Population estimates are fundamentally important for sound wildlife conservation and management, and yet, are well known to be subject to biases and inaccuracies. Flying-foxes (Pteropus spp.) roost in the canopies of trees and form colonies of tens to thousands of individuals. They are difficult to survey accurately, due to inaccessibility, lack of visibility within colonies, and between-counter variability. This study aims to develop more accurate, precise and less-biased methods for quantifying the number of individuals within flying-fox colonies, as well as monitoring changes in the number of individuals, area occupied, shape and animal density of flying-fox colonies. A method for quantifying the number of flying-foxes in roosts was developed, whereby a drone-acquired thermal orthomosaic of a colony is generated. In an orthomosaic, flying-foxes appear as bright circular objects against a darker background. Flying-foxes may be counted manually, or a Computer Vision workflow can be used to generate semi-automatic counts of flying-foxes with relatively high accuracy. I validated the accuracy of the thermal orthomosaic counting method by comparing direct counts of small groups of flying-foxes to counts derived from drone-acquired thermal imagery. Then I compared whole colony ground counts to counts derived from drone-acquired thermal orthomosaics. Counts derived from thermal orthomosaics tended to be approximately twice as high as those from ground counting methods conducted by both the experimenter and National Flying-Fox Monitoring Program. This suggests that ground count estimates underestimate the true number of individuals within flying-fox colonies, and that densely roosting flying-foxes may be more drastically undercounted. Finally, I demonstrated the utility of drone-acquired thermal imagery for mapping colony roosting density, roost area occupied and movement throughout the roost over time. This study highlights the utility of a new monitoring method for accurately estimating the flying-fox colony size, assessing roosting dynamics and assisting in the conservation and management of flying-foxes.
Date of Award | 2020 |
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Original language | English |
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- flying foxes
- conservation
- Australia
- infrared imaging
- drone aircraft
Investigating the use of drone-acquired thermal imagery as an effective new tool to inform the management and conservation of flying-fox colonies
McCarthy, E. D. (Author). 2020
Western Sydney University thesis: Master's thesis