Papers by Dennis Evangelista
The Biological Bulletin, Oct 1, 2016
The paths animals take while moving through their environments affect their likelihood of encount... more The paths animals take while moving through their environments affect their likelihood of encountering food and other resources; thus, models of foraging behavior abound. To collect movement data appropriate for comparison with these models, we used time-lapse photography to track movements of a small, hardy, and easy-to-obtain organism, Aquilonastra anomala sea stars. We recorded the sea stars in a tank over many hours, with and without a food cue. With food present, they covered less distance, as predicted by theory; this strategy would allow them to remain near food. We then compared the paths of the sea stars to three common models of animal movement: Brownian motion, Lévy walks, and correlated random walks; we found that the sea stars' movements most closely resembled a correlated random walk. Additionally, we compared the search performance of models of Brownian motion, a Lévy walk, and a correlated random walk to that of a model based on the sea stars' movements. We found that the behavior of the modeled sea star walk was similar to that of the modeled correlated random walk and the Brownian motion model, but that the sea star walk was slightly more likely than the other walks to find targets at intermediate distances. While organisms are unlikely to follow an idealized random walk in all details, our data suggest that comparing the effectiveness of an organism's paths to those from theory can give insight into the organism's actual movement strategy. Finally, automated optical tracking of invertebrates proved feasible, and A. anomala was revealed to be a tractable, 2D-movement study system.
Carolina Digital Repository (University of North Carolina at Chapel Hill), 2017
Three-dimensional trajectories and network analyses of group behaviour within chimney swift flock... more Three-dimensional trajectories and network analyses of group behaviour within chimney swift flocks during approaches to the roost.
Biology Open, Jul 21, 2016
Ecological, behavioral and biomechanical studies often need to quantify animal movement and behav... 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.
The capacity for aerial maneuvering was likely a major influence on the evolution of flying anima... more The capacity for aerial maneuvering was likely a major influence on the evolution of flying animals. Here we evaluate consequences of paravian morphology for aerial performance by quantifying static stability and control effectiveness of physical models for numerous taxa sampled from within the lineage leading to birds (Paraves). Results of aerodynamic testing are mapped phylogenetically to examine how maneuvering characteristics correspond to tail shortening, forewing elaboration, and other morphological features. In the evolution of Paraves we observe shifts from static stability to inherently unstable aerial planforms; control effectiveness also migrated from tails to the forewings. These shifts suggest that some degree of aerodynamic control and and capacity for maneuvering preceded the evolution of strong power stroke. The timing of shifts also suggests features normally considered in light of development of a power stroke may play important roles in control.
Carolina Digital Repository (University of North Carolina at Chapel Hill), 2014
Stereo videography is a powerful technique for quantifying the kinematics and behavior of animals... more Stereo videography is a powerful technique for quantifying the kinematics and behavior of animals, but it can be challenging to use in an outdoor field setting. We here present a workflow and associated software for performing calibration of cameras placed in a field setting and estimating the accuracy of the resulting stereoscopic reconstructions. We demonstrate the workflow through example stereoscopic reconstructions of bat and bird flight. We provide software tools for planning experiments and processing the resulting calibrations that other researchers may use to calibrate their own cameras. Our field protocol can be deployed in a single afternoon, requiring only short video clips of light, portable calibration objects.
Nondimensional aerodynamic parameters versus disk loading (eq. 3) for all autorotative descents o... 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)
Synopsis Aerodynamic studies using physical models of fossil organisms can provide quantitative i... 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 r... 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.
Palaeontologia Electronica, 2015
The Biological Bulletin, 2016
The paths animals take while moving through their environments affect their likelihood of encount... more The paths animals take while moving through their environments affect their likelihood of encountering food and other resources; thus, models of foraging behavior abound. To collect movement data appropriate for comparison with these models, we used time-lapse photography to track movements of a small, hardy, and easy-to-obtain organism, Aquilonastra anomala sea stars. We recorded the sea stars in a tank over many hours, with and without a food cue. With food present, they covered less distance, as predicted by theory; this strategy would allow them to remain near food. We then compared the paths of the sea stars to three common models of animal movement: Brownian motion, Lévy walks, and correlated random walks; we found that the sea stars' movements most closely resembled a correlated random walk. Additionally, we compared the search performance of models of Brownian motion, a Lévy walk, and a correlated random walk to that of a model based on the sea stars' movements. We found that the behavior of the modeled sea star walk was similar to that of the modeled correlated random walk and the Brownian motion model, but that the sea star walk was slightly more likely than the other walks to find targets at intermediate distances. While organisms are unlikely to follow an idealized random walk in all details, our data suggest that comparing the effectiveness of an organism's paths to those from theory can give insight into the organism's actual movement strategy. Finally, automated optical tracking of invertebrates proved feasible, and A. anomala was revealed to be a tractable, 2D-movement study system.
Proceedings. Biological sciences, Jan 22, 2017
Chimney swifts (Chaetura pelagica) are highly manoeuvrable birds notable for roosting overnight i... 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...
Biology Open, 2016
Ecological, behavioral and biomechanical studies often need to quantify animal movement and behav... 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.
Paleobiology, 2015
Manifera talaris, a voltzian conifer from the late early to middle Permian (ca. 270 Ma) of Texas,... 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...
Three-dimensional motion capture based on high-speed videography is a staple technique of compara... 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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Papers by Dennis Evangelista