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COSEWIC assessment and update status report on the swift fox (Vulpes velox) in Canada (2000)

Habitat

General description

Swift foxes typically prefer short or mixed grass prairie with flat to rolling terrain and sparse vegetation.  Such conditions appear to provide optimum opportunities, in face of predators, for mobility and visibility.  The fox likely chooses areas with long sight-lines, therefore avoiding vegetation or topographic features such as canyons, steep hills, dense shrub, forests and coulees (Whitaker-Hoagland, 1997).  Vegetation of preferred areas usually is sparse and short (25 cm or less in height).  At times, swift foxes in the United States have also been present in areas considered somewhat non-typical such as Badland-like areas in Wyoming (Lindberg 1986; Wooley et al., 1995).  Sandhills of Nebraska (Blus et al., 1967) pinon-juniper habitat in Colorado (Covell 1992), cultivated areas adjacent to shortgrass prairies (Floyd and Stromberg 1981) or even in cultivated fields (Kilgore 1969;  Cutler 1958;  Jackson 1997).

In Canada and in the northern United States, swift foxes favour native grasslands over cultivated farmlands.  The reasons for this are not completely understood.  Food availability may be important.  In northern areas pasture sage (Artemisia frigida) and grasses, such as blue gramma (Bouteloua gracilis), spear grass (Stipa comata), and fescue (Festuca, spp.) are the dominant vegetation in these areas. 

In addition to native prairie, several other habitat features may be important to swift fox populations.  Unlike other canids, swift foxes use multiple den sites year round for shelter and rearing young, and to escape predators.  The presence of fossorial animals, such as badgers (Taxidea taxus) and ground squirrels (Spermophilus spp.), is therefore desirable, as swift foxes will modify existing burrows.  If the soil type is suitable for excavation, swift foxes will dig dens themselves.  Dens are usually located in well-drained sites.  Permanent water bodies and low predator abundance also enhance habitat suitability for swift fox (Mamo 1994b).

 

Habitat destruction

Habitat loss to swift foxes can include outright destruction (e.g. ploughing) or alternation (e.g. grazing regimes) and modification of components (keystone species) within the system.  Destruction involves the removal of habitat (native prairies), while modification changes the biological components and energy flow within the system.  A century and a half of European settlement on the Canadian prairies has left a marked imprint on the landscape.  Agriculture has transformed more than 80% of the native Canadian prairie landscape (Gauthier and Patino 1993).  American native prairies, likewise, have been extensively modified (Licht 1997).  This resulted in massive habitat degradation and loss to the swift foxes located at the northern portion of their range in North America.

In southern Saskatchewan (core areas of the former distribution) for example, 60% of the grasslands were already under cultivation by 1931 (the beginning of an era of major natural droughts), Rowe and Coupland 1984.  Today about 47% of Saskatchewan's total land base is farmland and about 24% is productive cropland (Gauthier and Patino 1993). 

Another cause of habitat loss is the change from ranching (grazing) lands to cultivation. Every 5th year, Agriculture Canada measures the land use categories of "improved" and "unimproved" pasture.  Those data show loss of pasture habitat. Burrowing Owls (Speotyto cunicularia), whose habitat requirements are somewhat similar to swift foxes, have been used as an "indicator species" for this habitat loss (Wellicome and Haug 1995).  In the case of Burrowing Owl habitat (as defined by Wedgwood 1978), the amount of total farm area allocated as pasture area within the owl's range from 1966 to 1991 decreased by about 8% in Alberta and 6% in Saskatchewan while croplands increased by about 15% in Alberta and 19% in Saskatchewan.  The most drastic losses occurred between 1976 and 1986, a decade following peak prices for wheat.  Progressive legislation was introduced in Saskatchewan, under the Wildlife Habitat and Protection Act, which prohibits the breaking of native grasslands on about 2 million hectares of crown lands in the grassland ecoregion.

We know that swift fox range in Canada, prior to the turn of the century, was greater than after that time (Soper 1964).  Therefore, if we roughly equate pasture land in mixed-grass areas with swift fox habitat, then a starting point for likely habitat losses can be calculated, if total swift fox range is to be equated with present pasture land (cf. Telfer et al., 1993).  The pasture remaining today represents approximately 46% of the original habitat within the species' former range in Alberta and 26% in Saskatchewan.  However, it is false to assume that all former rangelands were well suited for swift foxes.  Areas with hilly terrain and heavy shrublands are classified as pasture but are not areas where swift foxes normally occur.  Therefore, the pasture areas remaining today constitute only a small fraction of what once was swift fox habitat as much of the uplands, now in production, were likely better suited for foxes than the hilly terrain that survived cultivation.

 

Habitat degradation

Physical modification of grassland areas is not the only form of habitat destruction. Modification of biological composition can also affect the suitability of the area for species.  Cattle grazing, use of pesticides and herbicides and increase in prey that attract avian and mammalian predators all have impacts of varying magnitudes on the ecosystems.  Swift foxes prefer areas with sparse vegetation, interspersed with sites that are suitable for small mammal survival.  Grazing patterns by ungulates likely play an important role.  Overgrazing by cattle, or undergrazing are activities that will have impacts on swift fox prey.  Grazing by bison in pre-European settlement days likely resulted in different use patterns than with modern stocking rates of cattle.  Distribution of small mammals is of importance to swift fox ecology.  Vegetation cover influences species composition.  For example, in one area T. Wellicome (in prep.) noted that meadow voles (Microtus pennsylvaticus) and prairie voles (Microtus ochrogaster) were present only in areas with undisturbed vegetative cover.  Grazing impacts on vole numbers are not well understood.  Grazing pressures in mixed-grass prairie has increased by one-third in Saskatchewan and one-half in Alberta between 1956 and 1976 (Coupland 1987).

Agricultural activities also led to the extirpation of wolves (Canis lupus) from the prairies which allowed coyotes to spread and increase in numbers (Sargeant et al., 1993).  Populations of other predators fluctuated as well, thus impacting on habitat availability for foxes.  This applies to "meso predators" such as skunks (Mephitus mephitus), red foxes (Vulpes vulpes) and badgers (Taxidea taxus) (Roast 1987, Violet 1987; Voigt and Berg 1987 and others).

Avian predator habitat was also influenced by settlement.  Fire suppression and planting of shelter belts and trees around homesteads all contributed to increasing nesting opportunities for Great Horned Owls (Bubo virginianus) and various species of hawks and eagles (Schmutz et al., 1980; Licht 1997).  Badger numbers were negatively affected by man through direct persecution.  Loss of badgers has mixed impacts.  It reduces predation but also may affect availability of escape terrain.  Swift foxes use badger burrows as dens (Pruss 1994).  The exact nature and importance of this is not clear.  Dens with larger den entrance openings may not provide safe shelter for swift foxes against predators.

Criss-crossing of highways and roads through the prairie landscape creates a fragmentation that did not exist when swift foxes were more common under pristine conditions.  Swift foxes are killed due to collision with vehicles.  It may be possible that foxes spend more time along roads, if the prey base is greater along ditches than in upland areas.  Possibly, swift foxes may spend more time along roads if they are trying to avoid predation from coyotes.  Ranchers are known to shoot coyotes on sight, whenever possible.  Such actions appear to have a positive impact on swift fox survival, although ecological links may be more complex than it might first appear.  It is presumed that, as the number of roads and vehicles increases, there will be an increased likelihood that foxes would be killed by vehicles.  Increase over time, of fox fatalities from vehicles, may also be a function of increasing fox populations.

 

Habitat fragmentation

Approximately 24% of the mixed-grass prairie zone in Canada remains uncultivated  (Prairie Conservation Action Plan 1994).  Even though a substantial proportion of the southern prairies still remain as grasslands, those areas are also affected by man.  Conversion of native prairies to agricultural lands, building of highways, roads, oil and gas well sites and pipelines, service trails, and the presence of towns and urban areas have all contributed to habitat fragmentation.

Despite fragmentation, several large expanses of native grasslands exist in both southern Alberta, and south-western Saskatchewan.  Some of those areas are crown lands, others private rangelands.  Additional conversion of rangelands to cropland (cultivation) would destroy remnant native grasslands.  Conversion of privately-owned rangelands to croplands is largely driven by a market economy.  Should government financial incentives for cultivating croplands increase, or prices of grain or other agricultural products increase, conversion of native grasslands would occur, as in the past, and will inevitably result in further habitat destruction for swift foxes.

Oil and natural gas exploration fragment natural prairies to a lesser extent.  Some studies have shown that swift foxes can tolerate considerable disturbance.  Presence of roads may have both positive and negative effects.  On the positive side, prey abundance for swift foxes may increase in the ditches along roads.  However, increased mortality due to road kills, accidental shooting and trapping may also be a negative factor on swift fox survival.