The running kinematics of free-roaming giraffes, measured using a low cost unmanned aerial vehicle (UAV)
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Abstract
The study of animal locomotion can be logistically challenging, especially in the case of large or unhandleable animals in uncontrolled environments. Recent technological advances have permitted the use of Global Positioning System and inertial sensors in locomotion studies, but these methods require manual access to each study subject. Here we demonstrate the utility of a low cost unmanned aerial vehicle (UAV) in measuring two-dimensional running kinematics from free-roaming giraffes (Giraffa camelopardalis giraffa) in the Free State Province, South Africa. We collected 120 Hz video of running giraffes, and calibrated each video frame using metatarsal length as a constant object of scale. We tested a number of methods to measure metatarsal length. The method with the least variation used close range photography and a trigonometric equation to spatially calibrate the still image, and derive metatarsal length. In the absence of this option, a spatially calibrated surface model of the study terrain was used to estimate topographical dimensions in video footage of interest. Data for the terrain models were collected using the same equipment, during the same study period. We subsequently validated the accuracy of the UAV method by comparing similar speed measurements of a running human subject, with a gold standard method. We recommend that future users maximise the camera focal distance, and keep the subject in the central field of view.
The studied giraffes used a grounded rotary gallop with a speed range of 3.4 to 6.9 ms-1 (never cantering, trotting or pacing), and lower duty factors when compared with other cursorial quadrupeds. As this pattern might result in adverse increases in peak vertical limb forces with speed, it was notable to find that contralateral limbs became more in-phase with speed. Considering the latter pattern and the modest maximal speed of giraffes, we speculate that tissue safety factors are maintained within tolerable bounds this way. Furthermore, the angular kinematics of the neck were frequently isolated from the pitching of the body during running; this may be a result of the large mass of the head and neck. Further field experiments and biomechanical models are needed to robustly test these speculations.
Cite this as
2018. The running kinematics of free-roaming giraffes, measured using a low cost unmanned aerial vehicle (UAV) PeerJ Preprints 6:e27310v1 https://doi.org/10.7287/peerj.preprints.27310v1note This preprint is not peer-reviewed. You may wish to reference the subsequent peer-reviewed version of this article.
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This is a submission to PeerJ for review.
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Supplemental Information
Regression statistics describing how gait parameters vary with speed
Coefficients are in the form y = au+b. Significant p-values (green shading) were interpreted in the context of the Benjamini-Hochberg critical values, which are adjusted to account for multiple statistical comparisons.
Additional Information
Competing Interests
John R Hutchinson is an Academic Editor for PeerJ.
Author Contributions
Christopher K Basu conceived and designed the experiments, performed the experiments, analyzed the data, prepared figures and/or tables, authored or reviewed drafts of the paper, approved the final draft.
Francois Deacon conceived and designed the experiments, performed the experiments, contributed reagents/materials/analysis tools, approved the final draft.
John R Hutchinson conceived and designed the experiments, approved the final draft.
Alan M Wilson conceived and designed the experiments, contributed reagents/materials/analysis tools, approved the final draft.
Human Ethics
The following information was supplied relating to ethical approvals (i.e., approving body and any reference numbers):
This study had ethical approval from the Royal Veterinary College (URN 2016 1538) to carry out the study on giraffes and humans within its facilities and in fieldwork.
Animal Ethics
The following information was supplied relating to ethical approvals (i.e., approving body and any reference numbers):
Both the Royal Veterinary College (URN 2016 1538) and the University of the Free State, South Africa (UFS-AED2016/0063) provided full approval for this observational research on giraffes.
Field Study Permissions
The following information was supplied relating to field study approvals (i.e., approving body and any reference numbers):
Field experiments were approved by the Free State Province Department of Economic Development, Tourism and Environmental Affairs (permit number 01/34481)
Data Deposition
The following information was supplied regarding data availability:
Dryad. Data can only be deposited upon article acceptance.
Funding
This work was funded by NERC (PhD studentship for CKB; grant no. NE/K004751/1 to JRH), ERC (Advanced grant AD-G 323041 to AMW), National Research Foundation (South African project no. V106005 to FD), Society for Experimental Biology student travel grant (CKB), and a Company of Biologists Travelling Fellowship (CKB). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
