Biomimetic Design for Pest Bird Control UAVs: A Survey

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Biomimetic Design for Pest Bird Control UAVs: A Survey Zihao Wang 1, Dr. Andrew Lucas 2, Dr. KC Wong 1 and Prof. Gregory Charmitoff 1 1

School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney 2 Agent Oriented Software Pty Ltd

Abstract This paper presents a survey of biomimetic design on small unmanned aerial vehicles (UAVs) for pest bird management in agriculture. The current pest bird control methods used in agriculture are introduced first, followed by a discussion of the advantages and limitations of these control methods. A discussion of why biomimetic design on UAVs is of high interest is then presented. A few of the typical biomimetic designs implemented on small UAVs are then compared, with an emphasis on the key design elements used, feasibility and effectiveness. The limitations of these biomimetic designs are analysed, and potential pathways to resolve these limitations are discussed. A conclusion is drawn at the end of this paper to summarise the current biomimetic designs. Keywords: unmanned aerial vehicle (UAV), pest bird damage control, biomimetic design, autonomy

Introduction Pest bird damage in agriculture is a significant problem across the globe, especially for high value crops. The total loss of crops to pest bird damage in Australia is estimated to be at around $300 million annually [1]. Various pest bird damage control methods have been developed in the past few decades. These methods, such as netting, shooting and artificial scaring tactics, are either ineffective or not economically viable. In addition, these solutions are temporary, the pest bird problem persists as soon as the treatment is stopped. In fact, the most effective long term solution is natural predation. Studies have shown that by training natural predatory birds such as falcons and eagles, the predator-prey population dynamics can be stabilized on a large scale [2]. However, the cost for hiring a trained falconer is not economically viable for most farms [3]. Hence, there is interest in designing a biomimetic pest bird damage control system that is both economical and as effective as natural predation. With the recent increase in popularity and development of UAV technologies [4], many individuals, research groups and companies are starting to explore the idea of using small UAVs to control damage caused by pest birds [5-8]. Many of these systems employ one or a combination of a few biomimetic elements to attempt to achieve the same effectiveness of natural predation [5-8]. These biomimetic elements range from using a simple audio system to broadcast predatory bird cries to combining predatory bird appearance, movement and behavior on a single UAV platform. This paper provides a broad overview of the current biomimetic design implementations on UAVs for pest bird damage control in agriculture.

Current Pest Bird Control Methods There are many bird control strategies currently employed by farmers around the world [9,10]. These control strategies can be generally divided into four categories: scare tactics, population reduction methods, exclusion methods, and natural predation.

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Scare Tactics These methods rely on a scare stimulus that presents an unusual, sudden or dangerous event to the birds [9]. There are many possible scare stimuli, and some of them are related to natural predation. Stimuli are required to be life-like, highly visible or loud, and in motion to be effective [9]. Some non-biomimetic examples are spinning metal strips and loud air-cannons. Scaring devices that include biomimetic elements are predatory bird silhouettes, speakers that broadcast distress calls, and remote controlled (RC) aircraft carrying predatory bird features [9]. RC aircraft can perform continuous unexpected motions, the RC aircraft itself can be considered a visual scare stimulus. The issue with scare tactics is that birds becoming habituated to them. Solutions to habituation include irregularity in the scaring pattern, combining visual and acoustic scaring methods, and presenting a real threat to the birds [9]. Population Reduction Methods Population reduction methods are usually lethal, such as poisoning, shooting and capturing [9]. The intention is to reduce the total number of pest birds in the local area, hence the damage to the crops should reduce accordingly. Shooting is in fact the most common method in Australia [9]. However, studies have shown that population reduction is often ineffective [9]. There are also legal issues in some countries with these methods, as some protected species can be accidently injured or killed [9]. Exclusion Methods Exclusion methods control pest bird damage by preventing birds from accessing the crops. Some popular methods include chemical repellents, nets over the crops, or using sleeves to cover individual crops [9]. Exclusion methods are highly effective. However, netting and sleeving are labour intensive. They can also hinder crop inspection and harvesting, which translates into high cost to the farmers [9]. Natural Predation Natural predation utilises birds of prey such as falcons and eagles to hunt pest birds near the farms. These predatory birds are usually highly trained by falconers who are sometimes employed by farmers [9]. Natural predation is an effective but expensive control method. This method is most effective when multiple predatory birds are used, making the cost associated with employing falconers uneconomical in most situations [10,11].

Pest Bird Control UAVs The literature suggests that none of the existing pest bird control methods are both effective and economical means for protecting agriculture from birds. One of the potential solutions is to mimic natural predation. Some studies have shown that UAVs mimicking natural predatory birds are effective in scaring pest birds [5]. Coincidently, the interest in using UAVs for this application is growing [12,13]. The cost of human UAV operators can also be eliminated with the fast-growing autonomous technologies. The small UAVs mentioned in this paper refer to power-driven, reusable, remotely operated or autonomous aircraft. In the past, UAVs were expensive and sophisticated machines primarily used by the military. UAVs have become affordable to researchers and consumers thanks to the development of high energy density batteries, miniaturised electronics, and fast wireless networking equipment [4]. The most common UAV types are fixed-wing, rotary-wing (e.g. 17th Australian Aerospace Congress, 26-28 February 2017, Melbourne

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quadcopters, helicopters), and fixed-wing with vertical take-off and landing (VTOL) capabilities.

Typical Biomimetic Designs The typical biomimetic designs implemented using UAVs for bird control are introduced and compared in this section. Due to commercial interests, it is difficult to compare the effectiveness of these designs directly from literature survey. Appearance Mimicking Designs Appearance mimicking is the simplest form of biomimetic design. Feather patterns, colour patterns, and large eye spots are typical features used. The aircraft structure is sometimes modified to resemble predatory bird shapes as well, such as wingtip and tail designs. These have been implemented by farm owners in the past on static objects. Kites or wooden boards with predator-shaped silhouettes are still used today in agriculture for pest bird control (Fig. 1).

Fig. 1: Scare Hawk Decoy by Birds Off – A commercial product for bird control, an example of appearance mimicking that uses static silhouette [14] Unfortunately, the predictable and static nature of the silhouette render them ineffective over time, as birds habituate to them very quickly. Appearance mimicking on UAVs are more effective as autonomous or remotely-piloted UAVs can exhibit unpredictable behaviour, which cause a significant delay to habituation. Appearance mimicking has been adopted by researchers (Fig. 2 [15]) as well as industries (Fig. 3 [16]). One common feature is that appearance mimicking is usually used on fixed-wing UAVs. This is due to the fact that conventional fixed-wing aircraft have large wings and small tails that resemble the typical shape of predators. It is therefore easier to make the mimicked appearance more life-like.

Fig. 2: A biomimetic autonomous aircraft for bird management from Royal Melbourne Institute of Technology (RMIT), Australia [15] 17th Australian Aerospace Congress, 26-28 February 2017, Melbourne

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Fig. 3: Shepherd, a remotely piloted UAV designed by Ecotactical Technologies for commercial bird control [16] Flapping Wing Designs Another form of visual mimicking is to replicate the wing flapping motion of predatory birds. A flapping design is quite complex. While replicating life-like motion, the design must still provide appropriate aerodynamic lift and propulsion. This design is much more difficult to implement and much less common in commercial practice. An example of implementing the flapping wing approach is Robirds by the company Clear Flight Solutions (Fig. 4). The company claimed a maximum of 50% reduction in bird numbers in some experiments [17].

Fig. 4: Robirds – Designed by Clear Flight Solutions for pest bird control, equipped with flapping wings and appearance of birds of prey [18] Audio Mimicking Designs Apart from visual cues, birds detect the presence of predators by sound as well. This has inspired products such as the Sparrow Repeller, which is a system consisting of loud speakers that broadcast recordings of distress, predator and harassment calls [18], designed to give the impression of a falcon attacking a sparrow. The audio recording combined with the unpredictable movement and the physical presence of the UAVs is effective against numerous bird types as claimed by some manufacturers [6,7]. Systems such as Sparrow Repeller can be easily implemented onto rotary UAVs, such as the Vulcan UAV Bird Control Drone “The ScareCrow” in Fig. 5. On the other hand, these systems are more challenging to implement on small fixed-wing UAVs due to the size. Birds will also habituate to the audio eventually if no real threat is present.


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Fig. 5: Left: BirdGard Sparrow Repeller. Right: Vulcan UAV Bird Control Drone – “The ScarCrow” quadcopter, with BirdGard Sparrow Repeller attached. Flight Pattern and Behaviour Mimicking Designs A different approach to the aforementioned designs is to mimic the flight pattern and behaviour of predatory birds. An interview with a North American wildlife biologist conducted by a research group from Oregon State University revealed that, the flight pattern and behaviour are as important as the appearance and sound [5]. More importantly, the flight pattern and behaviour should adhere to that of the local predatory bird species.

Fig. 6: Illustration of flight path designed by researchers at Oregon State University [5]. In these experiments, the researchers programmed a fixed-wing glider UAV to mimic the flight patterns of a Cooper’s Hawk [5]. The Cooper’s Hawk species prefer to perch and wait for appetizing prey, then swoop down for the kill [5]. The glider is programmed to loiter behind trees while gaining altitude, and then swoop down towards the vineyard using GPS coordinates, as illustrated in Fig. 6. The issues with the system is that no information of the bird location is available to the UAVs. While they claimed to achieve successful results from initial trials, it is likely to be inefficient if pest birds are not targeted more directly [5].

Potential Pathways to Resolve Current Limitations It is evident from this literature survey that there are limitations with existing biomimetic designs for UAV-based pest bird control. Appearance mimicking and audio mimicking designs are simple but pest birds eventually habituate. Flapping wing designs are mechanically complicated to satisfy both aerodynamic and propulsion requirements. Flight pattern mimicking designs are effective but not well targeted. There are several potential pathways to resolve these limitations. Pest bird location can be identified with a system that consists of bird-scaring UAVs, ground sensors and a ground control station (GCS). The ground sensors can be radar or cameras with vision processing modules that detect birds and inform the GCS where most of the pest birds are located. This 17th Australian Aerospace Congress, 26-28 February 2017, Melbourne

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information can then be transformed into waypoints for the UAVs. The UAVs can also be equipped with cameras with on-board processing. The cameras could aid in precision navigation during the swoop manoeuvres, so that it is more apparent to the birds that the UAVs are intentionally attacking them. Any UAV type could be used for this approach, but ideally, flapping wing designs combined with appearance and audio mimicking should be used to maximise effectiveness. To eliminate the difficulties with flapping wing designs, the aircraft can be replaced by a bird model with simple flapping wings that is towed or mounted to a multi-rotor. By doing so, the flapping wings do not have to provide lift and propulsion, which reduces the complexity significantly. Such a system could also mimic the predatory bird appearance more accurately.

Conclusion Pest bird damage in agriculture is a persistent problem across the globe, and existing solutions are not adequately addressing the issues. Many methods, such as scaring, trapping, excluding, and natural predation have been developed and tried. These methods, however, have limitations that have not yet been overcome. The literature demonstrates that the most effective solutions, even if temporary, are biomimetic designs. The emergence of highenergy-density lithium polymer batteries and miniaturized electronics has accelerated the availability of small UAVs, and there is much promise in the application of this technology for bird damage control in agriculture. This survey has discussed four approach categories for biomimetic bird control: appearance mimicking, flapping wings, audio mimicking, and behaviour mimicking. While commercial products employing some of these methods claim to work, other studies indicate that pest birds adapt quickly. A novel biomimetic approach is proposed, which incorporates the previous methods in a “smart” system that targets pest birds directly and takes advantages of recent developments in miniaturisation and energy storage density to combine all four approaches in a more natural predator-like design.


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