The dynamics of hummingbird flight

Using rufous hummingbirds (Selasphorus rufus Gmelin) as test subjects, this paper addresses issues surrounding the energetic cost of acceleration. Hummingbirds have been the subjects of extensive aerodynamic and energetic studies, but current aerodynamic theory ignores acceleration as an energy expenditure during flight. Using four experiments, this thesis explores acceleration as an important part of the daily energy expenditures of rufous hummingbirds (Selasphorus rufus). In experiment 1,1 estimate velocity and acceleration continuously in hummingbirds. This experiment indicates that for short flights (< 3.5 m), hummingbirds accelerate for 100% of the flying time. For longer flights, a section of constant maximum velocity is inserted between two "acceleration envelopes" (one positive; one negative). These envelopes are independent of the length of the flight. Since most of hummingbirds' daily flights are less than 2 metres long (patch to patch and between flowers in patches), this suggests that most of the foraging time of hummingbirds is spent accelerating. This experiment shows that hummingbirds actively accelerate and may passively decelerate. Experiment 2 is a preliminary theoretical exploration of the possible energetic costs of acceleration. Using current aerodynamic theory, a thought experiment was performed to assess this cost. Current aerodynamic theory predicts a high cost for accelerating flights. However, due to its steady-state assumptions and small range of applicable velocities around Vmp, aerodynamic theory probably underestimates the cost of acceleration. In experiment 3,1 estimate the power required for acceleration by measuring the acceleration of hummingbirds in relation to the inclination of flight. This experiment indicates that hummingbird flight is energy limited and acceleration may cost as much as 3 times that of steady-state flight. It also shows that the power required for acceleration is close to the maximum sustainable power output estimated in other stud In experiment 4,1 estimate the power required for acceleration by measuring total power input and mass changes and by estimating energy expenditures from a complete time budget. Since the costs of all other component activities have been measured previously, the only term unknown is the cost of acceleration. This experiment supports the conclusion that acceleration is an expensive activity approximating the cost of maximum sustainable power output.Science, Faculty ofZoology, Department ofGraduat