Understanding movement parameters
We assessed the movement patterns of 4 large mammals using two movement
parameters such as mean displacement (step length) and net squared
displacement (NSD). Displacement is defined as the straight-line
distance between two consecutive GPS locations of an animal trajectory.
Varying inter-fix intervals across species were made uniform by
post-processing all data into hourly data format for further analysis
(Abrahms, 2007; Leblond, St-Laurent, & Cote 2016). Mean displacement
during day and night was also compared across individuals. For
comparison, day was defined from 0600h to 1800h and night from 1801h to
0559h.
We also calculated NSD, which is the squared distance between original
location and each successive location (Papworth, Bunnefeld, Slocombe, &
Millner-Gulland 2012). A graph of NSD vs. time gives a curve starting at
the point of origin of a movement trajectory gradually reaching maximum
NSD. NSD can remain constant or begin to drop as the animal returns to
the point of origin where NSD = 0. Based on NSD, we calculated the time
required for an animal to reach maximum displacement and return to the
point of origin within the home range. The time required to complete one
such cycle starting at a randomly chosen original location was
calculated. All movement parameters were quantified using the package
‘adehabitatLT’ (Calenge, 2006) in R software (R V3.5 R Core Development
Team, 2018).