Climatic and Water Flow Triggers Assoc. With Breeding and Movement in a Foothill Yellow-legged Frog Population on the North Fork Feather River,CA

Joseph E. Drennan

Garcia and Associates

San Francisco, CA

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DRENNAN, JOSEPH E*, RONALD JACKMAN, KARLA R. MARLOW, and KEVIN D. WISEMAN.
Garcia and Associates (GANDA), San Francisco, CA, jed@garciaandassociates.com

Climatic and Water Flow Triggers Associated With Breeding and Movement in a Foothill Yellow-legged Frog (Rana boylii) Population on the North Fork Feather River, California

We conducted visual encounter surveys and radio telemetry of R. boylii within six tributaries and associated breeding sites of the regulated North Fork Feather River (NFFR; Butte Co., California) in 2004-2005. Local environmental data (tributary/river temperature, tributary/river flow, air temperature, precipitation) was collected from data loggers, a local weather station, and hydroelectric gages. Using chin and flank patterns to identify individuals, we collected movement data on 476 individual frogs including 47 individuals that were captured both years. Frogs showed high site fidelity within tributaries to the NFFR, which act as refugia for frogs during the non-breeding season. Initial movements to the NFFR were triggered by day length, and male frogs left tributaries earlier than females and stayed longer at breeding sites. Females moved at more than twice the rate of males (♀= 58.1 m/day) and covered distances up to 1,899 m in ≤ 6 days for a maximum movement rate of 316.5 m/day. Once at the river, frogs initiated breeding when mainstem water temperatures were ≥10 °C and mainstem flow was ≤ 55% of baseflow, on a descending hydrograph. Length of stay by females at river breeding sites was determined by flow level and sex ratio. While males commonly utilized mainstem breeding sites adjacent to the confluence of “home” tributaries, several males made considerable river movements to breeding sites adjacent to other tributaries.