Ontario Snakes are at Risk

Ontario is home to 19 species of snakes, but many of these species are either of special concern, threatened or endangered (Rowell, 2012). The Committee on the Status of Endangered Wildlife in Canada (CSEWIC) has determined that 7 Ontario snake species are endangered, meaning they face immediate extirpation/extinction, and that 2 species are threatened, meaning that unless actions are taken the species is very likely to become endangered. Three of these at risk Ontario species are the eastern hog-nosed snake, gray ratsnake and queensnake.

Fig. 2. A gray ratsnake. Photo credit: Nick Caims (Argue, 2015).

Fig. 3. A queensnake. Photo credit: Scott Gillingwater (Crowley, “Queensnake” 2015). 

Eastern Hog-Nosed Snake (Heterodon platirhinos)

Fig. 1. An eastern hog-nosed snake, notice the characteristic upturned nose.  Photo Credit: Joe Crowley (Crowley, “Eastern Hog-Nosed Snake” 2015).

            As indicated by its common name, the eastern hog-nosed snake has a unique upturned snout, but other than this, appearance tends to vary between individuals (Crowley, “Eastern Hog-Nosed Snake” 2015).

Fig. 4. The current and historic Ontario range of the eastern hog-nosed snake (Crowley, “Eastern Hog-Nosed Snake” 2015).

            There are two regional populations of the eastern hog-nosed snake in Ontario, the southwestern population and the north-central population (Rowell, 2012). Figure 4 outlines the current and historic ranges of these two populations. Note that while the ranges appear quite large, in reality there are only a few locations that have viable population sizes, that is, populations of an adequate size to support survival (Rowell, 2012). As is demonstrated in the range map, the eastern hog-nosed snake is experiencing range reductions and population declines, mostly as a result of human activity (Rowell, 2012).

            The eastern hog-nosed snake faces a number of human-caused threats, including habitat disturbance, persecution, and road mortality.

·      Habitat Disturbance: The preferred habitats, specifically soil types, of the eastern hog-nosed snake tend to also be ideal sites for agriculture and waterfront development (Crowley, “Eastern Hog-Nosed Snake” 2015). Subsequently, human land use has lead to large-scale destruction of suitable area for this snake, and any remaining habitat is at threat of being developed and disturbed (Crowley, “Eastern Hog-Nosed Snake” 2015).

·      Persecution: While the eastern hog-nosed snake is harmless, under threat it sometimes carries out a frightening, cobra-like defensive display (Rowell, 2012). As a result, individuals are often killed by humans who mistake these snakes as being dangerous (Crowley, “Eastern Hog-Nosed Snake” 2015).

·      Road Mortality: Death due to vehicle collision is an increasing threat to eastern hog-nosed snakes, especially as road construction increases with the range of this species (Government of Ontario, “Eastern Hog-Nosed Snake” 2015).

These negative impacts that humans have on the eastern hog-nosed snake have lead to the species becoming threatened (Government of Ontario, “Eastern Hog-Nosed Snake” 2015). Unless action is taken to mitigate the threats human activates pose to these snakes, the species is likely to become endangered, even extinct.

Gray Ratsnake (Pantherophis spiloides)

            The gray ratsnake is the largest snake species in Ontario with individuals growing up to 2 m long (Government of Ontario, “Gray Ratsnake” 2015)! Considering its large size you may be surprised to learn that these snakes are excellent climbers and can often be found in trees, hunting for prey such as birds (Government of Ontario, “Gray Ratsnake” 2015).

Fig. 5. The current and historic Ontario range of the gray ratsnake (Argue, 2015).

            As shown in Figure 5, two populations of gray ratsnakes occur in Ontario, the Carolinian population and the Frontenac Axis population. While both are experiencing population declines they are at different levels of risk. The Carolinian population is endangered as a result of isolation caused by severe habitat disturbance, persecution and road mortality (Argue, 2015). This area is now densely inhabited by humans who have cut down much of the snake’s preferred forest habitat and often kill the harmless species out of unprecedented fear (Rowell, 2012). The same human activities have lead to the Frontenac Axis population, near Kingston ON, becoming threatened (Rowell, 2012). It is interesting to note that this population does benefit from the fragmenting of its habitat for agriculture as it increases the incidence of prey, but any benefit is offset by mortality caused by persecution and road kill as well as habitat disruption for cottage and urban development (Rowell, 2012).

Queensnake (Regina septemvittata)

            The queen snake is a semi-aquatic species and an excellent swimmer (Crowley, “Queensnake” 2015). These snakes never venture far from their very specialized habitats; clear water bodies with rocky bottoms like streams, rivers and lakes, where it preys predominantly on crayfish (Government of Ontario, “Queensnake” 2015). Due to their need for specific habitat and small home ranges, queensnakes are very poor dispersers  (Government of Ontario, “Queensnake” 2015). The inability to move to new habitats combined with multiple human-induced threats has lead to range and population declines of this species (as can be seen in figure 6), which have ultimately caused the queensnake to become endangered (Rowell, 2012).

Fig. 6. The current and historic Ontario range of the queensnake (Crowley, “Queensnake” 2015).

The extensive development that has occurred in southwest Ontario, particularly near waterways where queensnake are most common, pose many threats to the species (Rowell, 2012). Water control via dams, wetland draining, and shoreline development cause changes in water flow and turbidity, making habitats unsuitable for queensnakes (Rowell, 2012). In addition, queensnakes are more sensitive to water pollution than other reptiles as pollutants can easily penetrate their skin (Rowell, 2012). Aside from their direct negative impacts on queensnakes, all of these factors also indirectly harm this species as the resulting poor water quality leads to extreme population declines in crayfish, the queensnake’s main food source (Rowell, 2012). Recreational use of queensnake habitat also contributes to population declines. These snakes hide in shoreline rocks and so are often unintentionally trampled, in addition to being killed on purpose out of fear, even though queensnakes are harmless to humans (Crowley, “Queensnake” 2015).

            You may have noticed that these three Ontario snake species are threatened or endangered as a result of a common set of threats, all of which are founded in human activity. Indeed these threats (habitat disruption, persecution, and road mortality) in addition to climate change and the dangers of resulting small populations are putting snakes at risk all across Ontario.

References:

Argue, A. (2015). Gray Ratsnake. Ontario Nature. http://www.ontarionature.org/protect/species/reptiles_and_amphibians/gray_ratsnake.php.

Crowley, J. (2015). Eastern Hog-Nosed Snake. Ontario Nature. http://www.ontarionature.org/protect/species/reptiles_and_amphibians/eastern_hog-nosed_snake.php.

Crowley, J. (2015). Queensnake. Ontario Nature. http://www.ontarionature.org/protect/species/reptiles_and_amphibians/queensnake.php.

Government of Ontario. (2015). Eastern Hog-Nosed Snake. http://www.ontario.ca/page/eastern-hog-nosed-snake.

Government of Ontario. (2015). Queensnake. http://www.ontario.ca/page/queensnake.

Government of Ontario. (2015). Gray Ratsnake. http://www.ontario.ca/page/gray-ratsnake.

Rowell, J. (2012). The Snakes of Ontario: Natural History, Distribution and Status. Toronto, ON.