BC Conservation Data Centre: Conservation Status Report
Anaxyrus boreas
Western Toad
| Scientific Name: | Anaxyrus boreas |
|---|---|
| Scientific Name Synonyms: |
Bufo boreas
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| English Name: | Western Toad |
| Provincial Status Summary | |
| Status: | S4 |
| Date Status Assigned: | December 31, 2016 |
| Date Last Reviewed: | April 12, 2022 |
| Reasons: | Western Toad is a wide-ranging species, occurring over 80% of the province. Threats were evaluated in 2012 by the Provincial Western Toad Working Group (2014), resulting in an overall score of High-Medium. There have been some declines noted in southern B.C., resulting in an overall provincial decline of 10-30%. When taking into account the number of occurrences and range, along with the threats and declines, the resulting provincial rank is S4. |
| Range | |
| Range Extent: | G = 200,000-2,500,000 square km |
| Range Extent Estimate (km2): | 1,072,719 |
| Range Extent Comments: |
The Range extent as estimated using a convex polygon around known observations is 1,072,719 km2 . This was calculated using known occurrences plus iNaturalist points (Accessed 20 February 2022). They are absent from the northeast corner of B.C. from north of Wonowon and Buckinghorse River and east of Liard. They also appear to be absent from the northwest portion of Alberta. Wind and Dupuis (2002) estimated that Western Toads extend over at least 80% of the province. It appears to be absent from the Teslin River basin in the northwest; there is an acoustic record of a release call from 2001 east of Teslin Lake (shown in Matsuda et al. 2006) that remains unconfirmed after 4 subsequent surveys (Slough unpubl. data 2001, 2004, 2005, 2007, cited in COSEWIC 2012h). |
| Area of Occupancy (km2): | H = 2,501-12,500 |
| Area of Occupancy Estimate (km2): | 4948 |
| Area of Occupancy Comments: |
The estimate of 4948 4km2 grid cells is based on iNaturalist observations (Accessed 20 February 2022) so therefore will be a minimum and calculated via GeoCat, Geospatial Conservation Assessment Tool from Kew Gardens. The species is patchily distributed in relation to breeding sites, suitable upland habitat, and hibernacula. On a landscape level, populations are likely relatively evenly distributed throughout much of their BC range, except perhaps in areas that contain extensive rural and urban development (e.g., Lower Mainland and Vancouver Island), are relatively dry (e.g., south Okanagan), or are at high elevation in northern regions (Slough 2004), where populations may be isolated, rare, or absent. |
| Occurrences & Population | |
| Number of Occurrences: | E = > 300 |
| Comments: | The species is wide-ranging in BC; more than 700 locality records were reported in Wind and Dupuis (2002) for BC. |
| Number of Occurrences with Good Viability / Ecological Integrity: | U = Unknown |
| Percent Area with Good Viability / Ecological Integrity: | U = Unknown |
| Comments: | There is some uncertainty regarding the viability of this species because EO's have not been mapped or ranked, few inventories and no long-term monitoring have taken place, and population declines have been observed in some areas. The species can appear very common or abundant due to the mass metamorph groups that are encountered in late summer, but adults and breeding sites may be rare (i.e., patchy distribution) (Wind and Dupuis 2002; Slough 2004; E. Wind, pers. comm.). As well, populations in the Lower Mainland, Vancouver Island, and in the U.S.have declined or been extirpated, even in pristine areas where declines may be difficult to detect (Wind and Dupuis 2002). |
| Number of Occurrences Appropriately Protected & Managed: | U = Unknown |
| Comments: | Several large Provincial and National parks occur within the range of the Western Toad in BC; e.g., Tweedsmuir, Wells Gray, Manning, and Strathcona Provincial Parks, and the Rocky Mountain National Parks. However, because the cause of the toad declines remain unknown, the protection of land alone may not protect the species from the effects of disease, climate change, etc. For example, declines have been observed in a national park in AB (Taylor and Smith 2003). The continued practice of fish stocking in BC's Provincial parks could negatively impact toad populations, especially as it pertains to disease issues in amphibians and toads in particular (Wind, 2010). |
| Population Size: | G = 100,000 - 1,000,000 individuals |
| Comments: | Estimated; there are many occurrences and the species is wide ranging within BC. |
| Threats (to population, occurrences, or area affected) | |
| Degree of Threat: | BC = High - medium |
| Comments: |
"High and moderate impact threats to the species in B.C. include urban development, road mortality, livestock impacts on wetlands, forestry practices, oil and gas developments, invasive species, disease epidemics (chytrid fungus Batrachochytrium dendrobatidis), and climate change." (Provincial Western Toad Working Group 2014). In 2008/09, samples of post-metamorphic Wood Frogs and tadpoles in B.C. tested positive for Batrachochytrium dendrobatidis (Bd), an aquatic fungus that causes the disease chytridiomycosis in amphibians (Deguise and Richardson 2009; Govindarajulu et al. 2013). Anaxyrus boreas is vulnerable to Bd which has been shown to cause population collapses (Muths et al. 2003). The impact on a population has been difficult to ascertain with high degrees of uncertainty and a lack of long term studies or monitoring on an affected population (Russell et. al. 2019). Climate change is an issue, particularily with drying of breeding habitat (L. Isaac, pers. comm. 2022). 2010: The primary threat to the majority of Western Toads in BC is likely habitat degradation and loss, especially in the Lower Mainland and on Vancouver Island where populations have declined (Wind and Dupuis 2002). Habitat degradation includes urban development, pollutants, non-native species such as fish, and impacts from forestry and roads. Increasing road density around breeding sites also pose a serious threat to persistence of the population. Toads return to traditional breeding sites and are vulnerable to road mortality during this time. Toad metamorphs gather in large post-metamorphic aggregations that could contain hundreds of thousands of animals and these aggregations are also very vulnerable to roadkill (P. Govindarajula, pers. comm. 2007). Secondarily, the threat of disease and parasites is a serious concern throughout the range based on trends in parts of the US. It is difficult to define the scope, severity and immediacy of threats to Western Toads because of their extensive range (e.g., impacts vary across the range, as does the potential for recovery), and because the cause of declines in the US remains unclear. Habitat loss has surely resulted in the slow, and potentially permanent, loss of some toad populations in BC. However, if a disease outbreak or parasite infection occurs it could result in rapid extirpations of toad populations like those observed in the southern Rocky Mountains, including pristine areas where declines may go unnoticed (e.g., chytrid fungus, Aeromonas bacteria, Saprolegnia fungus, trematode infections) (Wind and Dupuis 2002). |
| Trend (in population, range, area occupied, and/or condition of occurrences) | |
| Short-Term Trend: | F = Decline of 10-30% |
| Comments: |
2022: Further evidence of declines has not been determined. A local extirpation has been documented from a large wetland complex, Jordan Meadows, on southern Vancouver Island and additional population declines have been documented from the Lower Fraser Valley, and from the East Kootenays. Ohanjanian et al. (2006) visited 87 wetlands known to have Western Toads historically and found Western Toads breeding at less than a third of these sites (COSEWIC 2012h). 2010: Although the species has not been systematically monitored, recent surveys suggest that toads have declined in the Lower Mainland and on Vancouver Island, while populations throughout the remainder of the provincial range appear to be stable (Wind and Dupuis 2002). On Vancouver Island there are a few documented incidences where the population has declined catastrophically to levels where they may be extirpated or too few to count (e.g. Hanson Island (P. Spong, pers. comm.) and Sooke Watershed (T. Davis, pers. comm.)). There is also anecdotal evidence that this species is declining on the Queen Charlotte Islands (B. Wijdeven, pers. comm. 2007), but monitoring is needed to determine this. Rapid declines of populations in parts of the U.S. have been observed in the past decade, especially in mountainous areas (Wind and Dupuis 2002). Surveys in Waterton National Park in 2003 suggest declines may have occurred there as well (Taylor and Smith 2003). Based on the remote/pristine location and rapidity of some toad declines in the U.S., population declines in many areas of BC could go undetected. |
| Long-Term Trend: | U = Unknown |
| Comments: | No long-term monitoring has taken place. |
| Other Factors | |
| Intrinsic Vulnerability: | B=Moderately vulnerable |
| Comments: | Toads reach sexual maturity at 3-4 yrs for males and 4-6 yrs for females. Males may breed more than once per season, and in consecutive years, but females rarely do so and may breed only once in their lifetime (COSEWIC 2012h) .Toads exhibit high site fidelity and they have small home ranges with only occasional long-distance movements (Davis 2000), making recolonization potentially slow. Newly metamorphosed toadlets congregate in large groups in terrestrial habitats (e.g., to bask) making them vulnerable to risk of mass mortality events (e.g., predation, disease outbreaks, road traffic) (Wind and Dupuis 2002). Researchers suggest that toad populations may be easily 'stressed', which may account for their high susceptibility to disease and the declines observed in the Lower Mainland and on Vancouver Island (e.g., populations do not adjust well to urban development) (Wind and Dupuis 2002). |
| Environmental Specificity: | C=Moderate. Generalist or community with some key requirements scarce. |
| Comments: | The species appears to occupy a range of terrestrial habitat types within BC. However, surveys for breeding sites suggests that these habitats may be limiting. For example, no toad breeding sites were found in a survey of more than 70 small ponds on Vancouver Island (breeding sites for all other aquatic species were found) (E. Wind, pers. comm.). This suggests that toads may be very rare or that they tend to breed in larger water bodies, which are less abundant and result in greater isolation among populations. Surveys in northwestern BC suggest that suitable breeding sites are relatively isolated so that populations are susceptible to stochastic events (Slough 2004). Surveys of aquatic sites in Waterton Lakes National Park in 2003 found evidence of toad breeding at only 9 of 120 sites, and at only 10% of historic sites (Taylor and Smith 2003). Species requirements for breeding are unclear. |
| Other Rank Considerations: | |
| Information Gaps | |
| Research Needs: | Until we know what is causing toad declines, we need to understand potentially limiting factors for the species within BC that may hinder its ability to rebound from the impacts of stochastic events (e.g., disease outbreak). For example, breeding site and hibernacula requirements, the impacts of rural and urban development and the density of roads (a growing concern for herpetofauna) on the distribution of toad populations, and the impacts of non-native species and subsidized predators (fish, Bullfrogs, pets). As well, we need to know whether disease is an issue for toad populations within BC (e.g., chytrid fungus, saprolegnia). |
| Inventory Needs: | Inventories are needed to identify the location of known breeding sites before they can be adequately protected, especially in the Lower Mainland and on Vancouver Island. Without this information it is difficult to know whether breeding sites are rare or if populations are isolated and particularly susceptible to stochastic events (e.g., disease). |
| Stewardship | |
| Protection: | We don't fully understand what is needed to protect the species, based on declines in pristine areas of the U.S. However, identifying and protecting breeding sites and surrounding upland habitat in the Lower Mainland and on Vancouver Island is needed to ensure the long-term survival of the species. This is particularly important in this region of the province because it has extensive rural and urban development, and populations on Vancouver Island have no potential for rescue effect. |
| Management: | Identify and protect known breeding sites and adjacent upland forest areas. Maintain connectivity among breeding sites, and between breeding sites and upland forested areas (e.g., buffer riparian corridors). Wetland legislation is needed that protects all wetlands regardless of size. Limit fish stocking on a provincial level, survey sites for native amphibian species during lake assessments, and discontinue fish stocking in parks, especially known amphibian breeding sites. |
| Version | |
| Author: | Gelling, L. Wind, E., P. Govindarajulu, and L.Ramsay |
| Date: | February 21, 2022 |
| References | |
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COSEWIC. 2012h. COSEWIC assessment and status report on the Western Toad Anaxyrus boreas in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. xiv + 71 pp.
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Davis, T.M. 2000. Ecology of the western toad (Bufo boreas) in forested areas on Vancouver Island. Final Rep., For Renewal B.C., Minist. For., Victoria, BC.
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Davis, Ted. Post-Doctoral Fellow, University of Victoria, PO Box 1700 STN CSC Victoria, BC V8W 2Y2. Personal communication.
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Deguise, I. and J. Richardson. 2009. Prevalence of the chytrid fungus (Batrachochytrium dendrobatidis) in Western toads in southwestern British Columbia, Canada. Northwestern Naturalist. 90:35-38.
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Govindarajulu, Purnima. Personal communication. Biologist. B.C. Ministry of Environment. Victoria, B.C.
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Govindarajulu et al. 2013. Batrachochytrium dendrobatidis surveillance in British Columbia 2008-2009, Canada. 5pp.
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Muths, E., Corn, P.S., Pessier, A.P. and Green, D.E. 2003. Evidence for disease related amphibian decline in Colorado. Biological Conservation. 110:357-365.
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Provincial Western Toad Working Group. 2014. Management plan for the Western Toad (Anaxyrus boreas) in British Columbia. Prepared for the B.C. Ministry of Environment, Victoria, BC. 29 pp
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Russell, R.E., B. J. Halstead, B. A. Mosher, et al. 2019. Effect of amphibian chytrid fungus (Batrachochytrium dendrobatidis) on apparent survival of frogs and toads in the western USA, Biological Conservation, Vol, 236, Pp 296-304.
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Slough, B.G. 2004. Western Toad inventory in the Chilkoot Trail National Historic Site, July-August 2004. Parks Can. Species at Risk Inventory Fund Proj. SARINV04-30. Rep. to Parks Can. Yukon Field Unit, Haines Junction, YT. 54pp.
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Taylor, M., and C.M. Smith. 2003. Northern leopard frog and western toad inventory in Waterton Lakes National Park, Alberta, in 2003. Unpubl. Tech. Rep. Parks Can., Waterton Park, AB. 81pp.
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Wind, E. 2010. Impacts of non-native predators on aquatic ecosystems. Rep. for B.C Minist. Water, Land and Air Prot., Victoria, BC.
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Wind, E., and L. Dupuis. 2002. Status of the Western toad Bufo boreas in Canada. Rep. for the Comm. on the Status of Endangered Wildl. in Can. (COSEWIC), Can. Wildl. Serv., Environ. Can., Ottawa.
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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. 2022. Conservation Status Report: Anaxyrus boreas. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Apr 24, 2024).