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Przewalski’s Horses (Equus ferus przewalskii) Responses to Unmanned Aerial Vehicles Flights under Semireserve Conditions: Conservation Implication

Przewalski’s Horses (Equus ferus przewalskii) Responses to Unmanned Aerial Vehicles Flights under... Hindawi International Journal of Zoology Volume 2021, Article ID 6687505, 6 pages https://doi.org/10.1155/2021/6687505 Research Article Przewalski’s Horses (Equus ferus przewalskii) Responses to Unmanned Aerial Vehicles Flights under Semireserve Conditions: Conservation Implication 1 2 2 Vanessa Lu , Feng Xu , and Mardan Aghabey Turghan e acher School, 5025 acher Road, Ojai, CA 93023, USA State Key Laboratory of Desert and Oasis Ecology, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China Correspondence should be addressed to Mardan Aghabey Turghan; mardan@ms.xjb.ac.cn Received 19 December 2020; Revised 23 May 2021; Accepted 11 August 2021; Published 28 August 2021 Academic Editor: Lesley Rogers Copyright © 2021 Vanessa Lu et al. )is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Recent technological innovations have led to an upsurge in the availability of unmanned aerial vehicles (also known as drones and hereafter referred to as UAVs)—aircraft remotely operated from the ground—which are increasingly popular tools for ecological research, and the question of this study concerns the extent to which wildlife responses might allow aerial wildlife monitoring (AWM) by UAVs. Our experiment tests the hypothesis that the wildlife-UAVs interaction depends strongly on flight altitude that there may be a lowest altitude range for which the ungulates are not exceedingly disturbed, dictating a practically achievable level of discernibility in flight observation, for this question might influence the future viability of the UAVs in the study and protection of the other wildlife in China’s semiarid ecosystem. We examined the behavioral responses of a group of enclosed Przewalski’s horses (Equus ferus przewalskii) to the presence of different in-flight UAVs models by conducting flights at altitudes ranging from 1 to 52 meters and recorded the heights at which each horse reacted to (noticed and fled) the UAVs. All horses exhibited a stress response to UAVs flights as evidenced by running away. )e results suggest strong correlations between flight altitude and response across the different subjects that adults generally noticed the UAVs at the larger heights (20.58±10.46m) than the immature (4.67±0.87m). Meanwhile, reaction heights of females (15.85±6.01m) are smaller than that of males (26.85±18.52m). Supported by their biological roles in herds (e.g., males must give protection to his entire herd while females are purely responsible for their offspring), our results also show that age, closely followed by gender, are the two most significant elements that determine a horse’s level of alertness to the UAVs. )is research will help future scientists to better gauge the appropriate height to use a drone for animal observation in order to minimize disturbance and best preserve their natural behavior. livestock [1–3].)e lastrecorded sighting ofa wild Przewalski’s 1. Introduction horse occurred in the Dzungarian Gobi of Mongolia in 1969 1.1. Przewalski’s Horses. Przewalski’s horses (Equus ferus [4],andsincethen,thisspecieshasbeenextinctinthewildwith przewalskii), also known as Mongolian wild horses or Dzun- only a few remnant populations existing in small captive garian Horses, are the last surviving subspecies of wild horses. breedingherdsinWesterncountries,makingthesurvivalofthe Althoughinitiallysightedinthe15thcentury,thesehorseswere taxon possible [5–7]. All Przewalski’s horses alive today are not scientifically documented until 1880, and these horses were descendants from only 13 individuals that were the nucleus for sighted in the Mongolian Gobi Desert, by a Russian officer, captive breeding [1, 3, 6, 8, 9]. After another 20 years of captive Colonel Nikolai Przhevalsky, so the horses were named after breeding on four different continents, including Asia, the total him [1, 2]. After being captured and transferred to Europe in number of horses rose to almost 1000 individuals the early 1900s, Przewalski’s horses soon became endangered [3, 6, 7, 10–14], and many organizations have since then also due to habitat loss, over hunting, and competition with attempted to release the horses in semiwild habitats such as the 2 International Journal of Zoology horses remain somewhat of a mystery to scientific world today, Kalamaili Nature Reserve in Xinjiang, China. Although this may be a step in the right direction, these populations remain primarily because of their rarity. )e purpose of our study was to better understand Przewalski’s horses, in particular their somewhat dependent on human support for their survival. )erefore,recommendationforthesuccessofthisprojectstates response to UAVs under semireserve conditions. Previous to limit the number of domestic animals in the area, in order to studies of Przewalski’s horses and domestic and feral horses ensure a long-term self-sustaining population of Przewalski’s (Equus caballus) have shown left side bias in vigilance re- horses [1–3]. sponseswithhorsesreactingsoonerwhenapproachedfromthe left side by novel stimuli [39–41]. In this study, we wanted to look at the influence of the height of novel stimuli. We spe- 1.2. Previous Use of Unmanned Aerial Vehicles in Studies of cifically focused on discerning how individual horses reacted to WildlifeResearch. Unmannedaerial vehicles (UAVs)have the the height of UAVs and which factors influenced their reac- potential to revolutionize the way in which research is con- tions, whetheritbeage,gender,or theherdthatthey residedin. ducted in many scientific fields [15, 16]. UAVs have proven to Our hypothesis is that wildlife-UAVs interaction depends beusefuldevicesfortheobservationofwildlife,inparticularthe strongly on flight altitude, that flying too low could excessively production of systematic data with high spatial and temporal disturb them and that there may be a lowest altitude range for resolution because the devices can access remote or difficult which the ungulates are not exceedingly disturbed. terrain [17], collect large amounts of data for lower cost than Additionally, we hoped to learn the height at which UAV traditional aerial methods, and facilitate observations of species flights could operate without disturbing the horses and that are wary of human presence [18]. Currently, despite large whether UAVs can be a reliable tool in the observation of regulatory hurdles, UAVs are being deployed by researchers their behavior and other wild wildlife. We also hypothesized and conservationists to monitor threats to biodiversity, collect that horses would respond to the UAV flight in one of four frequent aerial imagery, estimate population abundance, and ways: no discernable responses (positive) and discernable deter poaching [19–24], but with the widespread increase in responses (negative) (i.e., attention, eye/head movement UAV flights, it is critical to understand whether UAVs act as and/or turning of the upper body, increased movement stressors to wildlife and to quantify that impact. It is likely that rates, and/or moving away slowly from the UAVs). We also UAVs could also have unwanted and unanticipated risks on hypothesized that the degree of responses would vary with wildlife and their delicate ecosystems. Research has shown that respect to age and gender. retaliation against UAVs by terrestrial mammals was different from that of marine mammals and aquatic birds [25, 26]. For 2. Materials and Methods example, a study into the free-roaming American black bears (Ursus americanus) proved that the presence of UAV flights )e design of the experiment began determining a range of bringssignificantdistress tothe physiological state,which often flight altitudes. )e range of flight altitudes was determined does not manifests itself in terms of behavioral changes, through preliminary tests, flying at altitudes from 1 meter to proving difficult for observers to discern [27]. Furthermore, a 100 meters in10m increments. Wedetermined that1–5mwas study on guanacos (Lama guanicoe) revealed that low-flying a suitable lower bound because of safety concerns and that UAVs at any speed, as well as high-flying UAVs at an 50–60m was a suitable upper bound because negative response accelerated velocity, caused a disturbance to the guanacos’ had already significantly dropped off by that altitude. behavior [28]. Although UAVs have potential for success, a great deal of 2.1. Study Area. )is study was conducted at three separate uncertainty still surrounds their use, and scientists must be enclosures of the Wild Horse Breeding Research Center of cautious of the impact that they bring to each new investi- Xinjiang Uygur Autonomous Region, China (44 12′20.5′N, gation, especially when endangered species or ecologically 88 44′52.8′E). )is area has a semiarid, desert climate with sensitive habitats are involved [27]. Moreover, it is vital that UAVs are manufactured and selected to minimize visual and great seasonal temperature differences: the hottest recorded ° ° summer temperatures 40 C, 104 F, and winter temperatures audio stimuli in order to reduce disturbance of wildlife. Shape, volume, and color are all factors to be taken into consideration often fall below −15 C. To maintain natural breeding pat- terns and social structures of Przewalski’s horses, the horses thus to mimic nonthreatening wildlife native to the studied habitat in order to decrease disruption [29]. Sporadic move- typically remained in their native herd following birth to be raised by their mothers. Once they reached a mature age, ments and threatening or alarming trajectories should be avoided at all costs, and if an operation proves to be excessively they would be reallocated to herds corresponding to their genders. Occasionally, mares would be regrouped to create a disruptive,itmustbeceasedimmediately[27].Withthesebasic novel mixed herd, while stallions would be reintroduced to regulations in place to ensure safety and ethicality, UAV flight such mixed herds to determine dominance. )e defeated are sure to make steady progress and evolve into more effective stallion returns to his single-sex herd, while the victorious devices for the study of animal behavior. stallion gains control over his new mixed-sex herd. 1.3.SummaryandHypothesis. Asthelastsurvivingsubspecies of wild horses, Przewalski’s horses are a great subject of interest 2.2. Data Collection. )e unmanned aerial vehicle (UAVs) tothescientificcommunity.Despiteextensivestudiesespecially we used was a Mavic 2 Zoom drone, powered by a 1/2.3inch on their social behavior and time budget [30–38], Przewalski’s 12MP sensor with up to 4x zoom, including a 2x optical International Journal of Zoology 3 can range from subtle ear swivels indicating auditory in- zoom (24–48mm) to capture all shorts from wide angle to midrange. )e 4x lossless zoom and 2x optical zoom enabled fluence to indirect glances at the UAVs. Once a subject displays any of these reactions, it becomes aware of the a closer, high-definition view of faraway subjects while maintaining our distance to decrease the disruption to our existence of the drone, and the height of the UAVs was horses. )e Mavic 2 cameras utilized DJI’s latest 3-axis recorded as the alert height. Level 2, known as the run away gimbal technology and recorded videos at higher bitrates height, was the height of the UAVs at which the subject with advanced H.265 compression. Videos in H.265/HEVC physically displaced itself to avoid the UAVs. codecmaintain 50%more information thanvideos inH.264/ AVC, which leads to better preserved details allowing us to 2.3. Data Analysis. Data were tested for normality with the clearly recognize behavioral signals in our horses. Addi- one sample Kolmogorov–Smirnov test. Because all of the tionally, FOC sinusoidal drive ESCs and low-noise pro- data showed a normal distribution, we used the t-test to pellers reduce flight noise, thus reducing disturbance to the detect the differences of alert height and flight initiation horses. Binoculars (10x magnification) were used when height between the age and sex. We then used the general needed. Horses were followed on foot and watched at dis- linear model to test the effect of age, sex, and their inter- tances of 30–100m. Individual horses were identified using action on alert height and flight initiation height. We ac- sex, size, color, and distinguishing markings. cepted statistical significance at the level of p>0.05, and all UAV flights were conducted from August 1, 2020, to the data were analyzed using the SPSS 19.0 statistical December 08, 2020, at consistent times during daylight package. hours in order to reduce the influence of other factors that may affect the reaction times of Przewalski’s horses. )e 3. Results research team consists of four personnels: (1) a pilot, (2) a primary observer, (3) a ground camera operator, and (4) a Przewalski’s horses responded to UAV flights in all 62 data recorder. )e pilot was responsible for flying the UAVs. flights. Tables 1 and 2 display the comparative makeup of Only one horse was scored when the drone was flown over a each response for the different altitudes. First, notice that the herd. Flights were made of 62 horses including 53 adults and positive responses (no discernable movement and alert) nine immature horses (adult male, N �9; immature male, increases with altitude, while the negative responses (dis- N �5; adult female, N �44; and immature male, N �4) living cernable movement and alert) decrease with altitude. )e under natural social conditions at three separate enclosures. results help us illustrate the general pattern of less negative )e ages of the horses were obtained from records of the response at higher altitudes supporting the hypothesis that reserve association (horses ranged from 1 day to 2 years were altitude plays a large role in animal response from UAVs. categorized as immature until they had left their natal band). Next, notice that the degree of response varied with respect Since these horses have been studied extensively, they were to age and gender: the alert height (height for horse to notice habituated to observation and were not highly vigilant and UAVs) and run away height (height for horse to move away) reactive to the presence of the observer, who could watch of adult horses ranged 11–52 and 1–36 meters while that of from a distance up to as little as 20–50m while remaining immature ranged 3–6 and 1–2 meters, respectively. )e stationary. result also showed that immature compared to adults )e UAVs were launched approximately 100m from the showed a greater effect in males than in females (Table 1). targeted location of the horse. )e total dataset consisted of Additionally, alert height and run away height for female of 62 flights that ranged in altitude from 1 to 100 meters. Each all tested herds ranged 8–30 and 1–4 meters, while for male flight began with taking off from a launch point, flying about ranged 29–52 and 4–36 meters, respectively, showing that 100m high from a focal individual animal, changing altitude male horses are more alert than the females (Table 2). In as appropriate when passing over the subject. )e UAVs summary, age, sex, and their interaction have significant were flown over the animal or herd at 10m/s. )e next pass effects on alert height and run away height (Table 3). was flown at another randomly selected altitude. If an af- firmative response was invoked, the drone would wait at a 4. Discussion distance, while the animals would settle back to a sedentary behavior. With the widespread increase in UAV flights, it is critical to We used the live video feed which also offers a recorded understand whether UAVs act as stressors to wildlife and to video after a completed flight and the location stamp, which quantify that impact [27]. Prior to this study, [27] assessed informs us of the exact height and angle of the drone to effects of UAV flights on movements and heart rate re- determine the vertical distance from our subjects, as well as sponses of free-roaming American black bears and con- the exact measurements at which they individually displayed cluded that UAV flights induced strong behavioral as well as the two levels of reaction that we were measuring. To avoid physiological responses, but most bears did not respond confusion, the term “response” is used here for all levels of behaviorally by increasing movement rates or moving to a behavioral responses, as it is for a broad range of species to different location. However, horses responded rather refer to an animal interrupting feeding, by lifting or cocking strongly to UAV flights in all 62 tests in this study. Prze- its head, and to attend to its surroundings [41]. Level 1, walski’s horses were unhabituated to the UAVs, and the known as the alert height, was determined through the eye study was conducted in the presence of stress-inducing and ear movements of Przewalski’s horses; these reactions events that occur naturally in the environment. )e results 4 International Journal of Zoology Table 1: Comparison of alert height and run away height of Przewalski’s horses. Variables Number Alert height (m)±SE t-test Run away height (m) ±SE t-test Immature males 5 5.0±0.71 P<0.001 1.40±0.55 P � 0.003 Males Adults males 9 40.33±9.38 18.67±12.80 Immature females 4 4.50±0.50 P<0.001 1.25±0.50 P � 0.130 Females Adults females 44 16.68±5.26 2.16±0.83 Alertheight,heightforhorse tonoticeUAVs; runawayheight,heightfor horsetomove away(meanswith standarderrors).“Number” refersto thenumber of flights: only one horse was scored when the drone was flown over a herd. Table 2: Comparison of alert height and run away height between age and sex of Przewalski’s horses. Variables Number Alert height (m)±SE t-test Run away height (m) ±SE t-test Immature 9 4.67±0.87 P<0.001 1.22±0.4 P � 0.013 Age Adults 53 20.58±10.46 5.18±8.82 Males 14 26.85±18.52 P � 0.025 11.50±12.61 P � 0.01 Sex Females 48 15.85±6.01 2.11±0.84 Alertheight,heightforhorse tonoticeUAVs; runawayheight,heightfor horsetomove away(meanswith standarderrors).“Number” refersto thenumber of flights: only one horse was scored when the drone was flown over a herd. Table 3: Effects of age, sex, and their interaction on alert height and run away height. Factors Alert height (m) Run away height (m) F �19.345 F �15.111 Age P≤0.001 P � 0.002 F �13.383 F �28.510 Sex P � 0.001 P � 0.01 F �13.133 F �17.324 Interaction of age and sex P � 0.001 P � 0.004 Alert height, height for horse to notice UAVs; run away height, height for horse to move away (means with standard errors). of her entire herd, she is accountable for the wellbeing of her suggest strong correlations between flight altitude and re- sponse which support our hypothesis 2 that UAVs induced foal(s). )us, her alertness, though not as high as that of a behavioral responses, including relocation (moving out of stallion, is increased to the point where she is still able to the way of the UAV but still in sight) and flee (movement ensure the safety of her offsprings [27]. from sight) as well as eye/head movement and/or turning of )erefore, height cannot be the only factor involved in the upper body. our experiment. Disturbance caused by UAVs depends not Hypothesis 3 was also strongly supported by our result. only on sound intensity (dB) and frequency (Hz) but also by )e strength of the responses varied among sex and age, and the duration and pattern of the noise. Further investigation our results suggest that age and gender are the significant in this area would be desirable. As mentioned above, age plays an important role in determining factors of a horse’s reaction to UAVs. Mature horses were significantly more vigilant of the UAVs than determining the alert level of Przewalski’s horses due to the immature as demonstrated by the higher heights at which nature of their role in their herds; younger horses have no adult horseswere alerted to theflying UAVscomparedto the need to remain vigilant, while stallions and mares have to immature. )erefore, this can be attributed to the lack of care for their herds and foals, respectively. Furthermore, the experience of younger horses; thus, a lower level of response, sex of adult horses also obviously influences the distance at which supports previous data on the behavior of Prze- which they noticed foreign objects, again, due to the level of walski’s horses, will be further discussed later. )e results responsibility that they take on within their herds. also sets gender (exclusive to mature horses) as the second In terms of the practicality of unmanned aerial vehicles used as a tool in the field of animal research, our experiment most influential factor of UAVs reaction height for the fact that alert height for female of all tested herds was lower than leads us to believe that UAVs are an extremely useful in- strument for remotely observing the behavior of certain that of any male horse. Both of these conclusions are not only supported by our animals. However, as has been suggested in previous ex- data but also justified by the works of other scientists, as periments, UAVs must be used with caution and environ- Kolter mention the role of a stallion as the protector of his mental consciousness [29]. In order to avoid disturbance to herd, especially one that includes mares and foals [26]. An an animal’s natural routine during observation, we, as sci- integral element of his responsibility depends on his ability entists, must be aware and in full control of the drone’s to fend off unknown creatures, which includes the UAVs. proximity to the subjects [28]. In our research, the furthest Meanwhile, though the mare is not responsible for the safety vertical distance at which the UAV was first noticed was 52 International Journal of Zoology 5 meters. )is informs us that the optimum height for ob- thank Guest Professor Zhongze Niu for supporting them to servation of the Przewalski’s horses will certainly be above 52 conduct the present research in the study area. )e authors meters, though, without additional data, it will not be are also grateful to Senior Engineer Entemakh for his help on possible to determine the exact optimum height. Our ex- field survey. )e authors are also grateful for advice given by periment informs us that with minimized disturbance, Paul Jason Buzzard, China Exploration and Research So- UAVs are technologically advanced and practical scientific ciety, Hong Kong, China. devices. 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Przewalski’s Horses (Equus ferus przewalskii) Responses to Unmanned Aerial Vehicles Flights under Semireserve Conditions: Conservation Implication

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Copyright © 2021 Vanessa Lu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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Hindawi International Journal of Zoology Volume 2021, Article ID 6687505, 6 pages https://doi.org/10.1155/2021/6687505 Research Article Przewalski’s Horses (Equus ferus przewalskii) Responses to Unmanned Aerial Vehicles Flights under Semireserve Conditions: Conservation Implication 1 2 2 Vanessa Lu , Feng Xu , and Mardan Aghabey Turghan e acher School, 5025 acher Road, Ojai, CA 93023, USA State Key Laboratory of Desert and Oasis Ecology, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China Correspondence should be addressed to Mardan Aghabey Turghan; mardan@ms.xjb.ac.cn Received 19 December 2020; Revised 23 May 2021; Accepted 11 August 2021; Published 28 August 2021 Academic Editor: Lesley Rogers Copyright © 2021 Vanessa Lu et al. )is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Recent technological innovations have led to an upsurge in the availability of unmanned aerial vehicles (also known as drones and hereafter referred to as UAVs)—aircraft remotely operated from the ground—which are increasingly popular tools for ecological research, and the question of this study concerns the extent to which wildlife responses might allow aerial wildlife monitoring (AWM) by UAVs. Our experiment tests the hypothesis that the wildlife-UAVs interaction depends strongly on flight altitude that there may be a lowest altitude range for which the ungulates are not exceedingly disturbed, dictating a practically achievable level of discernibility in flight observation, for this question might influence the future viability of the UAVs in the study and protection of the other wildlife in China’s semiarid ecosystem. We examined the behavioral responses of a group of enclosed Przewalski’s horses (Equus ferus przewalskii) to the presence of different in-flight UAVs models by conducting flights at altitudes ranging from 1 to 52 meters and recorded the heights at which each horse reacted to (noticed and fled) the UAVs. All horses exhibited a stress response to UAVs flights as evidenced by running away. )e results suggest strong correlations between flight altitude and response across the different subjects that adults generally noticed the UAVs at the larger heights (20.58±10.46m) than the immature (4.67±0.87m). Meanwhile, reaction heights of females (15.85±6.01m) are smaller than that of males (26.85±18.52m). Supported by their biological roles in herds (e.g., males must give protection to his entire herd while females are purely responsible for their offspring), our results also show that age, closely followed by gender, are the two most significant elements that determine a horse’s level of alertness to the UAVs. )is research will help future scientists to better gauge the appropriate height to use a drone for animal observation in order to minimize disturbance and best preserve their natural behavior. livestock [1–3].)e lastrecorded sighting ofa wild Przewalski’s 1. Introduction horse occurred in the Dzungarian Gobi of Mongolia in 1969 1.1. Przewalski’s Horses. Przewalski’s horses (Equus ferus [4],andsincethen,thisspecieshasbeenextinctinthewildwith przewalskii), also known as Mongolian wild horses or Dzun- only a few remnant populations existing in small captive garian Horses, are the last surviving subspecies of wild horses. breedingherdsinWesterncountries,makingthesurvivalofthe Althoughinitiallysightedinthe15thcentury,thesehorseswere taxon possible [5–7]. All Przewalski’s horses alive today are not scientifically documented until 1880, and these horses were descendants from only 13 individuals that were the nucleus for sighted in the Mongolian Gobi Desert, by a Russian officer, captive breeding [1, 3, 6, 8, 9]. After another 20 years of captive Colonel Nikolai Przhevalsky, so the horses were named after breeding on four different continents, including Asia, the total him [1, 2]. After being captured and transferred to Europe in number of horses rose to almost 1000 individuals the early 1900s, Przewalski’s horses soon became endangered [3, 6, 7, 10–14], and many organizations have since then also due to habitat loss, over hunting, and competition with attempted to release the horses in semiwild habitats such as the 2 International Journal of Zoology horses remain somewhat of a mystery to scientific world today, Kalamaili Nature Reserve in Xinjiang, China. Although this may be a step in the right direction, these populations remain primarily because of their rarity. )e purpose of our study was to better understand Przewalski’s horses, in particular their somewhat dependent on human support for their survival. )erefore,recommendationforthesuccessofthisprojectstates response to UAVs under semireserve conditions. Previous to limit the number of domestic animals in the area, in order to studies of Przewalski’s horses and domestic and feral horses ensure a long-term self-sustaining population of Przewalski’s (Equus caballus) have shown left side bias in vigilance re- horses [1–3]. sponseswithhorsesreactingsoonerwhenapproachedfromthe left side by novel stimuli [39–41]. In this study, we wanted to look at the influence of the height of novel stimuli. We spe- 1.2. Previous Use of Unmanned Aerial Vehicles in Studies of cifically focused on discerning how individual horses reacted to WildlifeResearch. Unmannedaerial vehicles (UAVs)have the the height of UAVs and which factors influenced their reac- potential to revolutionize the way in which research is con- tions, whetheritbeage,gender,or theherdthatthey residedin. ducted in many scientific fields [15, 16]. UAVs have proven to Our hypothesis is that wildlife-UAVs interaction depends beusefuldevicesfortheobservationofwildlife,inparticularthe strongly on flight altitude, that flying too low could excessively production of systematic data with high spatial and temporal disturb them and that there may be a lowest altitude range for resolution because the devices can access remote or difficult which the ungulates are not exceedingly disturbed. terrain [17], collect large amounts of data for lower cost than Additionally, we hoped to learn the height at which UAV traditional aerial methods, and facilitate observations of species flights could operate without disturbing the horses and that are wary of human presence [18]. Currently, despite large whether UAVs can be a reliable tool in the observation of regulatory hurdles, UAVs are being deployed by researchers their behavior and other wild wildlife. We also hypothesized and conservationists to monitor threats to biodiversity, collect that horses would respond to the UAV flight in one of four frequent aerial imagery, estimate population abundance, and ways: no discernable responses (positive) and discernable deter poaching [19–24], but with the widespread increase in responses (negative) (i.e., attention, eye/head movement UAV flights, it is critical to understand whether UAVs act as and/or turning of the upper body, increased movement stressors to wildlife and to quantify that impact. It is likely that rates, and/or moving away slowly from the UAVs). We also UAVs could also have unwanted and unanticipated risks on hypothesized that the degree of responses would vary with wildlife and their delicate ecosystems. Research has shown that respect to age and gender. retaliation against UAVs by terrestrial mammals was different from that of marine mammals and aquatic birds [25, 26]. For 2. Materials and Methods example, a study into the free-roaming American black bears (Ursus americanus) proved that the presence of UAV flights )e design of the experiment began determining a range of bringssignificantdistress tothe physiological state,which often flight altitudes. )e range of flight altitudes was determined does not manifests itself in terms of behavioral changes, through preliminary tests, flying at altitudes from 1 meter to proving difficult for observers to discern [27]. Furthermore, a 100 meters in10m increments. Wedetermined that1–5mwas study on guanacos (Lama guanicoe) revealed that low-flying a suitable lower bound because of safety concerns and that UAVs at any speed, as well as high-flying UAVs at an 50–60m was a suitable upper bound because negative response accelerated velocity, caused a disturbance to the guanacos’ had already significantly dropped off by that altitude. behavior [28]. Although UAVs have potential for success, a great deal of 2.1. Study Area. )is study was conducted at three separate uncertainty still surrounds their use, and scientists must be enclosures of the Wild Horse Breeding Research Center of cautious of the impact that they bring to each new investi- Xinjiang Uygur Autonomous Region, China (44 12′20.5′N, gation, especially when endangered species or ecologically 88 44′52.8′E). )is area has a semiarid, desert climate with sensitive habitats are involved [27]. Moreover, it is vital that UAVs are manufactured and selected to minimize visual and great seasonal temperature differences: the hottest recorded ° ° summer temperatures 40 C, 104 F, and winter temperatures audio stimuli in order to reduce disturbance of wildlife. Shape, volume, and color are all factors to be taken into consideration often fall below −15 C. To maintain natural breeding pat- terns and social structures of Przewalski’s horses, the horses thus to mimic nonthreatening wildlife native to the studied habitat in order to decrease disruption [29]. Sporadic move- typically remained in their native herd following birth to be raised by their mothers. Once they reached a mature age, ments and threatening or alarming trajectories should be avoided at all costs, and if an operation proves to be excessively they would be reallocated to herds corresponding to their genders. Occasionally, mares would be regrouped to create a disruptive,itmustbeceasedimmediately[27].Withthesebasic novel mixed herd, while stallions would be reintroduced to regulations in place to ensure safety and ethicality, UAV flight such mixed herds to determine dominance. )e defeated are sure to make steady progress and evolve into more effective stallion returns to his single-sex herd, while the victorious devices for the study of animal behavior. stallion gains control over his new mixed-sex herd. 1.3.SummaryandHypothesis. Asthelastsurvivingsubspecies of wild horses, Przewalski’s horses are a great subject of interest 2.2. Data Collection. )e unmanned aerial vehicle (UAVs) tothescientificcommunity.Despiteextensivestudiesespecially we used was a Mavic 2 Zoom drone, powered by a 1/2.3inch on their social behavior and time budget [30–38], Przewalski’s 12MP sensor with up to 4x zoom, including a 2x optical International Journal of Zoology 3 can range from subtle ear swivels indicating auditory in- zoom (24–48mm) to capture all shorts from wide angle to midrange. )e 4x lossless zoom and 2x optical zoom enabled fluence to indirect glances at the UAVs. Once a subject displays any of these reactions, it becomes aware of the a closer, high-definition view of faraway subjects while maintaining our distance to decrease the disruption to our existence of the drone, and the height of the UAVs was horses. )e Mavic 2 cameras utilized DJI’s latest 3-axis recorded as the alert height. Level 2, known as the run away gimbal technology and recorded videos at higher bitrates height, was the height of the UAVs at which the subject with advanced H.265 compression. Videos in H.265/HEVC physically displaced itself to avoid the UAVs. codecmaintain 50%more information thanvideos inH.264/ AVC, which leads to better preserved details allowing us to 2.3. Data Analysis. Data were tested for normality with the clearly recognize behavioral signals in our horses. Addi- one sample Kolmogorov–Smirnov test. Because all of the tionally, FOC sinusoidal drive ESCs and low-noise pro- data showed a normal distribution, we used the t-test to pellers reduce flight noise, thus reducing disturbance to the detect the differences of alert height and flight initiation horses. Binoculars (10x magnification) were used when height between the age and sex. We then used the general needed. Horses were followed on foot and watched at dis- linear model to test the effect of age, sex, and their inter- tances of 30–100m. Individual horses were identified using action on alert height and flight initiation height. We ac- sex, size, color, and distinguishing markings. cepted statistical significance at the level of p>0.05, and all UAV flights were conducted from August 1, 2020, to the data were analyzed using the SPSS 19.0 statistical December 08, 2020, at consistent times during daylight package. hours in order to reduce the influence of other factors that may affect the reaction times of Przewalski’s horses. )e 3. Results research team consists of four personnels: (1) a pilot, (2) a primary observer, (3) a ground camera operator, and (4) a Przewalski’s horses responded to UAV flights in all 62 data recorder. )e pilot was responsible for flying the UAVs. flights. Tables 1 and 2 display the comparative makeup of Only one horse was scored when the drone was flown over a each response for the different altitudes. First, notice that the herd. Flights were made of 62 horses including 53 adults and positive responses (no discernable movement and alert) nine immature horses (adult male, N �9; immature male, increases with altitude, while the negative responses (dis- N �5; adult female, N �44; and immature male, N �4) living cernable movement and alert) decrease with altitude. )e under natural social conditions at three separate enclosures. results help us illustrate the general pattern of less negative )e ages of the horses were obtained from records of the response at higher altitudes supporting the hypothesis that reserve association (horses ranged from 1 day to 2 years were altitude plays a large role in animal response from UAVs. categorized as immature until they had left their natal band). Next, notice that the degree of response varied with respect Since these horses have been studied extensively, they were to age and gender: the alert height (height for horse to notice habituated to observation and were not highly vigilant and UAVs) and run away height (height for horse to move away) reactive to the presence of the observer, who could watch of adult horses ranged 11–52 and 1–36 meters while that of from a distance up to as little as 20–50m while remaining immature ranged 3–6 and 1–2 meters, respectively. )e stationary. result also showed that immature compared to adults )e UAVs were launched approximately 100m from the showed a greater effect in males than in females (Table 1). targeted location of the horse. )e total dataset consisted of Additionally, alert height and run away height for female of 62 flights that ranged in altitude from 1 to 100 meters. Each all tested herds ranged 8–30 and 1–4 meters, while for male flight began with taking off from a launch point, flying about ranged 29–52 and 4–36 meters, respectively, showing that 100m high from a focal individual animal, changing altitude male horses are more alert than the females (Table 2). In as appropriate when passing over the subject. )e UAVs summary, age, sex, and their interaction have significant were flown over the animal or herd at 10m/s. )e next pass effects on alert height and run away height (Table 3). was flown at another randomly selected altitude. If an af- firmative response was invoked, the drone would wait at a 4. Discussion distance, while the animals would settle back to a sedentary behavior. With the widespread increase in UAV flights, it is critical to We used the live video feed which also offers a recorded understand whether UAVs act as stressors to wildlife and to video after a completed flight and the location stamp, which quantify that impact [27]. Prior to this study, [27] assessed informs us of the exact height and angle of the drone to effects of UAV flights on movements and heart rate re- determine the vertical distance from our subjects, as well as sponses of free-roaming American black bears and con- the exact measurements at which they individually displayed cluded that UAV flights induced strong behavioral as well as the two levels of reaction that we were measuring. To avoid physiological responses, but most bears did not respond confusion, the term “response” is used here for all levels of behaviorally by increasing movement rates or moving to a behavioral responses, as it is for a broad range of species to different location. However, horses responded rather refer to an animal interrupting feeding, by lifting or cocking strongly to UAV flights in all 62 tests in this study. Prze- its head, and to attend to its surroundings [41]. Level 1, walski’s horses were unhabituated to the UAVs, and the known as the alert height, was determined through the eye study was conducted in the presence of stress-inducing and ear movements of Przewalski’s horses; these reactions events that occur naturally in the environment. )e results 4 International Journal of Zoology Table 1: Comparison of alert height and run away height of Przewalski’s horses. Variables Number Alert height (m)±SE t-test Run away height (m) ±SE t-test Immature males 5 5.0±0.71 P<0.001 1.40±0.55 P � 0.003 Males Adults males 9 40.33±9.38 18.67±12.80 Immature females 4 4.50±0.50 P<0.001 1.25±0.50 P � 0.130 Females Adults females 44 16.68±5.26 2.16±0.83 Alertheight,heightforhorse tonoticeUAVs; runawayheight,heightfor horsetomove away(meanswith standarderrors).“Number” refersto thenumber of flights: only one horse was scored when the drone was flown over a herd. Table 2: Comparison of alert height and run away height between age and sex of Przewalski’s horses. Variables Number Alert height (m)±SE t-test Run away height (m) ±SE t-test Immature 9 4.67±0.87 P<0.001 1.22±0.4 P � 0.013 Age Adults 53 20.58±10.46 5.18±8.82 Males 14 26.85±18.52 P � 0.025 11.50±12.61 P � 0.01 Sex Females 48 15.85±6.01 2.11±0.84 Alertheight,heightforhorse tonoticeUAVs; runawayheight,heightfor horsetomove away(meanswith standarderrors).“Number” refersto thenumber of flights: only one horse was scored when the drone was flown over a herd. Table 3: Effects of age, sex, and their interaction on alert height and run away height. Factors Alert height (m) Run away height (m) F �19.345 F �15.111 Age P≤0.001 P � 0.002 F �13.383 F �28.510 Sex P � 0.001 P � 0.01 F �13.133 F �17.324 Interaction of age and sex P � 0.001 P � 0.004 Alert height, height for horse to notice UAVs; run away height, height for horse to move away (means with standard errors). of her entire herd, she is accountable for the wellbeing of her suggest strong correlations between flight altitude and re- sponse which support our hypothesis 2 that UAVs induced foal(s). )us, her alertness, though not as high as that of a behavioral responses, including relocation (moving out of stallion, is increased to the point where she is still able to the way of the UAV but still in sight) and flee (movement ensure the safety of her offsprings [27]. from sight) as well as eye/head movement and/or turning of )erefore, height cannot be the only factor involved in the upper body. our experiment. Disturbance caused by UAVs depends not Hypothesis 3 was also strongly supported by our result. only on sound intensity (dB) and frequency (Hz) but also by )e strength of the responses varied among sex and age, and the duration and pattern of the noise. Further investigation our results suggest that age and gender are the significant in this area would be desirable. As mentioned above, age plays an important role in determining factors of a horse’s reaction to UAVs. Mature horses were significantly more vigilant of the UAVs than determining the alert level of Przewalski’s horses due to the immature as demonstrated by the higher heights at which nature of their role in their herds; younger horses have no adult horseswere alerted to theflying UAVscomparedto the need to remain vigilant, while stallions and mares have to immature. )erefore, this can be attributed to the lack of care for their herds and foals, respectively. Furthermore, the experience of younger horses; thus, a lower level of response, sex of adult horses also obviously influences the distance at which supports previous data on the behavior of Prze- which they noticed foreign objects, again, due to the level of walski’s horses, will be further discussed later. )e results responsibility that they take on within their herds. also sets gender (exclusive to mature horses) as the second In terms of the practicality of unmanned aerial vehicles used as a tool in the field of animal research, our experiment most influential factor of UAVs reaction height for the fact that alert height for female of all tested herds was lower than leads us to believe that UAVs are an extremely useful in- strument for remotely observing the behavior of certain that of any male horse. Both of these conclusions are not only supported by our animals. However, as has been suggested in previous ex- data but also justified by the works of other scientists, as periments, UAVs must be used with caution and environ- Kolter mention the role of a stallion as the protector of his mental consciousness [29]. In order to avoid disturbance to herd, especially one that includes mares and foals [26]. An an animal’s natural routine during observation, we, as sci- integral element of his responsibility depends on his ability entists, must be aware and in full control of the drone’s to fend off unknown creatures, which includes the UAVs. proximity to the subjects [28]. In our research, the furthest Meanwhile, though the mare is not responsible for the safety vertical distance at which the UAV was first noticed was 52 International Journal of Zoology 5 meters. )is informs us that the optimum height for ob- thank Guest Professor Zhongze Niu for supporting them to servation of the Przewalski’s horses will certainly be above 52 conduct the present research in the study area. )e authors meters, though, without additional data, it will not be are also grateful to Senior Engineer Entemakh for his help on possible to determine the exact optimum height. Our ex- field survey. )e authors are also grateful for advice given by periment informs us that with minimized disturbance, Paul Jason Buzzard, China Exploration and Research So- UAVs are technologically advanced and practical scientific ciety, Hong Kong, China. devices. 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International Journal of ZoologyHindawi Publishing Corporation

Published: Aug 28, 2021

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