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

Limiting Factors

Predation

The greatest limiting factor relates to the "robustness" of the species itself (Kitchen et al., 1998).  Swift foxes are small and vulnerable.  In contrast coyotes have a much easier time surviving all the potential mortality factors in prairie ecosystems.  Swift fox predators such as coyotes may kill and abandon victims.  Alternatively, predators like eagles, coyotes, and badgers may kill and consume foxes.

Of 89 foxes found dead between 1983 and 1992, 34 were either known or suspected coyote kills (Carbyn et al., 1994).  Badgers accounted for 3 kills and 3 suspected kills.  Known avian predation (golden eagle) accounted for 5 foxes and 2 were suspected avian kills.

In post-mortem examinations conducted by S. Black of the Calgary Zoo, 12 foxes (9 females, 3 males) out of 39 carcasses examined were killed by coyotes.  Avian predation (Golden Eagle) accounted for 6 out of 39 (4 females, 2 males) and 1 out of 39 was a confirmed badger kill (S. Black pers. comm.).  In 1997, a number of foxes were killed by eagles, and the kill rate that year was higher than that by coyotes (J. Michie, pers. comm.).  More information will be required in the future to understand eagle migration and wintering patterns.  The same applies to Snowy Owls and Great Horned Owls.  Availability of prey is key to understanding the dynamics within the prairie ecosystem.

A new threat to swift fox survival may be the spread of red foxes.  In all of the previous years, only rare sightings of a red fox were reported (Mamo, pers. comm.) for the Saskatchewan/Alberta border area.  Since 1996 sightings of red foxes have increased (Carbyn, Michie, Moehrenschlager field notes).  In some cases red foxes were moving into areas known to be frequented by swift foxes.  Since this is apparently an evolving threat, there is a need to begin a study on red fox ecology and the potential impact on swift foxes, before red foxes become more widespread.  If a similar pattern of increased red fox competition is to prevail, as in other areas (c.f. North Dakota; M. Sovada pers. comm.), we could expect a problem developing that may impact swift fox numbers in the future.

 

Collision with vehicles

From 1983 to 1992, 5 of 89 foxes killed were road kills (Carbyn et al., 1994).  Black (pers. comm.) noted that 8 out of 39 foxes necropsied were road kills.  Out of the eight, 6 were pups and 2 were adults.  Pups are particularly vulnerable if dens are close to highways.  In San Joaquin Valley, California, 8% of deaths recorded on kit fox from 1980 to 1994 were as a result of road kills (Cypher pers. comm.). 

 

Range management

The once common bison have been replaced within the last 125 years by cattle as grazers on the mixed grass prairies.  Domestic livestock grazing patterns differ from those of native ungulates, resulting in different plant composition and carry over of duff on prairie soils.  The reintroduction results to date, have shown that swift foxes have become established, and survive without the presence of bison.  However, we do not know what effects different grazing pressures have on the availability of small mammals, particularly in winter.  Little is known about the effects of range management on swift foxes, however, it is generally considered that foxes prefer grazed areas.

 

Pipelines

Knowledge from current radio-tracking studies is now being integrated into land use management decisions in Alberta (J. Taggart pers. comm.).  Recent studies appear to indicate that pipeline construction may not be a major factor in swift fox survival, as long as physical destruction of dens does not occur (A. Moehrenschlager pers. comm.)

Guidelines for activity restrictions and disturbance near swift fox natal dens are currently under review by Alberta Natural Resources and Saskatchewan Environment and Resource Management.  These guidelines recommend that a 200 m buffer zone around natal dens be set to exclude passive activity (photography, walking), in the breeding and pup-rearing period (15 February to 31 July).  A 500 m buffer zone is recommended to exclude all industrial and natural resource development activity.

The potential for continued habitat fragmentation is a major concern.  Recent announcements by the Saskatchewan Environment and Resource Management  (February 1998) of large-scale habitat protection through the Representative Areas Network program, are encouraging.  Nearly 1.8 million acres, part of the network of community pastures administered by the Prairie Farm Rehabilitation Administration (PFRA), is to be secured as an area for prairie ecosystem protection.

 

Fur harvests

The fur of swift foxes is not a much sought after commodity.  In the United States, where harvesting has been greatly reduced since 1982, pelt prices varied from $3-10 during the last 10 years (Kahn et al., 1996).  In Colorado, the state with the greatest harvest, the species remained abundant despite 55 years of harvest.  Harvest of swift foxes in Kansas was prohibited until 1982.  Since opening of the season in 1982, no detectable reduction in range or numbers has been recorded.  On the other hand, in South Dakota, Nebraska and Oklahoma, no increase in distribution nor abundance has occurred since protection was provided in these states.

The conclusion from the above is that it is unlikely that light harvest of foxes in areas of abundance will have a significant impact on numbers.  Biological factors are likely more important in declines.  Nevertheless, trapping can reduce numbers if it is widespread and intensive, as swift foxes are readily caught in traps.

Within the Canadian context, a total of 4 foxes (possibly more, but details are unrecorded) have been known to have been trapped as incidental take to trapping for other species.  The loss of at least 2 foxes have been recorded due to hunting and at least 2 foxes are known to have been poisoned incidental to coyote poisoning.  Details of a trapper having killed or released 9 swift foxes in Montana remains unsubstantiated. Swift foxes are becoming vulnerable when entering traps legally set for other fur bearing species.  Modern trends in farming practices have resulted in increased numbers of large farms.  This meant that there was an exodus of people leaving the rural settings and relocating to urban areas, resulting in the reduction of weekend and part-time trappers.

Chances of swift foxes being killed by trappers is less today than in the past.  Use of roads by vehicles, and the increase of new road systems may impact foxes. To date, indications are that swift fox family units and dispersers can exist close to roads, occupied farms and towns.  Field data from North Dakota, suggests that red foxes thrive in areas close to towns and occupied farmsteads, if these areas are avoided by coyotes.  Red foxes from such sites could expand into open prairie areas if coyote abundance is reduced.  Such appears to be the case in the border area.  Red foxes were rarely seen until 1995/96 when severe winter conditions in that year and in 1996/97 allowed ranchers to kill more coyotes.  Red fox numbers, based on sightings along the Alberta/Saskatchewan border area, increased in 1997 and the situation should be monitored in the future.

 

Impact of droughts

Swift fox ecology is linked to environmental conditions that influence food availability.  It is not inconceivable that the disappearance of the species from northern ranges was linked to drastic and widespread climatic factors.  Severe winters, droughts and icing of ranges are elements that impact vertebrate populations that survive in northern limits of the species ranges.  In isolation, such factors may not have been of great consequence if occurrences were patchy and distinct, but the synergistic effects of competition for food, increased predation and/or diseases may account for local and widespread extirpation of the carnivore.

Droughts have become a fact of life on the Canadian prairies.  The last significant drought within the Canadian swift fox study area occurred in 1988; at a time 17 foxes were being monitored.  Eight of which were radio-collared.  The Recovery Team, at the time, had decided to provide emergency supplemental feeding.  The results were positive.  By August 1989, only one of the eight radio-collared foxes was lost, and all others had survived the critical winter conditions.  Supplemental feeding has not been part of the program since 1988.

 

Predator control programs

Intensive predator control programs directed at coyotes, skunks and other species may affect non-target species such as swift foxes.  On the other hand, if applied selectively for coyote control, swift fox/kit fox survival is enhanced due to reduction in interspecific competition (exploitive competition - competition for food or interference competition - larger predators killing smaller predators).  For example, Linhard and Robinson 1972; Robinson 1953, 1961 documented the changes in composition of predator guilds as a result of coyote controls.  Cypher and Scrivner (1992) reported on the population responses of kit foxes to coyote controls in the San Joaquin Valley in California.  Dorrance (1992), has reviewed the status of coyotes in Alberta from 1920 to 1991.

Skunks (Mephitis mephitis) are primary vectors of the rabies virus in Alberta (Gunson et al., 1978).  The use of strychnine has been important for Alberta's rabies control program (Dorrance 1987; Hutchings 1991).  Because of the impact of the disease on humans and livestock, any outbreaks are immediately dealt with vigorous anti-rabies programs.  These outbreaks historically have been in southern Alberta and in potential swift fox ranges.  Swift fox are vulnerable to strychnine poisoning.  For skunk control the strychnine is injected into chicken eggs or tallow baits.  Baits are placed in culverts, under abandoned buildings, ground dens and brush piles, hence accessible to swift foxes.  Alberta Department of Agriculture is aware of the potential impact of their programs on swift fox survival, and have co-operated with the Swift Fox Recovery Team regarding areas of mutual concern.  There have been no recorded incidents in Alberta of rabies in skunks for the last 3 years (J. Meeks pers. comm. - Alberta Agriculture).  All recent concerns are of skunk rabies within 20 km south of the Alberta border (in Montana).  The possibility of rabies in raccoons (Procyon lotor) is also an area of recent concern.

In southern Saskatchewan, swift fox survival may be impacted by 1080 bait programs set out for coyote control (SFRT Minutes 12-13/08/98).  In 1984 Saskatchewan had implemented a "no poison" zone south of the Trans-Canada highway, and west of Highway #2 (south of Moose Jaw and to the Alberta/ Saskatchewan border).  In 1994, the “no poison” zone was expanded to include areas further north.  By 1997, the "no poison" zone was extended to include the entire grassland areas of the province, however, due to specific pressures from sheep ranchers, the previous "no poisoning" policy was revoked in 1998 and replaced with a much reduced “no poison” zone.  The matter is under review and will likely result in some poisoning of coyotes.