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Red-legged Frog (Rana Aurora)

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 EOAppears 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 AODecline
Are there extreme fluctuations in AO?Unknown
Number of known or inferred current locationsca. 100
Specify trend in #Unknown
Are there extreme fluctuations in number of locations?Unknown
Specify trend in area, extent or quality of habitatDecline

Population Information

Generation time (average age of parents in the population)3 – 4 years
Number of mature individualsTens 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 generationsNot 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

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”

Status and Reasons for Designation

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
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.
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.
Criterion D (Very Small Population or Restricted Distribution):
total population size and area of occupancy too great to trigger this criterion.
Criterion E (Quantitative Analysis):
not applicable