# Networked Unmanned Aerial Vehicles for Surveillance and Monitoring: A Survey
## 4 Wildlife Monitoring UAVs
### Research Gap and Future Directions  
However, the use of UAVs raises biological and ethical concerns. When UAVs are used to monitor wild animals, one of the biggest issues is the resulting disturbances to the animals. Recent studies [86; 87; 88] have revealed that UAVs can cause significant interference to certain species, and many animals react negatively to the presence of UAVs in ecological field research. Unmanned aircraft systems have become a new source of disturbance for wild animals, according to a recent systematic literature review [89]. For instance, studies have shown that UAVs have negative impacts on various bird species [86]. Birds' typical negative reactions to UAVs include panic, delayed return times to the nest, and nest abandonment [90]. The impact of UAVs on terrestrial animals has also been studied. [PERSON] [87] found that, when UAVs fle overhead, black bears had consistently strong physiological responses, such as raised heart rates. [PERSON] [88] deployed two UAVs to approach different species of terrestrial mammalian wild animals (e.g., elephant, giraffe, zebra, etc.). The findings show that UAVs can elicit behavioural responses in a wide range of species. As a result, the authors concluded that strict regulations on the use of UAVs in wildlife areas are required to reduce disturbance. To solve this problem, a study by [PERSON] [91] proposed the best practice for minimizing UAV disturbance to wildlife in biological field research. They emphasized that minimum wildlife disturbance flight practices need to be exercised and that UAV trajectories that are potentially threatening should be avoided. There are growing appeals for researchers to develop effective strategies to safely apply UAVs to monitor wild animals to minimize the negative impacts [92; 93]. The research to date has only proposed some basic disturbance-reducing solutions such as increasing the UAVs' altitude or keeping a maximum useful distance to reduce disturbance [93; 94]. However, other than these, more specific methods for UAVs to perform covert monitoring of wildlife are still under investigation. Wildlife monitoring by UAVs can be broadly divided into two categories based on the mission types. The first typically involves flying over the animals to monitor the distribution of animals in a given area [92], referred to as \"overflight\". The second category is usually called \"close-up\" to closely inspect or observe a single animal or a small group of animals whose locations are known ahead of the launch. In general, close-up monitoring tends to induce stronger disturbance to subject animals. Several studies have emphasized that great caution should always be exercised when conducting close-up animal monitoring [91; 92]. To reduce the negative impact (disturbance) of wildlife-monitoring UAVs, a navigation control algorithm based on motion camouflage could be a possible solution. **Basic mechanism of motion camouflage:** When a pursuer approaches a moving prey, the former chooses its path so that it stays on a straight line segment connecting the current position of the target and a fixed reference point); see Figure 7.  
The target is unable to distinguish the moving pursuer from a stationary object because there is no optical flow on the target's visual system when using motion camouflage. Even without any advantage in speed, this motion strategy allows a pursuer to successfully follow a target while concealing its motion [95]. [PERSON] [95] also shows how motion camouflage can be used to conceal objects in both homogeneous and structured environments. Although the concept of motion camouflage is simple, experiments show that it can fool even humans with our advanced visual system [96]. By designing guardians laws for wildlife-monitoring UAVs based on motion camouflage, the visual disturbance induced by UAVs to wild animals could possibly be reduced. However, motion camouflage can not help reduce the noise disturbance of wildlife-monitoring UAVs.