Eastern Hog-nosed Snake (Heterodon platirhinos) COSEWIC assessment and update status report: chapter 5

Habitat

Habitat requirements

There have been few ecological studies on the Eastern Hog-nosed Snake, particularly in Canada. However, the research that has been done provides us with good insight into the habitat needs of this species. Platt (1969) described six features to define the preferred habitat of H. platirhinos: well-drained soil; loose or sandy soil; open vegetative cover such as open woods; brushland or forest edge; proximity to water; and climatic conditions typical of the eastern deciduous forest biome. An analysis of habitat use at Wasaga Beach PP in Ontario indicated that H. platirhinos preferred forested areas as well as wetlands adjacent to conifer plantations, and that meadows and areas currently being used by people (urban, agricultural, etc.) were the least suitable (Cunnington 2004b). Eastern Hog-nosed Snakes in shoreline areas such as Rondeau PP and Long Point PP often rely on driftwood and other ground cover in beach and beach dune habitats (Seburn 2005), where their prey of choice, Bufo fowleri, is found. A telemetry study done south of Parry Sound in Ontario suggests that, at the landscape level, Eastern Hog-nosed Snakes in that area preferred meadow, sand, human- impacted areas (i.e. private dwellings, trailer parks, sand/gravel pits), and forest habitats over rock, wetland, and aquatic habitats (Rouse 2006). In the Parry Sound study, telemetry locations of individual snakes were distributed somewhat evenly across the different habitat types; such distribution reflects this species’ vagility and tortuous (“meandering” versus linear) movements Rouse (2006). There are not many data regarding habitat use by juvenile Eastern Hog-nosed Snakes throughout the species’ range, but juveniles in Norfolk County appear to use the same habitat, including cover and thermoregulation sites, as adults (S. Gillingwater pers..comm.). Also, hatchlings at Rondeau PP use the same cover material as adults soon after hatching (S. Gillingwater pers. comm.).

Adult Eastern Hog-nosed Snakes are very mobile for snakes and have home ranges that can exceed 100 ha (Cunnington 2004b). Daily movements of 100 m occur (Cunnington 2004b) and the maximum straight-line distance moved over an active season approaches 5 km (Rouse 2006). However, actual distances moved can be much greater than these values because the snakes follow a tortuous path in their search for food or mates (Rouse 2006).

As the Eastern Hog-nosed Snake is a prey specialist, it is important to take into consideration the habitat requirements of both American Toads and Fowler’s Toads when discussing the snake’s survival. According to Harding (1997), if reported local declines in toad populations in parts of the Great Lakes region are sustained over time, Eastern Hog-nosed Snakes would face another challenge to their survival and, combined with other threats, this lack of food could cause a decline in this species’ populations as well. A report suggests some Great Lakes basin-wide declines in American Toads (Crewe et al. 2005), but the implications of the alleged declines for the Eastern Hog-nosed Snake are unknown.

Habitat trends

Much of the habitat of the Eastern Hog-nosed Snake in southern Ontario has been destroyed by land alterations linked to farming and urban sprawl (Bakowsky and Riley 1992; Snell 1987). The well-drained, sandy soils preferred by H. platirhinos in most of its range are, coincidentally, soils which are favourable for farming (Armason 2001; W. Chesworth pers. comm. 2007) and beach/water-related recreation (e.g. Wasaga Beach PP). Much of the area surrounding Wasaga Beach PP has been urbanized and is no longer suitable habitat for the snake. At the northern portion of its range, on the Canadian Shield (Parry Sound District and surrounding area, near the Muskokas), the terrestrial, upland habitat preferred by the Eastern Hog-nosed Snake is being altered and fragmented as people build cottages and demand the associated network of access roads (see Figures 3 and Figure 44.).

Natural habitat in Ontario south of the Canadian Shield is more fragmented than any region of comparable size in the Great Lakes Basin (Riley and Mohr 1994; Larson et al. 1999). This fragmentation is accentuated by the highest density of roads per capita in the world (Forman et al. 2003). The road density in the Shield region occupied by the Eastern Hog-nosed Snake continues to expand (Taylor et al. 2001, Figure 3), recently accelerated by the extension of a 4-lane highway through the heart of the Georgian Bay region north to Parry Sound. This road will be further “four-laned” through the remaining hognose habitat to the species’ northern limit (Ontario Government Notice, of Study Completion and Filing of Design and Construction Report. June 19, 2007.). This expanded highway will bring many more people to the region and stimulate construction of more roads into recreational and forest management areas. Snake abundance within a half km of roads has been shown to be less than half that more than 850 m from roads (Rudolph et al. 1999).

Figure 3. Map of Georgian Bay region showing roads, buildings, ProvincialParks, Conservation Reserves and Element Occurrences of Eastern Hog-nosed Snakes. Expansion of road networks and their associated development is increasingly isolating populations of hog-nosed snakes throughout their Ontario range, but especially in the southern Georgian Bay region (see text).

Figure 3. Map of Georgian Bay region showing roads, buildings,ProvincialParks, Conservation Reserves and Element Occurrences of Eastern Hog-nosed Snakes. Expansion of road networks and their associated development is increasingly isolating populations of hog-nosed snakes throughout their Ontario range, but especially in the southern Georgian Bay region (see text)

Figure 4.  Map of southern coast of Georgian Bay showing roads and buildings (represented by black dots).

Figure 4.  Map of southern coast of Georgian Bay showing roads and buildings (represented by black dots)

Habitat protection/ownership

Some of the known populations are in protected areas such as Pinery PP, Komoka PP, Rondeau PP, and Wasaga Beach PP (Table 1). However, snakes in these parks are still killed by visitors and nearby residents, either deliberately or accidentally by road traffic. For example, while conducting surveys for snakes in Rondeau PP in 2000-2001, Gillingwater interviewed several in-park cottagers who admitted killing hognosed and other snake species and two individuals stated that they would continue to do so (S. Gillingwater pers. comm. email May 2007).  In 2001, three Eastern Hog-nosed Snakes were found dead on Rondeau PP roads. Over 23 days of irregular sampling in Sept-Oct 2001, 241 snakes were found dead on just one part of one road in Rondeau PP (Gillingwater and Brooks 2002), although only two of these were hog-nosed snakes, as the species’ abundance has greatly declined there (Schueler 1997).  In Pinery PP, the Eastern Hog-nosed Snake was the snake species most commonly encountered as roadkill (Brad Steinberg pers. comm. 2007), but since 2003 it seems to have declined markedly and is now rarely encountered (A. MacKenzie, pers. comm. 2007). Similarly, in the northern part of the hognosed snake’s range, road mortality has been shown to be a significant factor in loss of Eastern Foxsnakes (Elaphe gloydii) in Killbear PP, to the extent that these snakes have higher mortality when in the park than when outside (A. Lawson, pers. comm. 2007). Another study of this species found that 9 of 13 mortalities occurred in protected areas (MacKinnon 2005). In a detailed study modelling factors affecting roadkill inside and adjacent to Point Pelee NP and Rondeau PP, rates of mortality of snakes per km per day were higher inside the parks than outside (Farmer 2006). Likely most of this difference occurred because there were more snakes and snake habitat inside the park, but nevertheless, roads and high park use make these protected areas poor havens for snakes (Lawson, 2004).

Overall, less than 3% of hognose distribution in Canada occurs in Provincial Parks and only 1.7% is in Conservation Reserves (Crowley 2006). Only 3% of Ontario Provincial Parks within the range of the Hog-nosed Snake have no roads (Crowley 2006). Less than 1% of southern Ontario is protected and virtually all of these areas are small and isolated (Kerr and Cihlar 2004, Figure 5). As Rivard et al. (2000) reported in an extensive review of Canada’s National Parks, parks may not be able to maintain species that are extirpated from the surrounding region because extinction in these protected areas is more closely related to regional patterns of extinction than to park characteristics. It seems a truism that this principle is most likely to hold for smaller parks as they are more permeable to the development features of the surrounding region (Rivard et al. 2000; Crowley 2006).

Figure 5. Map showing the Extent of Occurrence of the Eastern Hog-nosed Snake and protected areas within that range. (Note that the species is possibly extirpated from Algonquin Provincial Park, which is by far the largest protected area within the species putative range. Brooks et al. 2003). The apparent lack of protected areas, particularly in southwest Ontario is because the areas are too small to readily show up on this scale. (Map prepared by J.F. Crowley).

Figure 5. Map showing the Extent of Occurrence of the Eastern Hog-nosed Snake and protected areas within that range.

Although hog-nosed snakes have been found north to the mighty French River (Figure 2), most recent records in the Great Lakes/St. Lawrence region occur in and east of the southern third of the Georgian Bay region around Wasaga and in Muskoka and east to the Peterborough area  (Figure 2). This region is undergoing rapid development and has perhaps the highest rate and density of recreational development and activity on the Canadian Shield (Figures 3 and 4). Indeed, the Wasaga/Port Severn area in Simcoe County (see Figures 2,3,4) appears to be a stronghold for the Eastern Hog-nosed Snake, so it is noteworthy that the town of Wasaga is currently one of the fastest growing communities in Ontario (Watters 2003). Wasaga Beach PP is surrounded by development, and although the park has no public roads, the small size of the park (it is smaller than the home range of individual snakes), and intensive use of the surrounding area, means that snakes are either killed on roads or are confined to the Park (Cunnington 2004a). As these aforementioned provincial parks are not contiguous they do not provide the opportunity for snakes from these separated areas to interbreed (i.e. little potential for recolonization, and increasing tendency for inbreeding and loss of genetic variation).  Although the populations in the most northern portion of the range may sometimes be more or less contiguous, the majority of the habitat is not protected and is currently subject to development and land privatization. Much of the southern coast of Georgian Bay is covered in cottages, and roads to service these structures continue to proliferate (C. MacKinnon, pers. comm. 2007, J. Rouse pers. comm. 2007, Figure 4).

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