2.2.3 Camera trap surveys
A pilot study was conducted from May to July 2017 to fine-tune the
camera trap data collection method. Twenty four static camera traps were
deployed based on field rangers’ perception of areas where bushpigs
could be found. During the pilot study, the duration of each camera trap
placement was variable because NGR has a history of extensive theft of
cameras by poachers. Camera traps were removed immediately after signs
of human activity were observed near a camera. After the pilot study, 48
camera trap stations were randomly positioned within the four main
vegetation types (Fig 1). Camera trap surveys were conducted from
February to December 2018. At each camera trap station, a single camera
was tied to a tree or stump at bushpig height (30-50 cm above the
ground) or higher (150-200 cm) with a downward pointing inclination,
depending on the vegetation. Surrounding vegetation that would promote
triggering by wind in front of the camera was cleared. Despite the
nocturnal behaviour of the target species, camera traps were set to
record photographs 24 hours a day. Trophy Cam ® (Bushnell Outdoor
Products, USA) cameras had continuous triggering of a one-second
interval between consecutive images while ScoutGuard ® cameras were set
to record 10 s video footage each time a movement was detected within
the distance range (15 m). The date and time were shown on each
photograph/video. The objective was 60 consecutive days periods of
observation but the period was sometimes shortened in the case of
poacher activity around the camera traps. All images were downloaded
from the cameras after which the date and duration of each observation
of suids were entered into MS Excel, each record reflecting an event per
specific camera trap station (an event is an observation of at least one
suid within a single 30-min time interval). The following were recorded
a) camera trap station ID b) GPS coordinates of the camera, c) habitat
in which the camera trap was installed d) bushpig count (the total
number of animals seen for all the pictures taken during one event on a
camera trap station) e) duration of each event f) time duration since
the previous event. Wild suid rate is the number of wild suid
individuals (bushpig or warthog) photographed per camera day. Likewise,
events are the number of events per camera day. Due to the small sample
size of suid observations in the sand and bushveld habitats, these two
vegetation types were merged into a single category. Log transformation
of raw data was performed to obtain a normal-like statistical
distribution of abundance values. A 1-way ANOVA was performed for
detecting differences in wild suid rate between habitats.