Insights into feral goat movement in Australia using dynamic Brownian Bridges for movement analysis

Movement analyses were conducted for 50 goats across southern Australia using GPS satellite collars. A radio or satellite-tracked animal used to direct culling operations is generally called a 'Judas' animal. Goats used as 'Judas' animals in control operations were compared with non-'Judas' goats in the states of South Australia and Victoria, respectively. Their movement in two land systems were also compared. Dynamic Brownian Bridges Movement Models were used to calculate home ranges (95% utilisation areas). Changes in movement behaviour were identified to partition sedentary behaviour from long-distance movement events, defined here as ranging. Eleven goats exhibited ranging behaviour and moved from 9 to 33 km between their home ranges. After partitioning, their home ranges varied from 1.97 to 223.8 km ² . In this study in the Southern Australian Mallee regions, non-'Judas' goats had significantly smaller home ranges than 'Judas' goats. However, no significant differences were found in the ranging distances between non-'Judas' goats and 'Judas' goats. Understanding these two distinct forms of goat movement is important in the planning and budgeting of removal operations. To demonstrate this a simple goat management decision tool is used to illustrate the biases that can result in the expected hours of removal operations when the assumptions about goat movement are ill-defined.