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of the male fox, which essentially defines the territory of the group. Juveniles will
exploit a limited number of resource patches close to their dens and within the home
range of their parents, gradually expanding their ranges and separating themselves
through the late summer until the time of dispersal
32
. Group ranges inevitably over-
lap to some degree, since an individual fox will normally cover less than half of its
range in one night
33
. Encounters between foxes of different social groups in these
overlapping areas will undoubtedly result in territorial conflicts when they occur at
resource nodes.
Foxes that disperse from their home territories will normally travel in a relatively
straight line until they find another territory that is available for occupancy
34
.If
they are unable to find another territory within the dispersal season they become
transients, forced to move continually. Hunting is the primary source of fox mortal-
ity, accounting for approximately 80% of deaths
35
. Hunting pressure is the primary
mechanism for producing available territory during dispersal; that is when a major-
ity of young foxes establish a home range. Hunting season in the state of Illinois
extends from early November through the end of January.
Rabid foxes typically remain in their territories, but they do spend time resting
at the peripheries, where they are more likely to come in contact with foxes from
neighboring groups. Fox contact behavior however remains the most important un-
known parameter in the spread of fox rabies
36
. Foxes exhibit different social behav-
iors, which may be density dependent. At lower densities, animals may be solitary
or live in pairs. At higher densities, loose family groups occur and are generally
comprised of one male, several females, and their offspring. Data from Sheldon
37
indicates that females determine the home range of a family group and that males
are residents for only part of the year.
15.2.6 Model Design
A self-explanatory simplified flow chart of the spatial modeling procedure used in
the development of the fox rabies model can be seen in Figure 15.6.
In this grid-based approach, each 6-mile square cell defined by the GIS maps
is considered a typical fox home range. Each grid cell contains a highly nonlinear
STELLA model that simulates the dynamic interaction and movement of foxes in
one-month increments. The cellular model includes variables describing the propen-
sity for fox immigration and emigration (based on fox population density) between
adjacent cells. Each cellular model is automatically parameterized using the GIS
32
Storm et al. 1976.
33
Doncaster 1997.
34
Storm et al. 1976.
35
Storm et al. 1976.
36
White, P.C.L. and S. Harris. 1994. Journal of Animal Ecology 63 315-327.
37
Sheldon, W.G. 1950. Journal of Wildlife Management 14 33-42.
