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Red-legged Frog (Rana Aurora)

Summary of Status Report

This report provides a summary of the biology, distribution, and vulnerability of Canadian populations of the Red-legged Frog, focusing on new information that has become available since the preparation of the first status report by Waye (1999). This species has a restricted Canadian distribution in southwestern British Columbia, where it occurs on Vancouver Island, several of the islands in the Strait of Georgia, and the adjacent mainland. A new population was discovered on Graham Island, Queen Charlotte Islands in 2002; this population probably originates from a human introduction.

Wetland surveys and serendipitous observations since 1998 suggest that the Red-legged Frog remains relatively widespread on Vancouver Island and parts of the mainland British Columbia. Vancouver Island remains a stronghold for the Canadian populations of this species. Little is known of its distribution and status on the Sunshine Coast and coastal areas north of Powell River on the mainland, and the northern limits of the species’ distribution remain unknown. Surveys of the south and central coast north of Vancouver (up to Rivers Inlet) are required, as this area still contains vast tracks of forest relatively undisturbed by human activities and might provide a refuge for the frogs. At present it is unknown whether this area forms an important component of the species’ range or whether it is peripheral to their distribution.

The Canadian population of the Red-legged Frog numbers in the tens of thousands or perhaps more adults, but there is no detailed information on population sizes or trends in any area. The distribution of the species appears to be shrinking in areas where the introduced Bullfrog is established, suggesting declines or even local extirpations in disturbed habitats in parts of the southern Vancouver Island. In contrast, in some areas on Vancouver Island where the Western Toad has undergone local extinctions over past decade, the Red-legged Frog remains apparently abundant. However, declines could go unnoticed because (1) surveys that have included this species have been at the “presence/not detected” level, and there are no recent estimates of abundance, and (2) most areas within the species’ range have not been surveyed systematically or at all. In the past, extensive loss of wetland and forest habitats have resulted in local declines and disappearances from populated areas on southern and eastern Vancouver Island and the Lower Mainland. Habitats continue to be lost and fragmented at an alarming rate.

Populations of the Red-legged Frog are vulnerable because (1) a large proportion of the species’ known Canadian distribution overlaps with the densely populated southwestern part of the province; (2) populations are vulnerable to clearcut logging, in particular, and forestry activities are converting old growth and mature second-growth forest into young seral stages at a rapid rate; (3) introduced species, particularly the rapid spread of the Bullfrog, appear to adversely affect the use of wetland breeding sites and reproductive success; (4) ranid frogs appear to be particularly susceptible to disease, and chytrid fungi has been isolated from two other species of Rana in British Columbia; (5) habitats are becoming increasingly fragmented due to land conversions, draining and other human activities. Populations of this species are inherently vulnerable to local extinctions and habitat fragmentation –alteration of habitats and global climate change can be expected to exacerbate isolation effects and local extinctions and adversely affect amphibian species that require much space, such as the Red-legged Frog.

Draft guidelines for managing Identified Wildlife have been prepared for this species under the BC Forest and Range Practices Act. The measures in the guidelines will become mandatory on public forestry lands in the near future and will help protect habitats and populations. The Identified Wildlife Management Strategy contains guidelines for the protection and management of the Red Legged Frog through the establishment of Wildlife Habitat Areas (WHAs) and associated General Wildlife Measures (GWMs). However, much uncertainty exists on how the guidelines will be implemented; furthermore, the guidelines are not mandatory on private lands, such as the vast tracts of private forests on Vancouver Island.