2.2.1 Warthog numbers derived from annual transect counts
NGR has eight permanent line transects used for annual game counts,
ranging from 1.5 km to 8 km with a combined length of 50.915 km. The
transects cut across the four vegetation types. ArcGIS 10.6 (ESRI,
Redmont, California, USA) was used to measure lengths of transects based
on their position within different vegetation types (Table 1,
supplementary material). These transects were used to conduct annual
warthog counts and bushpig track counts. To maximise the accuracy of
estimates, the eight transects in NGR were walked 16 times annually,
during the dry seasons (April-September) of 2017 and 2018 and using
distance sampling methodology. The researcher, together with NGR game
scouts and students from Tshwane University of Technology (TUT),
conducted the counts in the morning (5-8 am) to maximise chances of
detecting warthogs because they are difficult to detect later in the day
when they rest in the shade. Two observers, each focusing on one side of
the transect, counted warthogs observed and, for each encounter,
recorded the coordinates of the observer, distance from observer to
animal (r), group size (n), and angle of the animal from the transect
(Ө). In addition, transect count data from 2013 to 2016 were made
available for analysis by Ezemvelo KwaZulu Natal Wildlife (EKZNW). The
number of warthogs in the reserve was estimated using the Distance
sampling software (Distance V8) using the negative exponential cosine
model as the detection function. This function computes the likelihood
contributions for off-transect sightings distances, scaled
appropriately, for use as a distance likelihood. Only those years with
consistent and reliable count data that fitted statistical models were
used. Warthog transect sightings were mapped according to vegetation
types using ArcGIS V10 and recorded in Excel (Microsoft Corporation,
2018) as follows: a) year of transect counts b) transect number c)
vegetation type in which that observation was made d) length of the
transect within that specific habitat e) number of warthogs seen and f)
a the number of warthogs per km of transect. Descriptive analyses and
linear mixed effect regression (Pinheiro and Bates, 2006) were
performed. Summary statistics, including mean and standard error of the
mean (SEM), were computed.