ANCHORAGE, Alaska – The common murre on Sarah Schoen’s examination table lived a short, hungry life.
Measurements of its beak and leg indicated it hatched in June. Its stomach and breast showed how it died. The 3-inch-long stomach was empty, and the pectoral muscles that powered its wings, allowing it to "fly" underwater after fish, were emaciated.
"As the bird starves, the body eats the muscle for energy," Schoen said.
Schoen, a wildlife biologist for the U.S. Geological Survey, and Rob Kaler, a biologist for the U.S. Fish and Wildlife Service, on Friday performed necropsies on common murres, part of an effort by dozens of scientists to explain the massive die-off of common murres that began one year ago.
Common murres are one of the northern hemisphere’s most common seabirds. The Alaska population is estimated at 2.8 million out of a world population of 13 million to 20 million birds. Awkward on land, common murres can dive to 600 feet hunting fish or krill.
Die-offs have occurred before, but not on this magnitude. Abnormal numbers of carcasses, all showing signs of starvation, began washing ashore on Alaska beaches in March 2015. Numbers spiked to alarming levels in early winter.
The confirmed carcass count is now up to 36,000, Schoen said. That’s far higher than previous common murre die-offs, and many beaches have not been surveyed.
The USGS’s National Wildlife Health Center in Madison, Wisconsin, is testing murres for signs of disease or parasites. Though the murres appear to have starved, researchers wonder whether something caused them to quit eating or to be less successful funding food.
Schoen and Kaler extracted samples of liver, which can indicate what the bird ate a week before it died, and muscle, which can indicate what it ate in the last month. They took feather samples for isotope analysis regarding diet.
Sudden diet changes could be telling. If they were eating at one level of the food web, and a regular food source became unavailable, it could provide insight into the deaths, Schoen said.
Schoen in January necropsied 61 birds found in Prince William Sound. They were heavier than birds sampled in a 1993 die-off, Schoen said.
"So it doesn’t look like just starvation is killing them," she said. "It looks like there’s something else that could be tipping them over the edge."
Possible culprits are a toxin that the birds ingested from tainted algae, or severe winter storms that kept weakened birds from feeding.
"The ravens and eagles make it easy to see that birds are continuing to die and get washed up," Kaler said. The scavengers eat the dead murres.
In previous die-offs, researchers estimated that only about 15 percent of carcasses reach shores, which means the total this time may be in the hundreds of thousands.