Why Are Seabirds Abandoning Their Ancestral Nesting Grounds in Gulf of California?

10/9/2018 UCR Today: Why Are Seabirds Abandoning Their Ancestral Nesting Grounds in Gulf of California?

Why Are Seabirds Abandoning Their Ancestral Nesting Grounds in Gulf of California? Warming oceanographic conditions and fishing pressure are driving nesting seabirds away from their ancestral breeding ground in Mexico into California harbors

By Iqbal Pittalwala On JUNE 26, 2015

RIVERSIDE, Calif. – Isla Rasa, in the Gulf of California, is renowned for its massive aggregations of nesting seabirds. Over 95 percent of the world populations of Elegant Terns and Heerman’s Gulls concentrate unfailingly every year on this tiny island to nest. Ever since the phenomenon was described by L. W. Walker in 1953 the island has been a magnet for tourists, naturalists, filmmakers, and seabird researchers.

During some years in the last two decades, however, the seabirds have arrived to the island in April, as they usually do, but leave soon after without nesting. The first event was the 1998 “El Niño”, when oceanic productivity collapsed all along the eastern Pacific coast from Chile to California. But then colony desertion happened again in 2003, and since then it has recurred with increasing frequency in Yellow-footed Gull and Heermann´s Gulls 2009, 2010, 2014, and 2015. Researchers and conservationists feeding on Elegant Tern eggs at the were asking themselves where are the birds going when they leave abandoned nesting colony when the terns their ancestral nesting ground, and what is causing the deserted it after food conditions worsened in abandonment of their historic nesting site. May 2009. PHOTO CREDIT: E. VELARDE. A group of researchers from Mexico and the U.S. set out to analyze what was happening to the nesting Elegant Terns (Thalasseus elegans), a model species to monitor ocean dynamics. Their results, published in the AAAS journal Science Advances (Enriqueta Velarde, Exequiel Ezcurra, Michael H. Horn, & Robert T. Patton; Warm oceanographic anomalies and fishing pressure drive seabird nesting north. Science Advances, 26 June 2015) show that ocean warming and overfishing are producing the ecological collapse of the Gulf of California’s productive Midriff region.

Using nest counts in seabird colonies from Mexico and California, they found that Elegant Terns have expanded from the Gulf of Sardine fishing boat in the Gulf of California´s California, in Mexico, into Southern California during the last two Midriff Island Region, hauling the purse-seine decades, but that the expansion fluctuates from year to year. net after a fishing operation in 2013, when their “Whenever the terns perceive the conditions in the Gulf as catch of Pacific sardine had nearly collapsed. inadequate to ensure successful reproduction,” says Enriqueta PHOTO CREDIT: E. VELARDE. Velarde, project leader, “they move to alternative nesting grounds in Southern California including the San Diego Saltworks, Bolsa Chica Ecological Reserve, and Los Angeles Harbor.”

The decision to remain in the Gulf or move to Southern California is related to the fact that during the last 15 years the Gulf of California has been getting abnormally warm during some seasons, and those peaks in sea surface temperatures https://ucrtoday.ucr.edu/30111 1/3 10/9/2018 UCR Today: Why Are Seabirds Abandoning Their Ancestral Nesting Grounds in Gulf of California? have not been equally high along the California Current and Southern California Bight in the Pacific coast. “When the Gulf waters get unusually warm,” explains Exequiel Ezcurra, a longtime collaborator of Velarde and a professor of ecology at the University of California, Riverside, “the sea becomes capped by a layer of warm surface water and the upwelling of cold, nutrient-rich waters fails to reach the surface. Productivity declines and, with it, the availability of small pelagic fish, on which the seabirds feed, also falls.” The collapse in food for the seabirds that results from warming waters, the study shows, is compounded by the reduction in sardine populations brought by intensive fishing in Mexico. Confronted with lack of food, the seabirds take off towards the coasts of Southern California.

Increased frequencies of abnormally warm waters in the Gulf of Partial view of healthy Elegant Tern nesting California, possibly as a result of globally warming oceans, coupled colony in Isla Rasa, in the Midriff Island Region with extremely high fishing pressure, are delivering a combined blow of the Gulf of California in 2011. to the legendary productivity of the Gulf of California, forcing seabirds PHOTO CREDIT: E. VELARDE. to fly away in search for more suitable environments, even if that means abandoning their ancestral nesting grounds and moving into highly transformed industrial landscapes such as the San Diego Saltworks or the LA Harbor Container Terminal.

Exodus of Elegant Terns from their nesting colony in 2010, when food shortage made them abandon their traditional nesting grounds in Isla Rasa, in the Gulf of California.

PHOTO CREDIT: E. VELARDE. FOTO: E. VELARDE.

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As a result of the lack of food in the Gulf of California’s Midriff, Elegant Terns now often fly north to nest in the ports and harbors of the Southern California Bight, where food is more abundant.

PHOTO CREDIT: E. EZCURRA.

MEDIA CONTACT RELATED LINKS Iqbal Pittalwala About Exequiel Ezcurra

Tel: (951) 827-6050 Department of Botany and Plant Sciences E-mail: [email protected] du Twitter: UCR_Sciencen ews

ADDITIONAL CONTACTS Exequiel Ezcurra Tel: (951) 827-3546 E-mail: [email protected]

ARCHIVED UNDER: Science/Technology, Biodiversity, College Of Natural And Agricultural Sciences, Conservation, Department Of Botany And Plant Sciences, Ecology, Environment, Exequiel Ezcurra, Fish, Press Release, Seabirds, UC Mexico, UCMexus

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