Meeting Abstract
High elevations are characterized by reductions in environmental parameters, such as oxygen availability and air density, which can affect flight performance. Typically, larger hummingbirds tend to be overrepresented at high elevation and their predominance there has been attributed to having disproportionately larger wings relative to lowland populations. The larger wings may offset the increased energetic requirements for flight at high elevation and affect how hovering metabolic rates scales with mass, morphology, and kinematics amongst taxa found at different elevational ranges. Based on the relationship between wing size and elevation, it is hypothesized that hovering metabolic rate would decline with increasing wing area and length, after accounting for body mass effects on both parameters. Oxygen consumption rates were recorded from hummingbirds using open-flow mask respirometry. Combining this with literature values, we examined the scaling of metabolic rates, wingbeat frequencies, and wing morphologies of hummingbird species across a 2200m gradient. We did not find a relationship between wing area and elevation, and found no scaling relationship between hovering metabolic rate and any morphological variables or kinematics after controlling for body mass. Overall, there is no evidence of adaptation of wing morphology to reduce energetic demands. Instead, high elevation performance may be related to their mechanochemical efficiency. Combining measurements of mechanical power output with the oxygen consumption data, efficiency displays positive scaling with body mass. The efficiency of the flight muscles may play a larger role in determining the upper elevational limits, as the more oxygen efficient muscles may provide greater aerobic scope at high elevations.
