July 24, 2006 — On these craggy, remote islands west of San Francisco, the largest seabird colony in the contiguous United States throbs with life. Seagulls swarm so thick that visitors must yell to be heard above their cries. Pelicans glide.
But the steep decline of one bird species for the second straight year has rekindled scientists' fears that global warming could be undermining the coastal food supply, threatening not just the Farallones but entire marine ecosystems.
Tiny Cassin's auklets live much of their lives on the open ocean. But in spring, these gray-and-white relatives of the puffin venture to isolated Pacific outposts like the Farallones to dig deep burrows and lay their eggs.
Adult auklets usually feed their chicks with krill, the minuscule shrimp-like crustaceans that anchor the ocean's complex food web.
But not this year. Almost none of the 20,000 pairs of Cassin's auklets nesting in the Farallones will raise a chick that lives more than a few days, a repeat of last year's "unprecedented" breeding failure, according to Russ Bradley, a seabird biologist with the Point Reyes Bird Observatory who monitors the birds on the islands.
Scientists blame changes in West Coast climate patterns for a delay in the seasonal upwelling of cold, nutrient-rich waters from the ocean's depths for the second year in a row. Weak winds and faltering currents have left the Gulf of the Farallones without krill, on which Cassin's auklets and a variety of other seabirds, fish and mammals depend for food.
"The seas are warmer. And the number of krill being produced is lower," said Bradley as he held a Cassin's auklet chick, the only one from a study of 400 nests he expected to survive.
"Normally we would have hundreds," he said.
Troubling Trend?
The failure of last year's Pacific upwelling killed seabirds from California to British Columbia. Scientists had hoped the change was just a natural temperature fluctuation in what is known as the California Current.
But the return of higher ocean temperatures and scarce food resources this year has scientists wondering whether last year's erratic weather was not a fluke but the emergence of a troubling trend.
"How many years in a row do you see this before you start raising your eyebrows?" said Frank Schwing, an oceanographer with the National Oceanic and Atmospheric Administration in Pacific Grove.
