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Pacific Southwest Research Station
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Research Topics Wildlife & Fish

About this research
Foothill Yellow-legged Frog (Rana boylii)
  • Map of R. boylii Distribution
  • Geographic Range of R. boylii [click to enlarge]
  • Contact
    • Amy Lind - Tahoe and Plumas National Forests. Note: this person is no longer a Forest Service Research & Development employee.
      Tel.: 530-478-6298.

    The California Energy Commission, Energy-Related Environmental Research Program contributed funding for the development of this topic area.
    Participating Programs:

    Foothill Yellow-legged Frog (Rana boylii)


    The river-dwelling foothill yellow-legged frog (Rana boylii) is currently a species of special concern in California, and has declined from over 50 percent of its historic range (Davidson et al. 2002, Lind 2005). Research on the ecology of R. boylii has increased our understanding of the habitat requirements (Kupferberg 1996, Yarnell 2005, Lind 2005, Haggarty 2006), development and competition (Kupferberg 1997), basic movement (GANDA 2008, Bourque 2008), phylogeny and genetic structure (Macey et al. 2001, Lind 2005, Dever 2007, Lind et al. 2011), and behavior (Van Wagner 1996, Wheeler and Welsh 2008) of this species.


    Rana boylii was initially described as a full species by Baird (1854), but endured several name changes before it was commonly recognized as a distinct species in the family Ranidae (Zweifel 1955). Lind et al. 2011) provide a good summary of the phylogenetic and molecular analyses relating to this species. Dever (2007) observed high levels of intra-tributary genetic diversity in R. boylii, and evidence of genetic differentiation among tributaries, in addition to support for reduced gene flow between populations separated by distances greater than 10 km. Lind et al. (2011) analyzed R. boylii mtDNA and observed genetic structuring correlated with hydrologic region and river basin, and strong evidence of among-river basin divergence, indicating genetic variation in this species is highly structured along hydrologic boundaries. Furthermore, Peek (2010) found evidence of greater genetic differentiation in R. boylii populations in regulated rivers (populations separated by reservoir, dam, or mainstem peaking reach) compared with unregulated rivers. Lind et al. (2011) also identified several populations at the extremes of the geographic range that were genetically distinct and warrant conservation attention.

    Life History

    Adult frogs are found primarily in or near rivers and streams and feed on aquatic and terrestrial insects (Nussbaum et al. 1983, Haggarty 2005). They use low gradient portions of streams for breeding and rearing (Zweifel 1955), but post-metamorphic individuals have been observed in a wide variety of habitats, including those with very steep gradients. Breeding and oviposition occur in the spring and females only deposit a single egg mass per season, consisting of several hundred to over 2,000 eggs (Zweifel 1955, Kupferberg 1996, Lind et al. 1996, Kupferberg et al. 2009c). Breeding occurs in hydraulically stable habitat (generally shallow, low water velocity areas) in rocky substrates, often near cobble or gravel bars with sparse vegetation near tributary confluences (Kupferberg 1996, Lind et al. 1996, Van Wagner 1996, Lind and Yarnell 2008). Initiation of oviposition is generally associated with the descending limb of the hydrograph (receding flow from spring snow melt), increasing day length, and warming of water temperatures, although additional variables may be involved (Zweifel 1955, Lind et al. 1996, Kupferberg 1996, GANDA 2008, Wheeler and Welsh 2008). Larvae emerge from eggs after approximately two weeks, but hatching times may vary depending on water temperatures (Zweifel 1955). Development from hatching through metamorphosis requires approximately three months, depending on water temperature and food availability, and R. boylii do not overwinter as tadpoles (Zweifel 1955). Reproductive maturity may not occur until the frog reaches two to three years in age, and it is unknown whether individuals breed every year (particularly females) (Kupferberg et al. 2009c). Rana boylii use habitat patches for breeding at or near tributary confluences (Kupferberg 1996), and generally seem to prefer heterogeneous habitat areas, such as braided channels or tributary junctures (Kupferberg 1996, Peek 2010).


    Rana boylii are stream-associated and historically occurred in foothill and mountain streams from northern Baja California to southern Oregon west of the Sierra-Cascade crest, from sea level to approximately 1830 m (6000 ft) elevation (Stebbins 2003). Rana boylii habitat requirements are closely linked to seasonal variation in stream habitats and can be divided into three main categories: breeding and rearing habitat, non-breeding habitat, and overwintering habitat.

    Breeding and Rearing Habitat

    Breeding and rearing habitat is generally located in gently flowing, low-gradient stream sections, with variable substrate predominated by cobble and boulder (Kupferberg 1996, Van Wagner 1996, Yarnell 2005). Rana boylii breed at locations that provide suitable velocities and depths over a relatively broad range of discharge volumes, including small tributaries and large rivers (Kupferberg 1996, Lind and Yarnell 2008). Egg masses are typically attached to the lee (i.e., flow protected) side of substrate (generally cobble, boulder, or bedrock), near river margins in shallow and relatively slow habitat (see Lind and Yarnell 2008 for range of depths and velocities, Kupferberg 1996). Larvae are found in the same habitat as egg masses, and require protection from scouring flows, particularly immediately after hatching and as larvae near metamorphosis (Kupferberg et al. 2009c)

    Breeding and rearing habitat at (a) South Fork  Eel River. Breeding and rearing habitat at (b) Butte Creek.
    Breeding and rearing habitat at (a) South Fork Eel River, and (b) Butte Creek (Photos: R.Peek).

    Non-breeding Habitat
    Post-metamorphic R. boylii remain in terrestrial riparian and riverine habitat adjacent to the wetted channel during the non-breeding season (Bourque 2008, Kupferberg 1996, Lind et al. 1996, Moyle 1973, Van Wagner 1996, Zweifel 1955). Rana boylii have been documented in a wide range of habitats, but all generally occur within a short distance of flowing water (see Bourque 2008) although differences appear to vary both regionally and seasonally (Bourque 2008, Haggarty 2006, Van Wagner 1996, Yarnell 2000, Yarnell 2005).

    Overwintering Habitat
    Very little data are available relating to overwintering habitat. Van Wagner (1996) observed R. boylii both in the water and along the stream-edge habitat beneath rocks, leaf litter, and Carex sp, and found frogs appeared to be active whenever ambient conditions were favorable. Habitat use in large rivers may vary compared to Van Wagner’s observations, and R. boylii may move into smaller lateral tributaries to avoid risk of scouring (Kupferberg 1996), or move into adjacent terrestrial habitat to avoid winter flood events altogether.

    Ecological Details:

    (Adapted from Table 1.2 in Ecological relationships of the foothill yellow-legged frog (Rana boylii) [from Lind 2005])


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      (Eggs: March-June, depending on location)
      (Larvae: March-August, depending on location)

      1. Food
        1. Algae: preference for Cladophora sp. with epiphytic diatoms (Kupferberg 1996)
      2. Cover
        1. Suitable Water Depths:
          1. 10-13 cm (Fitch 1936)
          2. 7-22 cm (Fuller and Lind 1992)
          3. 4-43 cm (Kupferberg 1996 & 1997)
          4. 6-28 cm (Van Wagner 1996)
          5. 6-40 cm (Lind 2005)
          6. Eggs: 90% found in 14-67 cm (Yarnell et al. 2011)
          7. Early Stage Tadpoles (90% within): 1-54 cm, Late Stage Tadpoles (90% within): 1-51 cm (Yarnell et al. 2011)
        2. Suitable Water Velocity:
          1. 0.0-0.06 m/s (Fuller and Lind 1992)
          2. 0.01-0.14 m/s (Kupferberg 1996 & 1997)
          3. 0.0-0.03 m/s (Van Wagner 1996)
          4. 0.00-0.21 m/s (Lind 2005)
          5. 0.04-0.17 m/s (Wheeler and Welsh 2008)
          6. Eggs: 90% found in 0.00-0.15 m/s (Yarnell et al. 2011)
          7. Early Stage Tadpoles (90% within): 0.00-0.16 m/s, Late Stage Tadpoles (90% within): 0.00-0.12 m/s (Yarnell et al. 2011)
          8. Critical velocities ranged from 0.01-0.04 m/s depending on developmental state, body size, and population of origin (Kupferberg et al. 2009c)
        3. Substrate: most common – cobbles and boulders
          1. "clean" (no algae/sediment) surface for egg attachment (Kupferberg 1996 & 1997, Van Wagner 1996, Lind 2005, Wheeler et al. 2003)
      3. Water Quality
        1. Dissolved Oxygen: unknown, but likely important especially during larval rearing in warmer summer months (see Duellman and Trueb 1986 for info on related species)
        2. Thermal Regime:
          1. Critical thermal maximum (embryos) <26 C° (Zweifel 1955)
          2. Initiation of Oviposition – water temperatures 10-12 C° (Kupferberg 1996, GANDA 2008, PG&E 2009)
          3. Suitable/preferred larval water temperature
            1. 16.5-20 C° had highest growth and survival rates (S. Kupferberg, pers. comm.)
            2. Maximum temperatures of 15-16 C° throughout the breeding season result in low survival or no breeding success (PCWA 2007, PG&E 2009; S. Kupferberg pers. comm.)
      4. Predators: wide variety of organisms
        1. Eggs:
          1. Sacramento pike minnow (Ashton and Nakamoto, pers. comm., Corum 2003)
          2. rough-skinned newt (Evenden 1948)
          3. Crayfish (Wiseman 2004)
        2. Larvae:
          1. garter snakes (Fitch 1941, Fox 1952)
          2. Pacific coast aquatic garter snake (Lind and Welsh 1994)
          3. American dipper (Lind, pers. obs.)
          4. Crayfish (Wiseman 2004)
          5. Centrarchid fish (Werschkul and Christensen 1977)
        3. Unknown/Opportunistic:
          1. Trout
          2. Bullfrogs
          3. Raccoons and other mammals
      5. Competitors: Bullfrogs (Kupferberg 1997, Moyle 1973)

      Look a little closer? Click any thumbnail to enlarge... you can view more than one enlarged image at once, drag enlarged images to arrange on the screen, view them as a slide show, or scroll through all the photos. To download high resolution image, right click on the "Hi Res" link, and "save [link/target] as..."

      • Juvenile R. boylii. The reddish-orange coloration is not distinctive for identification; coloration among individuals can vary widely and ranges from light gray to very dark brown. (Photo: R. Peek)
        Right click, to save High res image

      • Adult R. boylii. The reddish-orange coloration is not distinctive for identification; coloration among individuals can vary widely and ranges from light gray to very dark brown. (Photo: R. Peek)
        Right click, to save High res image
      1. Food: Aquatic and terrestrial invertebrates and arachnids (Zweifel 1955, Van Wagner 1996, Haggarty 2006)
      2. Cover
        1. Aquatic Habitat
          1. Most common along pool, glide, riffle (Lind and Yarnell 2008, Bourque 2008, Haggarty 2006, Yarnell 2005, Van Wagner 1996, Lind 2005)
        2. Near-Stream Cover
          1. Shoreline rocks (especially cobble), leaf litter, overhanging vegetation [e.g. Carex sp.] (Bourque 2008, Haggarty 2006, Yarnell 2005, Hayes and Jennings 1988, Van Wagner 1996)
        3. Riparian Habitat
          1. Overhanging vegetation (e.g. Carex sp.), moderate shade (Van Wagner 1996, Zweifel 1955, Moyle 1973, Hayes and Jennings 1988)
        4. Ground Cover: requirements unknown
        5. Upland Habitat: Likely remain within the linear stream network (Bourque 2008)
      3. Terrestrial Microclimate
        1. Humidity: Unknown, but likely important for some life functions [e.g. cutaneous respiration], (GANDA 2008, Duellman and Trueb 1986).
        2. Light: Unknown, but day-length likely affects breeding readiness (GANDA 2008, Duellman and Trueb 1986)
      4. Dispersal Habitat: Likely remain within the linear stream network (Bourque 2008), but detail unknown. Young-of-the-year frogs may move upstream at greater rates than downstream (Twitty et al. 1967)
      5. Mating
        1. Calling behavior: Males (MacTague and Northern 1993, Wheeler 2007)
        2. Sex ratios:
          1. Male biased at breeding sites (Wheeler 2007)
          2. Female biased over breeding season (Wheeler 2007)
        3. Territoriality
          1. Males defend territory and aggregate, but ultimately females select oviposition sites (Wheeler 2007)
          2. Bullfrogs may interfere with successful mating of Rana boylii (Lind et al. 2003)
        4. Oviposition: Females "clean" substrate prior to oviposition (Rombough and Hayes 2005)
        5. Breeding Frequency : no data available
      6. Life Span
        1. Females- may live 7+ years (Drennan, pers. comm.)
        2. Males have unknown life span, observations for males 3-4 years old (GANDA 2008)
      7. Predators
        1. Fish
          1. Sacramento pike minnow (Ashton and Nakamoto, pers. comm., Corum 2003)
        2. Herpetofauna
          1. Garter snakes & bullfrogs (Fitch 1941, Lind and Welsh, pers. obs.)
        3. Mammals
          1. Raccoons and other mammals (Bourque, pers. comm.)
    Other Threats & Risks
    General Amphibian Decline

    Amphibian populations continue to decline on local and global scales (Davidson et al. 2002, Lannoo 2005, Pounds et al. 2006, Hamer and McDonnell 2008, Wake and Vredenburg 2008), and the underlying reasons behind these declines often remain unknown (Moyle and Randall 1998, Beebee and Griffiths 2005, Brito 2008). Human activities have been directly linked to all of the key factors in this recent era of amphibian decline, including climate change, invasive species introductions, habitat fragmentation, and habitat destruction (Karr and Chu 2000, Beebee and Griffiths 2005). Therefore, current amphibian declines may not only represent a severe change in the balance of global biodiversity, but also indicate significant and widespread ecological degradation. This degradation may have ramifications not only for amphibians, but all species that rely on the benefits that "ecosystem services" (Daily 1997) provide, such as drinking water, food supply, purification of human and industrial wastes, and habitat for plant and animal life (Wilson and Carpenter 1999).

    Beebee, T.J.C. and R. A. Griffiths. 2005. The amphibian decline crisis: A watershed for conservation biology? Biological Conservation. Vol. 125, pp. 271–285.

    Brito, D. 2008. Amphibian conservation: Are we on the right track? Biological Conservation. Vol. 141 (11), pp. 2912–2917.
    Daily, G. 1997. Nature’s services. Island Press, Washington D.C., USA.

    Hamer, A. and M. McDonnell. 2008. Amphibian ecology and conservation in the urbanising world: A review. Biological Conservation. Vol. 141 (10), pp. 2432–2449.

    Karr J.R. and E.W. Chu. 2000. Sustaining living rivers. Hydrobiologia. Vol. 422/423, pp. 1–14.

    Lannoo, D. (ed). 2005. Amphibian Declines. Conservation Status of United States Species. Regents of the University of California, University of California Press.

    Moyle, P. B. and P. J. Randall. 1998. Evaluating the biotic integrity of watersheds in the Sierra Nevada, California. Conservation Biology. Vol. 12 (6), pp. 1318–1326.

    Pounds, J.A., Bustamante, M.R., Coloma, L.A., Consuegra, J.A., Fogden, M.P.L., Foster, P.N., La Marca, E., Masters, K.L., Merino-Viteri, A., Puschendorf, R., Ron, S.R., Sanchez-Azofeifa, G.A., Still, C.J., Young, B.E. 2006. Widespread amphibian extinctions from epidemic disease driven by global warming. Nature. Vol. 439 (7073), pp. 161–167.

    Wake, D. and V. Vredenburg. 2008. Are we in the midst of the sixth mass extinction? A view from the world of amphibians. PNAS. Vol. 105 (1), pp. 11466–11473.

    Wilson, M. and S. Carpenter. 2008. Economic valuation of freshwater ecosystem services in the United States: 1971–1997. Ecological Applications. Vol. 9 (3), pp. 772–783.

    Other Risks for Foothill Yellow-Legged Frogs
    Suction-dredge mining, North Fork Middle Fork American River (Photo: R. Peek)

    Rana boylii face a range of risks which adversely affect conservation of populations and their habitat. Major limiting factors include: land use change, shifts in precipitation and climate (Lind 2005, Kupferberg et al. 2009b), parasites and disease (Kupferberg et al. 2009a), toxins /pesticides (Davidson et al. 2002, Davidson et al. 2007, Hothem et al. 2009, Sparling and Fellers 2008), invasive species (Moyle 1973, Kupferberg 1997), and habitat alteration (including fire/fuel management, habitat fragmentation, and mining).

    These factors may act synergistically. Recent research has identified synergistic sub-lethal affects of pesticides in relation to the Batrachytrium dendrobatidis (Bd) infection fungus (Davidson et al. 2007), and Kupferberg et al. (2009a) found evidence between unusually warm summer water temperatures and outbreaks of the parasitic non-native copepod Lernaea cyprinacea, and malformations in R. boylii tadpoles and young of the year. Habitat alteration unrelated to flow regulation in the current range of R. boylii continues in the form of urbanization, land use change, and suction-dredge mining.

    Last Modified: Jun 3, 2016 06:03:04 PM