The use of drones in wildlife research and management is increasing. Recent evidence has demonstrated the impact of drones on animal behavior but the response of nocturnal animals to drone flight remains unknown. Utilising a lightweight commercial drone, the behavioral response of southern hairy-nosed wombats (Lasiorhinus latifrons) to drone flights was observed at Kooloola Station, Swan Reach, South Australia. All wombats flown over during both day and night flights responded behaviorally to the presence of drones. The response differed based on time of day. The most common night-time behavior elicited by drone flight was retreat, compared to stationary alertness behavior observed for daytime drone flights. The behavioral response of the wombats increased as flight altitude decreased. The marked difference of behavior between day and night indicates that this has implications for studies using drones. The behavior observed during flights was altered due to the presence of the drone, and therefore shrewd study design is important (i.e.acclimation period to drone flight). Considering the sensory adaptations of the target species and how this may impact its behavioral response when flying at night is essential.

Preliminary flights (n = 16 flights, n = 30 total transects) were flown over wombats using the same transect methodology and at the same flight altitudes used in the final data collection. The preliminary flights were conducted to refine the methodology and ensure reliable capture of data. The final data collection occurred during 3 consecutive days in October with similar weather conditions to reduce variability of responses.

A DJI Phantom 4 Pro™ drone was used during the final data collection. The drone flew horizontally at 5 metres per second (m/s) directly over the located wombat/s at predetermined altitudes (100m, 60m, 30m). After take-off, the drone immediately ascended to an altitude of 100m and flew along a transect over the wombat to a distance of approximately 100m past the wombat and back to the launch position. If the wombat did not retreat to its burrow, the drone descended to the next lowest altitude (60m) and the same horizontal transect was flown. This process was repeated until; (a) the wombat retreated into its warren, or (b) all flight altitudes were exhausted. A single transect constituted flying over the wombat to the predetermined distance past the wombat (100m) and back to the original launch position.

Sixty-eight flights (n = 127 transects) were undertaken over wombats during daytime and night-time, with 59 flights occurring during the night (n = 101 transects) and 9 taking place during day (n = 26 transects). Flights were on average 20 minutes apart during the day and approximately 14 minutes apart during the night. Despite some flights occurring a short distance apart from each other (n = 100m), the temporal separation between flights was long enough for wombats to revert to their original behavior before location with the spotlight.

Locating wombats for daytime drone flights (5:30pm to 7:30pm)

Searching for wombats for daytime drone flight experiments involved driving a 4WD vehicle slowly along tracks on the property searching for wombats on, or near, their warrens. Once a wombat was spotted the vehicle was positioned behind the closest bush and stopped, to ensure the wombat was not disturbed prior to launching the drone. The drone was then deployed at a safe distance from the vehicle and out of sight of the wombat. The observers stood motionless and semi-obscured from the wombat to avoid any disturbance and monitored the animal’s behavior through binoculars (8x40mm).

Locating wombats for night-time flights (9:30pm to 2am)

Searching for wombats at night involved two observers walking along the vehicular tracks at the station using a spotlight (Ledlenser™ H14R.2 headlamp; Low 60 lumens, Power 450 lumens and Boost 1000 lumens) to scan for wombats on or near their warrens. The drone pilots followed behind at a distance of approximately 100m. If a wombat was identified, a red light was used to signal to the drone pilots to stop and set up ready to launch the drone. Whilst this was happening, the spotlight was shone on the wombat for ~2 minutes to ensure that any change in behavior observed following deployment of the drone was caused by the presence of the drone and the sound it created, and not associated with the spotlight. Previous experience spotlighting wombats over multiple surveys across decades has indicated that wombats are highly tolerant of spotlights, of which poor eyesight can be attributed to. Typically no change is observed in behavior following detection by spotlight unless the animal is within a close proximity (~25m).

Detailed notes and observations were made associated with each drone flight. Information was collected on: time, flight altitude, location, moon phase, latitude and longitude of drone launch site on the property, Warren ID, distance between the drone launch site and the wombat (Yukon™ Extend LRS-1000 Rangefinder) and wombat behavior.

Wombat behavior was classified as follows:

 No behavioral response exhibited (0)

 Alert but stationary (1)

 Alert with movement in any direction, but did not retreat to burrow (2)

 Alert and retreat into burrow (3)

SHN wombat behavior was categorised and tabulated into an ethogram. Behavioral observations using binoculars (8x40mm) occurred approximately 40-120m from the wombat/s during drone flights. Other anthropogenic sources of disturbance, such as cars driving on a road adjacent to the property, or planes flying overhead, were noted but were rarely present. In the event these disturbances occurred, flights were postponed until vehicles were clear of the area and the study environment returned to its natural state. A wombat was considered alert if it was observed to lift its head and prick up its ears as a result of the disturbance activity (e.g. drone noise, spotlight, vehicle noise). If there was no change in behavior pre and post drone flight, the wombat was considered to have been unaffected behaviorally by drone flight.

All statistical analysis of wombat behavior taken from the field behavioral observations were undertaken in the R environment. A general linear mixed effects model (GLMM) was used to evaluate the significance of the covariates time of day, flight altitude, moon phase and distance between launch site and the wombat. None of these covariates except flight altitude had a significant effect on wombat behavior.

In order to evaluate the response of wombats to drone flight altitude, we used the ‘survival’ package. In this instance, ‘survival’ denotes a wombat remaining above ground and not retreating into its burrow. ‘Survival’ probability was calculated as a response to drone altitude, but not for time. This analogy allows for the estimation of confidence intervals around the wombats staying above ground and to separate between night and day responses.

All data is presented as is and is ready to analyse.