Monitoring GPS-collared moose by ground versus drone approaches: efficiency and disturbance effects

Efficient wildlife management requires precise monitoring methods, e.g.,
to estimate population density, reproductive success, and survival. Here,
we compared the efficiency of the drone (equipped with an RGB camera) and
ground approaches to detect and observe GPS-collared female moose (Alces
alces) and their calves. Moreover, we quantified how drone (n = 42) and
ground (n = 41) approaches affected moose behavior and space use (n = 24
individuals). The average time used for drone approaches was 17 minutes
compared to 97 minutes for ground approaches, with drone detection
probability being higher (95% of adult female moose and 88% of moose
calves) compared to ground approaches (78% of adult females and 82% of
calves). Drone detection success increased at lower drone altitudes (50-70
m). Adult female moose left the site in 35% of drone approaches (with
> 40% of those moose becoming disturbed once the drone hovered
< 50 m above ground) compared to 56% of ground approaches. We
failed to find short-term effects (3-h after approaches) of drone
approaches on moose space use, but moose moved > 4-fold greater
distances and used larger areas after ground approaches (compared to
before the approaches had started). Similarly, longer-term (24-h before
and after approaches) space use did not differ between drone approaches
compared to days without known disturbance, but moose moved comparatively
greater distances during days of ground approaches. In conclusion, we
could show that drone approaches were highly efficient in detecting adult
moose and their calves in the boreal forest, being faster and less
disturbing than ground approaches, making them a useful tool to monitor
and study wildlife.