title: Warm oceanographic anomalies and fishing pressure drive seabird nesting north.
abstract: Parallel studies of nesting colonies in Mexico and the United States show that Elegant Terns (Thalasseus elegans) have expanded from the Gulf of California Midriff Island Region into Southern California, but the expansion fluctuates from year to year. A strong inverse relationship between nesting pairs in three Southern California nesting areas [San Diego saltworks, Bolsa Chica Ecological Reserve, and Los Angeles Harbor (1991 to 2014)] and Isla Rasa in the Midriff (1980 to 2014) shows that terns migrate northward when confronting warm oceanographic anomalies (>1.0°C), which may decrease fish availability and hamper nesting success. Migration pulses are triggered by sea surface temperature anomalies localized in the Midriff and, secondarily, by reductions in the sardine population as a result of intensive fishing. This behavior is new; before year 2000, the terns stayed in the Midriff even when oceanographic conditions were adverse. Our results show that terns are responding dynamically to rapidly changing oceanographic conditions and fish availability by migrating 600 km northwest in search of more productive waters.
authors.affiliation: Instituto de Ciencias Marinas y Pesquerías, Universidad Veracruzana, Hidalgo 617, Colonia Río Jamapa, Boca del Río, Veracruz 94290, Mexico.
authors.forename: Enriqueta
authors.initials: E
authors.lastname: Velarde
authors.affiliation: Department of Botany and Plant Sciences, University of California, Riverside, 900 University Avenue, Riverside, CA 92521, USA.
authors.forename: Exequiel
authors.initials: E
authors.lastname: Ezcurra
authors.affiliation: Department of Biological Science, California State University, Fullerton, Fullerton, CA 92834-6850, USA.
authors.forename: Michael H
authors.initials: MH
authors.lastname: Horn
authors.affiliation: Avian Research Associates, 830 Orange Avenue, Suite K, Coronado, CA 92118, USA.
authors.forename: Robert T
authors.initials: RT
authors.lastname: Patton
keywords: El Niño; Elegant Terns; Pacific sardines; SST anomalies; island conservation; nesting-range shifts; rodent eradication; seabird breeding; seabird population growth; seabird-fishery interactions