Seasonal movement patterns and the importance of upland habitats for the foothill yellow-legged frog, Rana boylii
Introduction:
All species of native true frogs Ranidae have declined in the western United States over the past two decades (Jennings 1995). These reductions in range or and declines in population size seem to be a recent phenomenon (Hayes and Jennings 1986). The foothill yellow-legged frog (FYLF), Rana boylii (Baird 1854), is a species that has suffered population declines. The cause of these declines may include habitat loss and degradation, disease, UV rays, pesticides, and invasive species.
Historically, this species ranged from northern Oregon west of the Cascade Mountains, south along the coast to the San Gabriel Mountains and south along the foothills of the western side of the Sierra Nevada Mountains to the Tehachapi Mountains with an isolated population in the San Pedro Martir Mountains in Baja California which is now possibly extinct (Ashton et. al 1998). FYLFs have been recorded at elevations ranging from sea level to 6,700 feet (Loomis 1965). This frog has disappeared from approximately 45% of its range in California and an estimated 66% of their range in the foothills of the Sierra Nevada Mountains. Rana boylii is currently listed by the California Department of Fish and Game as a Species of Special Concern (Jennings and Hayes 1994). Jennings and Hayes recommended a threatened status in the “west slope drainages of the Sierra Nevada and southern Cascade Mountains east of the Sacramento-San Joaquin river axis” (Jennings and Hayes 1994).
Adult FYLFs are highly mobile moving between suitable habitats during breeding and non-breeding seasons, and studies have shown that male FYLFs exhibit site fidelity by often returning to the same breeding habitat as previous years (Wheeler and Welsh 2008). Adult FYLFs have been observed traveling hundreds of meters or more to congregate at optimal breeding sites. Once the breeding season comes to an end, recently metamorphosed and adult FYLFs migrate upstream to more suitable overwintering habitats. One study suggested that these movements are synchronized with the seasonality of runoff during the predictable cycle of seasons and precipitation levels (Lind et. al 1996).
Critical aspects in the seasonal movement patterns of R. boylii are still essentially unknown (Bourque 2008). The results of this study will identify winter habitat use patterns which will enable land managers to better account for this species and manage for it during the non-breeding season.
Research Objectives:
• Observe R. boylii seasonal movement patterns (year-round) and use of upstream tributaries during wintering months. • Determine if precipitation affects tributary and upland habitat usage by R. boylii during wintering months. • Estimate current population size of R. boylii in the Big Chico Creek Ecological Reserve by using a mark-recapture technique.
Study Site: Big Chico Creek Ecological Reserve (Butte County, CA)
Significance:
Amphibians are good indicators of the quality of their surroundings because they are sensitive to changes in habitat and the environment (Pechmann and Wilbur 1994). They have permeable skin so they are directly affected by changes in air and water quality. Also, they are important facets to the ecosystem by consuming large numbers of aquatic and terrestrial invertebrates and serve as a suitable food source to many predators. Some common predators of R. boylii larvae include diving beetles, water bugs, rough-skinned newts, and western toads. Most predators of adult R. boylii are mid-sized carnivores and raptors. Understanding the seasonal movements of FYLFs will allow scientists to better understand critical aspects of the natural history of this species. Also, it will assist land managers in determining future conservation plans.
References Ashton, D.T., A.J. Lind and K.E. Schlick. 1998. Foothill yellow-legged frog (Rana boylii) natural history. USDA Forest Service, Pacific Southwest Research Station, Arcata, California.
Baird, S. F. 1854. Descriptions of new genera and species of North American frogs. Proceedings of the Academy of Natural Sciences of Philadelphia 7(2):59-62 Bourque, R. M. 2008. Spatial ecology of an inland population of the foothill yellow-legged frog (Rana boylii) in Tehama County, California (Doctoral dissertation, Humboldt State University).
Hayes, M.P. and M.R. Jennings. 1986. Decline of ranid frog species in western North America: are bullfrogs (Rana catesbeiana) responsible? Journal of Herpetology 20(4): 490-509.
Jennings, M. R. and M. P. Hayes. 1994. Amphibian and reptile species of special concern in California. California Department of Fish and Game, Final Report. 255 pp.
Jennings, M. R. 1995. Native ranid frogs in California. Our Living Resources: A Report to the Nation on the Distribution, Abundance, and Health of US Plants, Animals, and Ecosystems. US Department of the Interior, National Biological Service, Washington, DC xi: 131-134.
Lind, A.J., H.H. Welsh and R.A. Wilson. 1996. The effects of a dam on breeding habitat and egg survival of the foothill yellow-legged frog (Rana boylii) in northwestern California. Herpetological Review 27(2): 62-67.
Loomis, R.B. 1965. The yellow-legged frog, Rana boylii, from the Sierra San Pedro Martir, Baja California Norte, Mexico. Herpetologica 21(1):78-80.
Wheeler, C. A. and H.H. Welsh Jr. 2008. Mating strategy and breeding patterns of the foothill yellow-legged frog (Rana boylii). Herpetological Conservation and Biology 3(2): 128-142.