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Spatial ecology of an inland population of the Foothill yellow-legged frog (Rana boylii) in Tehama County, California
Understanding the movements of anurans is important for developing successful conservation plans because breeding, foraging, and overwintering resources are often separated by time and space. I used radio-telemetry to study the movements and habitat use of the Foothill Yellow-legged Frog (Rana boylii), a stream-dwelling species experiencing significant population declines. Seventy-nine frogs (11 males and 68 females) inhabiting an inland watershed were opportunistically captured, fitted with radio-transmitters, and monitored during three two-month study periods. Females were tracked during one spring (2004) and two fall/winter seasons (2004 and 2005), while males were tracked during one spring season (2004). Site-specific weather conditions were monitored to evaluate associations with frog movement and habitat use. Movements and habitat use were highly variable among individuals during all study seasons. Frogs either centered activities at their initial capture locations or moved hundreds to thousands of meters among different stream habitats. The greatest distances traveled by male and female frogs were 0.65 km and 7.04 km, respectively. Frog size and age were independent of seasonal distances traveled. Mobile males and females moved 65.7 and 70.7 m/day (median), respectively, in spring and mobile females moved 37.1 m/day (median) in fall/winter. The maximum travel rate was 1386 m/day. Frogs used watercourses as movement corridors and rarely moved > 12 m from the stream channel. Spring movements were not associated with weather, but fall/winter movements were associated with increasing rain and humid conditions. Females showed an upstream directional bias during spring movements and a downstream bias for fall/winter movements. The results from this study highlight the need to manage R. boylii populations at the watershed scale to ensure protection of spatially separated resources commonly used by individuals throughout the year.