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Recovery strategy for the Eastern ribbonsnake (Thamnophis sauritus), Atlantic population in Canada

1. Background

1.1 Species assessment information from COSEWICFootnote 1

Common name (population): Eastern ribbonsnake (Atlantic population)

Scientific Name: Thamnophis sauritus

Status: Threatened

Last examination and change: 2002

Canadian occurrence: In Canada, the eastern ribbonsnake occurs in Ontario, Quebec and Nova Scotia. The Atlantic population occurs only in Nova Scotia.

Reasons for designation: This ribbonsnake population is a small, isolated postglacial relict confined to a small area in Nova Scotia. As such, it is unique and susceptible to demographic and environmental fluctuations. In addition, shoreline development poses a threat (COSEWIC 2002).

Status history: Designated Threatened in May 2002. Assessment based on a new status report.


1.2 Name and classification

The eastern ribbonsnake (Thamnophis sauritus) has four recognized subspecies: the eastern or common ribbonsnake (T.s. sauritus), the peninsula ribbonsnake (T.s. sackinii), the blue-striped ribbonsnake (T.s. nitae) and the northern ribbonsnake (T.s. septentrionalis). Of these, only the northern ribbonsnake, occurs in Canada (Smith 2002). Throughout this document the species will be referred to as eastern ribbonsnake or simply ribbonsnake, and to avoid confusion, use of sub-specific names will be avoided. Throughout this strategy it will be explicitly stated if knowledge presented is specific to the Nova Scotia population or was obtained elsewhere in the species’ range, as populations may exhibit local and regional adaptations and display differences in habitat use and behaviour that will affect species recovery.


1.3 Species description

The eastern ribbonsnake (Thamnophis sauritus) is a small, slender, semi-aquatic snake. Like all snakes in Nova Scotia, it is not poisonous and completely harmless to people. Total adult length for the species throughout its range varies from 46 cm to 86.2 cm (Smith 2002). In Nova Scotia, the recorded maximum length is 75.8 cm, but most are considerably smaller (NS ribbonsnake database). The tail is long, accounting for almost one third of the total length (Gilhen 1984).


Figure 1: Distinctive yellow stripes on a ribbonsnake in Nova Scotia

Figure 1: Photo of an Eastern ribbonsnake (see long description below).

Description of Figure 1

Photo of an Eastern ribbonsnake. The snake has 3 distinctive bright yellow stripes running vertically down the length of the snake’s dark body, one on each side and one along the back. Its underside is a pale yellow. It is resting on a slate rock on the water’s edge.


Eastern ribbonsnakes can be recognized by the three bright yellow stripes that run along the length of their dark body: one on each side and one along the back (Figure 1). The side stripes occur on the third and fourth scale rows up from the ventral (belly) scales, which are creamy white. In Nova Scotia populations, a caramel-brown stripe separates the side stripes and the ventral scales (Figure 2, Gilhen 1984). The head is small and slender, and there is a small vertical white line in front of the eye (Logier 1967).


Figure 2: Ribbonsnake in Nova Scotia showing the caramel-brown stripe below the side stripe

Figure 2: Photo of an Eastern ribbonsnake (see long description below).

Description of Figure 2

Photo of an Eastern Ribbonsnake showing the caramel-brown stripe that runs the length of its body, separating the pale yellow underside and the bright yellow side stripe. The snake is submerged in water, sticking only its head above the surface.


Eastern ribbonsnakes can be confused with eastern garter snakes (Thamnophis sirtalis), which also have three stripes along their bodies. However, the side stripes on garter snakes occur on the second and third scale rows, and there is no caramel-brown stripe below them (Gilhen 1984). In Nova Scotia, garter snake stripes tend to be less distinct than those of ribbonsnakes. Additionally, garter snakes lack the vertical white line in front of the eye and are typically thicker bodied and larger than ribbonsnakes.


1.4 Distribution

1.4.1 Global and Canadian range


Figure 3: Global range of the eastern ribbonsnake (Thamnophis sauritus)

Figure 3: Map showing the global range of the eastern ribbonsnake (see long description below).

Adapted from Smith 2002 and Conant and Collins 1991.

Description of Figure 3

Map of Eastern North America showing the range of the Eastern Ribbonsnake. The ribbonsnake occurs east of the Mississippi River from Florida to southern Canada. It is found in every state east of the great lakes. The Canadian range includes southern Ontario, southwestern Quebec and southwestern Nova Scotia. The map shows that the Nova Scotia population is isolated from the rest of the population.


The eastern ribbonsnake occurs east of the Mississippi River from Florida to southern Canada (Rossman 1970). In Canada, the ribbonsnake occurs in southern Ontario, southwestern Quebec, and Nova Scotia (Smith 2002). Ribbonsnakes in Nova Scotia are isolated from the species’ main range and have been listed separately by COSEWIC (2002) as the “Atlantic population.”

Although the eastern ribbonsnake is considered globally secure (G5Footnote 2, NatureServe 2006) and is not listed under the United States Endangered Species Act, it is listed at some level of risk in 10 of the 28 (2 S1, 3 S2, 5 S3Footnote 2) states and districts in which it occurs (NatureServe 2006).

1.4.2 Nova Scotia range

The “Atlantic population” of ribbonsnakes appears to be limited to the southwestern interior of Nova Scotia (Figure 4). Confirmed sightings remain confined to three watersheds: the Mersey, Medway, and LaHave Rivers (NS ribbonsnake database 2010). Within these watersheds, several individual concentrations of ribbonsnakes have been identified; the extent of movement between these sites is currently unknown.

The eastern ribbonsnake belongs to a suite of species at risk in southwest Nova Scotia that are geographically separated from their main ranges. Many of these species, including the eastern ribbonsnake, are believed to be climatic relicts that became isolated in Nova Scotia at the end of a warmer period 5000 years ago (Smith 2002).


Figure 4: Currently known distribution of the eastern ribbonsnake in Nova Scotia (April 15, 2010)

Figure 4: Map showing the currently known distribution of the eastern ribbonsnake in Nova Scotia (see long description below).

Description of Figure 4

Map of southwestern Nova Scotia showing the known distribution of the Eastern Ribbonsnake. The map shows scattered sightings throughout Queens, Annapolis, and Lunenburg counties, with the largest concentration in Queens county. The map also shows the boundaries of Kejimkujik National Park and National Historic Site and provincial wilderness areas. While most sightings are inland, in the center of the province, there are a few that are closer to the coast.


Isolated populations may be significant, particularly if they occur at the edge of the species’ range, as is the case of the Nova Scotia eastern ribbonsnake population, because they may have diverged genetically from populations in the main range and may display local adaptations (Lesica and Allendorf 1995). The degree of genetic variability of ribbonsnakes in Nova Scotia remains unknown. There is no signal pattern of genetic variation yet detected within other isolated populations in Nova Scotia. Some species have diverged significantly from the main range and maintain high levels of genetic variation (Mockford et al. 1999) while others show little variation within Nova Scotia or between the province and the main range (Cody 2002).

1.5 Traditional knowledge and recovery

As a preamble to this section, there are two important considerations. First, this recovery strategy, as a requirement of SARA, adheres to the directives set out in that legislation. Second, Section 1.5 is a special contribution by the Native Council of Nova Scotia, through consultation, and is offered to provide insight on Aboriginal perspectives on the recovery of the Eastern ribbonsnake. A broader treatise, prepared by the Native Council of Nova Scotia on this subject area, can be obtained by request from the Ribbonsnake Recovery Team.

Eastern ribbonsnake habitat falls within Kespukwitk, one of the seven traditional districts of Mi’kma’ki. For this reason, it is important that the involvement of the Mi’kmaq living on and sharing the land, is actively sought and encouraged. It is this continuum of Mi’kmaq throughout Kespukwitk, who through their sages, talks, and walks, will begin to reveal aspects of the Eastern ribbonsnake. Mi’kmaq can make important contributions to the recovery of ribbonsnakes through traditional teachings, revealing the importance of traditional practices, and sharing an Aboriginal eco-centric world view. Mi’kmaq customary use of biodiversity embodies the Mi’kmaq principle of netukulimk; a way of harvesting resources without jeopardizing the integrity, diversity, or productivity of our natural environment (Native Council of Nova Scotia 1994). A more inclusive approach to ecosystem based management may be particularly useful for eastern ribbonsnake recovery and also to other rare and at risk species that are tied to similar habitats in the watersheds of southern Nova Scotia. This recovery strategy cannot hope to ever capture the total knowledge of the Mi’kmaq. Recovery planning can be augmented over time as involvement with the Mi’kmaq grows.

1.5.1 Aboriginal traditional knowledge

In order to integrate Aboriginal Traditional Knowledge (ATK) with other types of knowledge, it is important for recovery planners to understand how the Mi’kmaq world view may differ from other Aboriginal and scientific world views. Mi’kmaq traditional knowledge is not necessarily written, peer-reviewed, or published. ATK is a living knowledge, captured in oral language and culture, and which is highly specific to place and time – it is the ki of Mi’kma’ki. In sharing ATK, Mi’kmaq will often end by saying tan teli kji’jitu (as I know it to be), recognizing that the knowledge is living. In other words, the knowledge shaped from the land, e.g. about the eastern ribbonsnake, carried forward, and shared will differ between those experiencing that place at different times. It may change because of another action or because of another’s perspective.

There are several petroglyphs of snakes in the Kejimkujik area (Figure 5, Robertson 1973), one of the few places these are known to occur. The abundance of snake petroglyphs, as well as known legends and dances regarding snakes, may indicate that ribbonsnakes were once more plentiful than currently known, or that they were of cultural significance. For example, there are legends that speak of snakes as bad omens if crossed.

It is known that Mi’kmaq people hold specific knowledge of ribbonsnake biology and habitat but that information has not yet been accessed. For example, ATK may be able to inform changes that have occurred in ribbonsnakes’ range and provide insight as to whether changes in distribution may be related to changes in habitat.


Figure 5: Example of a snake petroglyph from the Kejimkujik area (Keji Slide Library)

Figure 5: Example of a snake petroglyph from the Kejimkujik area (see long description below).

Description of Figure 5

Photo of a Mi'kmaq petroglyph portraying a snake, on a slate rock found in Kejimkujik.


1.5.2 Commitment to include the Mi’kmaq and consider traditional knowledge

This Recovery Strategy seeks to recognize and include Mi’kmaq in the recovery of the Eastern ribbonsnake and its habitat.

  • First, by recognizing the significance that the Mi’kmaq People have shared a long
    history with the ribbonsnake in Kespukwitk.
  • Second, by inviting Mi’kmaq individuals and communities to sit with others, as peers, to discuss, draft, and implement recovery strategies and action plans.
  • Third, by recognizing and acknowledging that it is important to gather and understand the collective knowledge of the Mi’kmaq about ribbonsnakes and their habitats.
  • Fourth, by recognizing the need to include Mi’kmaw worldviews to ensure the value of netukulimk for the long term sustainability of Kespukwitk.
  • Finally, by recognizing the valuable contribution of the Mi’kmaq and their traditional knowledge as an important step towards reconciling Aboriginal and scientific world views.


1.6 Population size and trends

The size of the population of eastern ribbonsnakes in Nova Scotia is not known, and data is lacking on abundance, distribution, and population trends. The current range appears to be limited to the southwest interior of the province, with confirmed sightings encompassing only three watersheds and approximately 2500 km2 (Figure 4). While ribbonsnakes have been found at a number of places within this range (Table 7), only a few sites are known to currently have high concentrations (Table 1). It is possible that these concentrations may be highly ephemeral and dependent on specific habitat conditions. Ribbonsnakes have apparently disappeared from one site (Colpton Pond), which in the 1980’s contained the highest density of ribbonsnakes recorded in Nova Scotia (40+ snakes found in a single day). The habitat at this site has changed dramatically and the population may have either decreased and/or migrated to adjacent habitats. While ribbonsnakes are still known to occur in nearby habitats, such dense concentrations have not been recorded since.

The most reliable data on population size comes from a single site at Grafton Lake. While quantitative data are lacking, it is believed that ribbonsnakes at this site increased in numbers after the removal of a dam on the lake in the mid 1990’s, which exposed the original lakeshore. A small area within this site has been the subject of an intensive mark-recapture study since 2004. Initial abundance calculations in 2004 estimated that there were approximately 100 individuals in the 4 ha study site (McNeil 2005). A reduction in the number of captures per unit effort in 2005 and 2006 suggests that this population may be declining; however, there is uncertainty in the reliability of these estimates. The marking technique (primarily scale clipping) was not as permanent as hoped and was prone to identification errors. The habitat at this site is also changing rapidly as the shoreline vegetation regenerates following dam removal. This could affect both snake abundance and the detectability of ribbonsnakes within the habitat. In addition, the population within the study site is not closed and the rate of immigration from and emigration to adjacent habitats is not known.

 

Table 1. Sites with 50 or more recent, confirmed sightings of ribbonsnakes in Nova Scotia (1997-2010)
AreaTotal # of sightingsSightings per total search effortYear discoveredOther species at riskLand ownershipCurrent habitat protection?Research/recovery efforts underway
Grafton Lake14541313 sightings/ 3096.1 hrs1955Blanding’s turtleFederal crown (National Park)YesVolunteer surveys; intensive annual research; hibernacula location
Cobrielle Brook10093 sightings/ 173.1 hrs1998 Federal crown (National Park)2011-2015Surveys
Barren Meadow/Keddy Brook8849 sightings/ 141.5 hrs2004Blanding’s turtlePrivate and provincial crownNo (1 NSNT property in progress)Surveys; landowner contact; NSNT collaboration
Molega Lake /Hog Lake419360 sightings/ 830.6 hrs1976RedrootPrivate (primarily cottage owners)Partial (one land NSNT)Landowner contact; Survey extant populations to determine
McGowan/Deans Lake9952 sightings/ 146.8 hrs1999Blanding’s turtleProvincial crown; private (industry, individual landowners)Provincial crown Integrated Resource Management PlanLandowner contact; Surveys

 


1.7 Biological needs, ecological role, and limiting factors

1.7.1 Thermal biology

Ribbonsnakes must rely on heat from their surroundings to regulate their body temperatures. The need to maintain appropriate temperatures affects their behaviour and habitat use (Carpenter 1956, Rossman et al. 1996). Eastern ribbonsnakes in Michigan were found to be most active when their cloacal temperatures were between 20 and 30 degrees Celsius (Carpenter 1956). In cool weather, ribbonsnakes often bask in order to gain sufficient heat for movement and digestion (Carpenter 1952, Rossman et al. 1996) and they may be able to restrict blood flow to the tail to maintain a higher body core temperature (Amiel and Wassersug 2010). Because ribbonsnakes give birth to live young, maintaining appropriate temperatures may be particularly important to females while their young are developing (Charland and Gregory 1995, Rossman et al. 1996). In Nova Scotia, mean body temperatures of gravid female ribbonsnakes (i.e., those with developing young) implanted with temperature-sensitive radio transmitters during summer ranged from 25.3ºC to 31.98ºC (Bell 2003). Ribbonsnakes must also avoid overheating and may enter water, climb bushes, or take refuge under vegetation, rocks, or logs to cool off (Carpenter 1952, Carpenter 1956, Tinkle 1957). During the fall, ribbonsnakes move into their hibernacula, which must provide an environment that prevents both freezing and dehydration (Carpenter 1953, Costanzo 1989).

In Nova Scotia, ribbonsnakes occur near the northern limit of their range and may be constrained to the warmer southwest part of the province by temperature and climatic trends (Bleakney 1951).

1.7.2 Growth, maturity and reproduction

Ribbonsnakes are typically less than 25 cm in total length when born. Size and age at maturity in Nova Scotia are not known, but in Michigan, female eastern ribbonsnakes reach maturity in their second year of growth (Carpenter 1952) and most other species in the genus Thamnophis reach maturity during their second or third year of growth (Rossman et al. 1996). Reproductive frequency in Nova Scotia is also unknown. In general, female Thamnophis produce one litter per year, although they may skip years, particularly in northern populations (Rossman et al. 1996). Carpenter (1952) found approximately 60 percent of the female ribbonsnakes in a Michigan population reproduced in a single year.

In Nova Scotia, mating has been observed in spring, just after emergence from the hibernacula (NS ribbonsnake database 2010). Spring mating is consistent with more southern populations of eastern ribbonsnakes (Ernst and Barbour 1989). However, aggregations of adults observed in September suggest that mating may also occur in fall (NS ribbonsnake database 2010).

Carpenter (1952) found that the greatest feeding in eastern ribbonsnakes in Michigan occurred from June through October, with feeding activity continuing until they move to their hibernacula (Carpenter 1952). In Nova Scotia, ribbonsnake with food bulges have been observed from April 9 to November 4 (NS ribbonsnake database 2010). Most shed skins are found from June through September, suggesting that this is the period of greatest growth.

1.7.3 Ecological role

Throughout their range, adult ribbonsnakes feed primarily on amphibians and small fish (Bell et al., 2007, Brown 1979, Carpenter 1952). Diet in young ribbonsnakes is largely unknown, although a small ribbonsnake in Nova Scotia regurgitated an earthworm on 21 May 2006 (NS ribbonsnake database 2010). Additionally, in August 2006, a newborn ribbonsnake from the Nova Scotia population ate two earthworms while in captivity (Josie Todd, pers. comm.).

Ribbonsnakes have many potential predators (e.g., raccoons, hawks, other snakes and fish), but the rate of predation is unknown. Ribbonsnakes likely rely heavily on blending in with their environment (crypsis) and hiding under cover to avoid detection by predators (Scribner and Weatherhead 1995).


1.8 Habitat needs

1.8.1 General habitat

Ribbonsnakes are highly associated with wetlands, and most sightings in Nova Scotia occur within 5 m of water (NS ribbonsnake database 2010). They are typically found in slow flowing wetlands with abundant aquatic and terrestrial vegetation, including fens, along meadow streams, and in lake coves and shorelines. Many of these areas contain shallow pools and side channels. Ribbonsnakes have been found in a variety of vegetation, including sphagnum moss; grasses, sedges, and rushes; and emergent and shoreline shrubs. The occurrence and densities of ribbonsnakes in an area may be affected by disturbance regimes and stages of habitat succession, but the role of these factors is not yet understood. For instance, beaver activity occurs at many sites containing ribbonsnakes, and may play an important function in maintaining appropriate habitat.

Six important elements of life history are currently recognized for which habitat must be described: overwintering, basking, cover, gestation and birthing, feeding and shedding, and mating. At this time, most knowledge of specific sites in Nova Scotia comes from the intensive study sites at Grafton Lake and Molega Lake (Table 2).

 

Table 2. Known ribbonsnake habitat in Nova Scotia
Seasonal activity (function)Site descriptionTiming
Overwintering (allow survival through the winter)
  • One known hibernacula in mixed forest 150 m from nearest wetland; other forested hibernacula areas suspected based on late fall or early spring sightings
  • Also suspected in the upper floodplain under ground in areas of fractured slate overlain with moss and under a gravel walkway near the water’s edge. Sites may be partially or fully submerged.
Oct. to Apr.
Basking (gain sufficient heat units for movement, digestion and gestation)
  • Early spring/ late fall: Near suspected overwintering sites
  • Summer: Adjacent to feeding sites
  • Sunny locations associated with moss, floating sphagnum mats, matted sedge or grass clumps, rocks, logs, mudflats, leaf litter, dams and causeways
~Mar. to Nov.
Cover (avoid predators and prevent overheating)
  • Includes moss, grasses and sedges, floating sphagnum mats, emergent vegetation, stumps, rock crevices, shrubs and small trees
  • Have been found under landscape fabric and hay bales at one site
~Mar to Nov.
Feeding/ shedding
  • Mostly near small pools, streams and offshoot channels.
  • Shed skins have been found on sphagnum mats, mud flats, grasses and sedges and in or under bushes and small trees
Apr. to Nov.
Gestation and birthing
  • Birthing areas unknown but small concentrations of neonates have been found in wetlands, usually near water
  • Gravid females have been found in wetlands, on roads and causeways and under landscape fabric and hay bales.
Birth – Aug and Sept
Mating
  • Observed adjacent to hibernacula in wooded area within 1 week following emergence in spring 2010
  • Concentrations of adults in vegetation adjacent to water in September suggest possible fall mating
March-April and possibly fall

Footnotes

Footnote 1

COSEWIC - Committee on the Status of Endangered Wildlife in Canada

Return to footnote 1

Footnote 2

Global rank (G): General status of the species throughout its range
Sub-national Rank (S): Species status in the provinces and the territories where they are present (S1- Critically imperiled, S2 -Imperiled, S3 -Vulnerable).

Return to footnote 2

Introduction