The Process Of Urbanization Biology Essay


The process of urbanization often results in extensive modification of the natural environment, and confronts organisms with a range of novel conditions (Dickman and Doncaster, 1987). Over the past century an increase in human population density has resulted in an increase in the process of urbanisation and the construction of industrial developments (REF); this in turn is effecting the natural environment in which mammals thrive. In the recent years the effect of urbanization on non-human species such as the red fox (Vulpes vulpes) has become of significant interest.

The concept that ecological interactions of animals may differ according to the type of habitat they occupy is not new (Lessells, 1991). Differences will arise depending on the nature of the animal's habitat interactions and their life history. For example the gray squirrel (Sciurus carolinensis) and the racoon (Procyon lotor) are strongly affected by urban variables such as proximity to houses, artificial feeders, or other physical structures (Flyger, 1970; Harris 1986).

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The foxes successful adaptation from a rural to an urban environment is not surprising as they are opportunistic animals that are distributed among a wide diversity of habitats. In Russia and Europe they can be found in the arctic tundra, and have been reported on sea ice 100km north of the nearest land (Harris, 1986). Southwards foxes are to be found in most European habitats. They are found across Asia to Japan and South into the North African deserts. The same species of fox is found throughout most of the mainland habitats in North America (REF). The wide distribution of the red fox, the diversity of habitats in which it can be found and the speed with which foxes have colonised areas such as Australia are all indications of its adaptability (Harris, 1986).

This review had two main objectives:

To describe habitat utilization of urban and rural foxes.

To discuss the variation in their diet, population density, dispersal causes of mortality, social organization and behaviour by linking these variations to differences in their habitat.

2. Habitat Utilization.

In both urban and rural environments foxes are most abundant in diverse habitats that offer a wide variety of food and cover (Goldyn, 2003; Harris and Rayner, 1986; Mac Donald & Sillero, 2004). They exercise choice in selecting a place to live within the restrictions imposed by their social behaviour (Lloyd, 1980). There are probably two main reasons for the success of the red fox in a diversity of habitats:

Size - The fox is small enough to be unobtrusive, yet large enough to be able to move long distances when necessary. Therefore, it can easily colonise new areas and search areas where recourses are scattered (Harris, 1986).

Lack of specialization - The red fox can thrive in a variety of locations as it has no particular habitat requirements (Lloyd, 1980).

2.1. Rural Habitat.

The general perception of a rural habitat suitable for a fox habitation is a dry mixed landscape consisting of scrub and woodland (Llyod, 1980). However rural habitats also include mountains (above the treeline), moorlands, costal dunes and agricultural habitat such as farmlands. Foxes are most abundant in diverse habitats as most of their movements and foraging takes place on habitat edges (Mac Donald and Sillero, 2004). In rural areas free of anthropogenic influence foxes have shown a marked preference for small coniferous woodlands that afford good shelter in upland areas (REF). Large coniferous plantations are poor foraging areas for the fox, but while ground vegetation remains they are also good habitats (Harris and Yalden, 2008).

The rural fox digs earths in a wide variety of habitats: extensive earths may be dug in banks; enlarged old rabbit burrows; disused or occupied badger setts; also natural holes in rock crevices, drains and tubaries (Harris 1977; Harris 1986). Vegetative cover needs to be within or close to denning sites for this species. They should also be located near water, and in areas with a good prey base as females seldom range more than half a mile from their dens (also kinwn as earths) (Hoover and Wills, 1987).

When fox habitats shift from rural secluded areas to agricultural habitats under anthropogenic influence some modification in their ecology will occur (Goldyn, 2003). In farmland areas, wood edges and woodlots are virtually exclusive habitats where fox dens are situated (Lariviere, 1966). In farmlands adjacent to wooded areas only a minority of foxes will locate in an open habitat such as arable land. This was shown by Goszozynski (1985) in an area with 21% forest coverage; only 2% of all dens were located in open habitats.

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Goldyn (2003) found that in farmlands where wood cover is lacking, foxes can successfully adapt to completely different conditions, reaching high den - sites. Banks of drainage ditches, marsh banks and boundary strips between fields were also frequently used as den locations. Dens have a crucial meaning for foxes, not only as breeding places, but also as a shelter for adults during the whole year (Meia and Weber, 1993). Their location of rural fox populations may be related to the distribution of food resources or the presence of adequate habitats (Goldyn, 2003).

2.2. Urban habitats.

For the purpose of this review an 'urban habitat' will refer to any habitat within a built up area that does not occur naturally outside it. Urban habitats include gardens, parks, wastelands, road verges, railway tracks, cemeteries, etc. Urban habitats have become ecosystems in which mammal populations have adapted their lifestyle in order to survive. These fragmented ecosystems provide breeding sites, food and shelter needed by the fox (Macdonald and Newdick, 1982).

In the past there has been some confusion as to which habits are important for the urban fox. It was noted by Llyod (1968) that urban 'foxes may live in gardens, but usually they shelter in daytime in woodlands, parks, cemeteries, and overgrown sites such as isolated building plots'. Similarly Beams (1969, 1972) found that foxes had occupied most of the suitable areas 'containing open spaces and large gardens in the southern half of the area'. Later Harris (1977) noted that the daytime rests of most importance are quiet gardens irrespective of their size and similar domestic habitats. Parks and public open spaces were only of little importance (Table 1). Habitat variables appear to have consistent effects on the distribution of foxes. As in rural areas the urban fox is most commonly found in areas of diverse habitat; in an urban environment diverse habitats include areas where industry, commerce or council - rented housing predominate (Harris and Rayner, 1986). In London suitable habitats for daytime harbourage is an important limiting factor for the distribution and numbers in fox populations (Harris, 1977).

It has also been suggested by several authors that railway lines may be a particularly important habitat for the urban fox. Radio-tracking in Edinburgh, found that the types of habitats visited largely reflected their availability, but railway lines in particular were selected by dog foxes as pathways between parts of their range (Treweila and Harris, 1990).


Number of Specimens

Percent of specimens

Percent of surburban land use

Resedential habitats - gardens, garden sheds, cellars, houses




Industrial habitats - sewage stations, factories, builders yards, nurseries




Vacant land, normally without public access




Parks and public open spaces
















British rail and underground lines




Golf courses



No data

Sports grounds and school fields




Rubbish tips








Road deaths




Other habitats




Totals (excluding road deaths)




Table 1: Harris (1977) collected 400 suburban fox corpses in London, in order to show the relative importance of the various suburban habitats as daytime harbourage. Road deaths were excluded as they do not supply such data.

The majority of dens in rural areas are situated on habitat edges (Goldyn, 2003) however in London regular disturbance is the main factor governing the distribution of breeding earths (REF). The majority of natal sites are situated under garden sheds, in quiet gardens and railway embankments, both of these habitats being undisturbed. Few litters are raised in areas of public access (Table 2) (Harris, 1977). In Kansas the type of soil, presence of water, presence of cleared areas and absence of man were important factors influencing selection of den sites (Stanley, 1963). Scott and Selko (1939) also found that the slope of den sites to be of importance.




Under garden sheds with raised floors



Under concrete floors of garages, out-buildings, and raised floors of summer-houses and portable huts

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In air-raid shelters



In drains



In banks of earth e.g. at bottom of gardens, railway embankments, etc,



In flat ground



In flower-beds, rockeries



In compost heaps, piles of rubbish, woodpiles






Table 2: Sitting of suburban fox earths used for rearing cubs (Harris, 1977).

3. Diet

As the fox is both a predator and a scavenger, it is presented with a huge variety of prospective foods (Lloyd, 1980). The composition of its diet will depend on its location and the time of year (Harris, 1986). Foxes are known to switch their diet to feed on what ever is abundant locally. They have adapted particularly well to humans by foraging in towns and hunting in areas cleared for agriculture (Hutchins at al, 2003).

It is important to remember that in different rural and in different urban areas a similar range of food types is likely to be eaten; however, the proportions of the various items will vary. For example urban foxes in London and Oxford have a broadly similar diet. Scavenged items comprised 37% of the diet of foxes in London (Harris, 1981) compared to 35% in Oxford (Doncaster, 1990). Foxes in Oxford, however, ate more earthworms (27% as opposed to 12%) and fewer birds and insects (Harris, 1981; Doncaster, 1990).

3.1. Seasonal Variation in Diet

Throughout the year vertebrates play an important role in fox diet across most of their range (Baker, 2006; Harris 1986). However the proportion of different mammals in their diet will vary according to their location and season. For example in agricultural areas sheep are mostly eaten in winter and spring, this roughly corresponds to the lambing season which extends from January to May (Fairley, 1984). In Britain the most important mammal eaten in urban areas is the short tailed field vole, which is more abundant in their diet during the winter months (Harris, 1986).

Fruits and berries are also of seasonal importance to fox, especially in the early autumn. Foxes will take blackberries, raspberries, bilberries, cherries, hawthorn berries and where they are able to strawberries in great quantities in the summer (Llyod, 1980). Lever (1959) also identified earthworms, slugs and snails as constituting a small proportion of the food of the fox in the summer months. On domestic lawns there is a more regular supply of scavenged foods and a greater availability (though not necessarily abundance) of earthworms than on rougher rural pastures (Llyod, 1980). As a result the seasonal differences in the diet of the rural fox are much more pronounced than in the urban fox, as there can be major variation at different times of the year (Harris 1986).

3.2. Scavenging

In most habitats scavenging is important. In upland regions of West Scotland where other food sources were scarce the fox was found to scavenge in an agricultural environment. Foxes fed largely on sheep carrion and field voles (65% of mass ingested), supplemented by deer carrion, rabbits and birds (Hewson, 1984). In Ireland foxes were also found to scavenge on sheep afterbirths (Fairley, 1984).

Scavenging is particularly important to the urban fox as it supplements its diet with a high proportion and variety of scavenged food (Doncaster, 1990). Foxes living in the centre of a city will eat more scavenged food, but, fewer earthworms, domestic pets and wild animals than foxes found closer to the suburban fringe. (Harris, 1986) In London, Oxford and Bristol scavenged food or food deliberately provided by householders accounts for over 35% of their diet (Harris, 1981; Doncaster, 1990; BRISTOL?). Foxes are known to raid dustbins for scraps ( and may also occasionally raid bird tables (Harris, 1986). 

3.3. The fox as a predator

In rural food studies medium sized animals (mainly rabbits) dominate in fox diet throughout all seasons (74% of mass ingested) (Baker, 2006). In Ireland foxes tend to switch to brown rats when rabbit populations are reduced by myxamatosis (Fairley, 1984). The intake of small rodents is much lower in Ireland than in Britain, it is therefore possible that rats, hares and rabbits are of greater importance to the rural Irish fox because of the restricted variety of mammalian prey (Fairley, 1970a) particularly due to the absence of field voles in Ireland (Lever, 1959).

In agricultural environments the red fox is known to be one of the most important predators (Lloyd, 1980). A study by Conova and Rosa (1993) on the diet of foxes on agricultural land in northwest Italy found that birds and small mammals made up more than 60% of their diet. Game birds such as mallards (Anas plutyrhynchos) and pheasants (Phasianus colchicus) along with domestic birds were also preyed upon. In Brittan game birds (mainly pheasants Phasianus colchicus), small mammals (mainly field voles Microtus agrestis) and large mammals comprise 11, 7 and 6% of their diet, respectively (Baker, 2006). In England and Ireland lambs are more susceptible to losses than poultry, since they are numerous and widely dispersed, in some areas they suffer from poor husbandry and are exposed to severe climatic conditions (Llyod, 1980).

In the urban matrix the predatory role of fox has not been abandoned, however medium sized mammals such as rabbits and lambs are largely absent from their diet (REF). The principal constitutes of the diet of foxes in Oxford city included birds and small mammals (Doncaster, 1990). These were found in similar proportions in the diet of a rural population situated 6km from Oxford city (MacDonald, 1981). Invertebrates and fruit also featured in similar proportions in the diets of both populations (Doncaster, 1990; Mac Donald, 1981). A diverse and abundant food base for this animal is supported in both the urban ecosystem and the surrounding countryside this is emphasised by similarities in the diets of urban and rural foxes (Dickman and Doncaster, 1987). The diets of urban and rural foxes are distinguished more by differences in degree than by differences in kind as some populations of rural foxes may also scavenge food from villages and farms (Doncaster, 1990).

4. Population Dynamics

4.1 Density

Fox population density is very variable and is largely dependent on the habitat foxes occupy (REF). In rural habitats fox abundance is most closely associated with variation in habitat - related variables. Densities may also be infuenced by prey availability and anthropogenic culling (C.Webbon et al, 2004?). In rural hill areas of Scotland densities may be as low as 1 pair/40km2 to 1 fox per 30 hectars on rich habitats (Lockie, 1964). In urban areas the fox population density is usually higher than in rural areas. The mean fox density in 14 cities ranged from 0.19 family groups/km2 in Wolverhampton to 2.24 family groups/km2 in Cheltenham (526). The highest density of foxes ever recorded was 37.0 adults/km2 in North West Bristol (Baker, 2000). This figure was recorded immediately before outbreak of mange.

Fox Population Densities




Number of foxes per km2


Number of Foxes per km2


0.79 - 2.23

Cheltenham (526)

8.96 - 11.2


1.39 - 1.88

Bristol (Baker, 2000)


Marginal Upland




Agricultural land

0.1 (breeding den per km2)

Hill areas of Scotland

4.2. Dispersal

The most important factor affecting dispersal is population density. Trewhella et al (1988) found that animals from areas of low fox density (rural areas) disperse farther than animals from areas of high or medium fox density (urban areas). In very low fox density parts of Europe exceptional movements will exceed 100km, however in Britain movements over 40 km are rare, even in hill areas where fox numbers are low (Harris and Yalden, 2008)

Not only do urban foxes move shorter distances but fewer of them actually leave the home. Trewhella et al (1988) also found that most of the urban foxes that dispersed did so by the end of their second year, the final proportions being 75.8% for males and 37.8% for females. The rest permanently stay on the home range where they were born. Storm et al. (1976) gathered data on rural foxes and found the proportion of foxes dispersing was somewhat higher than in Trewhella's urban study, reaching 96% for males and 58% for females.

In the countryside dispersal also starts earlier that in urban area. Dispersal begins in early autumn and is largely completed by the end of the year (Storm et al., 1976). Disturbance, especially by fox hunting, may be particularly important in splitting up a higher number of fox families and accelerating dispersal of juveniles (REF?). In urban areas cubs that do disperse tend to do so quite late in the season (December) this may be because most urban fox families are subject to less severe disturbance (Harris, 1986).

5. Causes of Mortality

5.1 Predators of the fox

Figure 1: Fox golden eagle fight!

Foxes have very few natural predators; in most cases where other larger carnivores kill foxes it is done to remove them as a competitor. In isolated parts of rural England and Scotland foxes are killed at earths by golden eagles (Picture 1) (Harris, 1981). In rare cases adult foxes can be killed by badgers, but it is usually cubs that are affected by badger predation (Harris and Yalden, 2008). In an urban environment dogs are a significant predator of young cubs and will also occasionally kill adults (Harris, 1981).

5.2. Human induced mortalities

In both urban and rural populations humans are responsible for a high proportion of fox deaths (Table 3). In urban areas road traffic is the main cause of fox mortalities (Baker, 2004; Harris and Smith 1987). In 2004, 58% of fox deaths in Bristol were road deaths; with the majority foxes being killed on major category roads (e.g. motorways) (Baker, 2004).

Urban Fox

Rural Fox

Cause of death


Cause of death

% Killed

Road accidents


Killed accidently by people


Killed deliberately by people


Killed deliberately by people








Table 3: Major causes of death for urban foxes in Bristol and rural foxes in Dorset. The figures are given as percentages and should be taken to indicate the relative importance of the different mortality factors (adapted from Harris and Smith, 1987; Reynolds and Tapper, 1995)

In rural areas the majority of deaths are caused by culling and hunting foxes. In rural Dorset 58% of foxes were deliberately killed by hunting…..(Reynolds and Tapper, 1995). In a survey of three rural regions in England foxes were culled in 70 - 95% of farms (Reynolds and Tapper, 1996). Hunting with dogs took a variety forms before the introduction of the Hunting Act in 2004: approximately 200 registered packs of foxhounds killed 21,000 - 25,000 foxes annually. 55,000 were dug out with terriers that were introduced into dens and 10,000 were killed by lurchers (Harris and Yalden, 2008).

5.3 Disease.

Due to higher densities and closer proximity, urban foxes are more susceptible to epizootic diseases such as mange and rabies, this is evident in table 3 (Harris and Smith 1987). Sarcoptic mange is a parasitic disease that spread across most of mainland Britain during the 1990s, this caused declines in both rural and urban foxes (Baker, 2000). However this decline was more noticeable in urban areas, due to higher densities of foxes. In some populations, more than 95% of all individuals died. Despite this, populations are slowly recovering (

Harris (1977b) demonstrated that spinal arthritis (sponodylosis deformans), was present in a very high proportion of urban foxes with an infection level of 34.5%. The average age of the foxes used in the study was only one year nine months. It is thought that development of this disease is related to their diet ( the high proportion of scavenged food present in urban fox diet). Fox (1939) suggested that the situation in urban foxes is unusual; however this has not yet been confirmed by reference to large collections of skeletal material from other populations.

6. Social Organisation and Behaviour

6.1 Territories

Davies (1978) recognises territoriality where "animals are spaced further apart than would be expected from a random occupation of suitable habitats". The size of fox territory varies largely between regions, depending on their habitat. However territories of the rural fox are generally larger than their urban counterparts. In hill areas of Scotland territories can be up to 4000ha (Lockie, 1964); in rural Dorset it has been averaged at 270ha (Reynolds & Tapper, 1995) and as 520ha in Sitka spruce populations (O' Mahoney et al, 1999). In urban areas territories may be as small as 8.5ha, this is due to availability anthropogenic food sources and the higher density of foxes living in cities. In Bristol the mean territory size is 27ha (Baker, 2000), 39 ha in Oxford (Doncaster and Mac Donald, 1991) and 100ha in Edinburgh (Kolb, 1986).

The drifting movement of territories appears to be unique among urban foxes and has been studied in Oxford. "City ranges were not spatially stable over months or even weeks. 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." (Doncaster and Mac Donald, 1991). Movement of home ranges may be a behavioural adaptation that has developed since the invasion of foxes into urban areas. The average amount of food available in an area of a city is usually higher than in a similarly sized rural area, but there is also a much greater variance in food availability (Doncaster, 1990; MacDonald, 1981?). Foxes must regularly explore new areas and re-explore old ones in order to make the optimum use of the resources in an urban environment. In a large rural home range this activity would not be viable as it would require far too much energy; this strategy survives and prospers in cities because of the high density of different habitat patches.

6.2. Relation with Humans

Foxes have had a very mixed relationship with humans. They are generally unpopular with rural communities, gamekeepers, sheppard's and the majority of farmers (Reynolds and Tapor, 1996). Fox culling in rural areas is undertaken by several disparate interest groups. The key reason for farmers' involvement in fox culling is the protection of livestock or poultry. Similarly gamekeepers undertake culling to protecting game on relatively large farms (Llyod, 1980). In rural areas fox hunting as a sport is often of substantial interest. In some cases landowners and gamekeepers curtail their culling effort to ensure sufficient foxes are available for hunting (Heydon and Reynolds, 2000).

In contrast urban foxes are welcomed by most residents and are often supported through deliberate feeding by householders ( During the 1970's and 80's there was a large reduction in the number of foxes killed by the local authority this was due to their increasing popularity in British cities such as London (Harris and Yaldin, 2008). Damage caused by foxes in urban areas is generally slight; however fox predation on domestic pets is another source of problems between humans and urban foxes. To find out how many people had lost pets to foxes Harris (1981b) questioned 5,191 households in Bristol during his study of food preference in suburban foxes. Of the households that owned cats only 2.7% had lost a cat to foxes, and most of the cats lost were kittens. In outdoor gardens accessible to foxes, families who kept pets other than cats or dogs, had lost of 8.0% pets to foxes within the past year, and 51.1% had lost a pet more than a year prior to the survey.

7. Discussion

Foxes are found anywhere with adequate food and shelter, they can live on the tundra in Alaska and in semi - desert scrub in Africa (Hutchins et al, 2003). Since foxes have exploited every other suitable habitat, it would be surprising if they had not become city-dwellers. It has been suggested by Mac Donald and Nedwick (1982) that there is no strict division between rural and urban foxes; radio tracked foxes regularly commuted between urban and rural areas. Nevertheless, living in the city requires special adaptations.

The urban fox is behaving no differently from rural foxes, except that the scene is different. The same controversy over predation on man's livestock exists in both areas, but in urban areas cats are substituted for lambs and domestic birds for poultry (REF). The main large - scale difference is the more regular supply of scavenged foods and the greater availability (though not necessarily abundance) of earthworms on domestic lawns than on rougher rural pastures (REF). However some populations of rural foxes may also scavenge substantial proportions of their food from villages and farms.

In urban areas where dense populations of foxes live in close proximity there must be greater social involvement than in the less associated rural fox communities. But in high-density rural fox communities such close shoulder rubbing probably also exists. The situation in urban areas is probably a normal behavioural adaptation to circumstances common in both urban and rural dwelling foxes. The entire way of life of the urban fox, including their behaviour is essentially no different from that of the rural fox. Population density is also important when considering the spread of epizootic diseases such as mange and rabies. Urban foxes due to their higher densities and closer proximity are more susceptible to epizootic diseases than their rural counter parts (Harris and Smith, 1987)

Behavioural or physiological differences observed in different places all seen to fall within the known range of response of the fox to external or environmental stimuli. However, the features which determine the distribution and abundance may be different for urban and rural foxes. The habitats of most foxes communities are determined by the availably and distribution of food and by competition for it according to the density of foxes in an area (Goldyn, 2003). But in some urban areas cover is at premium and the distribution of the urban fox is determined by the availability of suitable daytime refugee of whatever form, whether it be a pile of uncut timber in s timber yard, an dearth under a garden shed or an earth in a railway cutting. This is because in an urban environment food is not a limiting resourse - more food in urban habitat more densly populated areas.