Abstract from NY Times: Why Are Puffins Vanishing? The Hunt for Clues Goes Deep (Into Their Burrows)

Overfishing, hunting and pollution are putting pressure on the birds, but climate change may prove to be the biggest challenge.

“The puffin is the most common bird in Iceland,” said Erpur Snaer Hansen, acting director of the South Iceland Nature Research Center. “It’s also the most hunted one.”

Dr. Hansen is working with Dr. Fayet, a junior research fellow at the University of Oxford who is from France, on her project to monitor the activities of four puffin colonies, two in Iceland and others in Wales and Norway. Since 2010, he also has conducted a census, a twice-yearly “puffin rally” in which he travels more than 3,100 miles around Iceland, visiting some 700 marked burrows in 12 colonies, counting eggs and chicks.

The temperature of waters around the country is governed by long-term cycles of what is known as the Atlantic Multidecadal Oscillation,
with periods of colder water alternating with warmer. Between the 1965-1995 cold cycle and the current warm cycle, Dr. Hansen said, winter temperature records show about one degree Celsius of additional warming — a seemingly small amount, but disastrous for the sand eels.
His theory, he said, is this: “If you increase temperatures one degree, you’re changing their growth rates and their ability to survive the winter,” he said.

Dr. Hansen’s puffin rallies show that 40 percent of the population of Icelandic puffin chicks is losing body mass over time, another bad sign.

When the adults can’t catch enough to feed themselves and the chicks, they make an instinctive Malthusian choice; the chicks starve.
Dr. Fayet called her quest “heartbreaking”: “You put your hand in the burrow and feel with your hand a little ball on the floor, but then you realize it’s cold, and not moving.”

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