Climate and en route thermals affect long‐term population dynamics of soaring birds

Abstract Migration allows animals to capitalize on the availability of seasonal food resources or to avoid inclement weather that may jeopardize survival. However, migratory birds are challenged physiologically and ecologically by varying climatic conditions within a migratory annual cycle. Studies of the effects of seasonal climate on age‐specific survival of avian migrants are indispensable for understanding the fitness benefits and costs of migration. We investigated the effects of seasonal climatic and wind conditions on stage‐specific annual survival of soaring American white pelican ( Pelecanus erythrorhynchos ) (hereafter, pelicans) using Bayesian integrated population models and 55 years of band recovery‐resighting data and nest counts. We tested two hypotheses: that increases in winter temperature and precipitation would enhance annual survival of pelicans (Hypothesis 1) and that favorable winds and thermal updraft en route would increase survival of immature pelicans (Hypothesis 2). We calculated wind speed and thermal updraft along migration corridors, which were estimated with GPS tracking data during seasonal migration. Increased winter precipitation on the non‐breeding grounds enhanced annual survival of yearling and adult pelicans, supporting our Hypothesis 1. Increased summer breeding‐ground precipitation improved annual survival of adult pelicans but reduced hatch‐year survival with increasing Pacific Decadal Oscillation (PDO) index. Furthermore, increases in vertical velocity during autumn migration enhanced hatch‐year pelican survival, supporting Hypothesis 2. Uplift winds and thermals are the primary energy sources for soaring bird flight, particularly on the first migration trip of immature birds. Our findings demonstrated the joint signals of high‐frequency local climate and low‐frequency PDO on pelican population dynamics.