Swift fox (Vulpes velox) COSEWIC assessment and status report 2009: chapter 4


Distribution

Global Range

Historically, Swift Foxes occurred in mixed– or short–grass prairie from central Alberta, south to central Texas and from North Dakota, west to central Colorado (Allardyce and Sovada 2003; Figure 2) – an estimated range of approximately 1.6 million km² (Scott–Brown et al. 1987). The most dramatic reductions in the range of the Swift Fox occurred in the early 1800s to the mid 1900s; in the United States, the current range is believed to be about 40% of its historic range (Kahn et al. 1997).


Figure 2: Historic and Current Distribution of Swift Foxes in North America

Map showing the historical and current distribution of the Swift Fox in North America.

© 2003 Canid Specialist Group and Global Mammal Assessment.

Following extirpation from Canada in the late 1930s, Swift Fox reintroduction programmes were initiated in 1983 (Carbyn 1998). There are currently two self–sustaining Swift Fox populations in Montana, one of which is contiguous with adjacent Canadian populations and has arisen as a result of the Canadian reintroductions (Moehrenschlager and Moehrenschlager 2006). The other population occurs to the west on the Blackfoot Reservation (Ausband and Foresman 2007). This reintroduced population is quickly expanding by natural dispersal to vacant habitat over 100 km from the original release site (Giddings 2006).

Canadian Range

Swift foxes were once abundant in Canada. Between 1853 and 1877, 117,025 were traded by the Hudson’s Bay Company (Rand 1948), although the harvest decreased to a yearly average of only 508 pelts between 1922 and 1925 (Carlington 1980). Prior to 1900, the Canadian distribution of Swift Foxes approximated the Mixed Prairie Ecoregion in southern Alberta, Saskatchewan, and Manitoba (Merriam 1902; Seton 1909; Rand 1948; Soper 1964; Carbyn 1998), extending from the Pembina Hills in Manitoba west to the foothills of the Rocky Mountains in Alberta (Soper 1964; Carlington 1980). The northern distributional limit in Canada was originally the 53rd parallel in Alberta (Soper 1964). The last Swift Fox specimen collected in Canada prior to reintroduction was in 1928 near Govenlock, Saskatchewan, 14 km east of the Alberta border and 28 km north of the US border (Carbyn 1998). The last confirmed sighting of a Swift Fox in Canada prior to reintroduction was in 1938 near Manyberries, Alberta (Soper 1964). The species was designated as Extirpated by COSEWICin 1978 (Saskatchewan Department of Tourism and Renewable Resources 1978). From 1983 to 1997, 805 Swift Foxes were released into southern Alberta and Saskatchewan; in 2004, 15 animals were reintroduced to Blood Tribe lands in southwestern Alberta (see Reintroduction section).

To monitor restoration in southeastern Alberta and southwestern Saskatchewan, population censuses using live–trapping and sign surveys have been carried out every five years since 1996. In this region, there are two populations (Figure 3), although the distinction is gradually blurring owing to increasing evidence of connectivity between them (Moehrenschlager and Moehrenschlager 2006; Ausband and Moehrenschlager 2009). One population occurs in the Alberta–Saskatchewan border area (hereafter referred to as the Border population; Figure 4). The second occurs in the Grasslands National Park region (hereafter the GNP population; Figure 5). These populations are loosely connected by contiguous habitat that extends into northern Montana. Ausband and Moehrenschlager (2009) suggest that these populations (including northern Montana) should be considered one metapopulation based on evidence of long–distance dispersal of Swift Foxes between areas.

The three censuses since 1996 have used standardized methodology, although sampling effort increased each time to assess range expansion. This has enabled some evaluation of trends in distribution, number of animals, and the proportion of wild–born individuals in the Swift Fox population on both sides of the border since the reintroductions. Overall, the known Swift Fox distribution in the contiguous Alberta–Saskchewan–Montana region significantly increased in Canada because of a greater survey effort and also because of a greater occurrence of Swift Foxes in resurveyed regions. Most range expansion in the population at large since 2001 has taken place on the Montana side of the border (Moehrenschlager and Moehrenschlager 2006).


Figure 3: Map of Current Swift Fox Distribution in Canada and Northern Montana Produced Using All Confirmed Locations of the Species (reputable observer, road kill, live trap, or remote camera) Recorded Since the Early 1990s Less 9 Points that were Deemed to be Outliers

Map showing the current distribution of the Swift Fox in Canada and northern Montana.

The boundary shown uses a 99% kernel density estimator (map produced by Parks Canada).


Figure 4: Map Showing Trap Locations, Numbers of Swift Foxes Captured, and Incidental Sightings in the Border Population during the 2005–2006 Census

Map showing trap locations, numbers of Swift Foxes captured, and incidental sightings in the Border population during the 2005–06 census.

From Moehrenschlager and Moehrenschlager 2006.


Figure 5: Map Showing Trap Locations, Numbers of Swift Foxes Captured, and Incidental Sightings in the GNP Population During the 2005–2006 Census

Map showing trap locations, numbers of Swift Foxes captured, and incidental sightings in the Grasslands National Park population during the 2005–06 census.

From Moehrenschlager and Moehrenschlager 2006.

Beyond core Swift Fox range, post–reintroduction sightings have been documented in Suffield, Alberta and north of Swift Current, Saskatchewan. Carbyn (1998) reported on one 1997 sighting near Glenboro in south–central Manitoba when a Swift Fox was photographed at a den in atypical habitat on the edge of an agricultural field. This location was almost 600 km from the nearest known occurrence of this species in Canada (i.e., GNP East Block), and at least 300 km from the nearest sighting in the US (i.e., Morton or Cass County, North Dakota).

The current estimate of Swift Fox extent of occurrence (EO; based on a minimum–sided polygon encompassing the entire Canadian range [IUCN Standards and Petitions Working Group 2008]) of Swift Foxes in Canada is 21 544 km². This is about 2% of global EO (ASFRT 2007). Connectivity has improved with fox captures separated by no more than one township in 2005–6 as compared to three in 2000/2001 (Moehrenschlager and Moehrenschlager 2006), along with evidence of dispersal between populations (Ausband and Moehrenschlager 2009).

Between 2000–2001 and 2005–2006, the estimated area of occupancy (AO; area within EO occupied by Swift Foxes) for Swift Foxes in Canada increased by 7% (5901 km² to 6343 km² [Moehrenschlager and Moehrenschlager 2006; see ASFRT 2007]). This measure of area of occupancy is equivalent to an Index of Area of Occupancy (IAO; IUCN Standards and Petitions Working Group 2008). Although not based on the use of a grid of 2x2 km², the approach used by Moehrenschlager and Moehrenschlager (2006) using townships yields an IAO that should be close to the value derived from using the 2x2 km² grid methodology. The latter value would be difficult to calculate given the fact that not all townships were surveyed and the limited information on occupied vs. unoccupied habitats.

Reintroduction

Canada

Swift Foxes are vulnerable to trapping, and thus it is highly unlikely that they remained undetected for 45 years between the last confirmed sighting in 1938 and the first reintroductions in 1983. Hence, current populations of Swift Foxes in Canada are entirely attributable to reintroductions. About 90% of the Swift Foxes released in the Alberta–Saskatchewan border region and the GNP/Wood Mountain area came from captivity (Carbyn 1998). These were supplied by Cochrane Ecological Institute (formerly the Wildlife Reserve of Western Canada) of west–central Alberta which began a Swift Fox breeding program in 1971. Other facilities that contributed include: Calgary Zoo (Alberta; 1983–1994), Moose Jaw Wild Animal Park (Saskatchewan; 1984–1995), and Edmonton Valley Zoo (Alberta; 1989–1997) (Carbyn 1998). From 1973 to 1986, 151 Swift Foxes were imported from the US either for release or captive–breeding; with 99 from Wyoming, 40 from Colorado, and 12 from South Dakota (Carbyn 1998).

From 1983 to 1996, 479 Swift Foxes were released in the Alberta–Saskatchewan border area, and from 1990 to 1997, 420 individuals were released into the GNP and Wood Mountain areas (GNP population; Figure 6; for details see Carbyn 1998).


Figure 6: Location of Swift Fox Release Sites for the Border Population (top) and the GNP Population (bottom)

Two maps showing Swift Fox release sites for the Border population (top map) and Grasslands National Park population (bottom map).

From Smeeton and Weagle 2000. Prairie Farm Rehabilitation Administration (PFRA) Community Pastures have been mistakenly labelled as “pastures” and AB Hwy 48 in upper left map should be labelled as AB Hwy 41.

The last releases into the Border and GNP populations occurred in 1996 and 1997, respectively. Both populations have persisted without supplementation for more than 10 years. By 1996–1997, 81.3% of the captured Swift Foxes were wild–born (Cotterill 1997b), increasing to 98.6% by 2000–2001 (Moehrenschlager and Moehrenschlager 2001). In 2005–2006, all captures were of non–translocated, wild–born individuals (Moehrenschlager and Moehrenschlager 2006).

In 1989, a reintroduction was also attempted in the Milk River Ridge area of south–central Alberta with the release of 61 individuals (Brechtel et al. 1993). This program was discontinued after only one year due to high predator abundance and intensive predator and rabies control programs (Brechtel et al. 1993). Since this time there has not been any compelling evidence about Swift Foxes in the region over the last couple of decades including the existence of reproductively active animals that might contribute to the augmentation of an existing population or to a metapopulation (A. Moehrenschlager, 2009.).

In 2004, 15 Swift Foxes were released onto Blood Tribe lands in southwestern Alberta in a 1424–km² area of fescue prairie and foothills (Smeeton 2006). This area, to the west of current Swift Fox range, was within dispersal distance of the Blackfoot lands in Montana where reintroductions during 1998−2002 had established a small population of foxes (Ausband 2005). A verbal report to the Swift Fox Recovery Team from Blood Tribe staff in 2005 (J. Nicholson 2009) indicated that the five radio–collared individuals from this effort either went missing (3), shed their collar (1) or were found dead (1), and there has been no additional documented follow–up. Future reintroductions in the context of national Swift Fox recovery in the same area are currently being discussed (ASFRT 2007).

United States

Swift Foxes were extirpated from Montana by the mid–1950s (Hoffman et al. 1969). The Canadian reintroduction program in Alberta and Saskatchewan has been responsible for producing at least two apparently self–sustaining Swift Fox populations along the Canadian border and in Montana (see Global Range section; Zimmerman 1998). Elsewhere in the US range, Swift Fox reintroductions have occurred with some success in South Dakota (Grassel 2007; Dowd Stukel 2008; Licht and Schroeder 2008; Odell 2008) and other areas of Montana (Ausband and Foresman 2007; Kunkel et al. 2008).

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