Dens and Home Ranges
	The most distinctive feature of an urban environment is the 
abundance of man-made structures that offer shelter for many non-
human animals.  Foxes take advantage of man-made structures, 
sometimes even setting up their natal dens in occupied houses 
(Harris, 1981a; Harris, 1980).
	Harris (1977) and Storm et al. (1976) determined that the 
most important factor governing the distribution of breeding dens 
for both urban and rural foxes was human disturbance.  Harris 
(1977) located 97 dens in London, 46 of which were under 
residential buildings (36 of these under garden sheds).  Of the 
remaining 51, more than half (29) were in banks of earth, such as 
garden banks or railway embankments.  Some foxes raised their 
cubs under the floorboards of occupied houses, often gaining 
entrance through a pet door.  In one case, a domestic cat and 
dog, both of which tolerated the foxes, were present in the 
household where a fox den was located (Harris, 1980).  Usually, 
foxes avoid dogs; the distribution of foxes in Bristol showed a 
significant negative correlation to the distribution of feral 
dogs (Harris, 1981a).  
	Fox distribution in urban areas is also strongly influenced 
by the local habitat.  The number and type of habitats available 
to foxes in an urban area are highly variable.  Harris (1977) 
listed some of the habitats found in London, and noted that most 
of the foxes he studied were recovered from residential habitats, 
industrial habitats, and vacant land with no public access.  
Surprisingly, despite reports that open public parks were 
important for daytime shelter of foxes, Harris recovered only 
8.73% of his foxes from parks, although parks comprised 10.53% of 
suburban land.  By contrast, nearly 60% of his foxes were 
recovered from residential habitats, which comprised just over 
40% of suburban land.  Harris and Rayner (1986) found a 
significant positive correlation between areas of high fox 
density and residential areas where the housing was owner-
occupied.
	Harris (1977) speculated that space for daytime shelter is 
an important limiting resource in London, and that the 
availability of suitable daytime resting habitat has a strong 
influence on the distribution of foxes.  He found that between 
autumn and spring, several foxes will often share a daytime 
retreat.  This clumping is not unknown in rural fox populations, 
but it is more common and takes place for a longer period of time 
in urban and suburban fox populations (Harris, 1977).
	Clumping is to be expected in urban and suburban populations 
not only because daytime resting sites are rare, but also because 
fox densities are generally higher in urban areas than in rural 
areas.  Rural foxes are known to prefer regions of diverse 
habitat, such as edge habitats (Henry, 1993).  The abundance of 
such diverse regions in an urban area may account for the 
unusually high density of foxes found in cities -- Harris (1977) 
recorded up to five family groups per km2 in several of his 
studies.  By contrast, two families of foxes studied by Storm et 
al. (1976) in Minnesota stayed within separate well-defined areas 
of 9.6 km2 each.
	The average home range of an urban fox is significantly 
smaller than the average home range of a rural fox (Harris, 1980; 
Coman et al., 1991; Doncaster and MacDonald, 1991).  In a study 
of foxes in Australia, Coman et al. (1991) found that two family 
groups of foxes living on farmland had home ranges of 5.0 and 7.2 
km2, while three family groups of foxes on the fringe of an urban 
area had home ranges of 0.6, 1.3, and 0.8 km2.  Doncaster and 
Macdonald (1991) found a similar difference between foxes living 
in central Oxford and foxes living in suburban and rural areas 
around Oxford, and also found that the home ranges of urban foxes 
changed over time.
	"City ranges were not spatially stable over months or even 
weeks," Doncaster and MacDonald (1991) wrote.  "They moved in 
step-wise extensions to encompass new areas whilst at the same 
time contracting other parts of the range to expel old areas."  
This movement of territories is unique among foxes.  Doncaster 
and Macdonald speculated that movement of home ranges is a 
behavioral adaptation developed since foxes invaded urban areas 
in England in the 1930's.  The average amount of food available 
over the area of a city is higher than in a similarly sized rural 
area, but the variance in food availability is also much greater.  
For foxes to make the best use of the resources in urban 
environments, they must constantly explore new areas and re-
explore old ones.  This activity would require far too much 
energy to be viable in a large rural home range, but the high 
density of different patches in a city permit foxes following 
this strategy to survive and prosper.