The Decline of the Canadian Toad
Updated: Apr 21, 2020
If you’re walking by a wetland, through a forest, or even in your backyard and you see a frog-like amphibian with dry, leathery skin, covered in warts, you’ve found yourself a toad; one of which is a species at risk in Alberta due to dramatic declines in its population and distribution.
Alberta is home to three different true toad species: the western toad, the Great Plains toad, and the Canadian toad. The main way to tell them apart is that the western toad has no cranial crests (raised ridges on the top of the head), the Great Plains toad has cranial crests that come together at the front of the head to form a “V”, and the Canadian toad has cranial crests that connect on the back of the head forming a pronounced bump. The Canadian toad also has a light line running down the center of its back and reddish-brown warts surrounded by black spots.
Little is known about the life-history of Alberta’s smallest toad but one Alberta study found it to vary depending where in the province you are. Canadian toads were found to live 7 – 12 years and typically grow to a size of 50 – 70 mm with the toads found at higher latitudes living the longest and the toads from the lower latitudes growing the largest.¹
The Canadian toad is mainly active during the day, burrowing underground at night. It feeds on earthworms and insects in its preferred habitat along river valleys, near lakes or ponds, in forests, or even in ditches. The toads can be heard during their breeding season from mid-May to early June with their long, high-pitched call. It can be heard in the following audio recording by the University of Ottawa’s NatureWatch.²
Up until the mid 1980s the populations of the Canadian toad were stable with no signs of decline. Since then, however, the Canadian toad has disappeared from some areas of Alberta and appears to be on the decline where it does still live.³ So what is causing this decline? What are the threats the Canadian toad faces?
Disease has been known to cause the death of amphibians in Alberta such as in the case of the northern leopard frog with red-leg syndrome. This disease was thought to be a factor in its steep decline.⁴ It is thought that diseases could also be a factor in the decline of the Canadian toad as well.
In one study, 26 Canadian toads were captured and held in captivity. Twenty-one of the toads developed a clinical disease that could easily be confused with red-leg syndrome but was in fact caused by the fungus, Basidiobolus ranarum.⁵ Furthermore, the University of Wyoming did a study on the Canadian toad where they exposed the amphibians to this same fungus. When the scientists abraded the skin of the toads and exposed them to the fungus, they contracted clinical disease and died. The toads that were exposed to the fungus but has their protective skin barriers left intact, did not contract disease and survived.⁶ This study showed that healthy Canadian toads can be very resistant to disease but compromised toads can be very susceptible.
Further studies need to be done to know the full impact of disease on the Canadian toad but it seems as though other factors are more influential on the amphibian’s decline such as reduced quality of habitat.
Habitat Degradation, Destruction, and Fragmentation
No studies have been done on how the destruction of wetlands may have impacted the populations of Canadian toads specifically, however, there is an obvious link. Since the 1950’s, about 60% of wetlands in Alberta’s aspen parkland have been drained and over 90% of wetlands in the parkland and prairie regions of Alberta have been impacted by agricultural activities.⁷ Also, the areas of the province that have seen the greatest declines in Canadian toads are also the areas that have seen these decreases in wetland habitat. As wetlands are destroyed, the populations of the toads follow.
A 1999 study took a look at how fragmenting wetlands with roads and other barriers might impact the success of amphibians.⁸ It found that the lack of success of amphibian populations can, at least in part, be linked to both the loss of wetlands and to roads acting as barriers. The study found that the further wetlands were separated and the higher density of roads, the less rich the area was with amphibian populations.
The habitat of toads goes beyond wetlands, as well. Toads spend much more time in upland environments than frogs and require these terrestrial areas to be protected as well. A 2010 study about western toads pointed out that conservation of amphibian habitat is typically focused on a buffer area of no more than 100 m from the wetland.⁹ In the case of toads, this is not nearly enough as their critical habitat can extend 2 km from breeding ponds.
Both of these studies highlight the importance of protecting beyond just the wetland if conservation of the species is the goal. In order to protect toad habitat, their critical terrestrial habitat needs to be protected as well.
Toxins in environment
Habitat degradation can also occur in the form of lowering the quality of water through toxins. A Simon Fraser University study performed near Fort McMurray, Alberta found that wetlands containing oil sands effluent could not support viable populations of frogs or toads due to the impact on tadpoles.¹⁰ Amphibians are commonly used as a leading indicator to habitat degradation because of their sensitivity to toxins such as those output by the oil sands.
Tadpoles can also be affected by the presence of pesticides in the water. A study from 2004 found that when tadpoles were exposed to multiple pesticides, significant mortality resulted.¹¹ The waters where tadpoles of Canadian toads grow, need to be free of chemicals and toxins in order for the toad populations to effectively bounce back.
A less obvious impact on the habitat of toads in anthropogenic noise or noise caused by humans. Amphibians such as the Canadian toad rely heavily on auditory communication in breeding and reproduction. When humans introduce noise to this environment, the reproductive success of the toads is diminished. A 2014 study found that traffic noise does impact the reproductive behaviour of frogs and toads. It also found that loss of auditory habitat due to traffic noise introduced physiological stress in female wood frogs possibly decreasing their chance of survival.¹² When we look at protecting toad habitat it is crucial that we look at limiting anthropogenic noise as well.
Western toads could also be a factor in speeding up the Canadian toad’s population decrease. It has been observed that in areas where Canadian toads have declined, western toads have filled in the gap. Even though the two species do not directly compete for food or territory, the larger western toads are able to outcompete the Canadian toads for females as hybridization is known to occur between the species.¹³ This could exacerbate the problem and contribute to the already declining numbers of Canadian toads. If we don’t stop the decline of the Canadian toad, this issue will quicken their population drops.
More information is definitely needed to be certain of the exact cause of the decline in Canadian toads but in the meantime we need to stop the habitat loss through draining wetlands, habitat fragmentation through building of roads, and the habitat degradation through toxins being introduced to the water and the introduction of anthropogenic noise to critical habitat.
In order to be part of the solution, demand that crucial habitat — both wetland and terrestrial and not excluding auditory habitat — is protected. Speak out for protection of areas that are known to have populations of Canadian toads. This can be anything from noise restrictions to protecting an area from development. Get involved in the community and write to your government officials to protect local habitat that is home to the Canadian toad. In the city of St. Albert, where I live, the Grey Nuns White Spruce Park is a local forest that is home to the Canadian toad. This is an example of an area that we need to limit our impact on.
Shop for organic vegetables and cease using pesticides in your gardens or lawns. The more pesticides that you use whether directly applied by you or indirectly through the products you buy, the more species such as the Canadian toad are impacted.
The Canadian toad is a species that is declining. We need to do what we can to protect this species. Amphibians are an indicator species for ecosystems so the actions we take to protect this species will not only help prevent its decline, but could also save many others.
1. Eaton, B. R., Paszkowski, C. A., Kristensen, K., & Hiltz, M. (2005). Life-history variation among populations of Canadian Toads in Alberta, Canada. Canadian Journal of Zoology, 83(11), 1421-1430.
2. uOttawa NatureWatch. (2014, June 3). Bufo Hemiophrys. [Audio file]. Retrieved from https://soundcloud.com/uottawa-naturewatch/bufo-hemiophrys
3. Hamilton, I. M., Skilnick, J. L., Troughton, H., Russell, A. P., & Powell, G. L. (1998). Status of the Canadian Toad, Bufo Hemiophyrs, in Alberta. Alberta Environmental Protection, Wildlife Management Division, Status & Surveys Branch.
4. Roberts, W. E. (1986). The northern leopard frog-endangered in Alberta. Endangered species in the prairie provinces, 137.
5. Taylor, S. K., Williams, E. S., & Mills, K. W. (1999). Mortality of captive Canadian toads from Basidiobolus ranarum mycotic dermatitis. Journal of Wildlife Diseases, 35(1), 64-69.
6. Taylor, S. K., Williams, E. S., & Mills, K. W. (1999). Experimental exposure of Canadian toads to Basidiobolus ranarum. Journal of Wildlife Diseases, 35(1), 58-63.
7. Hamilton, I. M., Skilnick, J. L., Troughton, H., Russell, A. P., & Powell, G. L. (1998). Status of the Canadian Toad, Bufo Hemiophyrs, in Alberta. Alberta Environmental Protection, Wildlife Management Division, Status & Surveys Branch.
8. Lehtinen, R. M., Galatowitsch, S. M., & Tester, J. R. (1999). Consequences of habitat loss and fragmentation for wetland amphibian assemblages. Wetlands, 19(1), 1-12.
9. Browne, C. L., & Paszkowski, C. A. (2010). Hibernation sites of western toads (Anaxyrus boreas): Characterization and management implications. Herpetological Conservation and Biology, 5(1), 49-63.
10. Pollet, I., & Bendell‐Young, L. I. (2000). Amphibians as indicators of wetland quality in wetlands formed from oil sands effluent. Environmental Toxicology and Chemistry: An International Journal, 19(10), 2589-2597.
11. Relyea, R. A. (2004). Growth and survival of five amphibian species exposed to combinations of pesticides. Environmental Toxicology and Chemistry: An International Journal, 23(7), 1737-1742.
12. Tennessen, J. B., Parks, S. E., & Langkilde, T. (2014). Traffic noise causes physiological stress and impairs breeding migration behaviour in frogs. Conservation Physiology, 2(1).
13. Eaton, B. R., Paszkowski, C. A., Kristensen, K., & Hiltz, M. (2005). Life-history variation among populations of Canadian Toads in Alberta, Canada. Canadian Journal of Zoology, 83(11), 1421-1430.