Gray ratsnake (Elaphe spiloides) COSEWIC assessment and status report: chapter 13

Technical Summary

Elaphe spiloides (Great Lakes/St. Lawrence Population)

Gray Ratsnake
Couleuvre obscure de l’Est

Range of Occurrence in Canada: Frontenac Axis (southeastern Ontario)


Extent and Area Information

Extent of occurrence (EO) ( km2 )
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 ).
4114 km 2
Specify trend in EO
Decline
Are there extreme fluctuations in EO?
No
Area of occupancy (AO) (km 2 )
Based on the distribution of post 1985 occurrence records and suitable habitat map (see Habitat – Habitat Trends ; and Fig 3 ).
<1500 km 2
Specify trend in AO
Decline
Are there extreme fluctuations in AO?
No
Number of known or inferred current locations (see Fig. 3 )
~ 8-10
Specify trend in #
Decline
Are there extreme fluctuations in number of locations?
No
Specify trend in area, extent or quality of habitat
Decline


Population Information

Generation time (average age of parents in the population)
~10 years
Number of mature individuals
25 000 – 85 000
Total population trend
Decline likely, based on two long-term studies, but unknown for whole area
% decline over the last/next 10 years or 3 generations
Unknown
Are there extreme fluctuations in number of mature individuals?
No
Is the total population severely fragmented?
Yes
Specify trend in number of populations
Unknown
Are there extreme fluctuations in number of populations?
No
List populations with number of mature individuals in each
Unknown


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

Status of outside population(s)?
USA: Stable
Is immigration known or possible?
Yes
Would immigrants be adapted to survive in Canada?
Unknown, probably some populations (ie, NY )
Is there sufficient habitat for immigrants in Canada?
Yes
Is rescue from outside populations likely?
No. Barriers including highway 401 and the St. Lawrence River would make rescue from the US unlikely.


Quantitative Analysis

 


Current Status

COSEWIC: Threatened (1998, 2000 and 2007)
Ontario: S3 (NHIC) and Threatened under COSSARO

 


Status and Reasons for Designation

Status: Threatened
Alpha-numeric code: B1ab(i,ii,iii)+2ab(i,ii,iii)

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.

Elaphe spiloides (Carolinian Population)

Gray Ratsnake
Couleuvre obscure de l’Est

Range of Occurrence in Canada: southwestern Ontario


Extent and Area Information

Extent of occurrence (EO) ( km2 )
NHIC records (See Fig. 2 ).
7300 km 2
Specify trend in EO
Decline
Are there extreme fluctuations in EO?
No
Area of occupancy (AO) (km 2 )
NHIC records (See Fig. 2 ).
320 km 2
Specify trend in AO
Decline
Are there extreme fluctuations in AO?
No
Number of known or inferred current locations
4
Specify trend in #
Currently stable but likely to decline
Are there extreme fluctuations in number of locations?
No
Specify trend in area, extent or quality of habitat
Decline


Population Information

Generation time (average age of parents in the population)
Age Mat +1/mort rate=7 = 1/.32=10
~10 years
Number of mature individuals
Unknown, but small
Total population trend
Decline
% decline over the last/next 10 years or 3 generations
Unknown
Are there extreme fluctuations in number of mature individuals?
No
Is the total population severely fragmented?
Yes
Specify trend in number of populations
Currently stable but likely to decline
Are there extreme fluctuations in number of populations?
No
List populations with number of mature individuals in each
Skunk’s Misery, Big Creek, Oriskany, Niagara


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

Status of outside population(s)?
USA: Stable
Is immigration known or possible?
No
Would immigrants be adapted to survive in Canada?
Unknown
Is there sufficient habitat for immigrants in Canada?
No
Is rescue from outside populations likely?
No

 


Current Status

COSEWIC: Threatened (1998, 2000); Endangered (2007)
Ontario: S3 (NHIC) and Threatened under COSSARO

 


Status and Reasons for Designation

Status: Threatened
Alpha-numeric code: B2ab(iii,iv,v)

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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