Relevant Degree Programs
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G+PS regularly provides virtual sessions that focus on admission requirements and procedures and tips how to improve your application.
Graduate Student Supervision
Doctoral Student Supervision (Jan 2008 - Mar 2019)
The extent to which locomotor adaptations depend on evolution of morphological form or kinematic function remains an open question. Hummingbirds are a speciose group with exceptional aerial abilities across a large range of habitats, making them attractive models for biomechanical studies of coupled form and function. Here, I investigate the origin of hummingbird flight performance among and within species, and within individuals. I develop a novel biomechanical framework adapted from aerodynamic principles, and find that a weight-support strategy thus far only identified among hummingbird species is likely a response to selection for constant, mass-independent hovering and burst performance. Within species, hummingbirds exhibit an alternative weight-support strategy that instead results in reduced flight performance in larger individuals. I next develop experimental and analytical techniques to investigate the time- and behaviour-dependence of wing morphology and kinematics. Within individuals, flight performance depends on fine adjustments to wing kinematics and wing morphology, including wing twisting and cambering. I suggest that individual hummingbirds dynamically control their wing morphology to minimise the cost of flight rather than maximise force production, but can sacrifice flight efficiency to enable challenging flight behaviours. Wing morphing therefore offers flight control degrees of freedom that can be called upon as required. Taken together, I propose that evolution of wing form maximises average performance, but also maximises the scope for dynamic wing control.
Relatively little is known about how sensory information is used for controlling flight in birds. A powerful method is to immerse an animal in a dynamic virtual reality environment to examine behavioral responses. The research comprising this dissertation investigated the role of vision during free flight hovering in hummingbirds to determine how optic flow –image movement across the retina– is used to control body position. We filmed hummingbirds hovering in front of a projection screen with the prediction that stationary patterns would allow a hummingbird to maintain stable body position, but moving patterns would change hovering stability. When hovering in the presence of moving gratings and spirals, hummingbirds lost positional stability and responded in the direction of the stimulus motion. There was no loss of stability with stationary patterns (Chapter 1). How sensitive are hummingbirds to visual motion? We predicted that small changes in the direction of a looming motion would result in matched changes in backward flight response of hummingbirds. Providing stationary visual patterns in combination with looming spirals was predicted to rescue hovering stability. Our results suggest that hummingbirds are not only sensitive to small changes in motion direction, but also sensitive to any visual motion of the background, even when large stationary features are present (Chapter 2). The sensitivity of hovering hummingbirds to visual motion suggested that other senses might be involved to stabilize flight. When docked with a feeder, hummingbirds gain a stable physical reference through bill contact. We predicted that tactile feedback during docked feeding would provide the necessary stationary reference to help hummingbirds override their sensitivity to visual motion. We built an instrumented feeder that measured how much a docked hummingbird pushed laterally and vertically. Hummingbirds were not very precise during docked hovering and pushed against the feeder in an attempt to stabilize left, right, and downward visual motions. Upward motion was not matched by pushing against the feeder (Chapter 3). Collectively, these experiments demonstrate that hummingbirds control hovering position by stabilizing motions in their visual field both when hovering in space and when docked with their bill inserted into a flower.
The ability of a bird to maneuver in flight can determine its success at avoiding predators, catching prey, and other critical behaviors. Highly maneuverable animals, such as hummingbirds, are capable of diverse behaviors but it is unknown how their maneuvering is constrained by wing motion, wing morphology, and muscle capacity. The purpose of this dissertation was to determine: 1) if hummingbird wings create independent wakes; 2) if independent wingbeat kinematics are used to control maneuvers; and 3) how maneuverability is limited by intrinsic features, such as wing morphology, body mass, and physical properties of the air, versus facultative capacity, such as muscle power. The goal of chapter two was to determine if hummingbirds produce single or bilateral vortex wakes using flow visualization. The goal of chapter three was to determine if sustained maneuvers can be controlled by orienting the wings independently of the body. I tested this hypothesis by filming the three dimensional kinematics of a hummingbird feeding from a translating feeder. The goal of chapter four was to determine if the ability to perform voluntary maneuvers was associated with intrinsic or facultative features. I addressed this question using a tracking system to record a large data set of voluntary flight trajectories, with independent measurements of individual morphology and maximum muscle capacity. The goal of chapter five was to determine if maneuvering performance declines with increasing elevation and, if so, whether changes in oxygen availability or air density are most responsible. I addressed these questions by measuring maneuvering performance across elevation and in an airtight chamber with gas manipulations. Collectively, my results indicate that hummingbirds have wings that operate with a high degree of independence and that this feature influences their precision and control. Voluntary maneuvers at low elevation are primarily influenced by facultative capacity, specifically burst power, and to a lesser extent by intrinsic limits, specifically wing aspect ratio. At higher elevations, maneuvering performance declines due to decreases in air density. This research demonstrates that the remarkable maneuverability of hummingbirds derives from their ability to control their wings independently and from high muscle power reserves for generating aerodynamic force. Supplementary video material is available at: http://hdl.handle.net/2429/54568
Master's Student Supervision (2010-2017)
Avian wings change shape during the flapping cycle due to the activity of a network of intrinsic wing muscles. Wing control is believed to be the key feature allowing birds to maneuver safely through different environments. One control aspect is elbow joint motion, which relates to wing folding for the upstroke and re-expansion for the downstroke. Muscle anatomy suggests that if the muscles are actuating then the biceps flex the elbow, and the two heads of the triceps, the humerotriceps and scapulotriceps, extend the elbow. This set of antagonist muscles could thus actively modulate wing shape by regulating elbow joint angle. Control of the elbow joint angle remains uncertain as motor elements can have diverse functions such as actuators, brakes, springs, and struts, where specific roles and their magnitudes depend on when muscles are activated in the contractile cycle. The wing muscles best studied during flight are the elbow muscles of the pigeon (Columba livia). In vivo studies during different flight modes revealed variation in strain profile, activation timing and duration, and in contractile cycle frequency of the humerotriceps. This variation suggests that the pigeon humerotriceps may alter wing shape in diverse ways. To test this hypothesis, I developed an in situ work loop technique to measure the performance of the pigeon humerotriceps. My experiments tested how activation duration and contractile cycle frequency influenced muscle work and power across the full range of activation onset times. I found that the humerotriceps generated net positive power over a narrow range of activation times. The humerotriceps produced predominantly net negative power, likely due to relatively long activation durations, indicating that it absorbs work, but the work loop shapes also suggest varying degrees of elasticity and resistance. I was unable to examine the effects of variation in strain profile because current work loop technology does not allow for this. Nonetheless, these results, when combined with previous in vivo studies, show that the humerotriceps can dynamically shift among roles of brake, spring, and strut, based on activation properties that vary with flight mode.
Flying animals are hypothesized to direct the lateral force necessary to execute turns through two methods. The first is force vectoring, which is accomplished by banking the wing stroke plane and body in concert. Through this method, centripetal force is provided by the lateral component of aerodynamic force that is directed into a turn. An alternative hypothesis is that they generate lateral force through asymmetries in wingbeat kinematics between the left and right wings without varying body position. Examples of asymmetrical kinematics could include differences in angle of attack, stroke plane angle, or stroke amplitude. We studied turning hummingbirds as they tracked a revolving feeder to distinguish between these mechanisms. Comparing hovering and turning flight revealed that hummingbirds bank their stroke plane and body into turns and maintain the position of the stroke plane relative to their bodies, supporting a force vectoring mechanism. However, several wingbeat asymmetries were observed during turning, such as the outer wing tip path being higher and flatter, and the inner wing tip path being lower and more scooped than in hovering. Because the centripetal force necessary to complete a turn is determined by translational velocity and turn radius, we created four balanced turning treatments where these aspects of a turn were varied with a revolving feeder to determine how wing and body kinematics change in order to compensate for these challenges. We found that three asymmetric wingbeat kinematic variables were associated with changes in turn radius and two body kinematic variables related to force vectoring were associated with changes in translational velocity. There were no kinematics influenced by both radius and velocity. This suggests wingbeat asymmetries compensate for changes in turning radius and force vectoring is used to compensate for changes in velocity. Thus, rather than force vectoring and wingbeat asymmetries being mutually exclusive, our results indicate that the two mechanisms are used simultaneously and independently to meet different aerodynamic challenges.
The sampling of spatial and temporal visual information for all living organisms is finite. The speed and accuracy of visual systems contributes in part to an animal's sensitivity to visual motion. The ability to see swift motions is a crucial adaptation among bird species, which are high-speed animals that navigate in a three-dimensional world. Hummingbirds are emerging as important models for studying visual guidance in vertebrates. However, their sensitivity to visual motion remains unknown. A method that can be used to identify hummingbirds' sensitivity to visual motion is to characterise the spatial and temporal acuity of their visual system. It is hypothesised that temporal acuity scales positively with mass-specific metabolic rate and negatively with body size, and spatial acuity scales positively with body size. Given hummingbirds possess the highest mass- specific metabolic rates among vertebrates and the smallest body sizes among birds, I predicted that the Anna's hummingbird (Calypte anna) would have high temporal and low spatial acuities among bird species. Using operant conditioning and optocollic reflex experiments, I identified the temporal and spatial acuity thresholds of the Anna's hummingbird's visual system. Training hummingbirds to differentiate flickering from non-flickering lights at different rates and colours measured their temporal acuity for wavelengths of light between 380-750nm. Spatial acuity was measured by subjecting hummingbirds to rotating stimuli that varied in spatial frequency and luminance. The results indicate the hummingbird's temporal acuity is between 70 and 80Hz, and is unaffected by light colour (red, white, and ultraviolet). Spatial resolving capacity is measured to be between 4.95 and 6.18 cycles per degree in light conditions below 1.77 candela/m². Therefore, my measurements of spatial acuity in the Anna's hummingbird provide support for a positive relationship with body size, and my measurements of temporal acuity do not provide support for a positive relationship with mass-specific metabolic rate. This study marks the first time both spatial and temporal acuity is measured in a sustained hovering animal.
Hummingbird vision wired to avoid high-speed collisions (18 Jul 2016)
UBC team finds a glitch in hummingbird hovering (09 Dec 2014)
- Neurons Responsive to Global Visual Motion Have Unique Tuning Properties in Hummingbirds (2017)
Current Biology, 27 (2), 279-285
- Hummingbirds control turning velocity using body orientation and turning radius using asymmetrical wingbeat kinematics (2016)
Journal of the Royal Society Interface, 13 (116)
- Mechanical Constraints on Flight at High Elevation Decrease Maneuvering Performance of Hummingbirds (2016)
Current Biology, 26 (24), 3368-3374
- Visual guidance of forward flight in hummingbirds reveals control based on image features instead of pattern velocity (2016)
Proceedings of the National Academy of Sciences of the United States of America, 113 (31), 8849-8854
- Burst muscle performance predicts the speed, acceleration, and turning performance of Anna’s hummingbirds (2015)
eLife, 4 (NOVEM)
- Power reduction and the radial limit of stall delay in revolving wings of different aspect ratio (2015)
Journal of the Royal Society Interface, 12 (105)
- Erratum: Molecular phylogenetics and the diversification of hummingbirds (Current Biology (2014) 24 (910-916)) (2014)
Current Biology, 24 (9)
- Hovering flight in the honeybee apis mellifera: Kinematic mechanisms for varying aerodynamic forces (2014)
Physiological and Biochemical Zoology, 87 (6), 870-881
- Hummingbird wing efficacy depends on aspect ratio and compares with helicopter rotors (2014)
Journal of the Royal Society Interface, 11 (99)
- Hummingbirds control hovering flight by stabilizing visual motion (2014)
Proceedings of the National Academy of Sciences of the United States of America, 111 (51), 18375-18380
- Hydration history and attachment morphology regulate seed release in Chorizanthe rigida (Polygonaceae), a serotinous desert annual (2014)
American Journal of Botany, 101 (7), 1079-1084
- Molecular phylogenetics and the diversification of hummingbirds (2014)
Current Biology, 24 (8), 910-916
- The biophysics of bird flight: Functional relationships integrate aerodynamics, morphology, kinematics, muscles, and sensors (2014)
Canadian Journal of Zoology, 93 (12), 961-975
- Hummingbirds generate bilateral vortex loops during hovering: Evidence from flow visualization (2013)
Experiments in Fluids, 54 (1)
- Muscle activation patterns and motor anatomy of anna's hummingbirds calypte anna and zebra finches taeniopygia guttata (2013)
Physiological and Biochemical Zoology, 86 (1), 27-46
- North American ornithology in transition (2013)
Biology Letters, 9 (1)
- Very low force-generating ability and unusually high temperature dependency in hummingbird flight muscle fibers (2013)
Journal of Experimental Biology, 216 (12), 2247-2256
- Wingbeat kinematics and motor control of yaw turns in Anna's hummingbirds (Calypte anna) (2012)
Journal of Experimental Biology, 215 (23), 4070-4084
- Projected changes in elevational distribution and flight performance of montane Neotropical hummingbirds in response to climate change (2011)
Global Change Biology, 17 (4), 1671-1680
- Allometry of hummingbird lifting performance (2010)
Journal of Experimental Biology, 213 (5), 725-734
- Neuromuscular control of wingbeat kinematics in Anna's hummingbirds (CaIypte anna) (2010)
Journal of Experimental Biology, 213 (14), 2507-2514
- Trigeminal and spinal dorsal horn (Dis)continuity and avian evolution (2010)
Brain, Behavior and Evolution, 76 (1), 11-19
- Wake patterns of the wings and tail of hovering hummingbirds (2010)
Animal Locomotion, 46 (5), 273-284
- A higher-level taxonomy for hummingbirds (2009)
Journal of Ornithology, 150 (1), 155-165
- Fiber type homogeneity of the flight musculature in small birds (2009)
Comparative Biochemistry and Physiology - B Biochemistry and Molecular Biology, 152 (4), 324-331
- Oxygen consumption rates in hovering hummingbirds reflect substrate-dependent differences in P/O ratios: Carbohydrate as a 'premium fuel' (2007)
Journal of Experimental Biology, 210 (12), 2146-2153
- Phylogenetic systematics and biogeography of hummingbirds: Bayesian and maximum likelihood analyses of partitioned data and selection of an appropriate partitioning strategy (2007)
Systematic Biology, 56 (5), 837-856
- Flight performance and competitive displacement of hummingbirds across elevational gradients (2006)
American Naturalist, 167 (2), 216-229
- Short-amplitude high-frequency wing strokes determine the aerodynamics of honeybee flight (2005)
Proceedings of the National Academy of Sciences of the United States of America, 102 (50), 18213-18218
- Wing morphology and flight behavior of some north American hummingbird species (2005)
Auk, 122 (3), 872-886
- Aerodynamic forces of revolving hummingbird wings and wing models (2004)
Journal of Zoology, 264 (4), 327-332
- Conflicting terminology for wing measurements in ornithology and aerodynamics (2004)
Auk, 121 (3), 973-976
- Of Hummingbirds and Helicopters: Hovering Costs, Competitive Ability, and Foraging Strategies (2004)
American Naturalist, 163 (1), 16-25
- Resolution of a paradox: Hummingbird flight at high elevation does not come without a cost (2004)
Proceedings of the National Academy of Sciences of the United States of America, 101 (51), 17731-17736
- Take-off mechanics in hummingbirds (Trochilidae) (2004)
Journal of Experimental Biology, 207 (8), 1345-1352
- Darwin's hummingbirds (2003)
Science, 300 (5619), 588-589
- Flower Color, Hummingbird Pollination, and Habitat Irradiance in Four Neotropical Forests (2003)
Biotropica, 35 (3), 344-355
- Kinematics of hovering hummingbird flight along simulated and natural elevational gradients (2003)
Journal of Experimental Biology, 206 (18), 3139-3147
- The ecological and evolutionary interface of hummingbird flight physiology (2002)
Journal of Experimental Biology, 205 (16), 2325-2336
- Hovering performance of hummingbirds in hyperoxic gas mixtures (2001)
Journal of Experimental Biology, 204 (11), 2021-2027
- Observational learning in hummingbirds (2001)
Auk, 118 (3), 795-799
- Ultraviolet reflectance in fruits, ambient light composition and fruit removal in a tropical forest (2001)
Evolutionary Ecology Research, 3 (7), 767-778
- Maximal horizontal flight performance of hummingbirds: Effects of body mass and molt (1999)
Physiological and Biochemical Zoology, 72 (2), 145-155
- Novel interactions of non-pollinating ants with pollinators and fruit consumers in a tropical forest (1999)
Oecologia, 119 (4), 600-606