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Bird Flight

Submitted by kheredia on Thu, 11/07/2019 - 14:34

Bird flight is not as simple as wing-flapping and hovering above the trees. This primary mode of locomotion has evolved to possess many intricacies involving movement. Despite several studies covering migrational behavior in birds, there is little information about the aerodynamic principles and forces behind flight. This is precisely why researchers at the Department of Biology in the University of Portland have studied the mechanical power output of the pectoralis muscle in magpies, cockatiels, and doves. They hypothesized that a number of factors could contribute to the overall shape of a power curve such as morphology, wing kinematics, and ultimately flight style.

Cockatiels and doves were subjected to a variable-speed wind tunnel to measure velocity and any potential change of the pectoralis. Bone strain recordings and sonomicrometry were used to monitor tension and length of the pectoralis muscle, while work output per wing beat was calculated. 3D kinematic data was also used for analysis of mechanical movement. The data from the velocity of birds in power curves were plotted for comparison. The results revealed a significant difference in pectoralis power output and speed. The doves were found to have a higher minimum (7ms-1) and maximum (17ms-1) power output and mass specific power output compared to the cockatiels (5ms-1, 14ms-1) for most speeds. However, there was an exception at 14ms-1, which was most likely due to a trade-off in the dove’s larger wing size relative to body size. Therefore, the doves would require more power in comparison to the cockatiel’s to account for reduced maneuverability at that speed.

Nonetheless, both species exhibited a U shaped curve for their power curves. In comparison, the mechanical power curve for magpies was relatively flat. This was likely due to morphological differences. Unlike cockatiels and doves, the broad wings and long tails in magpies constrain power output, greatly increasing drag while decreasing thrust. Overall, these implications are consistent with the hypothesis of this study. Wing morphology and flight style indeed significantly alter the shape of the power curve. However, this study does have restrictions. For example, these results are species dependent. There are evident physiological and behavioral differences in birds because they have evolved to be the most fit in distinct habitats. Some species, like galliformes, do not rely much on mass specific pectoralis power output because they use flight specifically to elude from predators. In addition, the researchers failed to take into account the possibility that more than just the pectoralis muscle is responsible for power output. This study also assumed that wings are the primary source of reducing power requirements. They did not consider that the tail could also aid in work. Due to these flaws, this field of study requires more research to conclude which components are important for locomotion in birds.

In the future, any similar experiments should include a more diverse sample size, and the biologists should measure potential variables to prevent any holes or discrepancies in data. Regardless of any mistakes, the data extracted from this study will serve as a helpful guide for improving the structure of experimentation as well as getting a better look into the relationship between mechanical power output and forward velocity in birds.