Eastern foxsnake (Elaphe gloydi) (Carolinian)COSEWIC assessment and status report: chapter 10
Limiting Factors and Threats
- Inadvertent Mortality Caused by Human Activities
- Intentional Persecution by Humans Causing Mortality
- Case Study of Anthropogenic Impact on Foxsnakes in a Protected Area
The threats facing the Eastern Foxsnake in Ontario remain roughly the same as those identified in the previous status report: namely, habitat loss and degradation, road effects, inadvertent effects caused by human activities, and intentional persecution by humans. Studies conducted since the first report have helped clarify the relative importance of some of these threats and also expanded the list of potential threats.
Foxsnake habitat continues to be lost at varying rates throughout the species’ range, as discussed in Habitat Trends, and this loss of wetlands, hedgerows, ditches, shoreline habitat, etc. almost certainly has negative consequences for local populations. Loss of key microhabitats, such as oviposition and hibernation sites, occurs when areas are cleared for development or when they lie in the path of recreational motor vehicles such as ATVs.
As described previously (see Adaptability), foxsnakes can function reasonably well in areas occupied by humans (e.g., farms and cottages); however, recent studies have revealed that negative impacts inadvertently caused by human activities may be substantial. The most commonly reported source of mortality is by vehicles on roads. Substantial levels of road mortality have been documented for this species in several regions where investigators have conducted road surveys: Long Point (Ashley and Robinson 1996); Pelee Island (Brooks et al. 2000, Willson 2002); Georgian Bay (MacKinnon et al. 2005); and Rondeau (S. Gillingwater and R. Brooks unpubl. data, Farmer 2007) and Point Pelee (Farmer 2007). In addition, the Ontario Herpetofaunal Summary (OHS) contains a large number of roadkill records. Given the Eastern Foxsnake’s relatively slow locomotion, large size, and tendency to become immobile when vehicles or persons approach, it is not surprising that roadkills represent a major source of mortality for this species. Construction of new roads, as well as changes in traffic flow (i.e. volume and/or speed, (Farmer, 2007), increase the probability that foxsnakes inhabiting an area will be killed on a road. In addition to the loss of individuals via direct mortality on roads, foxsnake populations are also likely impacted indirectly by ancillary road effects: namely, reduction of habitat quality, resource inaccessibility, and population fragmentation (See: Crowley, 2006, Kerr and Cihlar 2004, Hawbaker et al. 2006, and Figure 11 for further data, discussion and references on fragmenting effects of roads, even in a protected area). Off-road vehicles also cause foxsnake mortality and include ATVs, farm machinery, bicycles (R. Willson, S. Gillingwater pers. obs.), and motor boats.
A second source of mortality related to people comes from other species associated with anthropogenic activities. For example, domestic cats and dogs, inevitably associated with any residential development, are known to kill even the most formidable snakes (e.g., Whitaker and Shine 2000). Raccoons and skunks, species that potentially prey upon foxsnakes, have also been documented to increase in number when human occupancy of a site, including provincial and national parks (see Case Study below, Figure 11), increases.
A third source of mortality is more unusual. There have been many observations of foxsnakes “snared” in nylon erosion fencing. For example, a 5-m section of nylon erosion fencing entangled and killed three foxsnakes in Amherstburg (J. Kamstra pers. obs), and M. Gartshore observed three foxsnakes trapped in garden netting (pers. obs.) and there have been advisories citing this problem both in Ontario and the USA. Mortality of snakes from netting may be much more significant than thought, but needless to say, data are hard to come by (See Figure 12 for example of Sistrurus catenatus tangled in netting).
There are other less significant sources of mortality caused by human actions, and these sources illustrate how intensive alteration of the habitat by people can kill snakes. For example, an unintentional spring fire at Rondeau PP killed at least 18 adult foxsnakes (S. Gillingwater pers. obs.), and three radiotagged snakes tracked by Lawson (2005) and MacKinnon (2005) were killed by motorized vehicles not on roadways (i.e., a ditch mower, forklift, and tractor/backhoe).
Figure 11: Aerial Picture of Rondeau Provincial Park Showing Cottages and Roads in this Protected Area
Photo courtesy of S. Gillingwater.
Figure 12: Massasauga (rattlesnake) entangled in garden netting in Parry Sound area
Photo by J. Rouse.
Environmental pollution also falls in the category of inadvertent negative impacts. Meeks (1968) found DDT residues in three Eastern Foxsnakes up to 12 months after application of dichloro–diphenyl trichloroethane (DDT) to a 1.5-ha marsh in Ohio and Russell et al. (1995) found that large snakes from Point Pelee NP, including E. gloydi, had high concentrations of DDT and metabolites in their tissues over 20 years after application had ceased. Kraus and Schuett (1983) found an aberrantly melanistic E. gloydi with visible deformities along with other oddly coloured individuals in a “moderate to heavily” contaminated industrial area in Lucas county, Ohio in 1977. Therefore, foxsnake populations residing in heavily contaminated regions (e.g., Fighting Island in the Detroit River) may be experiencing negative effects of environmental pollution.
The relative contribution to population persistence of any of these anthropogenic threats will of course vary by site. The increased individual mortality probabilities in areas where snake-human interactions are common may be considerable, and in some cases inadvertent mortality may simply be too high for the resident population to remain viable (see case study discussion below).
Many humans have an abhorrence of snakes and thus many Eastern Foxsnakes are killed on sight. The Eastern Foxsnake’s large size, reddish head colouration, bold markings, and habit of vibrating its tail when alarmed, have, because of its resemblance to some venomous species (e.g., copperheads, rattlesnakes) acted as cues to induce people to kill foxsnakes deliberately. An example of irrational fear of snakes comes from a hotel manager in Honey Harbour who assured a researcher that foxsnakes were quite capable of strangling and consuming human babies and even toddlers, and this was why she hired a man to kill the snakes on her property (R. Brooks pers. comm.). The species’ predation on birds has also elicited negative responses. Ashley et al. (2007) quantitatively demonstrated what some snake researchers have suspected for years: that is, a subset of the snakes killed by motor vehicles on roads were run over intentionally. Even when property owners tolerate or encourage the presence of foxsnakes on their lands, intentional persecution of the snakes by contract workers (e.g., construction, landscaping, crop harvesting) is common. The overall impact of intentional persecution of snakes by these groups is likely significant given that they may visit many locations where the species potentially resides. In areas such as Long Point there is tremendous pressure from visitors, and though the area is remote and not patrolled, many people traverse the dunes and many of them kill snakes including foxsnakes. Parks with roads and/or cottages (Figure 11) are also sources of intentional killing by vehicles or more personal methods.
Collection of foxsnakes for the pet trade could also be considered a form of persecution as individuals are permanently removed from their native populations. Because Eastern Foxsnakes often hibernate communally, their populations could potentially be significantly impacted by indiscriminate collection of individuals emerging from hibernation. Although E. gloydi seem to do fairly well in captivity, they have not been bred extensively and therefore few captive-bred Eastern Foxsnakes are available (Staszko and Walls 1994)--creating a demand for wild individuals.
A particularly insightful illustration of the effects of high levels of human activity on foxsnake survivorship comes from Killbear Provincial Park in Georgian Bay. Foxsnake mortality on the park’s main and campground roads have been monitored opportunistically since 1992. The road monitoring was conducted concurrently with a highly active natural heritage education program, with snakes and their preservation as a focus. The education and awareness programs make use of annual park tabloids, audio-visual presentations, ubiquitous posters (even erected in strategic locations in washrooms) and “Brake-for-Snake” signs on the park’s roads. Therefore, the park’s visitors, and also to a large extent the residents living just outside the park, have a heightened awareness of the need to protect snakes in the region. In 2000 and 2001, radiotransmitters were implanted in a number of Eastern Foxsnakes captured in the park. One of the most interesting results from that preliminary research was the observation that many of the radiotagged individuals actually moved to islands outside the park’s peninsular boundaries (Chora et al. 2001). As this finding had obvious implications for conservation-based management of species at risk within the park (see Paleczny et al. 2005), the research effort was expanded. Lawson’s (2005) M.Sc. research demonstrated that the majority of the foxsnakes observed in the park do indeed spend most of their time outside of the park’s boundaries, some moving up to 9 km from the peninsula. From a conservation perspective, one of the most alarming results obtained during the study was the number of radiotagged individuals that perished when they returned to the mainland (either to the peninsular parkland or close surrounds). For example, Lawson (2004) stated that “Of 23 transmitter-equipped Foxsnakes monitored in 2003 and 2004, nine were killed (and an additional three died over winter). Six of the nine deaths were likely caused by humans, two were likely caused by predators, and one died of unknown causes. All but two of these deaths occurred on the mainland (four in Killbear, three just outside of the park) and six of the seven mainland deaths were caused by humans and traffic. However, only 411 of 3176 telemetry locations (13%) collected during this time were on the mainland. This suggests the possibility that Killbear and the area immediately outside of the park may be acting as a sink for the local Foxsnake population”.
Given the enhanced environmental awareness of Killbear park visitors and residents living in the periphery, these results are both disconcerting and illustrative of a potentially unavoidable phenomenon. That is, there will be a baseline mortality level (i.e., the cumulative, compound, synergistic impact of human activity) associated with human occupancy of the landscape resulting from both inadvertent (e.g., motorized vehicles, domestic pets) and non-reducible intentional persecution--i.e., a proportion of the human population simply cannot be convinced not to kill snakes. It therefore follows that neither increased education, nor the foxsnake’s tolerance of human activity, will be able to reduce mortality levels below this baseline. Thus, when the level of human disturbance reaches a certain threshold, education, and the foxsnake’s adaptability to human disturbance will become irrelevant to questions of long-term population viability. Once the threshold is reached, the local population will simply not be able to sustain the baseline mortality level and will consequently be extirpated. Whether the mortality levels experienced by the foxsnake populations in the Killbear region exceed or approach the maximum sustainable level is unknown, but seems possible given the data in Lawson (2004, 2005). However, there are almost certainly foxsnake populations in Ontario where this threshold has been exceeded, even if individuals are still occasionally observed at these sites.
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