Final Report pdf file

Abstract

The movements and breeding activities of a population of foothill yellow-legged frogs (Rana boylii) were monitored to determine their relationship to climatic variables in six tributaries and their associated breeding sites on the Poe and Cresta reaches of the North Fork Feather River (NFFR) during spring in 2004 and 2005 by visual surveys and radio telemetry. Male frogs left tributaries earlier than females and stayed longer at breeding sites.  Breeding areas were located along the mainstem river adjacent to the tributaries, and tributaries acted as refugia for most of the year. While there was much variation in actual timing, day length (i.e., time of year) was the only parameter statistically correlated with initial movements in females. Females moved initially in late April/early May, and mean daily tributary temperatures were >10°C when females left home ranges on tributaries to eventually breed on the NFFR. Oviposition dates were clustered in periods when mean mainstem temperatures were between 10°C and 16°C and mainstem flow was between baseflow and <55% above baseflow. A small percentage of frogs laid eggs at somewhat higher flows, but only during a declining hydrograph. Length of stay by females at river breeding sites was extended by high flows and, on the Cresta Reach, relatively low numbers of males. Late season rains and associated high flows delayed breeding in 2005 when compared to 2004, especially in the Poe Reach, the warmer of the two reaches where breeding typically occurred first. Based on the model of environmental parameters affecting breeding activity, hydroelectric power managers are provided with information to enhance foothill yellow-legged frog breeding success (e.g., movement dates, temperature and flow preferences) by preventing sharp fluctuations in the hydrograph during the breeding season from April through June.

One of the breeding sites at Cresta Reach near the shallow, relatively calm part of the river	Section where Flea Valley Creek meets Poe Reach; GANDA biologists Kevin Wiseman and Ron Jackman searching for frog egg masses
Plexiglas box used for easier visibility (white stick pointed at a frog egg mass)	Pulsed Flow Program Administrative Officer Cincin Young learned how to monitor the egg mass development using a magnifying lens
Egg stage was compared to the Gossner chart to identify its development	Kevin Wiseman measuring  FYLF length using a Vernier caliper
Weight measurement using a small weighing scale	Water current at Flea Valley Creek was not as high and swift as in March 2005
Tracking of tagged FYLF using a receiver and antenna	A tagged frog was tracked hiding in the bush
A Sierra garter snake that swallowed a FYLF	Another Sierra garter snake that swallowed a trout

A walk up Flea Valley Creek searching for adult FYLF

Photo credit: Cincin Young, UCD
(Please request permission from psyoung@ucdavis.edu
and jed@garciaandassociates.com for use of pictures)