Abstract

The red fox (Vulpus vulpus) is an adaptable animal that can be found anywhere with adequate food and shelter, it is therefore not surprising that they have adapted from a rural to an urban setting. Few studies have directly compared urban and rural fox ecology. This review had two primary objectives; (1) To describe habitat utilization by urban and rural foxes and (2) to discuss the variation in their diet, population dynamics, causes of mortality, social organization and behaviour by linking these variations to differences in their habitat. Many similarities were observed between the urban and rural fox. It was concluded that the features which determine the distribution and abundance of foxes may differ depending on their habitat. The diets of urban and rural foxes are proposed to be distinguished by differences in degree rather than differences in kind. In urban areas where dense populations of foxes live in close proximity there must also be greater social involvement than in the less associated rural fox communities. Population density is important when considering the spread of epizootic diseases and the timing and degree of population dispersal.

1. Introduction

Over the past century increases in human population density have escalated the process of urbanisation (Mc Kinney, 2002). Organisms are now confronted with a range of novel conditions because of the modifications of the natural environment in which they ordinarily thrive. This can potentially impact both their life cycle and patterns of behaviour (Dickman and Doncaster, 1987). In recent years the effect of urbanization on the red fox (Vulpes vulpes) has been of particular interest.

The concept that ecological interactions of animals may differ according to the type of habitat they occupy is not new. 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 influenced by urban variables such as proximity to houses, artificial feeders, or other physical structures (Flyger, 1970; Harris 1986).

The fox’s successful adjustment from a rural to an urban environment is not surprising as they are opportunistic animals that are distributed across 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). Foxes are to be found southwards in most European habitats. They live from western Asia to eastern Japan and southwards into the deserts of North African. Throughout most of the mainland habitats in North America the same species of fox is found (Hutchins at al, 2003). 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 and Yalden, 2008).

This review has two primary objectives:

1. To describe habitat utilization by urban and rural foxes.

2. To discuss the variation in their diet, population dynamics, 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 two proposed reasons for the success of the red fox across its wide distribution:

1. 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).

2. 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 fox habitation is a diverse landscape consisting of scrub and woodland (Llyod, 1980). However, rural habitats also include mountains (above the treeline), moorlands, costal dunes and agricultural habitats such as arable and pastoral farmlands. Foxes have shown a marked preference for small coniferous woodlands in upland areas that are free of anthropogenic influence and afford good shelter (Goldyn, 2003). Large coniferous plantations are generally poor foraging areas for the fox; however, while ground vegetation remains they are also good habitats (Harris and Yalden, 2008). The main factor influencing the location of rural foxes is the availably and distribution of food shelter is generally not a limiting resource (Goldyn, 2003).

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

In farmland areas foxes have shown a preference for denning sites that are undisturbed by humans. 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. Goszozynski’s study (1985) showed that in an area with 21% forest coverage; only 2% of all dens were located in open habitats. However Goldyn (2003) found that in farmlands where wood cover is lacking, foxes can successfully adapt to completely different conditions, reaching high den sites. The banks of drainage ditches, marsh banks and boundary strips between fields were also frequently used as den locations. This is indicative of the adaptable nature of the fox in a sub-optimal habitat.

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 and cemeteries (www.wildberks.co.uk). 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 for foxes (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’. Later Harris (1977a) noted that the daytime rests of most importance are quiet gardens (irrespective of size) and similar domestic habitats, he proposed that parks and public open spaces were of little importance; this is evident in Table 1. Habitat variables appear to have consistent effects on the distribution of foxes. Similar to foxes found 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 the availability of suitable habitats for daytime harbourage is an important limiting factor for the distribution of and numbers in fox populations (Harris, 1977a).

Table 1: Harris (1977a) collected and recorded the location of 400 urban fox corpses in London. This data illustrated the relative importance of the various urban habitats as daytime harbourage.

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 revealed that the types of habitats visited by foxes largely reflected their availability. Railway lines were particularly important to dog foxes as pathways between parts of their range (Treweila and Harris, 1990).

In London regular disturbance is the main factor governing the distribution of dens. The majority of natal dens are situated in undisturbed habitats including under garden sheds, quiet gardens and railway embankments. Few litters are raised in dens in areas of public access; this is illustrated in Table 2 (Harris, 1977a). Rural foxes have also shown a preference for denning sites that are undisturbed by humans (Goldyn, 2003).

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

3. Diet

As the fox is both a predator and a scavenger, it is presented with a huge variety of prospective foods (Lloyd, 1980). Their diet depends on both location and time of year (Harris, 1986). Foxes are known to switch their diet to feed on whatever 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 rural and urban areas a similar range of food types are likely to be eaten; however, the proportions will vary. For example urban foxes in London and Oxford have a broadly similar diet; Harris (1981) found that scavenged items comprised 37% of the diet of foxes in London, compared to 35% in Oxford (Doncaster et al, 1990). Foxes in Oxford ate more earthworms (27% as opposed to 12%) and fewer birds and insects (Harris, 1981; Doncaster et al, 1990).

3.1. Seasonal Variation in Diet

Throughout the year vertebrates play an important role in the fox’s diet across most of their range (Baker et al, 2006; Harris 1986). The proportion of different mammals in their diet will generally vary according to their location and season. For example in agricultural areas sheep (Ovis aries) 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 field vole (Microtus agrestis), which is more abundant in their diet during the winter months (Harris, 1986).

Fruits and berries are also of seasonal importance to the fox. In the early autumn foxes include blackberries, raspberries, bilberries, cherries and hawthorn berries in their diet. They eat strawberries in great quantities during the summer months (Llyod, 1980). Lever (1959) also identified earthworms, slugs and snails as constituting a small proportion of the fox’s diet 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, 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 for the fox. 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 rural 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 et al, 1990). In the centre of cities foxes eat more scavenged food and fewer domestic pets, earthworms and wild animals than foxes found closer to the suburban fringe. (Harris, 1986) In London and Oxford scavenged food or food deliberately provided by householder’s accounts for over 35% of their diet (Harris, 1981; Doncaster at al, 1990). Foxes are known to raid dustbins for scraps (www.thefoxwebsite.org) and may also occasionally raid bird tables (Harris, 1986).

3.3. The fox as a predator

Medium sized animals play an important role in the diet of the rural fox throughout all seasons; rabbits for example may account for up to 74% of their diet (Baker et al, 2006). In Ireland foxes tend to switch to brown rats (Rattus norvegicus) 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, 1970) in particular 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 (1994) 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) as well as domestic birds were preyed upon. In Brittan game birds (mainly pheasants), small mammals (predominately field voles) and large mammals comprise 11, 7 and 6% of their diet, respectively (Baker et al, 2006). In England and Ireland lambs are more susceptible to losses than poultry, this is due to the fact that they are numerous and widely dispersed and often suffer from poor husbandry and exposure to severe climatic conditions (Llyod, 1980).

In the urban matrix the predatory role of fox has not been abandoned, despite the fact that lambs and wild rabbits are largely absent from their diet due to lack of availability. Instead, urban foxes prey on birds and small mammals to a greater degree than those in rural areas (Doncaster et al, 1990). Foxes are attracted to locations which have a diverse and abundant food base, whether these sources are situated in the urban ecosystem or the surrounding countryside (Dickman and Doncaster, 1987). This is emphasised by similarities in the diets of urban and rural foxes (Doncaster et al, 1990; MacDonald, 1981). 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 et al, 1990).

4. Population Dynamics

4.1 Density

Fox population density is influenced by factors such as prey availability and anthropogenic culling (Webbon et al, 2004) and varies depending on location (table 3) (Harris and Yalden, 2008). Webbon et al (2004) found that in rural hill areas, densities may be as low as 0.21 fox per km2 and peak at 2.23 foxes per km2 on arable land. High densities were positively related with areas of coniferous woodland, lowland marsh and grassland leys. In urban areas fox population density is usually higher than in similarly sized rural areas. The highest density of foxes ever recorded was 37.0 adults/km2 in North West Bristol (Baker et al, 2000). This figure was recorded immediately before an outbreak of mange.

Table 3: Population densities across urban and rural locations.

4.2. Dispersal

The most important factor affecting dispersal is population density. Trewhella et al (1988) found that in areas of low fox density (rural areas) animals disperse farther than those from areas of high and 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) found that by the end of their second year the final proportion of urban foxes that dispersed were 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, amounting to 96% for males and 58% for females.

Dispersal starts earlier in the countryside than in urban areas. Disturbance, especially by fox hunting, may be particularly important in splitting up a higher number of fox families and accelerating the dispersal of juveniles (Harris, 1986). Dispersal begins in early autumn and is largely completed by the end of the year (Storm et al., 1976). 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. 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 et al, 2004; Harris and Smith 1987b). In 2004, 58% of fox deaths in Bristol were road deaths; the majority being killed on major category roads (e.g. motorways) (Baker et al, 2004).

In rural areas the majority of deaths are caused by culling and hunting foxes. In all regions of mainland Britain there has been a steady increase in the mean number of foxes killed by gamekeepers per km2 since 1960 (Tapper 1992), with four times as many killed per km2 in 1990 as in 1960. In rural Dorset 58% of foxes were deliberately killed by hunting and culling (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 number of forms before the introduction of the Hunting Act in 2004. 21,000 – 25,000 foxes were killed annually by approximately 200 registered packs of foxhounds; with terriers digging out 55,000 dens and lurchers killing 10,000 foxes (Harris and Yalden, 2008).

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.

5.2. 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 1987b). Sarcoptic mange is a parasitic disease that spread across most of mainland Britain during the 1990s, this caused declines in both rural and urban fox populations (Baker et al, 2000). However this decline was more noticeable in urban areas due to higher densities of foxes. In some populations, more than 95% of individuals died. Despite this, populations are slowly recovering (www.thefoxwebsite.org).

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. 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 the availability of anthropogenic food sources and the higher density of foxes living in cities. In Bristol the mean territory size is 27ha (Baker et al, 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 the city is usually higher than in an equivalently sized rural area, but there is also a much greater variance in food availability (Doncaster et al, 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; however 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, shepherds 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 protect 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 with this, urban foxes are welcomed by most residents and are often supported through deliberate feeding by householders (www.thefoxwebsite.org). 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 contributes to the problematic relationship between humans and foxes. In relation to his study of food preferences in urban foxes, Harris (1981b) questioned households in Bristol regarding numbers of domestic animals killed by foxes. 5,191 households took part in the survey. Of the households that owned cats only 2.7% had lost a cat to foxes, most of which were kittens.

7. Conclusion

Foxes are found anywhere with adequate food and shelter; their habitat can vary widely in terms of climate and terrain, ranging from the extremes of the arctic tundra in Russia and Europe to the deserts of North Africa (Hutchins at al, 2003). Since foxes have exploited every other suitable habitat, it would be surprising if they had not become city-dwellers. Mac Donald and Nedwick (1982) have suggested 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 features which determine the distribution and abundance of foxes may be different in urban and rural habitats. The habitats of most communities of rural foxes 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). In an urban environment food is not usually a limiting recourse as vast amounts of food are available for scavenging. Instead, shelter becomes a high priority and their distribution is determined by the availability of suitable daytime refuge (Harris, 1977a).

The diets of urban and rural foxes are generally very similar, however the availability of these foods differ between environments. 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 (Harris, 1981, Hewson, 1984). The largest difference in their diets is the more regular supply of scavenged foods and the greater availability of earthworms on domestic lawns than on rougher rural pastures (Doncaster et al, 1990). If given the opportunity, 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 (Baker et al, 2000; Webbon et al, 2004). The closer proximity of high density urban fox populations results in higher susceptibility to epizootic diseases than their rural counter parts (Harris and Smith, 1987b). Density also has an affect on dispersal; generally animals from low density rural areas disperse farther than those from high or medium fox density urban areas (Trewhella et al, 1988). Not only do urban foxes move shorter distances but fewer of them actually leave the home (Trewhella et al, 1988; Storm et al, 1976).

In both rural and urban populations humans are responsible for the majority of fox deaths. However, they are perceived very differently in these habitats. The majority of urban fox deaths are accidental (Baker et al, 2004); they are generally welcomed and have provided people with a connection to the natural world. On the other hand, in a rural setting foxes are seen as an agricultural pest and the majority of deaths are caused by culling and hunting (Heydon and Reynolds, 2000).

This review highlights the influence of urbanisation on a highly adaptable and opportunistic animal. Foxes have become incredibly proficient at eking out a living in today’s world and are deeply entwined in our history and culture.This review ultimately shows that the entire way of life of the urban fox is extremely similar to that of the rural fox; any behavioural differences observed seem to fall within the known range of responses of the fox to environmental stimuli. The specifics of their divergent ecology may differ depending on the habitat they occupy; however the structures of their ecologies remain the same.

8. References

Baker, P.J., Funk, S.M., Harris, S., White, P.C.L. (2000). Flexible spatial organization of urban foxes, Vlpus vulpus, befo