The ferocity of most members of the weasel family is legendary, and so it is no surprise that long-tailed weasels (Mustela frenataI) are highly territorial. Home ranges vary in sizes between the sexes, and males usually have larger ranges that overlap several smaller female home ranges. Females will tolerate males with overlapping territories, although they will actively avoid the resident male unless they are attempting to mate. Females will aggressively defend their territory against other female weasels.
The actual size of weasel territories is variable and depends almost completely on prey density. In areas with high prey density weasels will have smaller territories and will make shorter trips to hunt, but in regions of low prey density territories can be up to ten times larger than prey rich areas. The average territory size is anywhere from 25 to 80 acres, but in the winter in low prey areas territories can be up to 300 acres in size. This large territory size is a result of a high metabolism that requires constant predation and large movements to find prey, and in most landscapes weasels live at relatively low densities. Even the average territory size is a huge area for an animal of the size of a weasel, which typically weigh an average of 8-11 ounces and are only a foot long. This means that they are rarely seen in the wild and are also rarely captured by camera traps!
Weasels will stay in areas of high prey density, and will sometimes kill more than they can eat and cache the extra prey for later. Weasels have used been found to use some unusual cache locations, including old bird nests in the winter to keep prey nicely frozen and off the ground and underneath the floorboards of a barn, where a neatly stacked cached of over 100 rats was once found!
Weasel territories are anything but stable, and territory size and population numbers fluctuate with prey density, especially in northern areas. Weasel populations may go locally extinct if prey populations drops too low, and populations living in low prey density areas will expand their territories and only defend core territory areas, tolerating more overlap with other weasels outside of these areas. Sometimes prey density has the opposite effect, and males will attack females they encounter with the same aggression usually reserved for male intruders. All weasel species show fluctuations in reactions to prey numbers, but long-tailed weasels have the most stable populations of the smaller weasel species, probably because they are the most generalist predators.
Weasels mark territory boundaries with scat and urine, so if you see a small, twisted, ropy looking scat near a brushy habitat edge or a brushy area near a waterway, you have found a weasel territory marking. If you are very lucky, you may even catch a glimpse of the weasel itself.
For more information about weasels see:
Elbroch, Mark and Kurt Rinehart. Behavior of North American Mammals. New York: Houghton Mifflin, 2011. 374 pgs.
Sheffield, S. R. and H. H. Thomas. 1997. Mustela frenata. Mammalian Species 570:1-9.