearest neighbours, regardless of their distance) rather than physical distance (e.g. neighbours within <i>x</i> m, regardless of number) to guide interactions, whether the chimney entry zone is more or less cooperative than the surrounding flock, and whether the characteristic subgroup size is constant or varies with flock density. We found that the swift flock is structured around local rules based on physical distance, that subgroup size increases with density, and that there exist regions of the flock that are less cooperative than others, in particular the chimney entry zone.
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Research Interests: Evolutionary Biology, Marine Biology, Geology, Paleontology, Fluid Mechanics, and 12 moreBiomechanics, Functional Morphology, Biology, Ecology, Invertebrate Zoology, Invertebrate Paleontology, Echinodermata, Flow Visualization, Fluid flow, Chapel, Echinoderm, and Fluid Mechanics Related to Low Reynold Numbers
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Chimney swifts (Chaetura pelagica) are highly manoeuvrable birds notable for roosting overnight in chimneys, in groups of hundreds or thousands of birds, before and during their autumn migration. At dusk, birds gather in large numbers... more
Chimney swifts (Chaetura pelagica) are highly manoeuvrable birds notable for roosting overnight in chimneys, in groups of hundreds or thousands of birds, before and during their autumn migration. At dusk, birds gather in large numbers from surrounding areas near a roost site. The whole flock then employs an orderly, but dynamic, circling approach pattern before rapidly entering a small aperture en masse We recorded the three-dimensional trajectories of ≈1 800 individual birds during a 30 min period encompassing flock formation, circling, and landing, and used these trajectories to test several hypotheses relating to flock or group behaviour. Specifically, we investigated whether the swifts use local interaction rules based on topological distance (e.g. the n nearest neighbours, regardless of their distance) rather than physical distance (e.g. neighbours within x m, regardless of number) to guide interactions, whether the chimney entry zone is more or less cooperative than the surrou...
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Ecological, behavioral and biomechanical studies often need to quantify animal movement and behavior in three dimensions. In laboratory studies, a common tool to accomplish these measurements is the use of multiple, calibrated high-speed... more
Ecological, behavioral and biomechanical studies often need to quantify animal movement and behavior in three dimensions. In laboratory studies, a common tool to accomplish these measurements is the use of multiple, calibrated high-speed cameras. Until very recently, the complexity, weight and cost of such cameras have made their deployment in field situations risky; furthermore, such cameras are not affordable to many researchers. Here, we show how inexpensive, consumer-grade cameras can adequately accomplish these measurements both within the laboratory and in the field. Combined with our methods and open source software, the availability of inexpensive, portable and rugged cameras will open up new areas of biological study by providing precise 3D tracking and quantification of animal and human movement to researchers in a wide variety of field and laboratory contexts.
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Manifera talaris, a voltzian conifer from the late early to middle Permian (ca. 270 Ma) of Texas, is the earliest known conifer to produce winged seeds indicative of autorotating flight. In contrast to autorotating seeds and fruits of... more
Manifera talaris, a voltzian conifer from the late early to middle Permian (ca. 270 Ma) of Texas, is the earliest known conifer to produce winged seeds indicative of autorotating flight. In contrast to autorotating seeds and fruits of extant plants, the ones ofM. talarisare exceptional in that they have variable morphology. They bore two wings that produced a range of wing configurations, from seeds with two equal-sized wings to single-winged specimens, via various stages of underdevelopment of one of the wings. To examine the effects of various seed morphologies on aerodynamics and dispersal potential, we studied the flight performance of paper models of three morphotypes: symmetric double-winged, asymmetric double-winged, and single-winged. Using a high-speed camera we identified the mode of descent (plummeting, gliding, autorotation) and quantified descent speed, autorotation frequency, and other flight characteristics. To validate such modeling as an inferential tool, we compare...
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Three-dimensional motion capture based on high-speed videography is a staple technique of comparative biomechanics. Historically, the necessary equipment has been cumbersome and expensive, thus largely precluding use of the technique in... more
Three-dimensional motion capture based on high-speed videography is a staple technique of comparative biomechanics. Historically, the necessary equipment has been cumbersome and expensive, thus largely precluding use of the technique in natural settings, by specialists in other fields (e.g. animal behavior, ecology), and in financially restricted situations. New consumer grade equipment (e.g. sports/action cameras, DSLR’s with HD video) offers far greater portability, and resolution and recording rates comparable to systems costing ten times as much. However, consumer grade equipment lacks the ability to synchronize among multiple cameras and may introduce substantial lens distortion. We have developed a workflow based on open-source Python or MATLAB modules that addresses such problems, and that automates some steps of 3D calibration and animal tracking to reduce both analysis time and reconstruction error. We present several data sets of flying animals (various species of insects ...
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ABSTRACT Many starfish live in environments where food is located in patches on sandy or rocky bottoms. Some organisms in similarly patchy environments have movement patterns and strategies that maximize their likelihood of encountering... more
ABSTRACT Many starfish live in environments where food is located in patches on sandy or rocky bottoms. Some organisms in similarly patchy environments have movement patterns and strategies that maximize their likelihood of encountering and remaining in food‐rich areas. To examine these behaviors in starfish, we used time‐lapse photography to film eleven Asterina anomala for periods of 18 hours in a tank with and without chunks of clam to feed on. We then used computer vision, namely a Haar cascade, to automatically track the positions of the starfish, followed by manual quality assurance to clean up the tracks. No differences in average speed or in time spent moving (as opposed to time spent sitting still) were observed between trials with clam and those without clam, suggesting that these starfish may not use decreased movement to remain in food‐ rich areas. Additionally, early analysis suggests that these starfish use a correlated random walk movement pattern, as opposed to other movement algorithms such as a Levy walk or Brownian motion.
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ABSTRACT Chimney Swifts (Chaetura pelagica) are highly maneuverable social birds notable for roosting overnight in chimneys in groups of hundreds or thousands of birds. At dusk, birds gather in large numbers from surrounding areas near a... more
ABSTRACT Chimney Swifts (Chaetura pelagica) are highly maneuverable social birds notable for roosting overnight in chimneys in groups of hundreds or thousands of birds. At dusk, birds gather in large numbers from surrounding areas near a few suitable roost sites. They then enter a very small aperture within a very short time, with the whole flock employing an orderly, but dynamic, circling pattern, even as winds shift and light levels decrease. Such repeatable, reliable behavior in a convenient urban area with fixed landmarks provides an excellent opportunity to use multi-camera videography to measure three dimensional kinematics of natural flight behavior, in the field and under challenging lighting conditions. We will describe ongoing efforts to automatically track every bird in the flock. We will also discuss kinematic and information metrics appropriate for analyzing the tracks, modeling components of the behaviors, and examining differences between strongly and weakly ordered group flight behaviors in other bird species. Information transfer within the flock may assist in accomplishing such a difficult navigational task.
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Research Interests:
ABSTRACT Chimney Swifts (Chaetura pelagica) are highly maneuverable social birds notable for roosting overnight in chimneys in groups of hundreds or thousands of birds. At dusk, birds gather in large numbers from surrounding areas near a... more
ABSTRACT Chimney Swifts (Chaetura pelagica) are highly maneuverable social birds notable for roosting overnight in chimneys in groups of hundreds or thousands of birds. At dusk, birds gather in large numbers from surrounding areas near a few suitable roost sites. They then enter a very small aperture within a very short time, with the whole flock employing an orderly, but dynamic, circling pattern, even as winds shift and light levels decrease. Such repeatable, reliable behavior in a convenient urban area with fixed landmarks provides an excellent opportunity to use multi-camera videography to measure three dimensional kinematics of natural flight behavior, in the field and under challenging lighting conditions. We present results from automatic tracking of every bird in the flock, discuss kinematic and information metrics appropriate for analyzing the tracks and modeling components of the behaviors, and provide comparison with Cliff Swallow field 3D kinematics to examine differences between strongly and weakly ordered group flight behaviors.
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Mechanisms of aerial righting in juvenile Chukar Partridge (Alectoris chukar) were studied from hatching through 14 days-post-hatching (dph). Asymmetric movements of the wings were used from 1?8 dph to effect progressively more successful... more
Mechanisms of aerial righting in juvenile Chukar Partridge (Alectoris chukar) were studied from hatching through 14 days-post-hatching (dph). Asymmetric movements of the wings were used from 1?8 dph to effect progressively more successful righting behaviour via body roll. Following 8 dph, wing motions transitioned to bilaterally symmetric flapping that yielded aerial righting via nose-down pitch, along with substantial increases in vertical force production during descent. Ontogenetically, the use of such wing motions to effect aerial righting precedes both symmetric flapping and a previously documented behaviour in chukar (i.e., wing-assisted incline running) hypothesized to be relevant to incipient flight evolution in birds. These findings highlight the importance of asymmetric wing activation and controlled aerial manoeuvres during bird development, and are potentially relevant to understanding the origins of avian flight.
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ABSTRACT Blastoids were a group of stalked, sessile echinoderm preserved in rocks that span the middle Ordovician (~}470 mya) to the end of the Permian (~{250 mya). These extinct echinoderms possessed hydrospires, uniquely complex... more
ABSTRACT Blastoids were a group of stalked, sessile echinoderm preserved in rocks that span the middle Ordovician (~}470 mya) to the end of the Permian (~{250 mya). These extinct echinoderms possessed hydrospires, uniquely complex internal thecal structures with putative respiratory function. Here, we present measurement and visualization of flow within the hydrospires using a 3D-printed and Reynolds-similar physical model of the interior of a hydrospire of the blastoid Pentremites rusticus, to examine in further detail possible functions of the hydrospire. Specifically, the model allows examination of the extent to which the pattern of flow within the hydrospire kept oxygen-rich incurrent water separated from water that had already been depleted of oxygen. If the flow pattern within the hydrospire fails to keep these two bodies of water separate, this would suggest some other function for the hydrospires. In addition, the model also allows for determination of whether active pumping would have been required to achieve optimal respiratory function, or whether passive pumping alone was sufficient. Furthermore, the model allows for testing of the hypothesis that the need for removal of digestive waste, thought to be associated with the hydrospires, is responsible for some unusual aspects of the hydrospires, such as the conical shape of the putative excurrent canals and the presence of cover plates over the remarkably large excurrent openings.
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Manifera talaris, a voltzian conifer from the late early to middle Permian (ca. 270 Ma) of Texas, is the earliest known conifer to produce winged seeds indicative of autorotating flight. In contrast to autorotating seeds and fruits of... more
Manifera talaris, a voltzian conifer from the late early to middle Permian (ca. 270 Ma) of Texas, is the earliest known conifer to produce winged seeds indicative of autorotating flight. In contrast to autorotating seeds and fruits of extant plants, the ones of M. talaris are exceptional in that they have variable morphology. They bore two wings that produced a range of wing configurations, from seeds with two equal-sized wings to single-winged specimens, via various stages of underdevelopment of one of the wings. To examine the effects of various seed morphologies on aerodynamics and dispersal potential, we studied the flight performance of paper models of three morphotypes: symmetric double-winged, asymmetric double-winged, and single-winged. Using a high-speed camera we identified the mode of descent (plummeting, gliding, autorotation) and quantified descent speed, autorotation frequency, and other flight characteristics. To validate such modeling as an inferential tool, we compared descent of extant analogues (kauri; Agathis australis) with descent of similarly constructed seed models. All three seed morphotypes exhibited autorotating flight behavior. However, double-winged seeds, especially symmetric ones, failed to initiate slow autorotative descent more frequently than single-winged seeds. Even when autorotating, symmetric double-winged seeds descend faster than asymmetric double-winged ones, and descent is roughly twice as fast compared to single-winged seeds. Moreover, the relative advantage that (effectively) single-winged seeds have in slowing descent during autorotation becomes larger as seed weight increases. Hence, the range in seed wing configurations in M. talaris produced a wide variation in potential dispersal capacity. Overall, our results indicate that the evolutionarily novel autorotating winged seeds must have improved conifer seed dispersal, in a time when animal vectors for dispersion were virtually absent. Because of the range in wing configuration, the early evolution of autorotative flight in conifers was a functionally imperfect one, which provides us insight into the evolutionary developmental biology of autorotative seeds in conifers.(Accepted September 22 2014)(Online publication March 12 2015)
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Jackson, Evangelista, Hedrick Three-dimensional motion capture based on high-speed videography is a staple technique of comparative biomechanics. Historically, the necessary equipment has been cumbersome and expensive, thus largely... more
Jackson, Evangelista, Hedrick
Three-dimensional motion capture based on high-speed videography is a staple technique of comparative biomechanics. Historically, the necessary equipment has been cumbersome and expensive, thus largely precluding use of the technique in natural settings, by specialists in other fields (e.g. animal behavior, ecology), and in financially restricted situations. New consumer grade equipment (e.g. sports/action cameras, DSLR’s with HD video) offers far greater portability, and resolution and recording rates comparable to systems costing ten times as much. However, consumer grade equipment lacks the ability to synchronize among multiple cameras and may introduce substantial lens distortion. We have developed a workflow based on open-source Python or MATLAB modules that addresses such problems, and that automates some steps of 3D calibration and animal tracking to reduce both analysis time and reconstruction error. We present several data sets of flying animals (various species of insects and birds) with sample volumes ranging from 0.3 m3 to over 20,000 m3. One of our example systems is based on three GoPro Hero cameras, fits in a small backpack, can record continuously for approximately an hour at 120 Hz (battery limited), and is extremely weather- and damage-resistant. Field setup and camera calibration required as little as three minutes, offering the ability to record relatively unpredictable behaviors in remote and harsh conditions. We foresee that such an affordable and intuitive setup will permit the use of 3D motion tracking across a wide range of size scales, environments, and study-areas in biology, and will bring this important technique to researchers with limited funding.
Three-dimensional motion capture based on high-speed videography is a staple technique of comparative biomechanics. Historically, the necessary equipment has been cumbersome and expensive, thus largely precluding use of the technique in natural settings, by specialists in other fields (e.g. animal behavior, ecology), and in financially restricted situations. New consumer grade equipment (e.g. sports/action cameras, DSLR’s with HD video) offers far greater portability, and resolution and recording rates comparable to systems costing ten times as much. However, consumer grade equipment lacks the ability to synchronize among multiple cameras and may introduce substantial lens distortion. We have developed a workflow based on open-source Python or MATLAB modules that addresses such problems, and that automates some steps of 3D calibration and animal tracking to reduce both analysis time and reconstruction error. We present several data sets of flying animals (various species of insects and birds) with sample volumes ranging from 0.3 m3 to over 20,000 m3. One of our example systems is based on three GoPro Hero cameras, fits in a small backpack, can record continuously for approximately an hour at 120 Hz (battery limited), and is extremely weather- and damage-resistant. Field setup and camera calibration required as little as three minutes, offering the ability to record relatively unpredictable behaviors in remote and harsh conditions. We foresee that such an affordable and intuitive setup will permit the use of 3D motion tracking across a wide range of size scales, environments, and study-areas in biology, and will bring this important technique to researchers with limited funding.
Research Interests:
Chimney Swifts (Chaetura pelagica) are highly maneuverable social birds notable for roosting overnight in chimneys in groups of hundreds or thousands of birds. At dusk, birds gather in large numbers from surrounding areas near a few... more
Chimney Swifts (Chaetura pelagica) are highly maneuverable social birds notable for roosting overnight in chimneys in groups of hundreds or thousands of birds. At dusk, birds gather in large numbers from surrounding areas near a few suitable roost sites. They then enter a very small aperture within a very short time, with the whole flock employing an orderly, but dynamic, circling pattern, even as winds shift and light levels decrease. Such repeatable, reliable behavior in a convenient urban area with fixed landmarks provides an excellent opportunity to use multi-camera videography to measure three dimensional kinematics of natural flight behavior, in the field and under challenging lighting conditions. We present results from automatic tracking of every bird in the flock, discuss kinematic and information metrics appropriate for analyzing the tracks and modeling components of the behaviors, and provide comparison with Cliff Swallow field 3D kinematics to examine differences between strongly and weakly ordered group flight behaviors.
Research Interests:
Chimney Swifts (Chaetura pelagica) are highly maneuverable social birds notable for roosting overnight in chimneys in groups of hundreds or thousands of birds. At dusk, birds gather in large numbers from surrounding areas near a few... more
Chimney Swifts (Chaetura pelagica) are highly maneuverable social birds notable for roosting overnight in chimneys in groups of hundreds or thousands of birds. At dusk, birds gather in large numbers from surrounding areas near a few suitable roost sites. They then enter a very small aperture within a very short time, with the whole flock employing an orderly, but dynamic, circling pattern, even as winds shift and light levels decrease. Such repeatable, reliable behavior in a convenient urban area with fixed landmarks provides an excellent opportunity to use multi-camera videography to measure three dimensional kinematics of natural flight behavior, in the field and under challenging lighting conditions. We will describe ongoing efforts to automatically track every bird in the flock. We will also discuss kinematic and information metrics appropriate for analyzing the tracks, modeling components of the behaviors, and examining differences between strongly and weakly ordered group flight behaviors in other bird species. Information transfer within the flock may assist in accomplishing such a difficult navigational task.
Research Interests:
Growth of ice on surfaces poses a challenge for both organisms and for devices that come into contact with liquids below the freezing point. Resistance of some organisms to ice formation and growth, either in subtidal environments (e.g.,... more
Growth of ice on surfaces poses a challenge for both organisms and for devices that come into contact with liquids below the freezing point. Resistance of some organisms to ice formation and growth, either in subtidal environments (e.g., Antarctic anchor ice), or in environments with moisture and cold air (e.g., plants, intertidal) begs examination of how this is accomplished. Several factors may be important in promoting or mitigating ice formation. As a start, here we examine the effect of surface texture alone. We tested four candidate surfaces, inspired by hard-shelled marine invertebrates and constructed using a three-dimensional printing process. We examined sub-polar marine organisms to develop sample textures and screened them for ice formation and accretion in submerged conditions using previous methods for comparison to data for Antarctic organisms. The sub-polar organisms tested were all found to form ice readily. We also screened artificial 3-D printed samples
using the same previous methods, and developed a new test to examine ice formation from surface droplets as might be encountered in environments with moist, cold air. Despite limitations inherent to our techniques, it appears surface texture plays only a small role in delaying the onset of ice formation: a stripe feature (corresponding to patterning found on valves of blue mussels, Mytilus edulis, or on the spines of
the Antarctic sea urchin Sterechinus neumayeri) slowed ice formation an average of 25% compared to a grid feature (corresponding to patterning found on sub-polar butterclams, Saxidomas nuttalli). The geometric dimensions of the features have only a small (∼6%) effect on ice formation. Surface texture affects ice formation, but does not explain by itself the large variation in ice formation and species-specific ice resistance observed in other work. This suggests future examination of other factors, such as material elastic properties and surface coatings, and their interaction with surface pattern.
using the same previous methods, and developed a new test to examine ice formation from surface droplets as might be encountered in environments with moist, cold air. Despite limitations inherent to our techniques, it appears surface texture plays only a small role in delaying the onset of ice formation: a stripe feature (corresponding to patterning found on valves of blue mussels, Mytilus edulis, or on the spines of
the Antarctic sea urchin Sterechinus neumayeri) slowed ice formation an average of 25% compared to a grid feature (corresponding to patterning found on sub-polar butterclams, Saxidomas nuttalli). The geometric dimensions of the features have only a small (∼6%) effect on ice formation. Surface texture affects ice formation, but does not explain by itself the large variation in ice formation and species-specific ice resistance observed in other work. This suggests future examination of other factors, such as material elastic properties and surface coatings, and their interaction with surface pattern.
Research Interests:
Chimney Swifts (Chaetura pelagica) are highly maneuverable social birds notable for roosting overnight in chimneys in groups of hundreds or thousands of birds. At dusk, birds gather in large numbers from surrounding areas near a few... more
Chimney Swifts (Chaetura pelagica) are highly maneuverable social birds notable for roosting overnight in chimneys in groups of hundreds or thousands of birds. At dusk, birds gather in large numbers from surrounding areas near a few suitable roost sites. They then enter a very small aperture within a very short time, with the whole flock employing an orderly, but dynamic, circling pattern, even as winds shift and light levels
decrease. Such repeatable, reliable behavior in a convenient urban area with fixed landmarks provides an excellent opportunity to use multi‐camera videography to measure three dimensional kinematics of natural flight behavior, in the field
and under challenging lighting conditions. I will summarize ongoing efforts to automatically track every bird in the flock.
decrease. Such repeatable, reliable behavior in a convenient urban area with fixed landmarks provides an excellent opportunity to use multi‐camera videography to measure three dimensional kinematics of natural flight behavior, in the field
and under challenging lighting conditions. I will summarize ongoing efforts to automatically track every bird in the flock.