Red-legged frog (Rana aurora) COSEWIC status appraisal summary: chapter 13
Technical Summary
Rana aurora
Red-legged frog
Grenouille a pattes-rouge
Range of Occurrence in Canada: BC
Extent and Area Information
Extent of occurrence (EO) (km2) [based on map Fig. 3] |
53 000 km2 |
Specify trend in EO | Appears to be stable |
Are there extreme fluctuations in EO? | No |
Area of occupancy (AO) (km2) [no more than 10% of EO is likely habitable] |
ca. 5 000 km2 |
Specify trend in AO | Decline |
Are there extreme fluctuations in AO? | Unknown |
Number of known or inferred current locations | ca. 100 |
Specify trend in # | Unknown |
Are there extreme fluctuations in number of locations? | Unknown |
Specify trend in area, extent or quality of habitat | Decline |
Population Information
Generation time (average age of parents in the population) | 3 – 4 years |
Number of mature individuals | Tens of thousands, perhaps more |
Total population trend [appears to be declining or extirpated in areas where Bullfrogs and Green Frogs are established] |
Probable decline |
% decline over the last/next 10 years or 3 generations | Not applicable |
Are there extreme fluctuations in number of mature individuals? [fluctuations are the norm for pond-breeding anurans] |
Undocumented but probable |
Is the total population severely fragmented? | Yes |
Specify trend in number of populations | |
Are there extreme fluctuations in number of populations? | no |
List populations with number of mature individuals in each: · Vancouver Island · Lower Mainland British Columbia coast (from Lower Fraser River Valley to Sunshine coast and to Powell River area) · Several small islands in the Strait of Georgia Each of the above areas has numbers in the thousands or tens of thousands |
Threats (actual or imminent threats to populations or habitats)
· Introduction and spread of non-native species (sport fish, Bullfrog, Green Frog)
· Loss, fragmentation, and modification of breeding habitats and surrounding terrestrial foraging habitats due to urbanization, agriculture, and forestry
· Loss, fragmentation, and modification of breeding habitats and surrounding terrestrial foraging habitats due to urbanization, agriculture, and forestry
Rescue Effect (immigration from an outside source)
Status of outside population(s)? | USA: N4 “apparently widespread” (1996) California: S2? “imperiled?” Oregon: S3 “vulnerable to extirpation or extinction” Washington: S4 “apparently widespread” |
Is immigration known or possible? | Possible on Lower Mainland only |
Would immigrants be adapted to survive in Canada? | Yes |
Is there sufficient habitat for immigrants in Canada? | Yes |
Is rescue from outside populations likely? | insignificant |
Quantitative Analysis
Not applicable
Current Status
COSEWIC: Special Concern
British Columbia: Blue list “Special Concern”
British Columbia: Blue list “Special Concern”
Status and Reasons for Designation
Status: Special Concern |
Alpha–numeric code: Not applicable |
Reasons for designation: A large proportion of the known Canadian distribution of this species occurs in the densely populated southwestern part of British Columbia. Habitats are becoming increasingly lost and fragmented due to land conversions and other human activities. Introduced Bullfrog and Green Frog, which are spreading rapidly, have replaced this species at many sites and appear to adversely affect the use of wetland breeding sites and reproductive success. Populations of this species, and other amphibian species that require extensive habitat, are inherently vulnerable to habitat fragmentation which can be expected to exacerbate isolation effects and local extinctions. |
Applicability of Criteria
Criterion A (Declining Total Population):
insufficient evidence to quantify declines
insufficient evidence to quantify declines
Criterion B (Small Distribution, and Decline or Fluctuation):
distribution is larger in extent than cutoff values for this criterion although declines and population fluctuations are inferred.
distribution is larger in extent than cutoff values for this criterion although declines and population fluctuations are inferred.
Criterion C (Small Total Population Size and Decline):
despite inferred declines, population fluctuations, and the fragmentation of the range, total population size remains large and decline rate cannot be quantified.
despite inferred declines, population fluctuations, and the fragmentation of the range, total population size remains large and decline rate cannot be quantified.
Criterion D (Very Small Population or Restricted Distribution):
total population size and area of occupancy too great to trigger this criterion.
total population size and area of occupancy too great to trigger this criterion.
Criterion E (Quantitative Analysis):
not applicable
not applicable
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