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BC Conservation Data Centre: Conservation Status Report

Spea intermontana
Great Basin Spadefoot

 
Scientific Name: Spea intermontana
English Name: Great Basin Spadefoot
   
Provincial Status Summary
Status: S3S4
Date Status Assigned: March 23, 2022
Date Last Reviewed: March 23, 2022
Reasons: This species is restricted to the dry, grasslands of south-central British Columbia and is facing multiple threats including direct mortality from roads and lower reproductive success due to climate change (drought) (COSEWIC 2007b; Southern Interior Reptile and Amphibian Working Group 2016b).
 
Range
Range Extent: F = 20,000-200,000 square km
Range Extent Estimate (km2): 37,738
Range Extent Comments: The range extent is 37,738 km2 based on records from 2000 to 2016 via COSEWIC (2019f). These records were obtained from the BC CDC and the Canadian Wildlife Service. The latter were records from surveys conducted in 2011 to 2015 and incidentals in 2016.
The B.C. CDC calculated very similar results of approximately 37,500 km2, based on occurrences mapped as of April 2018. As of 2021 there were no known new records that would expand this Range Extent (iNaturalist, CDC element records). COSEWIC (2007b) calculated the area to be approximately 30,770 km2. The current larger Range Extent reflects increased search effort (particularly in the northern portion of the currently known range) rather than a true range increase.

Spadefoot Toad is restricted to arid and semi-arid zones of south-central British Columbia between the Rocky Mountains and the coastal ranges. It occurs in the Okanagan Valley and in the Similkameen and Kettle-Granby river valleys in the south and in the Thompson and Nicola river valleys and the South Cariboo region as far north as 70 Mile House and Barriere (Matsuda et al. 2006; COSEWIC 2007b).

From 1996 to 2018, the species continued to be found within all portions of its range. Most records are from the South Okanagan.
Area of Occupancy (km2): F = 126-500
Area of Occupancy Estimate (km2): 1,164
Area of Occupancy Comments: The Area of Occupancy was calculated to be 1,164 km2 (COSEWIC 2019f) usuing records from 2001 to 2016. Previous calculations (COSEWIC 2007) were 619 and 864 km2. As with ther Range Extent, this increase is a reflection of search effort, particularly in the northern portion of the range, rather than an increase in abundance.
 
Occurrences & Population
Number of Occurrences: CD = 21 - 300
Comments: As of April 2018, the B.C. Conservation Data Centre had 102 occurrences mapped. The actual number of element occurrences appear to vacilate with the addition of sites between formally separated element occurrences based on a one kilometre separation distance and may show as low as 86.

Note that COSEWIC (2007b) states that there are about 235 sites, but this is based on a separation distance of 500m whereas the NatureServe specifications used by the B.C. Conservation Data Centre require a separation distance between sites of one kilometre and five kilometres, in unsuitable and suitable habitat respectively.
Number of Occurrences with Good Viability / Ecological Integrity: U = Unknown
Number of Occurrences Appropriately Protected & Managed: Rank Factor not assessed
Comments: Many of the occurrences and suitable habitat for the Great Basin Spadefoot is on lower valley bottoms that are privately owned, unprotected and subject to agricultural and residential development.

Examples of occurrences that are protected include the north end of Osoyoos Lake where a large population is partially protected by Haynes Lease Ecological Reserve and South Okanagan Wildlife Management Area. There are properties acquired by Nature Conservancy of Canada (NCC) and Nature Trust of BC such as White Lake Ranch west of Okanagan Falls that includes several smaller populations and the South Okanagan Grasslands Protected Area and NCC properties, Sage and Sparrow. These are protected from development but limited livestock grazing occurs in some portions. The Lac du Bois Grasslands Protected Area near Kamloops provides protection for another large population and has been recently extended. In the South Cariboo, all recent records have been found on Crown lands that are under grazing licenses.

This species is designated as "Identified Wildlife" under the BC Forest and Range Practices Act. As of 2021, there are a total of 21 approved Wildlife Habitat Areas throughout the range.
Population Size: F = 10,000 - 100,000 individuals
Comments: The 2007 COSEWIC report estimates at least 10,000 individuals and given that there has been a significant increase in the range extent and area of occupancy since that report, the estimate of at least 10,000 individuals is presumed to be still applicable. The Okanagan region is assumed to have over 5000 mature individuals (COSEWIC 2019f). Observations of eggs, tadpoles, or metamorphs in high densities (> 1000 individuals) were found on seven survey occasions in the South Okanagan valley (Ashpole unpubl. data).

Numbers are difficult to estimate due do the cryptic nature of the species and surveys are often done using call surveys and natural and anthropogenic influenced fluctuations.

Three major surveys conducted in the 1990s counted 4200 calling males (St. John 1993; Leupin et al. 1994; Cannings 1997; W. Weber, pers. comm.).
 
Threats (to population, occurrences, or area affected)
Degree of Threat: C = Medium
Comments:

Based on the summary of the April 2019 threat assessment in the 2019 COSEWIC report, the overall threats score is 'Medium'. The greatest threats were from road mortality (Transportation & service corridors), agricultural and forestry effluents (Pollution), and reduction in water table associated with droughts (Climate change & severe weather) affecting the availability of breeding sites. A very brief summary of these three threats follow.

In areas where there are old or new roads near breeding locations, there is high direct mortality of spadefoots on migration. Direct mortality also occurs where they use the road for thermoregulation. Higher risk comes with greater volume of traffic and with an increasing population, particularly in the Okanagan Valley it is predicted that this risk will increase. Roads also can add to fragmentation of locations. The primary source of pollution indicated is from agricultural effluents from herbicides, pesticides and fertilizers and an issue mainly in the southern Okanagan Valley. Drought and climate change is seen to have a varying impact on breeding sites depending on certain variables of those sites such as pond depth, degree of fragmentation and density of predators (COSEWIC 2019f).

Other threats individually scored as low compound the impacts of the main threats.

2016: Primary threats include direct mortality from roads and lower reproductive success due to climate change (drought). Lower ranked threats include habitat loss/alteration and direct mortality from residential and agricultural development, all-terrain vehicles, water management, non-native species (fish, bullfrogs), pollution and salvage logging (Southern Interior Reptile and Amphibian Working Group 2016b).

2010: Loss of wetland breeding habitat and upland foraging habitats to urbanization and intensive agriculture continue in the Thompson Nicola and Okanagan areas; this threat is not a significant concern in the Cariboo, as the majority of Spadefoot habitat is on Crown land (R. Packham, pers. comm. 2011). Trampling of shallow breeding sites by cattle degrades habitat througout the range; for example, in the Cariboo, 100% of habitat is subject to livestock grazing (although some historic dugouts (to provided water to livestock) have become Spadefoot breeding sites) (R. Packham, pers. comm. 2011). Fragmentation of habitat will likely disrupt traditional dispersal routes, this along with an increase in the number of roads and traffic may have a significant impact on spadefoot mortality (Cannings 1997). Groundwater use by humans may be lowering water table in the Okanagan, this reduces ephemeral pools. Earlier droughts or extended periods of drought that result in fewer ponds being available or cause the ponds to dry up during the breeding season are possible threats due to climate change (P. Govindarajulu pers. comm. 2007). For example, in the Cariboo in 2008, there were over 90 breeding ponds; however, in 2010 there were less than 10, due to drought caused by natural events (R. Packham, pers. comm. 2011). In the upper plateau area of the Nicola valley in 2010, a large percentage of the wetlands were dry; many of the wetlands in the grasslands had water only in dugouts (the dugouts usually contained spadefoot tadpoles) (J. Surgenor, pers. comm. 2011). Introduction of bullfrogs and predatory fish into lakes and ponds could be a threat to Spadefoot Toads. In 2008, samples of Spadefoot tadpoles in B.C. tested positive for Batrachochytrium dendrobatidis (Bd), an aquatic fungus that causes the disease chytridiomycosis in amphibians. Mortality, however, has not been recorded (P. Govindarajulu et al. 2013).

From 2014-12-05 Threats Calculator: Generation time 5 years, 3 generations = 15 years
 
Trend (in population, range, area occupied, and/or condition of occurrences)
Short-Term Trend: EF = Decline of 10-50%
Comments: Great Basin Spadefoot continue to be found throughout their range. A lack of long-term monitoring with systematic surveys make recent population trends difficult to determine (COSEWIC 2019f), however some local declines have been noted. There have been six private ponds filled or partially filled in the south Okanagan (Ashpole, pers. com. in COSEWIC 2019f) and one of the larger breeding ponds as determined in the early 1990s, has had very few calling males during surveys from 2004-2017 (Ashpole et al. 2018). A broad range of decline rate is used in the short-term trend to reflect this uncertainty.
The quantity and quality of wetland and grassland habitats continue to decline (e.g. droughts, increased land conversion, increased water usage) likely resulting in a decline of area occupied or numbers. (COSEWIC 2019f, Cannings 1997; COSEWIC 2007b).
Long-Term Trend: U = Unknown
Comments: The quantity and quality of wetland and grassland habitats have greatly declined since European settlement (COSEWIC 2019f and 2007b). The extent that this change will have affected the spadefoot population is unknown.
 
Other Factors
Intrinsic Vulnerability: B=Moderately vulnerable
Comments: Spadefoots can respond rapidly to changing environmental conditions and breed explosively when temperatures are suitable and breeding sites are full of water. Females lay 300 - 800 eggs in clusters of 20 - 40 in shallow water. Spadefoot tadpoles have short development times, as little as 5 weeks, but more typically 6 - 8 weeks. They attain reproductive maturity at 2 - 3 years and may live up to 10 years (COSEWIC 2007b).
Environmental Specificity: AB=Very narrow to narrow.
Comments: This species is restricted to grasslands and open woodlands in the southern interior of British Columbia. Grasslands in the arid southern interior of British Columbia are endangered and cover less than 1% of BC. Wetlands and temporary pools that they require for breeding are naturally rare. Suitable terrestrial habitats for foraging, hibernation, and aestivation must be available year-round. Loose, deep, and friable (crumbly) soils that allow for burrowing are thought to be important. As well, these habitats must be connected to allow for seasonal movements (COSEWIC 2019, COSEWIC 2007b).
Other Rank Considerations:
 
Information Gaps
Research Needs: Determination of all life stage requirements of the species would be useful in determining management strategies. This species spends a variable amount of time buried underground during dry and/or cold periods. The length of time that this species is able to survive under these conditions has not been documented.
Inventory Needs: Systematic surveys of all historic sites would help to determine whether there have been local extinctions or range contractions. In order to estimate population size, standardized inventories (Resources Inventory Committee 1997 manual #37) of calling males need to be undertaken in several successive breeding seasons throughout the provincial range. Mark recapture of adults would also provide a better estimate of abundance.
 
Stewardship
Protection:
Management:
 
Version
Author: S. Cannings and L. Ramsay (1999); L. Westereng (2007) and L. Gelling (2010 and 2018); L.Ramsay (2021)
Date: December 15, 2021
 
References
Ashpole, S.L., S.R. de Solla, C.A. Bishop, et al. 2018. Low species richness, relative density of adult early life stages of amphibians relative to land-use characteristics in an agriculturally dominated ecosystem. Diversity 10, no. 4: 108
Cannings, R.J. 1997. Status report on the Great Basin spadefoot toad, Spea intermontana. Unpubl. rep. submitted to COSEWIC, Ottawa.
Corkran, C., and C. Thoms. 1996. Amphibians of Oregon, Washington and British Columbia - A field identification guide. Lone Pine Publ. Co., Edmonton, AB. 175pp.
COSEWIC 2007b. COSEWIC assessment and status report on the Great Basin Spadefoot Spea intermontana in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vii + 34 pp. (www.sararegistry.gc.ca/status/status_e.cfm).
COSEWIC. 2019f. COSEWIC assessment and status report on the Great Basin Spadefoot Spea intermontana in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. xii + 69 pp.
Govindarajulu et al. 2013. Batrachochytrium dendrobatidis surveillance in British Columbia 2008-2009, Canada. 5pp. 
 
Green, D.M., and R.W. Campbell. 1984. The Amphibians of British Columbia. Royal B.C. Mus. Handb. No. 45. 101pp.
Iredale, F. and G. Ferguson. 2007. Auditory and larval census for the Great Basin Spadefoot Toad in the Thompson Region, British Columbia. BC Conservation Core report prepared for Ministry of Environment, Kamloops, BC. 15pp.
Leupin, E., D. Low, and B. Persello. 1994. Census and Life History Observations of the Great Basin Spadefoot Toad (Scaphiopus intermontanus) breeding populations in the Thompson Nicola regions. Unpubl. rep. prepared for B.C. Minist. Environ., Lands and Parks., Kamloops. 20pp.
Matsuda, B.M., D.M. Green and P.T. Gregory. 2006. Royal BC Museum handbook amphibians and reptiles of British Columbia. Royal B.C. Mus., Victoria, BC. 266pp.
Southern Interior Reptile and Amphibian Working Group. 2016b. Recovery plan for the Great Basin Spadefoot (Spea intermontana) in British Columbia. Prepared for the B.C. Ministry of Environment, Victoria, BC. 40 pp.
St. John, D. 1993. Spadefoot Toad surveys in the south Okanagan Valley, 1993. Unpubl. rep. submitted to Wildl. Program, B.C. Environ., Penticton. 12pp.
Verkerk, P., M. Janzen and R. Packham. 2006. Preliminary Great Basin Spadefoot Toad Survey in the Alberta and Meadow Lakes Areas of the 100 Mile House Forest District, British Columbia. Report prepared for the BC Conservation Corps (BCCC), BC. 5pp.
 

Please visit the website Conservation Status Ranks for information on how the CDC determines conservation status ranks. For global conservation status reports and ranks, please visit the NatureServe website http://www.natureserve.org/.

Suggested Citation:

B.C. Conservation Data Centre. 2021. Conservation Status Report: Spea intermontana. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Jun 4, 2024).