At least six times since 1975, the 50,000 tufted puffins on Triangle Island have failed to raise more than a handful of fledglings, rather than the usual thousands. The cause eluded scientists until ecologist Carina Gjerdrum of the University of Connecticut, Storrs, and her colleagues compared the colony’s success during 16 breeding seasons between 1975 and 2002 with records of sea-surface temperature from nearby Pine Island.

The team discovered that puffin nestlings grew the fastest in years when the sea surface was between 8.9ºC and 9.9ºC. During years when temperatures rose above 9.9ºC, growth rates plummeted, and very few--if any--nestlings lived to be fledglings, the authors report online the week of 14 July in the Proceedings of the National Academies of Science. Gjerdrum suspects that the warmer water may be affecting availability of the puffins?primary food source, a fish called sand lance. Sand lances may swim to colder waters away from Triangle Island. Because puffin chicks rely on several meals a day, their parents can’t fly very far from the island in search of food. So the puffins must make do with less nutritional substitutes such as rock cod, says Gjerdrum. The Pine Island records show that the average sea-surface temperature there has increased 0.9ºC over the last 66 years. If this trend continues, Gjerdrum fears that more and more often, ocean temperatures will rise above the threshold for puffins at Triangle Island, and eventually the colony may disappear. Although Triangle Island's population hasn't begun to fall off yet, declines have already been reported for puffin populations in California, Oregon, and Washington, likely for the same reasons, the authors say.

Marine ecologist William Sydeman of the Point Reyes Bird Observatory in California agrees that ocean temperatures are the likely cause of the puffins?problems. Luckily, he adds, the ocean surface has cooled in the Pacific since 1999, which could mean a better fish supply and improved breeding success. But if the long-term warming trend is real, Sydeman warns, “then that’s very bad news for puffins.?

--BETSY MASON