Hummingbird Hovering Energetics and Flight Capacities Across Elevational Gradients

High elevations are characterized by reductions in environmental parameters, including oxygen availability and air density. This can be problematic for volant species, as sustaining flight in hypodense air is more energetically demanding relative to normodensity. Animals meet these challenges by increasing wingbeat kinematics and mechanical power output, necessitating increased metabolic input, while at the same time aerobic metabolism is constrained by hypoxic conditions associated with increasing elevation. These limits may restrict the range of behaviours that can be aerobically sustained. This thesis explores the kinematic and aerobic capacities for exercise across an elevational gradient, and examines possible morphological adaptations associated with life at high elevations. Using hummingbirds, a group of animals with high hovering metabolic rates and wide elevational distributions, I examine the flight capacities and aerobic scopes across an 1800-m elevational gradient, as well as any morphological adaptations that permit high elevation flight. The angular velocity of the wings during hovering flight varies across elevations during hovering flight challenges, with higher elevations associated with higher angular velocities. Subsequently, the mechanical and metabolic power output of the muscles increases with rising elevation and challenge. Nonetheless, there is no relationship between aerobic scope and elevation. Overall, this suggests that hummingbirds are not metabolically limited and maintain the capacity to perform aerobic activities across their native ranges. Examination of morphology has previously indicated that high elevation species may have disproportionately larger wings than their lower elevation counterparts, hypothesized to be compensatory for high elevations. My analysis of hovering metabolic rate scaling has demonstrated that there is no relationship between elevation and morphological characteristics; there does not appear to be a compensatory effect of morphological variation upon hovering flight metabolic rates. However, there is a significant relationship between mass and mechanochemical efficiency of the flight muscles during hovering. Given that larger species tend to be overrepresented at higher elevations, greater efficiency may have permitted larger species to expand upwards because of their capacity to economize oxygen use. Overall, hummingbirds do not vary in flight scope across elevations, and many species are able to maintain large elevational ranges without apparent morphological or functional adaptation.

Department dc:contributor.department

Cell and Systems Biology

Year dc:date.issued

2017

Author dc:creator

• Groom, Derrick Jordan Edgar

Advisor dc:contributor.advisor

• Welch Jr., Kenneth C

• elevation
• energetics
• flight
• hovering
• hummingbird
• metabolism

Handle dc:identifier.uri

http://hdl.handle.net/1807/78982

OAI identifier oai:identifier

oai:utoronto.scholaris.ca:1807/78982