Neotropical migratory birds experience variable atmospheric conditions throughout their annual life histories, raising questions about drivers of annual survival. The Southwestern Willow Flycatchers (Empidonax traillii extimus, SWFL) breeding in the Kern River Valley (KRV), California declined over the last 20 years despite breeding and survival parameters that were comparable to other SWFL populations that were stable or increasing in size and management that increased nest success, indicating that non-breeding season mechanisms may be at play. We used a long-term (24-yr) mark-recapture dataset from 617 individually marked flycatchers in the KRV breeding ground to investigate additive and interactive effects of multiple atmospheric conditions in breeding, migration and winter ranges on annual survival to improve our understanding of this decline. Our analyses indicate that increased numbers of months with above normal drought severity on the wintering grounds decreased annual apparent survival, whereas years with increased drought severity on the breeding ground prior to and during the previous season increased survival. An additional subset analysis of the data during a steady decline (2000-2014) revealed that survival decreased in response to increased drought conditions prior to flycatchers arriving on the wintering grounds, with female survival exceeding that of males and unknown sexed birds.

MARY J. WHITFIELD is the founderand Research Director at the Southern Sierra Research Station. She holds a B.S. degree in Wildlife and Fisheries Biology from U.C. Davis, and a M.S. degree from CSU, Chico. She has over 35 years of fieldwork experience in the U.S. and also worked in numerous Latin American countries including work on wintering Willow Flycatcher ecology. Her research interests include conservation biology, breeding ecology, behavioral ecology, full lifecycle research, and riparian systems. She has been involved with the Partners In Flight Western Working Group for over 14 years and is currently leading the PIFWestern Motus Initiative.