Burt's (1943) definitions of these two similar words are simple, but have proved useful for decades: A home range is the area over which an animal travels in the normal course of its activities, and a territory is a home range (or part of a home range) that a resident animal defends against other members of its own species, or to which it has priority use. The word "territory" is appropriate for an exclusive, defended area, whereas "home range" is a better word when there is considerable overlap and tolerance between neighbors.
Weasels seem to display all variations from one extreme to the other. Most resident weasels of both sexes have a home range, but not all home ranges include defended territories, so the word "home range" is often more useful to describe what weasels do than the more restricted definition of a territory. Moreover, it is not always possible to say to what degree each resident's ground is defended, and there is nearly always some degree of overlap between neighbors —indeed, there has to be a common zone where each can deposit scent marks for the other to find.
Once a resident animal has established its home range, it patrols its ground more or less regularly, setting and renewing scent marks in the course of each hunting expedition, notifying all other weasels that it has priority of use of the area. The home ranges of the two sexes usually overlap, and the cores of their home ranges are defended as territories against members of the opposite sex for most of the year. This pattern of intrasexual territories is quite typical of mustelids in general (Powell 1979a). At least in favorable times and places, males defend their ground against other males, and females against other females, while both tolerate (or avoid) members of the opposite sex. At other times, overlap is extensive, or weasels simply abandon their home ranges and move on. The more recent data reviewed here and elsewhere (e.g., Johnson et al. 2000a) have generally supported Powell's description.
The amount of effort a resident makes to evict intruders depends on whether the resources contained in its area are defensible. A den is a point location and can be defended quite easily, at least while its owner is in residence. Food resources are widely scattered, and usually cost too much energy to defend inside an exclusive area, especially as the chances are high that the owner cannot detect all intruders anyway. Males will, therefore, maintain strictly exclusive territories only where prey are concentrated, especially in winter when males are not interested in large-scale searching for females. In spring the same males may completely change their behavior.
Females seem to stick to familiar ground all the time, and their problem is not, or not only, to evict other females but to watch out for the males that use the same ground. Females can be just as intolerant of each other as are males (Figure 8.7), but they meet neighboring females less often than they meet the male whose home range overlaps with their own. On the other hand, spacing patterns are not a general characteristic of any species, including weasels, because the spacing of individuals depends on the local conditions, especially the distribution of food, which can change from one month to the next (Powell 1987, 1989, 1994; Clutton-Brock 1989).
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