Biomechanics of hovering vertebrates
Abstract/Contents
- Abstract
- Insects, hummingbirds, and nectar bats evolved the ability to hover in front of flowers to get access to energy-rich nectar. It has been established that insects generate up to half of the lift needed to support their body weight during the upstroke. Estimates show that hummingbirds generate at least a quarter of their weight support during the upstroke by inverting their feathered wings more than generalist birds. In contrast, bats evolved membrane wings that they partially fold during the upstroke. While it has been hypothesized that hovering nectar bats generate vertical lift force during the upstroke, the complex structure of their wakes makes it hard to quantify this through flow measurement. To understand how hummingbirds and bats manipulate aerodynamic forces with their wings to perform these feats, we developed a new instrument that accurately measures these aerodynamic forces in vivo. This Aerodynamic Force Platform and an array of 3D-calibrated high-speed cameras simultaneously recorded the vertical aerodynamic forces and wing kinematics. The pressure field generated by the animal travels to the boundaries of the flight volume at the speed of sound. The top and bottom plate mechanically integrate the pressure distribution, which is measured by three force sensors on each plate. By using the Aerodynamic Force Platform to measure these wingbeat-resolved aerodynamic lift forces in vivo, we highlight similarities and differences across species and taxa. While it is known that insects improve efficiency by using elastic recoil for stroke reversal, it is unclear if hummingbirds converged on a similar solution, due to asymmetries in their lift generation and specialized flight muscle apparatus. We measured the aerodynamic force and kinematics of Anna's hummingbirds to resolve wing torque and power within the wingbeat. Comparing wingbeat resolved aerodynamic weight support measurements across species, we find that hummingbirds have low induced power losses similar to flies, much lower than typical for a generalist bird in slow hovering flight. We also show how hummingbirds' early muscle activation furnishes elastic recoil through stroke reversal to stay within the physiological limits of the pectoralis and supracoracoideus flight muscles. Expanding our species of interest, we traveled to Costa Rica with our new measurement device. We resolved the aerodynamic force and wing kinematics of 104 slow hovering hummingbirds and bats across 20 total species in vivo. While all hummingbirds we studied converged on an efficient horizontal wingbeat with an active upstroke to generate lift, the bats did not---they relied on drag to fully support their body weight. Remarkably, the nectar bats generate a significantly elevated vertical force during the upstroke compared to fruit bats---by inverting their wing more like hummingbirds---suggesting convergent evolution.
Description
| Type of resource | text |
|---|---|
| Form | electronic resource; remote; computer; online resource |
| Extent | 1 online resource. |
| Place | California |
| Place | [Stanford, California] |
| Publisher | [Stanford University] |
| Copyright date | 2018; ©2018 |
| Publication date | 2018; 2018 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Author | Ingersoll, Robert Rivers |
|---|---|
| Degree supervisor | Lentink, David, 1975- |
| Thesis advisor | Lentink, David, 1975- |
| Thesis advisor | Dabiri, John O. (John Oluseun) |
| Thesis advisor | Okamura, Allison |
| Degree committee member | Dabiri, John O. (John Oluseun) |
| Degree committee member | Okamura, Allison |
| Associated with | Stanford University, Department of Mechanical Engineering. |
Subjects
| Genre | Theses |
|---|---|
| Genre | Text |
Bibliographic information
| Statement of responsibility | Robert Rivers Ingersoll. |
|---|---|
| Note | Submitted to the Department of Mechanical Engineering. |
| Thesis | Thesis Ph.D. Stanford University 2018. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2018 by Robert Rivers Ingersoll
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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