Fig. 2

Examples of animal movements generated assuming constant step duration but variable step length. Three scenarios are shown whereby the straight-line step taken in any direction is specified as into East–West and North–South vectors using standard trigonometry. Scenario A shows random movement (where distances travelled both East–West and North–South per step (in metres) were randomly selected to be between −10 and +10), B shows random movement but with a directional component (distances travelled East–West were randomly selected to be between −10 and +10 while distances travelled North–South were randomly selected to be between −10 and +12) and C shows random movement with a highly directional component (distances travelled East–West were randomly selected to be between −10 and +10 while distances travelled North–South were randomly selected to be between −10 and +20). The left-hand panes show examples of the track simulations while the middle panes show the distances travelled according to whether the distance is determined by adding the cumulative distance between GPS points or the cumulative distance between dead-reckoned points and according to how often the GPS position is taken relative to that of the dead-reckoned position. In the middle panes, y-axes represent calculated distance travelled; x-axes represent the straight-line distance between the first and last of 10 points and the cumulative distance between 10 points (‘One GPS per 10 DR points’), the straight-line distance between the first and last of 100 points and the cumulative distance of 100 points (‘One GPS per 100 DR points’) and the straight-line distance between the first and last of 1000 points and the cumulative distance between 1000 points (‘One GPS per 1000 DR points’). The right-hand panes show the ratios of GPS-only to GPS-enhanced dead-reckoned distances for the various scenarios (note difference in y-axis scale for right hand panel in A–C). Error bars denote standard deviations of path lengths (middle panes) and ratios of path lengths (right hand panes) which were sampled 1990, 1900 and 1000 times, respectively for 10, 100 and 1000 DR points, respectively