Partial Migration by Great Egrets Ardea alba in Coastal California

Abstract. Migratory behavior of California Great Egrets (Ardea alba) is poorly understood. GPS tags were deployed on eleven Great Egrets on Tomales Bay, Marin County, California, USA. Six individuals displayed migratory behavior, four remained resident, and one individual employed both strategies across three winters. Both diurnal and nocturnal migratory movements were observed. Five of the Great Egrets flew through or wintered in the Sacramento-San Joaquin Delta and California's Central Valley, and one Great Egret moved through Nevada, Arizona, and Mexico, indicating use of wintering grounds outside of California. This study provides the first documentation of partial migration by Great Egrets, and the first information on round trip migration of this species on the U.S. west coast. Our results further illustrate the importance of connectivity between coastal and inland habitats for migratory birds.