A territory is a defended area which can be as small as the space around a female red-winged blackbird’s nest or as large as the backyard that your dog defends. A home range, in contrast, is simply the area where an animal spends its time. Home ranges may be shared with members of the same species and may overlap those of other species. For example, the home range of an adult polar bear may cover an area of 20,000 square miles (50,000 square kilometers), or an area about the size of Nova Scotia in Canada. The home range of each polar bear varies due to food availability and condition of the ice—a factor that is currently changing rapidly because of global climate change and the disappearance of Arctic ice.