Red-legged Frog (Rana Aurora)
- Assessment Summary
- Executive Summary
- COSEWIC History, Mandate, Membership and Definitions
- Species Information
- Population Sizes and Trends
- Limiting Factors and Threats
- Special Significance of the Species
- Existing Protection or Other Status
- Summary of Status Report
- Technical Summary
- Acknowledgements and Information Sources
- Biographical Summary of the Report Writers, Authorities Contacted, and Collections Examined
- Aquatic Breeding Habitats
- Terrestrial Foraging Habitats
- Dispersal Habitats
The Red-legged Frog is an inhabitant of moist, lower elevation forests and requires both aquatic breeding habitats and terrestrial foraging habitats in a suitable spatial configuration to complete the different phases of its life cycle. Hibernation can occur either on land on the forest floor or in water (Licht 1969), but little is known of specific requirements for over-wintering sites.
The species has been recorded from sea-level to elevations up to 860 m in Washington and to 1427 m in Oregon (Leonard et al. 1993). The highest locality record from British Columbia is from 1040 m (E. Wind, unpublished data), but most records from the province are from below 500 m. In the Clayoquot Sound area on the west coast of Vancouver Island, Beasley et al. (2000) found the Red-legged Frog more frequently in wetlands below 500 m (30% were occupied) than in those above 500 m (14% were occupied); the highest locality for this species was at 710 m. Wind (2003 and unpublished data) surveyed 236 wetlands ranging in elevation from sea-level to 1200 m for amphibians. The mean elevation where this species was found was 515 m, but most sites were lower (mode = 180 m).
The Red-legged Frog breeds in a variety of permanent and temporary water bodies, including potholes, ponds, ditches, springs, marshes, margins of large lakes, and slow-moving portions of rivers (Blaustein et al. 1995 and references therein). Abundant emergent vegetation is typically present at breeding sites (Adams 1999, Ostergaard and Richter (2001). Within breeding sites, females deposit their eggs in quiet waters in areas that receive sunlight for at least a part of the day (Licht 1969).
In the Puget Lowlands, Washington State, the most common wetlands where this species was found had shallow slopes and a southern exposure; these habitat attributes together explained 63% of the variation in wetland occupancy (Adams 1999). Breeding habitats that were in permanent water bodies tended to be large wetlands with structural complexity. Also in Washington State, Ostegaard et al. (2003) found this species breeding in storm water storage ponds (i.e., small natural or modified catchment areas used for storage of storm water run-off). Its presence was positively correlated with wetland complexity, measured as the ratio of coverage by emergent vegetation to open water, and percentage of forest cover in the surrounding area. Egg-masses were most numerous in ponds with over 30% forest cover within 200 m from the shore. In Clayoquot Sound, Vancouver Island, the Red-legged Frog was more frequently found in bogs and fens than in other types of wetlands that included marshes, swamps, and shallow water areas of larger water bodies (Beasley et al. 2000).
Adams (2000) found that the survival of tadpoles of the Red-legged Frog in experimental enclosures was highly variable among sites but tended to be lower in permanent than temporary wetlands. The difference was possibly due to habitat gradients or indirect effects of native or exotic predators. These results suggest that permanent water bodies, which harbour more predators, may sometimes act as sink habitats rather than as source habitats for recruits to the population. Caution should be exercised in inferring the suitability of breeding sites from presence/absence type of data, where survival characteristics of the young are unknown.
Metamorphosed individuals spend a large proportion of their life in terrestrial habitats, and adults are often encountered on land in the vicinity of wetlands or along forested stream banks (Blaustein et al. 1995 and references therein). Outside the breeding season, adults of the California Red-legged Frog remained within 130 m or less from their aquatic breeding sites (Bulger et al. 2003). The Northern Red-legged Frog is less closely tied to water bodies and riparian habitats than is the more aquatic California Red-legged Frog (Hayes and Miyamoto 1984). However, in one study on northern Vancouver Island, individual, radio-tracked frogs were relatively sedentary and typically remained within 36 m or closer to the edge of forest streams (Chan-McLeod 2003a; see section on Movements and Dispersal). When conditions are suitable, these frogs can be encountered on the forest floor far from water bodies; distances of 200-300 m away from water have been noted on rainy nights (Nussbaum et al. 1983).
The Red-legged Frog occupies a variety of forest types and ages but appears to be most abundant in older, moist stands (reviewed in Waye 1999 and Blaustein et al. 1995; also see Section “Limiting Factors and Threats” for interactions with forestry). In the Washington Cascade Range, this species was most abundant in mature stands and least abundant in young stands (Aubry and Hall 1991). Its abundance was negatively correlated with elevation and increasing slope. Captures were also associated with moderately moist conditions in older forest stands; very wet old-growth stands appeared to be somewhat less suitable. Within a younger set of chronoseries in second-growth Douglas Fir-dominated forest, Aubry (2000) found that this species was more abundant in stands that were near rotation age (50 – 70 years) than in younger stands, where only very few captures occurred. The near-rotation-age stands had a closed canopy and 30 – 45 m tall trees; the herb and shrub layer had re-established, but the abundance of coarse woody debris was depressed from old-growth conditions. In a study in Washington and Oregon, this species was most abundant at lower elevation habitats with relatively flat slopes, but there was no relationship to stand age (classed as old growth, mature, young) (Bury et al. 1991). It is possible that the association of the species with forest age varies geographically, with forest type, or with moisture or other conditions.
On Vancouver Island and the Gulf Islands, distribution records and anecdotal observations suggest that the species is commonly found in second growth forests, and occasionally occurs in suburban gardens and seasonal ponds in pasture- and agricultural lands adjacent to forested areas. On Vancouver Island, Wind (2003) found the species in wetlands within both recently logged and older forest. Relative abundance and survivorship characteristics were not studied (see section “Limiting Factors and Threats: Effects of Forestry Practices” for a review of effects of logging on this species). “Presence/absence” data are inadequate for determining patterns of abundance and whether particular habitats might act as dispersal sinks, where populations are maintained by immigration rather than through recruitment through reproduction.
Dispersal habitats are defined here as habitats that frogs must traverse to access different seasonal habitats during their life-cycle, such as between terrestrial foraging and aquatic breeding habitats, as well as those habitats that connect subpopulations or spatially separated units. Riparian areas have been postulated as corridors or conduits for movements of the Red-legged Frog across inhospitable habitats, but little evidence of such use exists. Migration movements of the California Red-legged Frog took place overland across a variety of habitats at distances up to 500 m away from water bodies; no associations with particular vegetation communities or topography were found (Bulger et al. 2003). These authors concluded that dispersal habitats were ubiquitous and widely distributed, making their protection difficult. However, habitats that retain moisture during periods of drought probably are more valuable for dispersal than are clearcuts.
On northern Vancouver Island, experimentally displaced adults were attracted to riparian areas along wider (3 m in width) streams but not to narrow streams (< 1.5 m in width) (Chan-McLeod 2003b). However, the frogs avoided non-forested parts of creeks in clearcuts and did not use them as travel corridors; whether they would travel along creeks with riparian buffer zones was not investigated. The permeability of clearcuts to movements increased on rainy days, while clearcuts acted as barriers to movements on hot, dry days. In another experiment on northern Vancouver Island, displaced frogs moved across clearcuts along random trajectories and failed to use residual tree-patches as stepping-stones; however, directional movements towards larger residual tree patches occurred from short (5 – 50 m) distances away (Chan-McLeod and Moy, in review). The authors suggested that open habitats, such as clearcuts, could act as habitat sinks, where dispersing or migrating frogs may be subject to mortality from predation or desiccation.
These frogs have been noted to move across roads, especially on rainy nights (Nussbaum et al. 1983). Road mortality can be considerable where dispersal routes are across highways or main roads (Beasley, 2003; B. Beasley, pers. comm.).
Over the past century, habitats of the Red-legged Frog have been altered by human activities over most of the species’ range in British Columbia. Habitat degradation and loss are extensive on southern and eastern Vancouver Island, the Lower Fraser Valley, and parts of the Sunshine Coast. The rate and permanency of habitat alteration are highest in these areas, as a result of agriculture, urbanization, forestry, and introduction of exotic species. Of particular concern is the exotic Bullfrog (R. catesbeiana), which adversely affects populations of the Red-legged Frog (Govindarajulu 2003; see Section “Limiting Factors and Threats: Introduced Species”). Although the highest abundance of both the Bullfrog and the Green Frog (Rana clamitans), another exotic species, is associated with human settlements, these species have started to spread to wetlands in rural areas, degrading their quality as breeding sites for the Red-legged Frog. Within the range of the Red-legged Frog, the Bullfrog is known from most of the Lower Mainland, southeastern Vancouver Island from Victoria to Parksville, and from some of the Gulf Islands (Govindarajulu 2003). The Green Frog in known from several localities on southeastern Vancouver Island and the Lower Mainland and may also adversely affect native species of amphibians, but potential interactions have not been studied.
Habitat alteration on the more remote areas on northern and western Vancouver Island and the mainland coast north of Powell River result primarily from forestry activities on crown lands. The impacts of forestry activities on crown lands subject to the Forest and Range Practices Act are potentially less severe and of shorter duration than impacts of other human activities, provided that wetlands are protected and forests are allowed to regenerate. However, road-building activities in particular have the potential to permanently degrade wetlands and cause collision mortality.
Urban and agricultural areas covered about 4% (about 1200 km2) of the total area of the island in 1989 (BC Ministry of Forests 1991) and are expanding rapidly. Agriculture and urbanization result in severe and long-term changes to habitats. Low-elevation forested and wetland habitats (< 500 m asl) overlap extensively with areas of human habitation on southern and eastern Vancouver Island. These habitats have been permanently degraded and fragmented by the drainage of wetlands, pollution of water bodies, and removal of forest cover. The human population on southern Vancouver Island grew by 2.7% from 1996 – 2001 and continues to expand rapidly (Statistics Canada 2003). Recently, a new double-lane highway was constructed inland from the coast between Campbell River and Nanaimo, which has facilitated increased development in these areas.
Logging has affected a large proportion of the low-elevation forests inhabited by the Red-legged Frog. Based on satellite imagery, about 45% of the land area of the island consisted of immature forest in 1989 (BC Ministry of Forests 1991). Logging activity is thought to be responsible for most of the immature forest in this area where wildfires, pest outbreaks, and blow-down are relatively uncommon (MacKinnon and Eng 1995). Logging activity has continued at a high rate over the past 14 years. In 1999, satellite imagery indicated that about 70% of low- to mid-elevation forests (excluding Mountain Hemlock and “muskeg” forests and bare ground) are immature (Sierra Club 2003). The southeastern portion of the island, from Campbell River to Victoria, consists mainly of private forestry lands, which have been logged extensively; almost all old-growth forest at low- to mid-elevations has been removed. The northern and western portions of the island are crown land, and more old-growth habitat remains. However, most of the area consists of a mosaic of recent clearcuts, young forests, and patches of old-growth. The exceptions are protected areas (see section on Protection and Ownership, below).
The effects of logging on frogs are likely medium-term, and habitats are expected to improve as second-growth forests mature and wetlands recover. However, on the south island, logging of low elevations second-growth forests is in progress, and the regenerated habitats are again being degraded. Recently developed Identified Wildlife habitat guidelines are expected to provide provisions to protect some of the remaining habitats in mature second-growth and old-growth forests (see section on Protection and Ownership, below).
The Lower Mainland, an area along and adjacent to the Lower Fraser River Valley from Vancouver to Hope, covers about 10% of the Canadian range of the Red-legged Frog. This region was likely an important component of the species’ range in British Columbia in the past, because it once provided productive and extensive low-elevation forested and wetland habitats. Prior to the early 1800s, the Fraser Valley contained vast forests of giant trees with extensive swamps and wetlands along the river courses (Boyle et al. 1997). Since European settlement, much of the old-growth forest has disappeared and wetlands have decreased from about 10% of the area to only 1% in 1990 (Boyle et al. 1997). Habitat degradation in the Lower Mainland has been severe over the past century, with many permanent landscape modifications. Urban development and agriculture continue to expand in this region, which is one of Canada’s fastest growing areas. The human population on the Lower Mainland grew by 8.3% from 1996 – 2001 (Statistics Canada 2003), and this growth is shifting from Vancouver to outlying communities in the Fraser Valley between Surrey and Chilliwack. Consequently, there is intense pressure to develop lands in this region, including remnant mature forest stands and wetlands. Agriculture in the Fraser Valley has resulted in extensive habitat loss from wetland drainage, pollution, and forest removal. Remaining habitats are highly fragmented, posing threats to populations of the Red-legged Frog, particularly where habitat losses continue and exotic species are spreading.
South-Central Coast (Sunshine coast north to Bramham Island/Rivers Inlet):
On the Sunshine Coast, residential development along coastal regions between Gibsons and Powell River has increased over the past decade with consequent alteration and loss of wetlands and adjacent forest cover. Areas subject to forestry are also extensive, especially in low-elevation habitats along the coast (Sunshine Coast Regional District 2003; forest cover map).
Permanent habitat losses are relatively minor in areas of the coast north of Powell River, where the human population is very low. Forestry occurs mainly on crown lands and is most extensive between Powell River and Knight Inlet, especially at low-elevations and on islands. Large tracts of old-growth forest are still present north of Knight Inlet (BC Ministry of Forests 2003). The Central Coast Region of British Columbia has been poorly surveyed for amphibians, and the northern distributional limits of the Red-legged Frog (north of 51° N) along the coast are unknown. Although the Central Coast region may be less productive for the species due to a harsh climate and rugged terrain, this area is relatively undisturbed and potentially could represent a significant component of the provincial population of the species. Surveys in this area are required to clarify distributional patterns.
Parks and Other Protected Areas:
On Vancouver Island, about 13% of the land-base is protected. A total of 24% of the island is privately owned, 75% of which is private forestry lands (Sierra Club 2003, van Kooten 1995). Most of the private forestry lands and urban/agricultural developments are found in southeastern quarter of Vancouver Island. This region appears to be an important area for the Red-legged Frog. The majority of historic locations occur there, and although the records probably reflect observation bias, it is possible that the abundance of low-elevation forests and wetland breeding sites also contributes to the pattern. Yet, this region contains relatively little protected land. In 2003, the Gulf Islands National Park Reserve was established off the southeastern coast of Vancouver Island. The new park is composed mainly of lands that were already protected as provincial or regional parks, but some new acquisitions were also included. Several areas within this park contain habitat for the Red-legged Frog. On the western and northern parts of Vancouver Island, most of the land is crown land and used mainly by forestry companies for logging.
On the Lower Mainland very little of the land base is protected, and much of it consists of small parks surrounded by urban and rural developments. Many of the known sites for the Red-legged frog in the Fraser Valley are located within these parks and, even though the land is protected, habitat degradation and fragmentation are of concern (Waye 1999). Wetland areas on the Lower Mainland are threatened by encroaching urban development, which can result in direct habitat loss, habitat degradation due to fragmentation, contamination from pollutants entering storm drains, changes in drainage patterns, and introduction and spread of exotic species (Schaefer 1994; R. Rithaler, pers. comm.).
The Sunshine Coast and south-central coast contain relatively few protected areas and the majority of the land base is zoned for forestry activities. The main existing or proposed parks in this region are Cape Caution/Bramham Island, Ahnuhati, Smokehouse, Broughton, Desolation Sound, and Tetrahedron. The Sunshine Coast currently only has 3.6% of the land base protected compared to 12% for the province as a whole (Sunshine Coast Regional District 2002).
Forestry Regulations and Guidelines:
The Forest and Range Practices Act provides some provisions for the protection of habitats of the Red-legged Frog through measures described in the Riparian Management Area Guidebook and General Wildlife Measures (GWMS) contained in the Identified Wildlife Management Strategy. The Riparian Guidebook recommends that buffer zones of undisturbed forest cover be retained around larger wetlands and streams. However, smaller wetlands (<0.5 ha) are used extensively by the Red-legged Frog and are not addressed by the provisions in the Riparian Guidebook.
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). Priority for WHA establishment will be networks of small ephemeral and perennial wetlands (a minimum of three wetlands that are within 300 m of each other), especially in areas where frogs are known to occur (Maxcy 2003). The size of WHAs is usually less than 10 ha. Other characteristics of potential WHAs will include high structural complexity of aquatic and terrestrial habitats, a humus substrate in the wetland, forest/vegetation cover surrounding wetlands, absence of predatory fish and the Bullfrog, low- to mid-elevation (<850 m asl), and presence of water until late summer. To date no WHAs’s for this species have been put into place, and none are currently proposed.
At present, the Identified Wildlife Management Strategy does not stipulate the percentage of wetlands that need to be protected from forestry activities to maintain the viability of frog populations in a particular region. General Wildlife Measures address the appropriate placement of logging roads to reduce collision mortality, maintenance of hydrological regimes and emergent vegetation in wetlands, and retention of forest cover and coarse woody debris in areas surrounding wetlands. Although habitat protection provided by these measures is potentially considerable, many uncertainties surround their implementation, the measures are largely untested, and their effectiveness is presently unknown.
The Forest and Range Practices Act also contains more general protection measures such as restrictions on the size of clearcuts and provisions for Wildlife tree patches/retention areas that may serve to protect habitats for the Red-legged Frog. Any protection measures for wildlife habitat on private forestry lands, which cover large tracts of the species’ habitat on southern Vancouver Island and the Lower Mainland, are currently undertaken on a voluntary basis only.
Urban Planning and Protection Initiatives:
Municipal and regional governments in the Lower Mainland, Vancouver island, and Sunshine Coast have prepared land use plans, by-laws, and zoning regulations, which offer some protection for wetland habitats. Developers are required to follow by-laws, mitigate impacts, and protect wildlife habitat, where possible. Recently, a set of province-wide Best Management Practices (BMPs) for amphibians and reptiles was developed by the Ministry of Water, Land and Air Protection (Ovaska et al 2003). BMPs provide guidelines and specific measures that developers and local governments can use to protect or restore habitats for these animals. Unfortunately, protected areas and restoration projects in urban and rural settings tend to be small, and habitats are often highly fragmented. They are probably of limited benefit for the Red-legged Frog, which requires relatively large areas of forest surrounding wetlands.
In 2003, the municipality of Delta (south of Vancouver) became the first municipality in British Columbia to assess thedistribution and status of amphibians in the community. They have developed detailed "In-Stream Works Windows" designed to protect amphibians and their habitats in riparian areas (R. Rithaler, pers. comm.). Conservation organizations such Ducks Unlimited, Nature Trust of BC, and The Land Conservancy are actively acquiring, protecting and restoring wetlands and adjacent terrestrial habitats in southwestern British Columbia. Some projects, such as Cheam Lake wetlands, Codd Island Wetlands, Pitt-Addison Marsh, Burns Bog, and Blaney Bog may be of sufficient size to protect both wetland and adjacent forest cover for the Red-legged Frog.
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