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Recovery Strategy for the Eastern Hog-nosed Snake (Heterodon platirhinos) in Canada (Proposed)


1. Background

1.1 Species Assessment Information from COSEWIC

Common Name: Eastern Hog-nosed Snake

Scientific Name: Heterodon platirhinos

Assessment Summary: 2001

Status: Threatened

Reason for Designation: The Eastern Hog-nosed Snake is rare and decreasing in abundance and area of occurrence. It suffers from loss of habitat and is unusually susceptible to persecution by people because it is a large snake that employs a threatening, though harmless, defensive display. Also, it is unusually vulnerable to road traffic because it moves slowly.

Occurrence: Southern Ontario

Status History: Designated as Special Concern in 1997, then reassessed as Threatened in 2001.

1.2 Description

The Eastern Hog-nosed Snake is a heavy-bodied snake with a distinctive upturned scale on its snout. It is typically 50-85 cm in total length. Colour and pattern are highly variable. Some individuals have a distinct pattern of dark blotches along the back alternating with blotches along the sides. Other individuals lack blotches and are gray, brown or olive, or rarely black (melanistic). Some Eastern Hog-nosed Snakes are intermediate in pattern with faint blotches (Figure 1).

Figure 1. Photo of Eastern Hog-nosed Snake. Photo by Jeremy Rouse
Figure 1. Photo of Eastern Hog-nosed Snake. Photo by Jeremy Rouse

The Eastern Hog-nosed Snake has an elaborate defensive display. When threatened, it will raise its head, flatten its neck in cobra-like fashion, gape its mouth and hiss loudly. It will strike forward at the perceived attacker with its mouth closed, but it rarely bites. It is not venomous. If the defensive behaviour does not drive off the attacker, the Eastern Hog-nosed Snake will writhe about, flip over on its back and play dead.

1.3 Populations and Distribution

The Eastern Hog-nosed Snake is widespread in eastern North America, with less than 10% of its global distribution in Canada. It occurs from Florida and Texas in the south, to southern New England, Ontario and Minnesota in the north. It is found as far west as western Kansas. The Eastern Hog-nosed Snake is absent from the St. Lawrence drainage (eastern Ontario and most of New York state). It is considered very common both globally (G5) and in the United States of America (N5), but rare to uncommon in Canada (N3). In general, the Eastern Hog-nosed Snake is more common in the south of its North American range and less common in the north (Figure 2)

Figure 2. Conservation ranks for the Eastern Hog-nosed Snake (NatureServe 2007).
Figure 2. Conservation ranks for the Eastern Hog-nosed Snake (NatureServe 2007).

In Canada, the Eastern Hog-nosed Snake is only found in the province of Ontario. Within Ontario, it is found in two geographically separate areas: the Carolinian Life Zone of southwestern Ontario and in central Ontario south of the French River and Lake Nipissing (Figure 3). The northern limit of the range corresponds approximately to the 120 day frost-free period (Schueler 1997).

Although the current distribution of the Eastern Hog-nosed Snake in Ontario is not completely known, it is clear that this species has declined. The Natural Heritage Information Centre (NHIC) of the Ontario Ministry of Natural Resources has determined that 8% of known element occurrences (EOs) or "populations" of Eastern Hog-nosed Snakes in Ontario have been extirpated (Oldham and Austen 1998). The Eastern Hog-nosed Snake has been extirpated from the Regional Municipalities of Halton, Peel and York as well as from Pelee Island and Point Pelee National Park (Oldham and Austen 1998). Although most extirpations occurred in southwestern Ontario, there are reports of extirpations from across the range.

In addition, 35% of element occurrences are ranked historic, or unconfirmed in the last 20 years. Although historically the Eastern Hog-nosed Snake has been reported in Bruce and Prince Edward counties, it may now be extirpated from these areas (Oldham and Austen 1998). Quantitative data on population sizes are lacking, but remaining populations may have declined as a result of increased rates of mortality.

Figure 3. Eastern Hog-nosed Snake Observations in Ontario
Figure 3. Eastern Hog-nosed Snake Observations in Ontario

1.4 Needs of the Eastern Hog-nosed Snake

1.4.1 Habitat and biological needs

The Eastern Hog-nosed Snake grows quickly and maturity can be reached in approximately 2 years in Kansas (Platt 1969), but possibly up to 4-5 years in Ontario (Cunnington pers. comm. 2004, Rouse pers. comm. 2004). Females in the northern part of their range lay an average of 25 eggs, with larger females laying more eggs (Platt 1969). At least some females breed two or more years in a row in Ontario (Cunnington and Cebek 2005).

There have been few in-depth studies concerning Eastern Hog-nosed Snake ecology. Additional research is required on habitat use in different areas of Ontario. Five physical features have been used to define the preferred habitat of the Eastern Hog-nosed Snake: well-drained soil; a 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 (Platt 1969). Analysis of habitat use at Wasaga Beach Provincial Park in Ontario found that Eastern Hog-nosed Snakes prefer forested areas and wetlands. Conifer plantations, meadows and developed areas were found to be less suitable (Cunnington 2004b). Snake use of habitat was clustered in areas that provided a diverse habitat mosaic. A Description of Residence will be posted on the Species at Risk Act Public Registry.

In southwestern Ontario, in areas such as Rondeau Provincial Park and Long Point, Eastern Hog-nosed Snakes use beach and dune habitat, often relying on driftwood and other artificial and natural ground cover (Gillingwater and Piraino 2004). Individual snakes have been found moving between driftwood and Cottonwood trees along the beach dune habitat actively foraging for Fowler's Toads (Gillingwater and Piraino 2004). Eastern Hog-nosed Snakes made use of a network of naturally formed tunnels at Long Point (Gillingwater and Piraino 2004). Tunnel entrance points often originated near exposed logs and continued on to wood and debris, which had been covered by a thick layer of sand in previous years. Eastern Foxsnakes (Elaphe gloydi) and Fowler's Toads also used these areas (Gillingwater and Piraino 2004).

1.4.2 Ecological role

The diet of the Eastern Hog-nosed Snake consists mainly of American Toads (Bufo americanus) and Fowler's Toads (Bufo fowleri) although it will also take frogs, salamanders, turtle eggs, small mammals and birds (Platt 1969). Juveniles feed upon small prey such as Redback Salamanders (Plethodon cinereus), Spring Peepers (Pseudacris crucifer) or invertebrates (Michener and Lazell 1989). Because Eastern Hog-nosed Snakes feed mainly on toads, their populations may respond to changes in toad populations. This reliance may be significant in the Carolinian Region where Fowler's Toad has declined, although the American Toad remains one of the most widespread and abundant amphibians in southern Ontario (Hecnar 1997).

1.4.3 Limiting factors

The Eastern Hog-nosed Snake reaches its northern limit in Ontario, hence climate is a limiting factor for this species. As such it is possible that the Eastern Hog-nose Snake has limited recruitment, particularly in the northern part of its range in Ontario.

Habitat is also a limiting factor for this species, because of its reliance on areas with sandy soil. As this habitat is developed, the amount of habitat available for the Eastern Hog-nosed Snake in Ontario is reduced.

Populations of the Eastern Hog-nosed Snake typically exist at low densities (Platt 1969, Michener and Lazell 1989, Cunnington 2006, Rouse pers. comm. 2004). It is unclear what effect increased rates of mortality have on the viability of populations.

Eastern Hog-nosed Snake adults are very mobile, with home ranges greater than 100 ha and daily movements of approximately 100 m (Cunnington 2004a). Range lengths (the maximum distance between any two radio locations) for 10 individuals radio-tracked in Georgian Bay averaged 2.7 km and the maximum range length recorded was over 6 km (Rouse and Willson, unpublished data). This mobility makes Eastern Hog-nosed Snakes more vulnerable to such threats as traffic mortality and habitat fragmentation than more sedentary species. It is further compounded by the fact that they are relatively slow-moving and, as such, are more susceptible to road mortality (Andrews and Gibbons 2005).

1.5 Threats

Threats to the Eastern Hog-nosed Snake, listed in order of perceived importance, are: habitat loss, degradation and fragmentation, roads, persecution, collecting and contaminants. All threats are range wide.

1.5.1 Threat classification

Table 1. Threat Classification Table
1 Habitat loss, degradation and fragmentationThreat Information
Threat CategoryHabitat Loss or DegradationExtentWidespread
 LocalRange-wide
General ThreatHousing developmentOccurrenceCurrent
FrequencyContinuous
Specific ThreatHabitat conversion; habitat fragmentation; isolationCausal CertaintyHighMedium
SeverityHighMedium
StressReduced population sizeLevel of ConcernHigh
2 Road killThreat Information
Threat CategoryHabitat loss or degradationExtentWidespread
 LocalRange-wide
General ThreatRoad constructionOccurrenceCurrent
FrequencySeasonal
Specific ThreatRoad kill; habitat fragmentationCausal CertaintyHigh
SeverityHigh
StressIncreased mortalityLevel of ConcernHigh
3 PersecutionThreat Information
Threat CategoryDisturbance or harmExtentWidespread
 LocalRange-wide
General ThreatDiscriminate killingOccurrenceCurrent
FrequencySeasonal
Specific Threat Causal CertaintyHighMedium
SeverityMedium
StressIncreased mortalityLevel of ConcernMedium
4 CollectingThreat Information
Threat CategoryBiological Resource UseExtentWidespread
 LocalRange-wide
General ThreatPet tradeOccurrenceCurrent
FrequencySeasonal
Specific ThreatCollection of animalsCausal CertaintyMedium
SeverityUnknown
StressReduced population sizeLevel of ConcernMedium
5 ContaminantsThreat Information
Threat CategoryPollutionExtentWidespread
 LocalRange-wide
General ThreatCrop production (e.g., pesticide, herbicide, or fertilizer application)OccurrenceUnknown
FrequencySeasonal
Specific ThreatConsuming contaminated preyCausal CertaintyLow
SeverityUnknown
StressReduced fitness or poor reproductive successLevel of ConcernLow

1.5.2 Description of threats

1.5.2.1 Habitat loss, degradation and fragmentation

Development continues to eliminate habitat for the Eastern Hog-nosed Snake. For example, Wasaga Beach is one of the fastest growing communities in Ontario (Watters 2003). Privately owned natural areas adjacent to Wasaga Beach Provincial Park used by Eastern Hog-nosed Snakes are being turned into housing developments. Even when habitat is not destroyed completely, housing developments can lead to increased interactions between snakes and people and this has led to at least three Eastern Hog-nosed Snakes being killed around Wasaga Beach Provincial Park (Cunnington pers. comm. 2004). Other forms of development (e.g. road construction, or sand or gravel pits) can also degrade or destroy habitat for Eastern Hog-nosed Snakes.

The landscape of southwestern Ontario in particular has been greatly modified by humans during the last century. One of the impacts of this is the fragmentation of natural areas. Although the effects of habitat fragmentation on the Eastern Hog-nosed Snake have not been studied, research on a wide variety of vertebrates suggests that increasing fragmentation leads to reduced population levels, increased risk of extirpation due to stochastic events, reduced gene flow among populations, increased inbreeding, and loss of genetic diversity (Young and Clark 2000).

1.5.2.2 Roads

Roads are a widespread and significant ecological threat (Trombulak and Frissell 2000). In southern Ontario, the primary road network expanded from approximately 7000 to over 35 000 km of roads from 1935 to 1995 (Fenech et al.  2001). It is unclear how significant a threat traffic mortality is for the Eastern Hog-nosed Snake. Traffic mortality had been reported from Point Pelee National Park before the snake became extirpated (Point Pelee National Park, unpublished data), as well as in Petroglyphs, Pinery, Port Burwell and Rondeau Provincial Parks (NHIC, unpublished data). This indicates that even populations within protected areas are not immune from this threat. Eastern Hog-nosed Snakes are relatively slow moving and are therefore at greater risk of being hit while crossing roads, however they have also been found to exhibit road avoidance, which could contribute to population fragmentation (Andrews and Gibbons 2005). In addition, road construction can destroy, degrade and fragment Eastern Hog-nosed Snake habitat and allow development to occur in previously roadless areas, which increases the likelihood of negative human-snake interactions. Off-road vehicle use also poses a threat to snakes and their nests. ATV tracks have been found within 1 m of a known nest (Cunnington pers. comm. 2004) and off-road mountain bike traffic may also pose risk in this same regard.

1.5.2.3 Persecution

The fear of snakes that some people have is exacerbated by the defensive behaviour of the Eastern Hog-nosed Snake. This results in many snakes being needlessly killed around homes, cottages, farms, and even in protected areas. The Eastern Hog-nosed Snake is listed as a specially protected reptile in the Fish and Wildlife Conservation Act (FWCA) which prohibits its killing, capture, hunting or trapping, however persecution continues. For example, a pair of Eastern Hog-nosed Snakes was killed by a landowner adjacent to Wasaga Beach Provincial Park in 2002 (Cunnington 2004a). The landowner was successfully prosecuted under the FWCA. At Rondeau Provincial Park, local cottagers have stated that they have or know of others who have routinely killed Eastern Hog-nosed Snakes in the park (Gillingwater pers. comm. 2004) and the species is now rare within the park. Local landowners surrounding the park have also stated that they have killed this species in the past (Gillingwater pers. comm. 2004). Although it is difficult to quantify the level of this threat, it primarily targets adult snakes and hence removes valuable breeding members from populations.

1.5.2.4 Collecting

There is a large community of reptile keepers. While most are law-abiding, illegal collecting of reptiles for the pet trade does occur. Although the Eastern Hog-nosed Snake cannot be legally sold in Ontario, individuals have been seen for sale in pet stores (Gillingwater pers. comm. 2004). Despite the fact that the Eastern Hog-nosed Snake has a reputation of being difficult to maintain in captivity, there is a growing demand for this species. A pair of Eastern Hog-nosed Snakes was selling for $160 US on the Internet in October of 2004. There was also an online advertisement from a dealer offering to buy wild caught Eastern Hog-nosed Snakes. There is even a multi-page website dedicated to the care, feeding and breeding of hog-nose snakes in captivity.

1.5.2.5 Contaminants

The Eastern Hog-nosed Snake may be sensitive to some contaminants, particularly through the effects of contaminants on their food source. For example, at Point Pelee National Park, where the Eastern Hog-nosed Snake is now extirpated, total DDT concentrations in Spring Peepers have been found to approach levels where toxic effects are expected to be observable (Russell and Haffner 1997). Small amphibians such as Spring Peepers may be a major food source for juvenile Eastern Hog-nosed Snakes (Michener and Lazell 1989). DDT was sprayed within the park from approximately 1950-1965 (Linke 1994). It is also noteworthy that Fowler's Toad, a major food source for the Eastern Hog-nosed Snake, was extirpated from Point Pelee about the time DDT spraying began in the park (Russell and Haffner 1997).

1.6 Actions Already Completed or Underway

1.6.1 Research and Monitoring

  • Natural Heritage Information Centre maintains a database that has compiled all known records of the Eastern Hog-nosed Snake in Ontario. The database is updated as new information is obtained.
  • Research on Eastern Hog-nosed Snake demographics, movements and habitat use has been conducted at Wasaga Beach Provincial Park since 2001 (Cunnington 2002, 2004a,b, 2006, Doucette and Gurr 2001).
  • Surveys for Eastern Hog-nosed Snakes were undertaken at Rondeau Provincial Park during 2000 and 2001 (Gillingwater 2002).
  • Eastern Hog-nosed Snake surveys were conducted at Long Point National Wildlife Area from 1996-1999 and again in 2003-2004 (Gillingwater and Piraino 2004).
  • Sporadic surveys for Eastern Hog-nosed Snakes have been undertaken at the St. Williams Crown Forest from 1997 to 2004 (Gillingwater pers. comm. 2004).
  • Radio telemetry studies on movement patterns of Eastern Hog-nosed Snakes were conducted as part of the study of the effect of the Highway 69 expansion near Parry Sound on threatened snake species (Rouse 2006).
  • Inventory and monitoring of individuals at Pinery Provincial Park.
  • Surveys along the Trent-Severn waterway were conducted in 2005, with a focus on locations of historic sightings. While no Eastern Hog-nosed Snakes were located over the course of the field surveys, data from two confirmed sightings of the species were obtained (Cunnington et al. 2005).
  • Observations of Eastern Hog-nosed Snakes have been recorded for decades at Georgian Bay Islands National Park (GBINP). Since 1993, all Hog-nosed Snakes captured in the high use areas of the park have been implanted with a PIT tag, measured, weighed and released. Since that time, staff at GBINP have implanted 15 unique tags and had 13 of these recaptured. Between 2003 and 2005, road mortalities on neighbouring Muskoka Road 5 have also been recorded.
  • Element occurrence data cleanup for all NHIC records of Eastern Hog-nosed Snake completed in 2006.

1.6.2 Education

  • The Wasaga Beach Eastern Hog-nosed Snake Research Program has undertaken a school education program since 2000. In conjunction with the Georgian Bay Reptile Awareness Program, a snake awareness program was delivered to students at the four elementary schools in Wasaga Beach from 2001-2003 (Doucette and Gurr 2001, Cunnington 2004a). Approximately 1700 students attended these presentations each year.
  • The Wasaga Beach Eastern Hog-nosed Snake Research Program prepared a 5-minute educational video in 2002 on the Eastern Hog-nosed Snake and the research being conducted at Wasaga Beach Provincial Park. The video is used during programs at the park and is also available on the Internet.
  • A full colour educational display card on the Eastern Hog-nosed Snake was distributed to homes and businesses in Wasaga Beach in 1999 and 2003. A new card was produced in 2005.
  • The Georgian Bay Reptile Awareness Program, based out of Parry Sound, provided extensive outreach on all reptile species at risk to the entire Georgian Bay area. They reached about 2000 students and 2300 members of the general public with programs in 2003 (in addition to those in conjunction with Wasaga Beach Eastern Hog-nosed Snake Research Program, mentioned above). Programs were taken to schools (targeting grades 4 and 10) and cottage associations, and snake sensitivity training was provided to construction workers (G. Clayton pers. comm. 2004). They also produced a poster and brochure on the reptiles of the Georgian Bay area that have been widely distributed.
  • Outreach programs by Upper Thames River Conservation Authority promote species at risk including the Eastern Hog-nosed Snake. This includes developing and distributing a full colour, double-sided handout on the Eastern Hog-nosed Snake. An updated card was produced in 2005.
  • Natural history interpretation programs, which include information on the Eastern Hog-nosed Snake, are in effect at some parks in Ontario with this species.
  • The Toronto Zoo created and distributes a "Snakes of Ontario" poster to promote snake conservation. Prior to that, the Norfolk Field Naturalists produced and distributed a "Snakes of Ontario" poster to every public school in Norfolk County.
  • A landowner survey and educational program on large snakes (Eastern Foxsnake, Eastern Hog-nosed Snake and Eastern Ratsnake) was undertaken by the Norfolk Field Naturalists in the Long Point area in 1992 and 1993.
  • Education on the Eastern Hog-nosed Snake, along with other species at risk, has been a consistent effort in the interpretation programming at GBINP for many years. The education effort reaches thousands of visitors and youth attending the two YMCA camps at GBINP. Programs and information are oriented to generate awareness and reduce human persecution.
  • Public outreach (including presentations and distribution of educational rack cards) was conducted along the Trent-Severn Waterway during summer 2005. Approximately 600 individuals were reached (Cunnington et al. 2005).

1.7 Knowledge Gaps

A number of issues must be resolved to better implement recovery activities:

  • Distribution. A better understanding of the current distribution is essential to identify the status of populations of this species. Additionally, more complete distribution information will allow for better ranking of key conservation areas. Given the difficulty of determining reliable population estimates, range occupancy is the best surrogate for population size.
  • Population density. Reliable estimates of population densities in different kinds of landscapes will provide key information for identifying the amount of various habitats and habitat mosaics required for successful conservation of populations.
  • Habitat use. Detailed understanding of habitat use across all seasons and for juveniles as well as adults in different landscapes is essential for identifying key habitat features and protecting adequate amounts of land and configurations. An understanding of habitat use will allow for investigation of the quality of remaining habitat across the province.
  • Genetic uniqueness. Measures of genetic variability of Eastern Hog-nosed Snake populations across the range will provide valuable information on the genetic uniqueness of various populations and help set conservation priorities. It will help determine if the northern and southern Ontario populations are genetically distinct, possibly representing different source populations.