This dissertation explores the comparative biomechanics of hummingbird flight and contextualizes the findings by addressing its ecological relevance. Hummingbirds are considered an adaptive evolutionary radiation and are thus ubiquitous, speciose, and rapidly evolving in the tropics. This rapid radiation is, in part, bolstered by the evolution of advantageous morphology associated with floral nectar exploitation. One such notable evolved trait is a relatively small body that has the ability to hover in place and feed from flowers. The three chapters of this dissertation further expand upon the effects of body size among different modes of flight in several species of hummingbirds that occur in the Colombian Andes. Forward flight, vertical descent, and rotational flight are the three modes that are explored in a comparative framework. Further, the effect of flight practice is tested as a correlate to temporal flight performance in the first two chapters.
Seven species of hummingbirds, comprising two sub-clades, were included in this dissertation at the Colibrí Gorriazul Research Station (Lat. 4.3759826, Long. -74.3458155, elev. ~1,700 meters above sea level), which is situated on the western slope of the eastern cordillera of the Andes Mountains of Colombia. Hummingbirds recorded between July 2018 to August 2019 were included in the three chapters of this dissertation. A combination of GoPro Hero5 (60 fps at 1920 X 1080 pixels) and Fastec IL5 high-speed (500 fps at 1220 X 900 pixels) were used to capture recordings of hummingbirds performing forward flight translations, vertical descents, and rotational movements. Performance metrics were compared among at least four species of hummingbirds for each chapter and tested for explanatory correlates.
The first mode of flight explored is forward translation. Through the use of a novel horizontal flight apparatus, hummingbirds were trained and subsequently filmed eliciting three-meter forward trajectories. Eight individuals including five total species (Saucerottia cyanifrons, Amazilia tzacatl, Colibri coruscans, Colibri delphinae, and Anthracothorax nigricollis) were measured for body mass and forward velocity. Across a two-fold difference in body mass of the study animals, there was no correlation with body mass and peak forward velocity, rejecting the study’s first hypothesis. However, the horizontal apparatus allowed for the temporal observation of hummingbirds in training, which led to the formation of a second hypothesis: peak velocity increases with repeated use of the same forward flight path. The results of the study partially supported the second hypothesis and confirmed that some hummingbirds (one individual each of S. cyanifrons, A. tzacatl, C. coruscans, and A. nigricollis) improve their flight performance with practice. These results bring to question how non-temporal performance data is reported in the literature.
The second mode of flight that we explore is vertical descent, defined as a flapping, straight line approach towards the ground. Vertical descent is a form of flight that ostensibly requires more control relative to forward flight, and is an important behavior used in arthropod foraging and nest visitation. Here, we compare vertical descents for nine individuals representing five species (two Saucerottia cyanifrons, one Anthracothorax nigricollis, two Chalybura buffonii, three Colibri coruscans, and one C. delphinae) to test the effects of body mass on descent time intervals. All hummingbirds are filmed performing three-meter descent trajectories using the same novel flight apparatus referenced in Chapter One. Across a two-fold body mass range, the results suggest there is no significant relationship with vertical descent time and body mass. Given the results of Chapter One, we also performed a single experiment to test if flight performance changed over time in a single individual (Colibri coruscans) involved in the study. The results indicate that vertical descent velocity increases with vertical flight practice, suggesting that flight practice influences performance in multiple modes of flight.
The last mode of flight that we explore is rotational flight, a proxy for maneuverability, defined as a rotation about the body’s axis that encompasses 180. Rotational ability likely plays a significant role in the outcome of chases, territorial defense, and mate selection. Twenty-three recordings of four species (Colibri coruscans, Colibri cyanotus, Anthracothorax nigricollis, and Saucerottia cyanifrons) were filmed performing volitional rotations in order to test for body size and species effects. As in Chapter one and two, there was a two-fold body mass range in the dataset. The study’s findings indicate no significant relationship with body mass and rotational time intervals, nor between body mass and species identity. These results reject the study’s hypothesis. However, when the hummingbirds are parsed by their sub-clades, a significant pattern emerges. The results suggest that rotational rate is influenced by complex factors that require more rigorous phylogenetic tests.
Body mass is considered a significant morphological feature in biomechanics and is often a foundation for understanding variation in performance across organisms. The findings of this dissertation conclude that perhaps body mass is of little relative importance, among several complex factors, in understanding flight performance in Trochilidae. The novel contributions of this study are the comparative framework and the temporal sampling regimen that allows us to investigate how performance shifts with time and flight practice. Hummingbird flight performance is a field laden with literature. And despite the abundance of hummingbird literature, very few studies emphasize a comparative context. Lastly, the findings of these chapters, particularly the temporal performance sampling approach, expose new avenues for continued inquiry and research.
