Inventory using a drone
A DJI Phantom drone (version 4 Pro V2.0) was used for the fieldwork.
This is a remotely controlled quadcopter device with a total weight of
1,388 grams, equipped with a camera capable of taking both still
photographs (max quality 5,472x3,648 pixels) and videos (max quality:
4,096 x 2,160 pixels), with the possibility of continuous tracking of
unrecorded images transmitted to the display coupled with the remote
control. Each photo records the geographic location and altitude in the
metadata.
A drone flight was performed over sites where birds were known to be
regularly present (Ławicki et al. 2010; Marchowski et al. 2018). The
distance from the observer to these sites was usually several hundred
metres, but never less than 100 m. This precluded any influence on the
part of the observer on the birds’ behaviour. But if birds were scared
away as a result of the observer’s presence, no attempt was made to fly
the drone. The flight height was set at about 100 m – the same as
recommended for bird counts from aircraft (Meissner 2011). From this
height, the planned census area was scanned for birds. If a flock or
individual birds were spotted on the remote controller display, a photo
was taken, and the birds were approached. Up to a height of 30 m, birds
were approached diagonally in such a way that the height and distance
from the birds were about the same. After reaching 30 m (when the birds
were still not responding to the drone), the drone was moved over the
birds, the distance was shortened while the height was maintained, after
which the drone was lowered to about 10 m. The birds’ reactions (if the
terrain permitted them to be seen) were recorded by a second observer
using a spotting scope mounted on a tripod. The birds’ reactions were
also monitored in real time via the display on the drone’s remote
controller. The behaviour of the birds was observed on a sample plot of
approximately 40,000 m² (200 x200 m), but if the site was smaller (e.g.
a small lake, pool or islet), the entire site was treated as a sample
plot.
My main research question was whether it would be possible/safe to
conduct bird research using a drone. How do birds react to a drone: do
they ignore it, attack it, or does the drone flush them? The birds’
reactions to the drone were first divided into two basic categories:
reaction – no reaction. In the reaction category, the following
subcategories were created: the birds 1 – moved slowly away, 2 –
dived, 3 – were flushed over a short distance but remained in the
sample plot, or quickly returned, 4 – were scared away, exhibited a
panic reaction, left the sample plot and did not return, 5 – attacked
the drone.
Reactions 4 and 5 were placed in an “unfavourable” category, i.e.
where the study of birds using a drone would not be recommended. No
reaction and non-invasive reactions (1-3) were placed in a separate
category. Statistical significance was tested using the chi-square
goodness of fit. The statistical analyses were carried out using the
software program R (R Core Team. 2021).
The second aim was to test the ability to count birds in non-breeding
aggregations or nests in breeding colonies using a drone. After the
initial recognition from a long distance of whether the birds were
responding to the drone’s presence, attempts were made to approach the
colony, with photos being taken continuously. If it was noticed that the
drone had disturbed the birds in any way, it was recalled beyond the
disturbing distance. The dates of drone flights over the breeding
colonies were adjusted so as to take place when the colony was at the
egg incubation stage. As a result, most of the nests present in the
colony, represented by an incubating bird, were visible.