Seabirds: Leaving Gulf of California for Food and Cool

Sea-birds have nearly always congregated in great numbers on one small island in the Gulf of California. More than 95 percent of the world's Elegant Terns and Heernan's Gulls gather here every year to nest. But in the last two decades, seabirds have arrived at the island in April--then left soon after without nesting. This first occurred during the 1998 El Niño. Since 2003, the colony desertion has occurred with increasing frequency. A group of researchers from Mexico and the U.S. recently published their research on why this is happening in the journal Science Advances.

The scientists have found that the seabirds have expanded into Southern California in the last two decades, although their expansion fluctuates from year to year, says Enriequeta Velarde, project leader, in a release.  

Peaks in temperature in that part of Mexico are behind the birds' expansions. "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, in a release, "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."

Intensive fishing in Mexico also reduces the sardine populations on which the birds rely. Confronted with a lack of food and spikes in temperature, the seabirds are taking off for the coasts of Southern California.