Data from: drones as a tool to study and monitor endangered Grey Crowned Cranes (Balaerica regulorum): behavioural responses and recommended guidelines

These data detail the results of an investigation into the impact of drones and on-foot approaches on the behaviour of the endangered Grey Crowned Crane (<i>Balearica regulorum</i>). In total, 313 drone flights and 56 on-foot approaches were conducted over three different Grey Crowned Crane group types - pairs (110 flights, 26 on-foot), families (66 flights, 7 on-foot), and flocks (110 flights, 23 on-foot). Response data describe the number of birds exhibiting a particular behaviour (1 - no behaviour change, 2 - heads raised to observe surroundings, 3 - wings raised, 4 -moving away, and 5 - flying away) based on a photograph taken during the approach. Predictor data include the distance between the drone or on-foot observer and the bird grouping and a description of the group type. The number of individuals in the group can be inferred from the response data.MethodsExperiment 1: Monitoring method comparison experimentTrial observations included recording the behavioural cues of GCC groupings (pairs, families, and flocks) in response to either of the two monitoring methods (on-foot, drone) across various distances and flight heights. Behavioural cues were categorised as follows: no behaviour change (1), heads raised to observe surroundings (2), wings raised (3), moving away (4), and flying away (5) (Figure 1). All trial observations were undertaken by the same observer and care was taken to wear similarly coloured clothing for each of the trials.On-foot monitoringUpon locating a GCC grouping, the observer approached the group at a constant walking speed of approximately 1 m.s^-1, making a reasonable effort not to disturb the grouping (e.g., avoiding noises and sudden movements). Observations were noted at the start of each trial, every 10– 15^th step thereafter, and again if any change in GCC behaviour was observed. Each observation included measuring the distance between the observer and the grouping using a range finder (Vortex Crossfire HD LRF-CF1400 Rangefinder) and taking a photograph (Nikon D7200 with 100-400mm Sigma lens) of the group which enabled <i>post hoc</i> behaviour coding. Observations were recorded until groupings displayed a type 5 response (flying away).Drone methodologyThe drone pilot positioned herself at least 100 m from GCC groupings before drone take-off and at a similar altitude to the GCC grouping. On rare occasions the pilot found it practically impossible to position herself at 100 m, but all drone experimental approaches were conducted from distances of at least 80 m from the GCC groupings. The drone was deployed from the pilot's location to a randomly pre-selected flight height (10, 30, 50, or 70 m above the deploy point), then flown over the grouping at the selected flight height at a speed of 5 m.s^-1 with video recording activated to facilitate <i>post hoc</i> behaviour coding. After reaching the grouping, the drone was flown ± 80 m beyond the grouping and then returned to the deploy point to avoid flying over the grouping during the return flight. All drone flights were conducted using a standard Mavic Air 2S drone (DJI Technology Co., Shenzhen, China) (595 g, 1-inch 20MP sensor, 8× zoom, 65dB low noise propeller).The precise height of the drone above the grouping was difficult to determine <i>in situ</i> as the drone only reports flight height relative to the take-off point. The flight height above GCC groupings was therefore determined post-hoc by extracting altitude values for the drone deployment and subject locations from a high-resolution (± 2 m) digital elevation model of the study area using the coordinates as recorded by the drone's Global Positioning System.Data collection from each grouping continued until a maximum of four trials had been recorded (with a 10-minute interval to allow birds to return to their prior behaviour) or until the subjects exhibited a type 5 response. As a precaution, the drone was always flown manually to allow the pilot to easily manoeuvre and control the drone to avoid any potentially aggressive behaviour from the target or non-target species in the study area. Each site was scanned for non-target species using binoculars before beginning a drone mission. Whilst in flight, the pilot remained aware of any new individuals of the target or non-target species entering the site. As far as practically possible, we avoided flights over any non-target species. If any non-target species displayed discomfort in the presence of the drone, the pilot avoided flying whilst that species was near the flight route; and if territorial, future flights at that site were terminated.Post-hoc behavioural codingVideo and photo footage were assessed <i>post hoc</i> by a single person. Each photo taken during the on-foot monitoring experiment was considered an observation. From each video recorded during the drone monitoring experiment the frame directly above the grouping was extracted and used as the observation. If birds responded with a type 5 response before the drone reached the grouping, the frame closest in time was used to determine the position of the drone whilst focusing on the initiated flight response of the grouping. For each observation, each bird's behaviour was identified and the total number of subjects displaying each of the five behaviours was recorded for each observation.Experiment 2: Nesting approach experimentWe identified breeding behavioural cues consisting primarily of a lone crane foraging close to a water body or wetland. A drone flight was initiated to locate either a nest site or the breeding birds themselves. If either of these were located, we considered it an observation. At ± 20 m from the subject, the drone was lowered to a flight height of ± 20 m. The drone was then manoeuvred towards the subjects either by flying diagonally (an angle of ± 45°) or vertically (flying horizontally until above the subjects and then descending at an angle of ± 90°), slowly descending until ± 7.5 m from the subjects. Because of the limitations of determining distances <i>in situ</i> via the drone the distances given here are approximate. Video recording was enabled throughout the approach to facilitate <i>post hoc</i> behavioural coding as follows; (1) little disturbance (either looking, remaining sitting, holding ground, or standing up), (2) moderate disturbance (raising wings, walking, or running away from offspring), or (3) major disturbance (flying away from offspring).