Non-invasive identification of individual polar bears by whisker spot patterns

Studies of free-ranging animals often require identifying individuals in a study population in order to obtain detailed data on population dynamics, movement patterns, and behavior. However, capturing and handling animals for identification can be difficult and expensive, and may affect the behavior of the animals being studied. We evaluated the reliability of a non-invasive method of identifying individual polar bears based on whisker spot pattern variations. Digital photographs of the profiles of fifty polar bears (taken in western Hudson Bay) were chosen on the basis of image sharpness and distance to the bear. Paralleling a method of identification and assessment of reliability developed for lions, we divided spot patterns for each bear into characters that corresponded to cells on a regular grid and estimated their overall complexity (i.e., information content). We calculated the probability of occurrence and complexity of each spot pattern based on the individual frequency values of each character. All fifty spot patterns contained enough information to be distinguished from other spot patterns in our study population. These results suggest that individual identification of polar bears in the field using whisker spot pattern variations can be used as a reliable method of non-invasive identification.