Observed herd size and animal association

Animal movement association is a “rarely pursued” issue in wildlife research, due largely to a lack of effective quantitative tools. In this work the authors propose a new approach based on conditional statistics in assessing the correlation between individual animals in their movement, which does not rely on pairwise observations. It is a sensitive yet robust method for detecting animal movement association that uses radio-tracking data efficiently. Furthermore, it gives the observed herd size a new meaning based on probability theory, linking it directly to animal association. This method was applied to a database of bison movements on 111 radio-collared, free-ranging bison in Wood Buffalo National Park in north-western Canada. Correlation coefficients of bison movement within five bison subpopulations were estimated using the new methods. These correlation coefficients, though numerically small, tested highly significant statistically. The seasonal effects on the association of bison movement were similarly assessed. In addition, an application to a risk assessment on the spread of brucellosis and tuberculosis from infected wood bison in Wood Buffalo National Park to domestic cattle and healthy wildlife was presented. The risk assessment model input on the maximum migration distance of particular bison herds was further refined through the approach elaborated in this paper.