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

Evaluation and Proposed Status

COSEWIC

Quantitative analyses of reintroductions are important (Griffith et al., 1989; Beck et al., 1994 and Wolf et al., 1996; Hein 1997, Kleiman et al., 1994 and Ralls et al., 1996).  Designation of the species as EXTIRPATED in 1978 was based on the fact that no substantiated reports, observations or specimens were available for a 50-year period from 1928 to 1978.  The carnivore is small and can easily retreat into dens, so "inconspicuousness" might have accounted for the lack of reports.  However, the period from 1928 to 1978 is also one in which trappers, settlers and ranchers have been setting traps throughout the prairie areas.  It is inconceivable that the species could have been present and gone unrecorded for all that time.

Following the reintroduction (1983 to 1997), swift foxes have re-occupied the Canadian prairies as part of the ecosystem in which, about 100 years before, it was a common species.  Trappers in Alberta and northern Montana began catching the species and road kill reports were obtained for Saskatchewan, Alberta and northern Montana.  This, in itself, is sufficient reason for downlisting the species from extirpated to another category.  However, it was important to carry out surveys and conduct detailed research, to find out how secure the numbers are before a decision is made to downlist the species.

In every year of investigation since 1986, unmarked foxes were captured, which is an indication of reproduction in the field.  In every year of investigation dens with pups were located.  The longest time recorded for the survival of a fox in the wild was 7 years. 

In the summer of 1991, survey efforts were greater than in previous years and 18 swift fox natal dens were discovered.  Pairs at these dens produced 56 pups.  Previous summer field work resulted in 28 litters as follows: 2 in 1986, 1 in 1987, 7 in 1988, 5 in 1989 and 13 in 1990.

Detailed ecological studies on swift foxes began in 1995 (Moehrenschlager, in prep. and Klausz 1997).  Prior to 1994, numerous studies and surveys to evaluate survival had been carried out (see listings in Section L - Project Notes and Reports).  Pruss (1994) began the first detailed behavioral field studies in 1991.

From 1984 to 1993, 55 pairs of foxes were studied using radio collars.  Those animals produced 183 young for an average of 3.3 pups per litter (Brechtel et al., 1993). Intensive trapping to survey numbers (research program) were carried out in 1990 (3 November to 7 December) and in 1996/97 (25 November, 1996 to 20 January 1997) (Cotterill 1997a).  Clearly, under COSEWIC rules, the species should be upgraded from Extirpated (no longer living in Canada) to another category.  The Threatened category is the most logical (a species likely to become endangered if limiting factors are not reversed), however, due to the uncertainties that contributed to the species' demise in the first place, the recommendation for now is to classify the species as Endangered (a species facing imminent extirpation).

 

IUCN and other conservation implications

Stanley Price (1991) recommended that reintroduction programs should be incorporated into both national and international conservation programs.  Reading et al., (1997) made a quantitative study on organizational aspects influencing the outcomes of a reintroduction project.  Ginsberg (1994) reviewed the relevance of captive-raised canids in conservation.  In retrospect, it can be seen how important these considerations are, when applied to the Canadian swift fox recovery project.

In addition to COSEWIC criteria, I have also subjected the current status review to the criteria set up through IUCN (International Union for the Conservation of Nature).  In the IUCN Species Survival Commission 1996 Red List Data Book on Threatened Animals, the swift fox appears on List 2 - Lower Risk: conservation dependent (IUCN 1996).

In that regard the species falls into a category of threat - the degrees of which are critically endangered, endangered and vulnerable.  The lower risk category being conservation dependent.

The Canadian/Montana swift fox population almost certainly is a "stand alone" population.  IUCN has defined five criteria (A to E) for the above three categories.  The sub-criteria being:

A.  Declining population (past or projected)

B.  Small distribution and decline or fluctuation

C.  Small population size and decline

D.  Very small population or very restricted distribution

E.  Quantitative analysis (e.g.) population viability analysis.

For reasons outlined below, the conclusion based on the review of this report, places the Canadian/Montana swift fox population in the IUCN category of Vulnerable and Very small or Restricted.  If however, the Canadian population is less than 250 foxes, then the IUCN criteria of Endangered would apply.

The Swift fox Recovery Plan (Brechtel et al., 1996) identified the goal of achieving a viable, self-sustaining population of swift foxes in two geographically-distinct, but genetically-connected core populations with a spring population density averaging 5 foxes per township on 80% of suitable habitat by the year 2000.  An estimate of 420 foxes was considered a suitable target.  This figure was an "administrative objective", without reference to parameters relating to a minimum viable population estimate over the short, medium or long term.  Now that foxes have become established, an assessment of long-term survival is required. 

Currently, the swift fox population is around 300 animals and is vulnerable to:

-     genetic problems due to loss of genetic variability, inbreeding, loss of heterozygosity and genetic drift.

-     demographic fluctuations due to random variations in death and birth rates.

-     environmental fluctuations - drought, winter severity, and possibly spring floods (at dens).

-     human activities, trapping, poisoning of predators, habitat destruction.

Despite severe droughts (1988) and severe winter conditions (1995/96 and 1996/97) the population continued to thrive.  The prognosis, therefore, is optimistic for the short term, but uncertain for the long term.

This raises the question - how many swift foxes are required to attain a viable minimum population?  The 1996/97 survey, resulted in an estimate of 289 foxes at the 95% confidence interval (range 179-412).  The 58 townships sampled constitute about 54% of the suspected range available (108 townships) in Canada.  The figure of 108 townships may be an underestimate.   Large areas that may be suitable are located west of the Suffield Military Base and north of the Red Deer River (see Figure 4).  There are additional areas in Montana that may contain suitable habitat (Zimmerman 1998).  In 1998, one such area was the site for reintroduction of 30 foxes (C. Smeeton pers. comm.)

It is important to evaluate the current (1997) population levels in relation to theoretical levels established as guidelines in general ecological theory.  One estimate is the 50/500 rule (Franklin 1980; Franklin and Frankham 1998; Ralls et al., 1996).  Fifty individuals, considered to be necessary to maintain genetic variability in a short time frame, but 500 are required to offset genetic variability arising through mutation.  A buffer is required to balance allele frequency losses due to genetic drift.  The current estimate of 289 (179-412), (plus the Montana population), likely brings us close to the 420 population target originally envisioned.  However, some of these foxes may not be producing young due to age, possible poor health, social status, lack of suitable mates and other factors.  Therefore, the effective number of breeding individuals is less than 289, determined from surveys or the 420 target level.  Rate of loss of genetic variability is based on the number of effective breeders, not the census population.  A more detailed population viability analysis will have to wait for another census, incorporating the modified techniques as described by Cotterill (1997a).  Such a census should include all areas with potential swift foxes in Canada and may not be necessary for some time.  The importance for releases to sites not yet occupied by swift foxes in Canada, may need to be considered as well.

 

Conclusion

For the time being a swift fox population level has been attained in Canada that may sustain viability in a short to medium time frame.  The Canadian effort to date has been a success and it is recommended that, under COSEWIC rules, the species be downlisted from extirpated to endangered.