Hummingbird flight mechanics and maneuvers
To elucidate the physical and physiological limits to animal flight capacity, I and postdoctoral fellow Victor Ortega-Jimenez are currently studying hummingbirds exposed to various kinds of aerodynamic challenge, including turbulent airstreams, heavy rain, and transient perturbations.  Graduate student Erica Kim is similarly studying flight within vertical and asymmetric airflow, and graduate student Marc Badger is assessing flight maneuvers through vegetational clutter.  Work with former postdoctoral fellow Nir Sapir (Hebrew University) assesses the effects of wingtip ablation on flight performance, and that with former postdoctoral fellow Marta Wolf (Lund University) is examining the consequences of these manipulations for vortex production in both hovering and forward flight.  For a comparative perspective on limits to flight performance, Michael Dillon (University of Wyoming) and I are evaluating the allometry of maximum mechanical power output for insect flight muscle.  Using eleven species of hovering orchid bee in Panama, we are quantifying the relative decline in maximum force and power output with increasing body size, a trend which characterizes all volant taxa.  Similarly, graduate student Sofia Chang is pursuing the limits to flight capacity in blood-loaded mosquitos.


Evolutionary origins of insect and bird flight
The origins of flight remain a topic of great interest among biologists.  Steve Yanoviak (University of Louisville) and I have continued to work on the remarkable phenomenon of directed aerial descent in wingless arthropods.  These results suggest that controlled aerial behavior preceded the origins of wings proper, and that flight initially began via stages of gliding and maneuvering in terrestrial hexapods.  Ph.D. graduate Yonatan Munk (University of Washington) has also carried out biomechanical investigations of aerial maneuverability in gliding arboreal ants.  Recent Ph.D. graduate Yu Zeng is analyzing gliding flight and the evolution of intermediate-winged forms in stick insects, using both lab colonies and conducting fieldwork in Malaysia.  Recent Ph.D. graduate Dennis Evangelista (University of North Carolina) has examined the aerial righting reflex in juvenile birds to assess ontogenetic shifts from asymmetric to symmetric wing flapping, as postulated by our general hypothesis for flight evolution.  Collaborative work with Professor Xing Xu (Institute of Vertebrate Paleontology & Paleoanthropology, Beijing) on the origins of bird flight is linking the now abundant fossil record of four-winged avian precursors with biomechanical assessment of flight capacity.


Biomechanical and physiological adaptation to altitude
Hovering at higher elevations requires simultaneous compensation for the effects of reduced air density on force production, and for the consequences of lower oxygen partial pressures on the aerobically challenging requirement for high metabolic power.  Jim McGuire of the Museum of Vertebrate Zoology, Chris Witt at the University of New Mexico, and I have been examining morphological parameters, resistance to hypoxia, and flight performance for more than sixty hummingbird species across a 4000 meter gradient in the Peruvian Andes.  This analysis is explicitly embedded within the framework of a recently completed molecular phylogeny for about three hundred trochilid species, and incorporates both metabolic and aerodynamic analyses of hovering flight.  In a similar vein, I and Michael Dillon (University of Wyoming) are evaluating flight-related morphological and physiological traits for bumblebees across steep elevational gradients in southwest China.  Comparison of maximal flight performance for numerous bumblebee species covering an altitudinal range of 800 – 4000 meters elucidates patterns of interspecific adaptation in morphometrics, kinematics, and the aerodynamics of hovering flight.


Ecophysiology of Neotropical butterfly migrations
Since 1987, I and collaborators (Bob Srygley, USDA; Phil DeVries, University of New Orleans) have been studying natural flight performance of long-distance migratory butterflies (and the diurnal moth Urania fulgens) during the early rainy season in central Panama.  This work has included assessment of airspeeds, thermoregulatory capacity, lipid reserves, use of geomagnetic and sun compasses, and sensory mechanisms of flight control.  Ongoing studies include relationships between migratory population dynamics and climate, and the use of the antennae in flight control and orientation (in collaboration with Sanjay Sane, NCBS, Bangalore).

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Ethanol and the ripening sequence of tropical fruits
A fundamental prediction of the “drunken monkey” hypothesis is that ethanol is a low-level but widespread constituent within the pulp of many tropical fruits consumed by primates.  Working with postdoctoral fellow Matt Medeiros, I am quantitatively assessing the ripening sequence of palm and fig fruits on Barro Colorado Island, Panama, including such parameters as color, texture, sugar content, and ethanol concentration.  Comparable work on the fruits of Spondias mombin (Anacardiaceae) is being done collaboratively with Chrissy Campbell at Cal State Northridge.  We are additionally organizing studies of ethanol content within fruits consumed by chimpanzees and gorillas in lowland African rainforests.