Gray ratsnake (Elaphe spiloides) COSEWIC assessment and status report: chapter 13
Technical Summary
Range of Occurrence in Canada: Frontenac Axis (southeastern Ontario)
Extent and Area Information
Generated using the NHIC records and knowledge from experts in the field (S. Thompson, J. Leggo and T. Norris pers. comm. 2005) (see Distribution – Great Lakes/ St. Lawrence population , and Fig. 3 ).
Based on the distribution of post 1985 occurrence records and suitable habitat map (see Habitat – Habitat Trends ; and Fig 3 ).
Population Information
Threats (actual or imminent threats to populations or habitats)
- Habitat loss and fragmentation by roads and various developments
- Mortality by human activities (e.g. road mortality, persecution, destruction of hibernacula)
- Disruption of communal hibernacula
Rescue Effect (immigration from an outside source): No
Quantitative Analysis
Current Status
COSEWIC: Threatened (1998, 2000 and 2007)
Ontario: S3 (NHIC) and Threatened under COSSARO
Status and Reasons for Designation
Reasons for Designation: This large snake occupies a restricted region in Ontario and is threatened by ongoing development and by expansion of the road network. Development is especially a threat to hibernacula, which may be limiting. Roads represent a significant threat because of the snakes’ late age of maturity and low reproductive rate. Snakes are also killed on roads because they move slowly and may bask on roads.
Applicability of Criteria
Criterion A (Declining Total Population):
Not applicable.
Criterion B (Small Distribution, and Decline or Fluctuation):
Meets Endangered B1ab(i,ii,iii) but population is still fairly large and widespread and not apparently in imminent danger of extinction. Meets Threatened because the Extent of Occurrence and Area of Occupancy are less than 20 000km2 and 2 000km2 respectively, populations are severely fragmented, and there is ongoing loss of habitat and snakes from development and road network expansion.
Criterion C (Small Total Population Size and Decline):
Not applicable. Population exceeds criteria.
Criterion D (Very Small Population or Restricted Distribution):
Not applicable. Population too large.
Criterion E (Quantitative Analysis):
Quantitative analysis incomplete and unpublished.
Range of Occurrence in Canada: southwestern Ontario
Extent and Area Information
NHIC records (See Fig. 2 ).
NHIC records (See Fig. 2 ).
Population Information
Age Mat +1/mort rate=7 = 1/.32=10
Threats (actual or imminent threats to populations or habitats)
- Insufficient amount of suitable habitat
- Habitat loss and fragmentation
- Mortality by humans (e.g. road mortality, persecution)
- Stochastic effects of isolated small populations
Rescue Effect (immigration from an outside source): No
Current Status
COSEWIC: Threatened (1998, 2000); Endangered (2007)
Ontario: S3 (NHIC) and Threatened under COSSARO
Status and Reasons for Designation
Reasons for Designation: This population consists of only 4 highly disjunct subpopulations in southwest Ontario, all of which are small and isolated, and surrounded by agricultural and developed terrain. Their slow rate of reproduction and late age of maturity makes them especially vulnerable to increases in adult mortality from road traffic and agricultural machinery.
Applicability of Criteria
Criterion A (Declining Total Population):
Not applicable.
Criterion B (Small Distribution, and Decline or Fluctuation):
Meets Endangered because the Area of Occupancy is <500 km2, fewer than 5 populations, and there is ongoing loss of habitat and snakes from development, agriculture and road network expansion.
Criterion C (Small Total Population Size and Decline):
The population very likely has fewer than 2500 adults, as only a handful of these very large snakes have been found over the past 2 decades. Decline is likely to continue given continuing development, the isolation of the small populations and the ubiquity of the road network. No population is likely to have more than 250 adults.
Criterion D (Very Small Population or Restricted Distribution):
Not applicable. Population may be too large.
Criterion E (Quantitative Analysis):
Not applicable.
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