Lack of sardines leads to chronic breeding failures for Galapagos boobies

Last year’s invasion of at least 100 Blue-footed Boobies into California and neighboring states raised concerns about the seabird’s food supply along the coasts of Mexico and Central America. Now, researchers report that the subspecies that lives on the Galapagos Islands has declined significantly and has not had a successful breeding season since 1997.

Seabird biologist David Anderson of Wake Forest University and two colleagues counted boobies at colonies on the archipelago and along its coasts in 2011 and 2012, and they visited breeding colonies from May 2011 through June 2013.

They report that the adult population totals 6,423 birds. The number represents a drop of at least 50 percent — and perhaps as high as 67 percent — since the 1960s, when a rough estimate put the population at 20,000 adults.

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Even more troubling, Anderson says that only 11 percent of adults were breeding at any one time; that the researchers counted only 134 fledglings; and that one formerly large colony of 1,600 boobies is now home to only a few birds. Long-term data, they write, suggest that poor breeding began in 1998, after the onset of an El Niño event in the Pacific.

A dramatic decrease in sardines, an important food for boobies, appears to have caused most birds to stop nesting. Consequently, due to a lack of juveniles, “the age structure of the current population must be strongly biased toward elderly individuals,” the scientists say.

They published their findings in June in the online journal Avian Conservation and Ecology.

A version of this article was published in the October 2014 issue of BirdWatching. Subscribe.

Originally Published September 30, 2014