Are unmanned aircraft systems (UASs) the future of wildlife monitoring? A review of accomplishments and challenges

Regular monitoring of animal populations must be established to ensure wildlife protection, especially when pressure on animals is high. The recent development of drones or unmanned aircraft systems (UASs) opens new opportunities. UASs have several advantages, including providing data at high spatial and temporal resolution, providing systematic, permanent data, having low operational costs and being low-risk for the operators. However, UASs have some constraints, such as short flight endurance. We reviewed studies in which wildlife populations were monitored by using drones, described accomplishments to date and evaluated the range of possibilities UASs offer to provide new perspectives in future research. We focused on four main topics: 1) the available systems and sensors; 2) the types of survey plan and detection possibilities; 3) contributions towards anti-poaching surveillance; and 4) legislation and ethics. We found that small fixed-wing UASs are most commonly used because these aircraft provide a viable compromise between price, logistics and flight endurance. The sensors are typically electro-optic or infrared cameras, but there is the potential to develop and test new sensors. Despite various flight plan possibilities, mostly classical line transects have been employed, and it would be of great interest to test new methods to adapt to the limitations of UASs. Detection of many species is possible, but statistical approaches are unavailable if valid inventories of large mammals are the purpose. Contributions of UASs to anti-poaching surveillance are not yet well documented in the scientific literature, but initial studies indicate that this approach could make important contributions to conservation in the next few years. Finally, we conclude that one of the main factors impeding the use of UASs is legislation. Restrictions in the use of airspace prevent researchers from testing all possibilities, and adaptations to the relevant legislation will be necessary in future.